Program

Tuesday, Aug 16th, 2016
13:00-13:15
Opening Remarks
13:15-13:40
Belinda Wilkes (SAO)
The State of The Observatory
As we celebrate 17 years of new, exciting, high impact science, the Chandra X-ray Observatory continues to operate smoothly and efficiently. A 2014 detailed engineering study of the spacecraft subsystems found no show-stoppers to 10+ more years of operation, and we are planning for the long-term. Critical to this planning is the involvement of the whole community in discussing future scientific directions and new and continuing multi-wavelength observational opportunities, to ensure Chandra continues to play a key role in advancing our knowledge, addressing the most important science questions of the day, and maximizing its legacy.
In recent highlights, Chandra received an excellent report from the 2018 NASA Senior Review, ensuring continued NASA funding as we move forward. The Cycle 18 peer review was held in June, and the approved target list posted in mid July. The Chandra X-ray Center continues to deliver reduced, calibrated data to PIs within ~1 day of observation, and to provide the CIAO analysis software, accompanied by detailed analysis threads for both experienced and novice users, and backed up by our helpdesk. The use of the archive continues to grow along with its size, and version 2 of the Chandra Source Catalog, including ~350,000 sources, will be released in the fall, 2016.
I will review the capabilities, current state, and future prospects for Chandra, along with community access routes to Chandra observations, data, the archive, and relevant multi-wavelength facilities. I challenge this workshop to discuss and consider potential ways in which that access, and coordination with other current and future observatories, should/could evolve to maximize Chandra's science and impact over the next decade.
Methods
13:40-13:55
Martin Elvis (Harvard-Smithsonian Center for Astrophysics)
The Greater Observatories: the Need for Pan-spectral Coverage in 21st Century Astrophysics
For over three decades astronomers have become used to having access to the entire X-ray, UV, optical, infrared and radio spectrum. Many of these windows depend on space mission, with X-rays most notable among them. This access is now threatened: after the 2018 launch of the James Webb Space telescope (JWST) in the X-ray, UV or far-IR there will be no match to its sensitivity until the late 2020s at the earliest. Here I explain and address this crisis.
The first generation of these observatories - IUE, IRAS, and Einstein (rapidly followed by ROSAT and ASCA) - opened our eyes to the realization that virtually all astrophysical systems emit across the spectrum and that each band provides unique clues to how these systems work. Now we have three Great Observatories - Chandra, Hubble and Spitzer - that have extended this insight in far more detail.
As JWST itself has only a 5 - 10 year lifetime, it will be dead before any matching capability outside of the near-mid-IR can be operational. The rapid feedback from one band to another that keeps astronomy vital and making fast progress will thus be gone in the 2020s.
I suggest two ways to deal with this crisis in astrophysics.
First, thanks to a fortunate technological convergence, the X-ray, UV and far-IR bands all have ways to gain 1 - 2 orders of magnitude in capability at relatively low cost, such that all three may be realized for a total cost comparable to JWST. The thin mirror adjustable optics for the X-ray Surveyor is the example best known to this audience. These "Greater Observatories" - with JWST being the first - should, I believe, be the #1 recommendation of the 2020 Astronomy Decadal Review for large space missions.
Second, we should actively engage with the NewSpace community to bring down mission costs. Astronomers have not recently had to consider how our capabilities in space would be different by the time our next flagships start being built. But this is not the case this time. By the 2020 Decadal, and certainly by the time the next flagship missions are undertaken, the space industry will have changed greatly.
NewSpace is a movement to rethink space as a commercial venture. The factor 3 cost reduction in $/kg to low earth orbit (LEO) already achieved by SpaceX is already impressive and further cost reductions are likely. This saving is enough to trigger a change in how spacecraft are built. Mass saving need not be the strong driver it has been to date. Studies have shown that relaxing mass constraints can cut spacecraft cost by factors of ~3. A fresh look at this possibility is badly needed as it could change how science is done in space.
The advent of commercial crew flights to the International Space Station in LEO will be reality by 2020, with contracts already awarded to Boeing and SpaceX. Both companies intend to sell passenger seats on other flights of their CST-100 and Dragon-V2 vehicles. This "space tourism" could bring on-orbit servicing back into discussion as its cost drops to reasonable values. This too may reduce costs for LEO missions by chaining the risk profile.
With sufficient savings we may be able to afford the other flagship missions, notably in exoplanet and gravitational wave science, that today's science demands.
There are difficulties in realizing this program that depend on the sociology of the field and of the funding agencies. I suggest that we should work actively together to promote these goals. We have much to gain.
13:55-14:10
Paul Green (CXC/SAO)
Chandra Joint Programs Past and Future
Chandra has a number of legacy and ongoing programs with our joint partner observatories (JPOs), enabling time awards on multiple facilities from a single peer review. We review the history of Chandra joint programs, and examine possibilities for the future.
14:10-14:25
Raffaele D'Abrusco (Smithsonian Astrophysical Observatory)
Knowledge Discovery in the era of Rich-Data astronomy: a Chandra perspective
The Chandra X-ray observatory has opened an unprecedented window on the Universe and revolutionized our understanding of high-energy astrophysics. Since its first light, Chandra has collected a large volume of complex data for a growing number of sources in a crucial energy range for most astrophysical investigations. After more than 15 years of activity and with another productive decade in sight, Chandra is uniquely positioned to offer an exciting opportunity to unlock new, original avenues for discovery. In this talk, I will discuss how strategies borrowed from the fields of Knowledge Discovery and Data Mining for the exploration of Chandra data, can benefit the X-ray community and the astronomical community at large, and advance the goal of maximizing the overall scientific impact of the mission. Projects like the Chandra Source Catalog and the Chandra Galaxy Atlas, represent great opportunities to explore the capabilities of advanced methods, based on unsupervised clustering and automatic pattern recognition, for the exploration of the dataset collected, processed and analyzed, potentially outlining a fresh and unexpected picture of the X-ray sky. Furthermore, in the context of the strong synergy established between Chandra and other observatories to foster multi-wavelength astrophysical research, I will described how knowledge discovery can be a promising alternative to the classical methods for the classification and characterization of the spectral energy distributions of several different classes of astronomical objects. Finally, I will stress the fundamental role that Chandra and similar high-impact missions will play in the near future to promote the development and diffusion of tools, algorithms and practices that will allow researchers to thrive in the coming age of data-rich astronomy.
14:25-14:40
Rosanne Di Stefano (CfA)
A New Era of Proper Motion Studies with Chandra
Chandra's superb angular resolution allows us to measure the proper motions of nearby X-ray sources. Many of the sources for which this is possible are X-ray-active stars. Proper motion measurements can also be used to identify young neutron stars, particularly those emerging from their natal star-forming clusters, and quiescent X-ray binaries, some about to enter their first phase of Roche-lobe filling. To make the requisite measurements, we need the long baseline now available, and the even longer baseline we expect Chandra to achieve during the coming years. We discuss the status of proper motion measurements by our team and by others in this exciting and evolving field of research.
14:40-15:10
Break
Accretion I
15:10-15:35
Andrea Comastri (INAF-Osservatorio Astronomico di Bologna)
AGN physics and evolution in the next decade
According to recent models for the joint growth of Super Massive Black Holes and their host Galaxies, the AGN phenomenon is ubiquitous and is expected to play a fundamental role in the feedback mechanisms linking SMBH activity with host galaxy properties. X-ray observations are relatively unbiased with respect gas and dust abosrption, thus nuclear activity can be studied over a wide range of redshifts as a function of both nuclear and host galaxies properties (luminosity, mass, SFR, ...). A quantum leap forward in this field was obtained thanks to the superb spatial resolution and point source sensitivity of Chandra. I will review the key results obtained by Chandra -- along with XMM, Suzaku & NuSTAR -- and our current understanding of AGN. I will discuss open issues and present a few suggestions on what Chandra should focus on in the next decade in synergy with other facilities both in the X-ray band and at longer wavelengths. I will conclude presenting the perspectives for future observations beyond the next decade with Athena and X-ray Surveyor missions.
15:35-15:50
David Pooley (Trinity University)
The Unique Power of Chandra Observations of Gravitationally Lensed Quasars
While it is widely appreciated that a galaxy can split a quasar into multiple ("macro") images, these macroimages can also be split, into microimages, by individual stars in the lensing galaxy. Such microlensing provides unique and powerful methods for determining properties of both the lenses (the galaxies) and the background sources of light (the quasars).
Although multiply imaged quasars have been studied for decades in the optical, it had been difficult to exploit the potential of microlensing because the size of the quasar emitting region in the optical is comparable to the size of the Einstein rings of the microlensing stars. Because the X-rays come from a much smaller region, they offer a far cleaner microlensing signal than the optical. In the past ten years, we have used this clean signal of microlensing, which only Chandra can provide, to measure the sizes of quasar accretion disks on the microarcsecond level, the dark matter content of elliptical galaxies, and the stellar mass-to-light ratio, a fundamental astronomical quantity and something nearly impossible to measure beyond the solar neighborhood through any other means.
In the coming decade, Chandra will remain the only instrument with which to study quasar microlensing in X-rays. Because we are currently limited by the small sample size of systems to study, progress will be made as more quadruply imaged quasars are discovered in the next generation optical all-sky surveys. It would be a great loss if Chandra failed to observe these newly discovered lensed quasars. I will discuss how the increased sample size will allow us to make much finer measurements than we are currently able to do and allow us to refine the estimate of the ratio of smooth dark matter to stellar matter.
In addition to these X-ray snapshots of newly discovered systems, Chandra monitoring of specific microlensing events in individual systems will determine the size and structure of the X-ray emitting regions in those quasars.
15:50-16:05
Peter Maksym (Harvard-Smithsonian Center for Astrophysics)
Imaging the Narrow Line Region with Chandra
The impact that active galactic nuclei have on their host galaxies is critical to understanding the co-evolution of massive black holes and their host galaxies. But a deeper understanding is necessary of the specific mechanisms by which AGN feedback occurs. Spatially resolved imaging X-ray spectroscopy of the Narrow Line Region in nearby AGN provides a critical diagnostic for disentangling the relative roles of photoionization, jets, and AGN winds. We present results from recent studies of nearby AGN selected via CHEERS and Galaxy Zoo, where Chandra's sub-arcsecond resolution enables a detailed view of the complicated processes at work in the inner kiloparsec of nearby AGN. Deep Chandra observations of the resolved NLR will provide a powerful synergy with JWST in the coming decade for our understanding of the MBH-host relationship.
16:05-16:20
Stephanie LaMassa (NASA GSFC)
Stripe 82X: A Wide-Area X-ray Survey in a Legacy Field
Current models predict that a majority of mass locked up in present day black holes was accreted in a luminous obscured AGN phase, where they may subsequently impact the growth of their host galaxy via strong winds. To discover this population and trace their evolution over cosmic time, we are undertaking a wide-area X-ray survey in the Stripe 82 field of the Sloan Digital Sky Survey. This region is a legacy field with a rich multi-wavelength investment from the ultraviolet to far-infrared and a high level of spectroscopic completeness. Currently, our "Stripe 82X" survey covers 31 deg² and contains ~6200 X-ray point sources detected at >=5σ level. I will review the characteristics of this survey, on-going programs to target obscured AGN candidates, and how we can use the lessons learned from the synergistic multi-wavelength coverage to develop strategic plans for future surveys and missions. Finally, I will comment on how extending the Stripe 82X survey area to 100 deg² will provide unprecedented insight into the evolution and host galaxy properties of the highest luminosity AGN at the highest redshifts.
16:20-16:35
Becky Canning (KIPAC/Stanford University)
X-ray selected AGN and large-scale structure
X-ray AGN surveys suffer little contamination, low absorption bias and provide direct access to most of the accretion power in the Universe. However, studies of AGN in clusters suffer from small sample sizes. We recently undertook a survey of X-ray AGN in the fields of 135 massive clusters and found the number density of AGN at r₅₀₀ scales inversely with cluster mass in a similar way to the predicted galaxy merger rate. Our statistical technique sidesteps the need for expensive optical follow-up, and allows us to exploit the longest possible lever arms in cluster radius, mass and redshift.
We are now increasing our statistical study to massive galaxy clusters from z=0 to z~1.5. We will identify ~40,000 X-ray point sources and have robust determinations of their environment, i.e. cluster mass, radius and redshift and will utilize multi-wavelength data to explore the AGN host properties. We will explore how far these techniques can be pushed with Chandra and beyond to trace the evolution of AGN in dense environments from early-times, through the peaks of AGN and SF activity, to the present day.
Cosmology I
16:35-16:50
Marat Gilfanov (MPA, Garching)
Fluctuations of unresolved CXB
Fluctuations of the CXB surface brightness carry unique information about faint and low luminosity source populations, which may be inaccessible for conventional LSS studies based on resolved sources. We used Chandra data on XBOOTES field to obtain the power spectrum of fluctuations of unresolved CXB on the angular scales from 3" - 17'. We find that at sub-arcmin angular scales, the power spectrum is consistent with the AGN shot noise, without much need for any significant contribution from their one-halo term. This is consistent with the theoretical expectation that low-luminosity AGN reside alone in their dark matter halos. However, at larger angular scales we detected significant LSS signal above the AGN shot noise. Its power spectrum follows a power law with the slope of 1.2±0.1 and its amplitude is much larger than what can be plausibly explained by the AGN two-halo term. We demonstrate that the detected LSS signal is produced by unresolved clusters and groups of galaxies. For the flux limit of the XBOOTES survey, their median redshift equals ~0.6, and the mean temperature of their ICM, ~1.4 keV, corresponds to the mass of M₅₀₀~ 10^13.5 M_☉. The power spectrum of CXB fluctuations carries information about the redshift distribution of these objects and the spatial structure of their ICM on the linear scales of up to ~Mpc, i.e. of the order of the virial radius.
16:50-17:05
Devon Hollowood (University of California Santa Cruz)
Calibrating the Cluster Richness-Mass Relation for the Dark Energy Survey
The number density of galaxy clusters as a function of mass and time places strong constraints the equation of state of dark energy. In order to measure this function, the Dark Energy Survey (DES) is using a mass proxy called richness. The scatter in the galaxy cluster mass-richness relation is not well known and is expected to be one of the largest sources of uncertainty in DES's cosmological constraints from galaxy clusters. To determine this scatter, I have examined a number of galaxy clusters from archival Chandra data, and compared their X-ray temperature with their richness as determined by redMaPPer, a red-sequence cluster-finding algorithm in use by DES. My comparison of the richness and X-ray temperature mass proxies for these clusters has made significant contributions to efforts to constrain the galaxy cluster richness-mass relation. Additionally, the same X-ray data allow us to investigate the frequency of optical cluster miscentering and selection effects.
17:05-17:20
Anastasia Fialkov (Harvard)
High-redshift X-ray sources and their effect on the 21-cm signal
Unresolved cosmic X-ray background may be produced by high-redshift X-ray sources which also imprint their signature in the spectrum and fluctuations of the neutral hydrogen 21-cm signal from early epochs (z~10-30). The nature of these sources, which are responsible for heating and partially ionization of the Universe, is still uncertain and can be constrained with future X-ray missions as well as radio telescopes probing the 21-cm signal. In my talk I will discuss the effect of X-ray sources on the 21-cm signal and possible synergy between the future X-ray and radio missions.
17:30-19:00
Reception
Wednesday, Aug 17th, 2016
Outflows I
9:00-9:25
Jesus Toala (Institute of Astronomy and Astrophysics (ASIAA))
Hot Stars, their Winds and Feedback
Chandra X-ray telescope has let to major strides in understanding hot stars and their feedback at different scales. High-quality X-ray spectra from hot stars are part of the fascinating legacy to the astronomical community. Furthermore, it has helped us to understand the feedback of their powerful winds and the production of soft, diffuse X-ray emission that permeates the interstellar and circumstellar medium. In this talk I review our current view of X-rays from O-type, Wolf-Rayet, and post-AGB stars and the physical conditions of the diffuse X-ray emission.
9:25-9:40
Joey Neilsen (MIT)
Beyond Photoionization: Understanding the Life Cycles of Black Hole Winds
After 17 years of Chandra HETGS observations, the ubiquity of massive accretion disk winds around stellar mass black holes is no longer in doubt: without (reported) exceptions, blueshifted ionized absorption lines abound in spectrally soft states of high-inclination systems in outburst. Yet the same set of observations indicates that detections of winds during spectrally hard states are few and far between. This empirical dichotomy is still not understood, but given that winds appear to regulate the mass accretion rate at the event horizon, it represents an obstacle to a complete understanding of black hole outbursts. Solving this open problem will require us to disentangle the effects of over-ionization, thermal (in)stability, and wind formation processes, all of which can play a role in the visibility of wind absorption. Using a suite of simulated HETGS observations along with new and archival data, analytical calculations, and numerical simulations, I will discuss the potential for progress in the field of disk winds in the next decade.
9:40-9:55
Lidia Oskinova (University of Potsdam, Germany)
Chandra high-resolution X-ray spectroscopy shocks a standard view on massive stars winds.
Chandra's unique capabilities in high-resolution X-ray spectroscopy revolutionized our ability to study massive star winds. Chandra's spectra provided wealth of information about the temperature and distribution of hot X-ray emitting plasma in winds, and allowed to probe the general wind properties, such as abundances, mass-loss rates, wind velocities, and clumping properties. Chandra spectroscopy demonstrated that winds of the majority of normal massive stars are best studied in X-ray wavelengths. But while we learned a lot about stellar winds using Chandra, we now clearly see many urgent open questions that will be answered during the next decade of Chandra's operation. In this talk I will briefly outline the already passed milestones in understanding of X-rays from massive star winds and present the results of our most recent grating observations of massive stars. But mainly I will concentrate on the most urgent questions in massive star research that shall be addressed by future Chandra observing programs. I will show that we are now on the threshold of making new large steps in massive star astrophysics with the help of Chandra X-ray observatory.
9:55-10:10
Francesco Tombesi (NASA/GSFC and University of Maryland)
The complex circumnuclear environment of radio galaxies revealed by Chandra HETG
Highly collimated relativistic jets are routinely observed in radio galaxies. Until recently, this was the main known mechanism for the deposition of mechanical energy from the central black hole into the host galaxy in these sources. Deep X-ray spectroscopic observations are changing this view, showing an increasing evidence for winds in radio galaxies as well. The relation between the relativistic jet and the winds is still unclear, but the latter may play a role in the initial jet collimation. A new 500ks long Chandra HETG campaign on three sources - namely 3C 390.3, 3C 111, and 3C 120 - shows a complex circumnuclear environment in these radio galaxies, with winds, hot and photo-ionized interstellar medium, and reflection features from the disk and torus. This is only the tip of the iceberg, and only future very deep Chandra observations will allow to shed light on the complex environment in radio and seyfert galaxies. Chandra HETG is currently the only instrument providing the highest combined sensitivity and energy resolution from the soft X-ray to the crucial Fe K band, and high resolution imaging using the zeroth order data.
10:10-10:40
Break
Hot Thermal Plasmas I
10:40-11:05
Salvatore Sciortino (INAF-Oss. Astronomico di Palermo)
Chandra studies of stars and exoplanets: The next ten years
After briefly outlining the impact of Chandra observations on the studies of mostly young/pre-main sequence stars/ultra cool dwarfs and planetary systems I will focus on some more promising and/or more controversial study areas. I will discuss the likely impact of future Chandra observations on their advance, as well as my current view of the study subjects in which the return of those observations will likely be more valuable while we are waiting for the next generation X-ray observatory(ies).
11:05-11:20
Cecilia Garraffo (Harvard-Smithsonian Center for Astrophysics)
Understanding the evolution of stellar X-ray activity in time
Stellar X-ray emission originates through dissipation of magnetic fields generated by the combination of stellar rotation and turbulent convection. Observations of young open clusters have revealed a bimodal distribution of the rotation periods of solar-like stars that indicate a rapid transition between fast and slow rotation. Recent studies suggest that magnetic complexity can play an important role in controlling the spin-down rates. By calibrating the evolution of spin-down with age against young open cluster observations it is possible to infer how magnetic activity and X-ray emission should change in time. In this talk I will discuss how X-ray activity evolves with time for stars of different mass and how Chandra surveys can test both stellar spin-down theory and the rotation - X-ray activity relation.
11:20-11:35
Scott Randall (SAO)
Heating the Intracluster Medium Through AGN Feedback
There is generally less cool phase gas at the centers of galaxy groups and clusters than what is predicted by purely radiative cooling models. AGN feedback, where the heating rate from the central AGN is coupled to the gas cooling rate in the intracluster medium (ICM), is a leading candidate to explain this apparent discrepancy. Although there is generally sufficient energy output by central AGN to balance gas cooling, the details of how this energy is coupled to the ICM are poorly understood. I will review the current observational evidence for different energy transport mechanisms, with an emphasis on the role of heating by weak shocks, and discuss what can be done with Chandra over the next ten years to advance our understanding of AGN feedback and take advantage of synergies between other current and future astrophysical observatories.
11:35-11:50
Ken Ebisawa (JAXA/ISAS)
Origin of the Galactic X-ray Emission Unresolved
The Galactic Ridge X-ray Emission (GRXE) is apparently extended X-ray emission along the Galactic plane, whose origin has been under debate for more than 30 years. The X-ray spectrum is characterized by hard continuum with a strong Fe K emission feature in the 6~7 keV band. Ebisawa et al. (2001, 2005) carried out deep (~200 ksec) Chandra observations on a Galactic plane region at (l,b)≈(28.5,0.0), and resolved ~25% of the GRXE into point sources. Revinivtsev and Sazonov (2007) claimed that ~100% of the GRXE in this region may be ultimately resolved into dim Galactic point sources, probably cataclysmic variables (CVs) and coronally active stars. Revnivtsev et al. (2009) carried out a ~900 ksec Chandra observation at (l,b)≈(0.08,-1.42), and claimed that ~80% of the GRXE is resolved into point sources.
Now, it is established that majority of the GRXE is composed of dim Galactic point sources. Then we face two new questions; (1) Is 100% the GRXE accounted for by dim point sources? Isn't there any diffuse Galactic X-ray emission at all? (2) What are those dim Galactic point sources which account for majority of the GRXE? Can CVs and coronally active stars explain all the dimmest Galactic point X-ray sources?
For the first question, recent observations suggest that there exists Galactic diffuse X-ray emission. Molaro et al. (2014) and Warwick (2014) suggest presence of X-ray scattering in the interstellar medium and/or young Galactic source populations. Nobukawa et al. (2015) indicated clear spatial correlation between the 6.4 keV emission line and molecular clouds, suggesting proton-induced fluorescence X-ray emission from interstellar clouds. However, we do not know exactly how much fraction of the GRXE is due to the diffuse emission.
In order to answer to the second question, we carried out near-infrared (NIR) follow-up spectroscopic observations in the two deep Chandra fields using NTT/SofI and Subaru/MOIRCS. We obtained well-exposed NIR spectra, and found that there are three main classes of Galactic sources based on the X-ray color and NIR spectral features: those having (A) hard X-ray spectra and NIR emission features such as HI (Br), He I, and He II, (B) soft X-ray spectra and NIR absorption features such as HI, Na I, Ca I, and CO, and (C) hard X-ray spectra and NIR absorption features such as HI, Na I, Ca I and CO. From these features, we argue that class A sources are cataclysmic variables (CVs), and class B sources are late-type stars with enhanced coronal activity, which is in agreement with current knowledge. Class C sources possibly belong to a new group of objects, which has been poorly studied so far. We suggest that this newly recognized class of the sources may contribute to a non-negligible fraction of the GRXE. In our talk, we review our current understanding of the GRXE, and discuss how we may resolve remaining problems of the GRXE using Chandra in next 10 years.
11:50-12:05
Smita Mathur (The Ohio State University)
Circumgalactic medium of galaxies
It is well-known that most galaxies are missing most of their baryonic mass. Perhaps more surprisingly, they also seem to be missing most of their metals. Theoretical models of galaxy formation and evolution predict that the circumgalactic medium of galaxies contains a huge reservoir of warm-hot gas that may account for a large fraction of missing baryons and metals. Chandra observations have already contributed significantly to this field and synergy with other missions has been very important. I'll review the current status of this field, and outline paths for progress in the next decade, as we get ready for Athena.
12:05-13:20
Lunch: X-ray Data Analysis for the Next Decade (Panel Discussion)
Structure of the Cosmos I
13:20-13:45
Giuseppina (Pepi) Fabbiano (CfA)
Chandra's contribution to galaxy evolution: discoveries and open questions
Chandra's observations of the X-ray emission of galaxies have uniquely advanced our understanding of galaxy evolutions in at least three areas: the final stages of the evolution of different stellar populations (SNae and populations of stellar remnants in binary systems); the physical and chemical evolution of the gaseous component of galaxies in different environments; and the entire range of 'activity' of nuclear supermassive black-holes. Moreover, these observations open a unique window on the study of feedback (both from SNae and XRBs and from AGNs) on the host galaxy. In this talk I will present illustrative examples, concentrating on open questions and avenues for future progress.
13:45-14:00
Dacheng Lin (University of New Hampshire)
Searching for Distant Wandering Massive Black Holes with Chandra
Hyper-luminous (>10⁴¹ erg/s) off-nuclear X-ray sources (HLXs) are strong candidates for hosting wandering massive (>100 solar mass) black holes (BHs) that are expected to be left over in several important astrophysical processes, such as galactic mergers. There are only about a dozen HLX candidates known so far, and they are generally found in nearby galaxies within 100 Mpc. The supreme angular resolution and high sensitivity offerred by Chandra should allow to search over much more distant galaxies (>1 Gpc) and find many more HLXs. I will demonstrate this using a new HLX that we just found (Lin et al. 2016, ApJ, 821, 25) as an example. This HLX is at a distance of d_L=2.3 Gpc and is at a projected offset of ~1 arcsec (5.2 kpc) from the nucleus of the main host galaxy. It was serendipitously detected, showing an outburst with ultrasoft X-ray spectra and a peak X-ray luminosity of 4×10⁴³ erg/s. It is best explained as a massive (~10⁵ solar mass) BH embedded in the nucleus of a tidally stripped merging satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. This is the most distant and the most luminous HLX known so far.
14:00-14:15
Q. Daniel Wang (University of Massachusetts)
Sgr A* and its environment: new insights from X-ray observations
Sgr A* at the center of our Galaxy provides us with an excellent laboratory to study the physics of a supermassive black hole, as well as its accretion process and time-dependent interaction with the circumnuclear environment. I will review a set of very recent studies, based primarily on extensive Chandra X-ray observations, including a systematic detection and statistical analysis of X-ray flares, as well as on quantitative comparisons of the observed quiescent X-ray emission with 2-D and 3-D hydrodynamic simulations suited to explore both the accretion close to the black hole and the detailed interplay with the stellar winds from individual massive stars orbiting around it. I will show what fascinating insights we have learned from these studies and how future work may further advance our understanding of Sgr A*, which is also important to the investigation of galactic nuclear phenomena in general.
14:15-14:30
Joseph Burchett (Univ. of Massachusetts - Amherst)
Combining X-rays and QSO spectroscopy to probe the intracluster and circumgalactic medium
While X-ray facilities are well suited to observe the hot (T>10⁶ K) phases of the intracluster and circumgalactic medium (ICM and CGM), UV absorption-line spectroscopy against background objects can uniquely constrain the warm (T~10⁴ K) and warm-hot (T=10^5-6 K) gas. I will present results from a program that leverages Chandra, XMM-Newton, the Hubble Space Telescope (HST), and ground-based galaxy surveys to (1) search for the missing baryons in galaxy clusters and (2) examine environmental effects on the gaseous halos of individual galaxies. This multiwavelength study of the ICM and CGM is yielding new insight into the cosmic baryon budget as well as the transformative processes galaxies encounter in cluster environments. Applying this combined methodology to poorer clusters and groups promises a bright future for galaxy evolution science as Chandra and other X-ray facilities supplement the vast (and growing) HST archive.
14:30-14:45
Scott Barrows (University of Colorado Boulder)
Building the Largest Catalogues of Offset AGN, HLXs and IMBH Candidates with Chandra
The excellent spatial resolution of Chandra allows the locations of X-ray sources within galaxies to be constrained to high accuracy. We have developed a custom and automated procedure that utilizes this capability to generate small uncertainties (sigma~0.3") on the relative astrometry between archival Chandra data and overlapping coverage of galaxies from optical databases such as the Sloan Digital Sky Survey and the Hubble Space Telescope (HST). Combining this procedure with optical observations covering Chandra fields, we can identify galaxies that host off-nuclear X-ray sources that will be useful in a variety of applications and fields of astronomy. For example, luminous hard X-ray sources that are off-center from galaxy nuclei may be offset active galactic nuclei (AGN), which form as products of galaxy mergers. Using our astrometric procedure, we have discovered and published the first systematic sample of spatially offset AGN consisting of 18 sources. We have used this sample to place constraints on the triggering mechanisms of AGN in galaxy mergers by probing down to nuclear separations of less than 1 kpc and finding that the fraction of AGN in mergers significantly increases at these small separations. Follow-up HST imaging has revealed stellar bulges spatially coincident with these offset AGN, vetting the effectiveness of our technique and demonstrating its usefulness beyond that of identifying offset AGN. For example, we used this procedure to identify objects of lower X-ray luminosity that fall into the mysterious classes of ultra-luminous and hyper-luminous X-ray sources (ULXs and HLXs). Many of these sources may represent events of exotic accretion onto stellar-mass compact objects. Alternatively, some of them may be in the elusive class of intermediate-mass black holes (IMBHs) that are valuable for understanding the origins of supermassive black holes. Previous catalogues of ULXs and HLXs had used XMM-Newton, limiting the studies to nearby galaxies, poor spatial resolution and small sample sizes. With Chandra, our procedure can push these studies to higher redshifts and better spatial resolution, thereby creating the largest catalogues of ULXs, HLXs and IMBH candidates. We have already identified over 300 HLXs, an order of magnitude larger than combined samples of previous studies. We find that 32 of these HLXs are strong IMBH candidates and excellent targets for follow-up multi-wavelength observations.
14:30-15:00
Break
Cosmology II
15:15-15:40
Steve Allen (Stanford University)
Cluster Cosmology for the Next Decade
Studies of galaxy clusters have proved crucial in helping to establish the standard model of cosmology, with a universe dominated by dark matter and dark energy. X-ray observations have been central to this work. I will summarize the latest results on cosmology and fundamental physics from galaxy cluster studies, highlighting Chandra's key role in providing precise, relative mass calibration. The prospects for progress over the next decade are outstanding, with new cluster catalogs, hundreds of times larger and with far greater redshift reach, being constructed across a variety of wavelengths. Chandra follow-up observations will be vital to the full exploitation of these data. I will discuss how to make this contribution as efficient and impactful as possible.
15:40-15:55
Kevin Schawinski (ETH Zurich)
The "missing seed" problem for massive black holes at high redshift
When, where and how the original seeds of black holes formed and grew is one of the major outstanding questions in astrophysics. The observational constraints for seed formation and growth consist of very massive quasars at z~6 with very low space densities on the one hand, and a lack of z>6 AGN in the deepest Chandra observations on the other hand. The lack of AGN at z>6 in the 4 Msec deep field in particular is puzzling as the same volume contains on the order of ~1e3 dropout galaxies detected by Hubble; Chandra detects neither individual AGN in these galaxies, nor an integrated signal of black hole growth from stacking. I will present a simple phenomenological model with meets both the observational constraints from the Chandra deep fields, and the quasar surveys. The only configuration which works is that black hole seed formation at z>6 is highly inefficient and suppressed in most galaxies. I discuss these results and their implications for future high redshift surveys with Chandra and synergy with JWST, ATHENA and other missions.
15:55-16:10
Nico Cappelluti (Yale University)
Early black holes: synergies between Chandra and surveyors of the 20's.
The search for evidence of the formation mechanism of SMBHs requires X-ray observations of the Universe at z>5. This is a challenge because the deepest Chandra observations combined with HST-WFC3 provide only a handful of candidate high-z AGNs to use to test SMBH formation mechanisms. Other than that, we need to search for their footprints in cosmic backgrounds. I am presenting recent observational results that may shed light on the first black holes in the Universe. In particular, the recently detected joint fluctuations of the Chandra CXB and the Spitzer CIB are opening a new window on this epoch of cosmic history and paving the way to JWST, Euclid, The X-ray Surveyor, and Athena. Recent LIGO detections of BH coalescence opened the fascinating hypothesis of primordial black holes as a possible solution for the DM problem. Such a contribution, if any, would leave peculiar signatures in the backgrounds' anisotropies. In any case, future wide field surveys will provide enough data to study the first generation of black holes. I will present future synergistic approaches between Chandra and multiwavelength facilities flying in the late 10s early 20s that will help to shed light on the earliest black holes in the Universe.
Synergies and Future Missions
16:10-16:35
Feryal Ozel (University of Arizona)
From Chandra to the X-ray Surveyor: Legacies and New Frontiers
Chandra's unprecedented angular resolution opened a new window onto the X-ray universe. From resolving the structure of clusters and supernova remnants to finding distant AGN, it has transformed our understanding of structure formation, galaxies, stars, compact objects, and our own Galaxy. As we get ready for the next decade and beyond, I will discuss, on behalf of the X-ray Surveyor Science and Technology Definition Team, the frontier science questions still to be answered and how a large area, high angular resolution mission can address them. I will describe the concept being developed for the X-ray Surveyor and its unique capabilities for finding the first black holes in the universe, hot baryons in the circumgalactic medium, and answer long standing questions about stellar lifecycles and the astrophysics of compact objects.
16:35-18:05
Panel Discussion: Synergies with Major Facilities
A panel discussion on synergies between Chandra and major facilities in the coming decade featuring invited panelists:
• Paul Nandra — Max Planck Institute for Extraterrestrial Physics
• Rachel Osten — STScI
• Norbert Schartel — European Space Agency
• Daniel Stern — NASA JPL
• Reinout Van Weeren —
Thursday, Aug 18th, 2016
Accretion II
9:00-9:25
Jeno Sokoloski (Columbia)
The Flows and Shell Burning of Accreting White Dwarfs
Determining why novae - the most common stellar explosions - produce gamma-rays was not one of Chandra's original scientific motivations. Within the next decade, however, Chandra could provide crucial information about the shocks in nova outflows, and thereby reveal the physics behind the recent paradigm-shifting discovery that normal novae produce GeV gamma-ray emission. With its high spatial resolution and spectral capabilities, Chandra is well suited to probing the shocked flows onto, and from, accreting and eruptive white dwarfs (WDs). It is also ideally suited for the study of populations of accreting and shell-burning WDs. After briefly reviewing select Chandra findings and potential future progress in the fields of accreting WDs, novae, and WD jets, I will speculate about how intensive Chandra observations of shocks in young novae shells might: 1) constrain the physics of particle acceleration; and 2) reveal the mechanisms by which ejecta from novae are expelled and shaped.
9:25-9:40
Jun Yang (University of Massachusetts, Harvard-Smithsonian CfA)
Time evolution of luminosity and spin period of X-ray pulsars in the Small Magellanic Cloud
We have collected and analyzed all XMM-Newton, Chandra and RXTE observations of the known pulsars in the Small Magellanic Cloud. We have classified various pulsar properties in the luminosity range of L_X=10³¹-10³⁸ erg/s, classified sources as pulsating and non-pulsating, and used the faintest and brightest sources to map out the boundaries of their X-ray emission. Our 15-year pipeline generates a suite of useful products for each pulsar detection in different energy bands: point-source event lists, high time-resolution light curves, pulse profiles, periodograms and X-ray spectra. After combining the observations from these telescopes, we have the complete histories of the spin period, pulse fraction, period amplitude and luminosity of the known pulsars. We found that 26 pulsars clearly spin up and another 17 pulsars spin down, illuminating the transfer of mass and angular momentum from an accretion disk or wind to the neutron star. The observed pulse profiles in our archive are being fitted to geometric models of X-ray emission in order to constrain the physical parameters of the pulsars. We will discuss the pulsar physics and evolution the survey is revealing, and point to future observations that can make the next steps in understanding these objects.
9:40-9:55
Herman Marshall (MIT Kavli Institute)
High Resolution Spectroscopy of X-ray Binaries in the M 31 Bulge using the HETGS
We obtained high resolution X-ray spectra using the Chandra High Energy Transmission Grating Spectrometer (HETGS) of the bulge of the nearby galaxy, M 31. We pointed Chandra for 230 ks each in three directions about 2 arcmin apart across the bulge, so that sources in a 4 arcmin diameter region would get about 700 ks exposure each and at a variety of roll angles. We found 43 sources with over 1000 net counts in 0th order and 12 with more than 5000 counts, all of which are suitable for HETGS analysis. We will present the first results from spectroscopic analysis of the brightest sources: spectral shapes, edges, and emission lines. Transients are also apparent in the year spanned by the observations. These data provide a foundation for much longer observations to trace abundances in the ISM of M 31 and in supernova remnants -- an ideal project for the next ten years of Chandra.
9:55-10:10
Vallia Antoniou (Smithsonian Astrophysical Observatory)
The Large Magellanic Cloud: Bridging the Metallicity gap
The Small Magellanic Cloud (SMC) has been the subject of systematic X-ray surveys over the past two decades, which have yielded a rich population of high-mass X-ray binaries comprising predominantly Be/X-ray binaries. In Cycle 14, we performed a deep Chandra survey of the SMC which targeted regions with stellar populations ranging between ~10-100 Myr. X-ray luminosities down to ~3×10³² erg/s were reached, probing all active accreting binaries and extending well into the regime of quiescent accreting binaries and X-ray emitting normal stars. This survey showed a clear dependence of the formation efficiency of X-ray binaries on age, and clear evidence for the propeller effect – the centrifugal inhibition of accretion due to the interaction of the accretion flow with the pulsar's magnetic field. Unlike the SMC, the Large Magellanic Cloud (LMC) has been neglected as a target for studies of X-ray binary populations. Consequently, we have a much poorer picture of its X-ray source populations: only 40 X-ray binaries have been identified in the LMC to date, in contrast to 120 in the SMC.A key project Chandra can and should accomplish in the next few years is a comprehensive survey of sources in the LMC brighter than few times 10³² erg/s. By selecting fields representing young (<100 Myr) stellar populations of different ages, we will match those sampled in our similar survey of the SMC. This way we will obtain a similarly deep census of the LMC X-ray binary populations, but at metallicities intermediate between those of the SMC and our Galaxy. In particular, the well-known star-formation history of the LMC will allow us to study the X-ray source populations associated with different stellar generations, and in combination with its proximity, to identify their optical counterparts and understand their nature. These observations will provide the deepest X-ray luminosity functions (XLFs) for X-ray binaries ever recorded, enabling us to: (a) directly measure their formation efficiency as a function of age and metallicity; (b) address the XLF evolution in the 10-100 Myr range, and particularly the influence of the propeller effect; (c) by comparison with X-ray binary population synthesis models constrain parameters relevant to their formation and evolution. The LMC and the SMC are the only galaxies near enough to allow this type of study at a depth similar to that of Galactic studies, but without the Galactic limitations of distance uncertainties and obscuration.
10:10-10:25
Javier Garcia (Harvard-Smithsonian CfA)
The question of hard-state disk truncation in black holes binaries.
X-ray spectroscopy is a powerful tool to probe the strong-field gravity near a black hole's event horizon. The spin of the black hole is measured under the critical assumption that the inner-edge of the accretion disk reaches the innermost-stable circular orbit (ISCO). This assumption is on firm footing for soft spectral states, but is contentious for hard spectral states. Spin measurements of stellar-mass black holes in the hard state have engendered controversy, as theoretical predictions for accretion flows can place the disk truncation at scales of ~100 ISCO radii. On the other hand, fits to observational data in the so-called "bright hard stater" indicate that the disk extends down to the ISCO, where it remains during the transition to soft states. Thus, the question of bright hard-state truncation remains unresolved and a source of major contention in the field. The direct detection (or absence) of emission associated with a disk extending to the ISCO is the smoking-gun test to rule truncation in or out. We discuss the current state of X-ray reflection modeling and measurements, and argue that by employing a new and self-consistent model on spectral data taken in the bright hard state while using the complementary capabilities of Chandra and NuSTAR, it is possible to achieve a definitive test of the truncation paradigm for the bright hard state.
10:25-10:55
Break
Outflows II
10:55-11:20
Jon Miller (University of Michigan)
High Spectral Resolution in the Next Decade
The X-ray imaging capability of Chandra is beyond compare, and it has enabled a multitude of scientific breakthroughs. The sharp images obtained with Chandra have better connected X-ray astronomy to longer wavelengths. The high spectral resolution delivered by the Chandra gratings spectrometers has also delivered breakthrough science, and it connects X-ray studies to optical and UV spectra. Moreover, a rich discovery space lies ahead. In the post-Hitomi era, Chandra will continue to be the flagship spectroscopy mission. This talk will explore ideas for how Chandra spectroscopy of black holes across the mass scale can make key progress over the next ten years, setting the stage for Athena.
11:20-11:35
Myriam Gitti (University of Bologna / INAF-IRA)
Radio mini-halos and AGN feedback in cool-core galaxy clusters: the Chandra legacy and the SKA perspectives
In the majority of cool-core galaxy clusters the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). Chandra observations revealed that the lobe radio plasma interacts with the surrounding thermal intra-cluster medium (ICM) by filling the X-ray cavities. This 'radio-mode AGN feedback' phenomenon, which is widespread, is critical to understand the cooling flow quenching and, more generally, the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to contribute to the turbulence in the central ICM. Such a turbulence may in turn supply additional heating to the thermal gas and also play a role for the origin of non-thermal emission on cluster-scales. Diffuse radio emission has been observed in a number of cool-core clusters in the form of a so-called 'mini-halo' surrounding the radio-loud BCG on scales comparable to that of the cooling region.In this contribution we will present a recent study of the current collection of known mini-halo clusters (~20 objects) based on a homogeneous re-analysis of X-ray Chandra data, indicating that the scenario of a common origin of radio mini-halos and gas heating in cool-core clusters is energetically viable. We will show that future radio surveys with LOFAR and SKA have the potential to increase the number of radio mini-halos to ~1000 objects, and further discuss the role of synergies of these radio surveys with current and future X-ray observations in establishing the radio mini-halo origin. In particular, with its unique role in providing spatially-resolved spectral measurements of the X-ray emitting regions associated to the radio mini-halos, the archival and dedicated Chandra observations of mini-halo clusters will deliver a unique legacy for future radio surveys.
11:35-11:50
Missagh Mehdipour (SRON Netherlands Institute for Space Research)
Multi-wavelength campaign on NGC 7469: deciphering variability of the ionised outflows
We have carried out an extensive multi-wavelength campaign on active galaxy NGC 7469 in 2015-2016. The goal of this recent campaign is to gain new insights into the AGN accretion/emission phenomenon and the associated ionised outflows, which couple supermassive black holes to the environments. Our campaign consists of multiple joint observations with five space observatories: Chandra, XMM-Newton, NuSTAR, Swift and HST. We present the highlights of our findings from the campaign, with a focus on new results obtained from the Chandra observations. Determining the physical structure and origin of outflows, and understanding their role in shaping AGN spectra and variability, is a crucial requirement for any general characterisation of the outflows and for advancing our knowledge of AGN/galaxy co-evolution. High-resolution spectroscopy using Chandra HETG, together with XMM-Newton RGS and HST COS, has enabled us to parameterise the multiple absorption components found in NGC 7469, and thus map the ionisation, chemical and dynamical structure of the outflow in this AGN. We determine the location of the outflow components through analysis of their variability, investigate the launching mechanism of the outflows, and study their impact on their environment.
11:50-12:05
Maurice Leutenegger (NASA/GSFC/CRESST/UMBC)
Assessing the accuracy of OB star mass-loss rate measurements using high-resolution X-ray spectroscopy
The powerful, radiatively-driven winds of massive OB stars can remove a substantial fraction of their mass over their main sequence lifetime, as well as injecting chemically enriched matter, energy, and momentum into the surrounding ISM. Thus an accurate quantitative characterization of the wind properties is crucial for both stellar evolution models as well as studies of feedback of massive stars into their environments.
A suite of diagnostics in different wavelength bands are used to diagnose the mass-loss rates of OB star winds. Optical emission lines such as Hα, as well as radio free-free emission, are sensitive to the wind emission measure. However, the emission measure contains information both about the mass-loss rate as well as density inhomogeneities, and these two effects are difficult to disentangle. UV absorption lines from moderately ionized species trace wind optical depth in a given ion, but are sensitive to assumptions about ionization balance, which may also be influenced by density inhomogeneities.
X-rays are generated in the winds of massive OB stars by shocks generated by instabilities in the radiative driving force, with the result that a small fraction of the wind is heated to temperatures of order a few to several MK. The transfer of X-rays is assumed to be mostly optically thin with respect to line transitions, but photoelectric absorption by the cool bulk of the wind can reduce the X-ray flux. The differential reduction in flux between the front and back hemisphere of the star results in blueward skewed emission lines, with the degree of skewness probing the wind optical depth, and thus mass-loss rate. Because the X-ray opacity is due to continuum photoelectric absorption and does not depend strongly on the ionization balance of the wind, the line-shape diagnostic is quantitatively robust against the effects that induce systematic errors in other diagnostics.
Mass-loss rate determinations from X-ray emission line shapes have their own associated systematic uncertainties, including the possible importance of geometrically large clumps ("porosity"), presence of contaminating spectral features from nearby companion stars, uncertainties in opacity, He ionization balance, atomic physics and plasma modeling, and assumptions about the spatial and temperature structure of the X-ray emitting regions. We quantify these uncertainties and place them in context with the uncertainties associated with diagnostics in other wavelength bands.
12:05-12:20
Demosthenes Kazanas (NASA/GSFC)
The Universal Magnetic Structure of Black Hole Accretion Disk Winds
Accretion disk winds are a ubiquitous feature of accreting black holes, manifest in their blue-shifted spectral absorption lines. Their importance lies partly in the fact that they may remove the accretion disks' angular momentum, a condition necessary for making accretion possible, and on their potential feed back and influence on their environment. The variety of processes that can launch such winds has made their origin contentious. However, X-ray spectroscopic data and analysis of the wind associated with the galactic black hole binary GRO 1655-40 have argued in favor of a magnetic origin but only by excluding the other candidate processes. We present our computation of absorption line spectra of self-similar MHD accretion disk wind that provide excellent fits to the Chandra HETG X-ray data of GRO 1655-40 by reproducing both their combined global ionization properties (i.e. the correct combinations of ionic columns and their ionization parameter) and also the detailed kinematic structure of their absorption features. Most importantly, our GRO 1655-40 wind models are the same ones we employed in the successful account of the X-ray absorber systematics of AGN as diverse as Seyfert galaxies and BAL quasars, modified only by the different ionizing spectrum of GRO 1655-40 and scaled to its black hole mass. The success of the present models argues for the universality of accretion disk wind properties across the entire (10 M_☉ - 10⁹ M_☉ black hole mass range.
12:20-12:35
Aneta Siemiginowska (CfA/SAO/CXC)
Relativistic Jets in the Next Decade of Chandra Science
X-ray studies of relativistic jets require (sub)-arcsec angular resolution to detect and resolve their structure. Chandra is currently the only X-ray telescope capable of mapping X-ray jets in nearby Active Galactic Nuclei and resolving X-ray jets associated with powerful quasars at high redshifts. Before Chandra only a few extragalactic X-ray jets have been studied. Now, after 16 years of Chandra observations many new X-ray jets have been discovered and the X-ray Jets web page contains about 100 jets associated with radio galaxies and quasars. However, until now quasar jet surveys with Chandra have been shallow (<10 ksec exposures), at low redshift (median at z<1) and focused on discovering the X-ray jets. Our knowledge of the most powerful quasar jets is based on 45 published quasars with short exposures and only 5 deep (>100 ksec) observations to date. These existing observations demonstrate that the quasar jets have complex dynamics, X-ray emission processes, trends along the jet and trends with redshift that we understand only poorly. We will discuss the Chandra next decade studies of jets necessary for making progress in understanding of the jets physics and in more general the quasar power.
12:35-13:35
Lunch
Hot Thermal Plasmas II
13:35-14:00
Helen Russell (Institute of Astronomy, Cambridge)
Driving hot and cold gas flows with AGN feedback in galaxy clusters
Powerful radio jets launched by a central supermassive black hole pump a substantial amount of energy into their host galaxies and cluster environment. This feedback from the central AGN is thought to regulate galaxy growth and cooling of the surrounding hot atmosphere. I will review ALMA Early Science observations of central galaxies in cool core clusters that have revealed massive molecular gas filaments extending 5-15 kpc, which likely formed from gas cooling out of the clusters' hot atmospheres. I will also present new ALMA observations of extended molecular filaments in the Phoenix and PKS0745-191 brightest cluster galaxies, which are drawn up around radio bubbles and show that radio jets interact with cold, dense molecular gas as well as the hot, diffuse intracluster medium.
14:00-14:15
Thomas Ayres (University of Colorado)
Voyage to Alpha Centauri A & B, Chandra's Favorite X-ray Stars
StarShot is a visionary, audacious, and frankly pretty crazy, project dreamed up by the Breakthrough Initiatives Foundation. The plan is to laser-launch a swarm of "star chips" on photon sails to fly to our nearest stellar neighbors, and send back close-up images of potentially habitable planets, before the end of the century. The initial target is the central binary of the Alpha Centauri triple system, containing sunlike Alpha Cen A and its cooler, K-type companion B. Chandra has contributed to the StarShot project, albeit in an accidental way, through a now ten-year record of the coronal X-ray activity of A and B. High-energy coronae are a key stellar characteristic influencing planetary habitability, as well as a proxy for age, but the main importance to StarShot is that activity is a crucial source of noise in up-coming intensive campaigns of photometric, Doppler-reflex, and astrometric searches for planets in Habitable Zone orbits around the Alpha Cen stars. For these reasons, Chandra will continue to inform efforts to characterize the Alpha Cen system, and find suitable planetary targets for the eventual interstellar nanobot swarm from Earth.
14:15-14:30
Scott Wolk (Harvard-Smithsonian CfA)
Observable Effects of Exoplanets on Stars
We discuss observational evidence for magnetic star-planet interactions (SPI) observed in X-rays and UV and the possibilities presented by the Transiting Exoplanet Survey Satellite (TESS) of discovering new targets in the next decade. Hot Jupiters can significantly affect the activity of their host stars through tidal and magnetic interaction, leading to both increased and decreased stellar activity levels. In the HD189733 system, not only is the star rotating faster than would be indicated by the activity of the stellar secondary, X-ray and UV flares are found preferentially in a very restricted range of planetary phases. We explain such recurrent, phased variability with the support of MHD simulations (Matsakos et al. 2015): planetary gas is launched forming a stream of gas that gets compressed and accrete onto the star. A very long flare, of order the planetary distance, is also suggestive. Further, the X-ray transit was surprisingly deep – three times the depth of the optical transit. This can be traced back to thin outer atmosphere layers of the planet, which are transparent at optical wavelengths but opaque to X-ray photons. We have calculated that TESS will identify about 35 additional bright X-ray sources which host transiting hot Jupiters.
14:30-14:45
Ignazio Pillitteri (INAF-OAPA)
X-rays as tools to identify and study stellar clusters in the era of GAIA
Star formation occurs in molecular clouds at different sizes and time scales. While infrared (IR) surveys provide deep knowledge of the cold emission of protostars and stars with disks, X-rays are important to identify embedded stellar objects and stars that have lost their disks and formed new planets. I will present two examples of a powerful synergy between X-ray and IR observations that allowed us to identify two new stellar clusters in Orion and Rho Ophiuchi, and determine their distances and ages. In the forthcoming era of GAIA and before the advent of Athena, Chandra and XMM-Newton can significantly contribute to the knowledge of the spatial scales, distances and ages of young stellar clusters and associations within 1 kpc, and eventually the mechanisms of stellar formation and evolution.
14:45-15:00
Alessandro Paggi (Smithsonian Astrophysical Observatory)
X-ray Mass Profiles from Chandra Galaxy Atlas
We present results of a Chandra/XMM-Newton joint analysis on two Early Type Galaxies (ETGs), NGC4649 and NGC5846. These two galaxies represent the best examples of opposite conditions for ISM distribution in ETGs. In NGC4649 the X-ray morphology is generally relaxed and symmetric, indicating that the interstellar medium (ISM) distribution is close to the hydrostatic equilibrium, with only minor disturbances on ~kpc scales connected with the faint central radio source. On the opposite, NGC5846 is a case of significantly disturbed morphology, showing large scale (~kpc) evidences of gas sloshing and ram pressure stripping caused by interactions with companion galaxies, as well as sub-parsec scale X-ray "bubbles" connected with recent AGN activity. X-ray observations of the hot ISM is used to measure the total enclosed mass assuming hydrostatic equilibrium, and comparison with mass distributions obtained through optical data of stellar dynamics (SD), globular clusters (GCs) and planetary nebulae kinematics yields informations about disturbances in the ISM distribution due to nuclear activity, merging history, etc. Our analysis makes use of Chandra data - exploiting the unmatched spatial resolution of the ACIS detectors to reveal fine ISM features and disturbances in the inner galactic regions - and XMM-Newton data - relying on the large field of view of EPIC detector to extend the mass profiles to larger radii. We then measured the mass profiles in various azimuthal sectors to separate different gas features (e.g., discontinuity and extended tail) and compared them with GC/SD based mass profiles. Since X-ray background evaluation is particularly relevant in the outer, fainter regions of the galaxies, extra care is put in comparing the effects of different background subtraction/modeling procedures, as well as the effects of element abundances gradient that may affect the total mass evaluation. The X-ray mass profiles of NGC4649 are generally relaxed and do not show azimuthal asymmetries, and the comparison with the optical mass profiles confirms the small deviations from the hydrostatic equilibrium between 0.5-5 kpc due to the non-thermal pressure component accounting ~30% of the observed gas pressure, and likely linked to nuclear activity. On the other hand, the faint wing-like features reported in the NE and SW directions and interpreted as a consequence of the motion of the galaxy through the Virgo ICM do not affect significantly the mass distribution in the NGC4649 halo. In NGC5846 the X-ray derived mass profiles show significant asymmetries in the ISM distribution, especially in the NE direction where the halo shows evidences of interaction with the group companion spiral galaxy NGC5850. The comparison with optical mass profiles shows in this direction evidences of gas compression and decompression due to gas sloshing on <10 kpc scales, and this effects disappear in the NW direction where the emission is smooth and extended. On larger scales, instead, the match between X-ray and optical data is recovered allowing for element abundance gradient, that shows decreasing abundances in the outer regions of the galaxy, likely as a consequence of intra-group interactions.
15:00-15:30
Break
Key Legacy Projects
15:30-17:00
Panel Discussion: Key Legacy Projects
A panel discussion on key legacy projects featuring invited panelists:
• Fabrizio Fiore — INAF-OAR
• Martin Laming — Naval Research Lab
• Leisa Townsley — Penn State University
• Alexey Vikhlinin — CfA
• Daniel Wang — University of Massachusetts
Evening
Banquet
Friday, Aug 19th, 2016
Transients and Periodic Sources
9:00-9:25
Raffaella Margutti (NYU)
X-rays from young Supernovae illuminate the diversity of their progenitors
X-ray observations are providing critical insights into Supernova explosions and the nature of their progenitors. In this talk I will highlight some recent results from our dedicated programs at high-energies that allowed us to (1) uncover the weakest engine-driven SNe and understand their link to Gamma-Ray Bursts; (2) Reveal a "sequence of evolution" of core-collapse progenitors in the mass-loss plane; (3) Detect X-rays at the location of super-luminous supernovae; (4) put the most stringent constraints to the progenitors of Type Ia SNe by using the deepest X-ray observations ever obtained. (5) Reveal the ejection of a massive, H-rich stellar envelope timed with the collapse of a stripped star. These observations represent the first solid detection of a young extragalactic stripped-envelope SN out to high-energy X-rays of ~40 keV.
9:25-9:40
Kari Frank (Penn State University)
Chandra Observations of SN 1987A: An Unprecedented View of the Life and Death of a Blue Supergiant
Chandra has now been observing SN 1987A for over half of its 30 year life. For the last 16 years Chandra observations have provided a pivotal and unique window into the evolution of the newborn supernova remnant and have been critical for interpreting optical, infrared, and radio observations and for constraining physical models of the SN 1987A system. The latest Chandra observations find that the 0.5-2 keV light curve has remained constant since ~9500 days, with the 3-8 keV light curve continuing to increase until at least 10000 days. The expansion rate of the equatorial ring is found to be energy dependent, and the spatially resolved images show a reversal of the east-west asymmetry between 7000 and 8000 days. The latest images suggest the southeastern side of the equatorial ring is beginning to fade. Consistent with the latest optical and infrared results, the Chandra analysis indicates the blast wave is now leaving the dense equatorial ring. Future observations of the X-ray light curve will trace the density profile of the material outside the equatorial ring, which records the history of the progenitor's stellar wind. Additionally, the impending brightening of the ejecta will soon allow measurements of its composition and structure via Chandra observations, placing constraints on properties of the supernova and progenitor star. In this new epoch, Chandra observations will continue to be a critically important part of an irreplaceable multiwavelength data set on this unique object.
9:40-9:55
Slavko Bogdanov (Columbia University)
X-ray Studies of Transitional Millisecond Pulsars
Just within the last three years, three millisecond pulsar (MSP) binary systems have been observed to alternate between clearly distinguishable rotation- and accretion-powered states, thereby cementing the long-suspected evolutionary link between low-mass X-ray binaries and "recycled" pulsars. These peculiar transitional MSPs hold the promise to elucidate multiple aspects of close binary evolution, as well as accretion and jet formation physics. In this talk, I will describe our on-going and upcoming Chandra studies of transitional MSPs and their newly recognized parent population, the so-called "redback" variety of binary radio millisecond pulsars. I will also offer thoughts on possible future advances in this exciting new field through coordinated multiwavelength studies.
9:55-10:10
Vinay Kashyap (SAO)
Flare After Flare
Over the course of its mission, Chandra has accumulated a rich database of observations of nearby active coronal sources, with high-quality timing and spectral data. Such data allow us to study the effect of energetic flare events at a fine-grained level, to explore how lines formed at different temperatures respond to the sudden injection of energy. We identify large flares on coronal sources observed with gratings, and compare flare onset times in high- and low-temperature lines. We find cases where the onset times from high-T lines lead or lag those from low-T lines, and discuss their implications for flare mechanisms. We also discuss the distribution of observed flares and comment on the apparent paucity of X-ray superflares. As the Chandra grating archive grows to include larger varieties of stars observed for longer durations, better observational constraints can be set.
10:10-10:25
Kazimierz Borkowski (North Carolina State University)
Expansion of Young Supernova Remnants in X-Rays
X-ray studies of young Galactic supernova remnants (SNRs) offer us the best opportunity to learn about the supernovae (SNe) that produced them and about particle acceleration in collisionless shock waves. But most young SNRs are still poorly understood, with even their most basic properties such as ages usually inferred through indirect and uncertain means. One effective, direct way to determine ages is through measurements of expansion. Time baselines of over a decade for Chandra observations are now enabling accurate X-ray expansion rate measurements even for remnants several thousand yr old, while much more detailed studies of the remnants' kinematics are now possible for still younger remnants. We report here on expansion rate measurements of the young core-collapse (CC) SNRs G11.2-0.3, Kes 73, and Kes 75, and on extensive kinematic studies of the historical SN Ia remnants Kepler and Tycho, and of the youngest Galactic SNR G1.9+0.3, produced by a (probable) Type Ia SN around CE 1900. For G11.2-0.3, we measure a mean expansion rate for the shell of 0.028±0.002% yr^-1, implying an age between 1400 and 2400 yr, and making it one of the youngest CC SNRs in the Galaxy. Kes 73 expands at a slightly slower rate, 0.023±0.002% yr^-1, so its age is between 1700 and 2900 yr. This is less than the characteristic age of 4800 yr of the magnetar at its center, but more than most indirect age estimates. There are only hints of nonuniform expansion in both SNRs. But strongly nonuniform expansion is apparent in G1.9+0.3, Tycho's, and Kepler's SNRs. We use the "Demons" method to study the complex motions within these remnants. This method provides a nonparametric way for measuring these motions globally, allowing determination of the expansion velocity field all over the remnants, not just at bright edges. In Kepler's SNR, shock speeds vary from 1500 km/s to over 6000 km/s, allowing us to study how the efficiencies of magnetic-field amplification and particle acceleration vary with shock speed. Unexpectedly, we found no apparent correlation between these efficiencies and the measured shock speed. We interpret the complex motions seen within Kepler's SNR with the help of 3D hydrodynamical simulations. G1.9+0.3 is strongly asymmetric at radio wavelengths, with a single bright maximum, but exhibits a bilaterally symmetric morphology in X-rays. Our expansion measurements based on 2011 and 2015 Chandra observations illuminate the origin of the radio asymmetry. We find motions varying by a factor of 5, from 0.09" to 0.44" per year. The slowest shocks are in the north, at the outer boundary of the bright radio emission, with speeds there as low as 3600 km/s, much less than the average shock speed of 12000 km/s. Such strong deceleration of the northern blast wave most likely arises from the collision of SN ejecta with a denser ambient medium, resulting in brighter synchrotron emission. But the lower shock speed would result in the spectrum cutting off below X-ray energies, explaining the contrasting morphologies. In several locations, significant morphological changes and strongly nonradial motions are apparent. As with Kepler's SN, the SN ejecta are likely colliding with the asymmetric circumstellar medium ejected by the SN progenitor prior to its explosion. We discuss future prospects for studying the expansion of young SNRs with Chandra.
10:25-10:55
Break
Structure of the Cosmos II
10:55-11:20
Oleg Kargaltsev (The George Washington University)
Chandra view of manifestations of neutron stars: particle outflows and synchrotron nebulae
While Chandra X-ray Observatory observations have delivered many outstanding results about neutron stars, one of the most significant and unique contributions is the detection and characterization of numerous pulsar wind nebulae (PWNe) created by pulsar winds shocked in the ambient medium. Such studies have been possible due to the Chandra's unsurpassed angular resolution aided by the high sensitivity and low background of the ACIS detector. I will review the most important achievements in this area including our current understanding of the PWN population, PWN dynamics, PWN spatial and spectral morphologies, and of the physical processes responsible for the rich phenomenology. I will also outline future promising directions for PWN studies with Chandra X-ray Observatory, such as the spatially-resolved spectroscopy, connection between the PWN and pulsar properties, and the studies of exotic types of PWNe that may be associated with transient or previously unexplored sources.
11:20-11:35
Chandreyee Maitra (SAP/CEA Saclay, France)
The intriguing double torus-jet PWN around PSR J0855-4644 with Chandra: an excellent opportunity to probe axisymmetric structures in young PWNe
PSR J0855-4644 is a nearby, fast spinning, and energetic radio pulsar spatially coincident with the rim of the supernova remnant RX J0852.0-4622 (aka Vela Jr). XMM Newton observation of the region has shown an arcmin scale extended emission, the pulsar wind nebula (PWN), around the X-ray counterpart of the pulsar. Taking advantage of the excellent spatial resolution of Chandra, we have found that the compact X-ray source seen with XMM can be further resolved into a hard and bright arc second scale compact PWN around the a soft, much fainter pulsar. The compact PWN morphology shows possible 'double torus+jet' features. This makes it only the third source of its kind, and being an nearby object provides us with the golden opportunity to investigate the physics of equatorial and polar outflows in PWNe. Modeling the geometry of this source is also crucial to understand why no gamma-ray pulsations have been detected by the Fermi-LAT telescope for this high $\dot{E}/d^{2}$ pulsar. In order to constrain the pulsar spin inclination angle, we model the double torus morphology and then compare it with theoretical phase-plots to understand this radio loud, gamma-ray quiet system. We further discuss the prospects of comparing the present results with a future Chandra observation to break the degeneracy in the morphology of the PWN. High resolution Chandra data in the timing mode will further provide the only opportunity to search for X-ray pulsations in this source, which might lead to independent constraints on the pulsar geometry. Obtaining radio polarization data in conjunction will be an added boon, and may ultimately lead measurement of the mass-to-radius ratio of the neutron star.
11:35-11:50
Max Bonamente (University of Alabama in Huntsville)
Discovery of an extragalatic OVIII WHIM absorption line towards PG 1116+215
I present the discovery of a new 5.2 sigma OVIII K-alpha X-ray absorption line system towards the quasar PG 1116+215, observed with the Chandra LETGS grating spectrometer. This absorption line is in close association to a broad HI Lyman alpha absorption line discovered with HST by Tilton et al. in 2012. The X-ray absorption line system features also lower S/N OVIII K-beta and OVII K-alpha lines at the same redshift, indicating a very high temperature and column density and the possibility of significant non-thermal velocity structure. The absorption line system corresponds to filamentary galaxy structures we discovered in the SDSS data. The detection highlights the importance of FUV absorption line systems to uncover the notoriously hard-to-detect high-temperature WHIM.
11:50-12:05
Efrain Gatuzz (Max-Planck Institute for Astrophysics)
ISM analysis through high-resolution X-ray spectroscopy
High-resolution X-ray spectroscopy, provided by the grating instruments on board of Chandra and XMM-Newton, is a powerful technique to analyze the Galactic interstellar medium (ISM). Using a bright X-ray source the absorption features due to the environment located between the X-ray source and the observed can be analyzed, offering the opportunity to analyzed physical properties such as ionization degree, elemental abundances and column densities. I will present an analysis of the H, O, Ne, and Fe absorption in the X-ray spectra of 24 bright galactic sources obtained with the Chandra and XMM-Newton observatories. Finally, I will review the state-of-the-art of the field, including the importance of the atomic data, the local ISM structure, the detectability of X-ray absorption features due to the presence of molecules and the influence of dust scattering.
12:05-12:20
Konstantina Anastasopoulou (Physics Department University of Crete Greece, FORTH-Hellas Greece)
A deep Chandra observation of the interacting star-forming galaxy Arp 299
We present results from a deep Chandra observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above ~4.0×10³⁸ erg s^-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metallicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. Furthermore the integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT=0.72±0.03 keV, contributing ~20% of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. Finally we discuss these results in the context of other star-forming galaxies with large ULX population and/or strong star-forming activity.
12:20-12:35
Sascha Zeegers (SRON Netherlands Institute for Space Research)
Characterizing Interstellar Dust with Chandra in the Next Decade
We present the latest results on the chemistry study of the ISM based on the synergy between Chandra-HETG data and new synchrotron measurements of Interstellar Dust (ID) analogues (Costantini et al. 2013, Zeegers et al. 2016, submitted). These results open the door to a comprehensive study of the largely unknown ID composition using the unique capabilities of the Chandra X-ray observatory. Bright X-ray binaries can be used as background sources to probe the intervening dust along several sight lines. The shape and observed energy of the edges present in the spectra of these sources does reveal the composition and size of the intervening dust grains, as well as the elemental abundances and depletion values in different environments of the Galaxy.
12:35-13:35
Closing Lunch
13:35
Fin