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Proposal Number: 10400006

Title: Weighing the ULX in M82 via QPO-Spectral Correlations from Simultaneous Chandra and XMM-Newton Observations

PI Name: Hua Feng

The ultraluminous X-ray source (ULX) X41.4+60 in M82 is one of the best intermediate-mass black hole candidates. It shows luminosities 500 times the Eddington limit of a neutron star and quasi-periodic oscillations (QPOs) at frequencies lower than typical in stellar-mass black holes. It is the only ULX from which QPOs have been detected that is in a hard state and, thus, provides a unique opportunity to determine if the QPO frequency is correlated with spectral state as in stellar-mass black holes. We propose simultaneous Chandra and XMM observations to determine the relation between QPO frequency and spectral properties for X41.4+60. This may lead to constraints on the compact object mass.

Proposal Number: 10400008

Title: INVESTIGATING NEW INTEGRAL SOURCES WITH CHANDRA

PI Name: Adamantia Paizis

We propose to trigger a maximum of 2 Chandra medium (4-12 days) ToO observations on new sources discovered by the INTEGRAL Observatory. We ask for 20 ksec per observation, using HETGS. The scientific aim is to determine the source position with sub-arcsecond accuracy that only Chandra can provide, enabling multi-wavelength follow-up observations (also coordinated within the proposing team), and to obtain the high resolution HETGS X-Ray spectrum, essential to determine the nature of the new source. With this proposal we aim to continue the successful INTEGRAL-Chandra monitoring program started since Chandra AO5.

Proposal Number: 10400009

Title: High Resolution Spectroscopy of a Black Hole Transient

PI Name: Jon Miller

We propose to continue our ongoing study of Galactic black hole transients in outburst in a streamlined form, via two (2) 30 ksec HETGS observations. This program has revealed relativistic Fe K disk lines, warm-absorber-like disk winds, and now a possible anti-correlation between winds and jets. Observations of a new transient outburst will permit a black hole spin constraint, and test connections between disks, winds, and jets as a function of accretion rate. We will support this program with a global multi-wavelength network of observatories.

Proposal Number: 10400046

Title: Chandra follow-up of weak persistent sources found in INTEGRAL maps

PI Name: Jelle Kaastra

We propose to obtain a 1 ksec exposure of up to 2 newly found unclassified INTEGRAL sources which are weak persistent X-ray sources (we exclude from this proposal the bright new transients discovered by INTEGRAL). The unique Chandra positional capabilities will allow for an optical follow-up study. Follow-up observations are of paramount importance for the classification of the sources (e.g. as HMXBs/LMXBs, pulsars (and pulsar wind nebula) or in a few rare cases as AXP/SGR or INS).

Proposal Number: 10400048

Title: Chandra follow-up of weak persistent sources

PI Name: Jelle Kaastra

We propose to obtain short exposures of a sample of unclassified sources which are likely weak persistent X-ray binaries. The unique Chandra positional capabilities will allow for an optical follow-up study. Follow-up observations are of paramount importance for the classification of the sources (e.g. as HMXBs/LMXBs, pulsars or in a few rare cases as AXP or DIM). The ACIS sensitivity for hard sources is best while pile-up is no major concern for source localization.

Proposal Number: 10400049

Title: Chandra LETG observation of an ultra-compact X-ray binary candidate

PI Name: Jelle Kaastra

We propose to obtain a long exposure of the Ultra-compact X-ray binary in Terzan 2.

Proposal Number: 10400067

Title: Observe Z sources at High Mass Accretion Rates

PI Name: Claude Canizares

We propose to test a new interpretation that links mass accretion rate to observed spectral changes in Z-sources in a diffwrent way than previously though. Integral part of the test is to catch Z-source on the horizontal branch (HB). There are a few sources where RXTE and previous observatories established a fairly accurate record of how often they appear on a specific spectral branch. 4 observations for 8 ks each has a 50% chance to observe GX 5-1 on the HB.

Proposal Number: 10400071

Title: Chandra Observations of the Low Mass X-ray Binary 4U 1556-60

PI Name: Claude Canizares

4U 1556-60 is a LMXB in a 9.1 hour orbit, that has been identified (based upon its X-ray colors) as an atoll source, although no bursts have been identified to secure its classification as a neutron star. Spectrally, models that consist of an accretion disk plus a Compton corona, or models that consist of a black body (e.g., neutron star surface emission) plus a hard, but very exponentially cutoff tail, both seem to fit BeppoSAX data equally well. Here we propose to view this system, for nearly one full binary orbit, with the Chandra HETG. We hope to better gauge whether the bulk of the soft emission is coming from a neutron star surface, or the atmosphere of a Comptonized accretion disk.

Proposal Number: 10400163

Title: X-Ray Jets in Microquasars

PI Name: Stephane Corbel

We propose Target of Opportunity (ToO) observations for detailed studies of X-ray jets from microquasars. We describe our discovery of radio/X-ray jets in two microquasars, why X-ray jets are probably much more common than previously thought, and transient X-ray jets offer an exciting new way to probe the physics of relativistic jets from black holes. The proposed ToO observations are optimized to discover and study (flux evolution, morphology, SED, proper motion, ...) of new X-ray jets from microquasars, triggered by their detection as radio lobes. This will have implications not only for the study of jets from Galactic X-ray binaries, but also for our understanding of relativistic jets from active galactic nuclei (AGN).

Proposal Number: 10400165

Title: Transient LMXBs in Globular Clusters: More Numerous Than We Thought?

PI Name: David Pooley

Since the discovery of globular cluster LMXBs in the 1970s, it was assumed that there was only one bright LMXB per cluster. Deep Chandra observations of several globular clusters have revealed that they contain numerous quiescent LMXB systems, any of which could go into outburst. Our observations will determine whether new outbursts from transient LMXBs in NGC 6440, Terzan 5, and Terzan 1 are from the same sources that were previously seen in outburst.

Proposal Number: 10400218

Title: ToO observations of the microquasar GRS 1915+105 in quiescence

PI Name: Paolo Soleri

We propose two Chandra observations (40 ks each) to detect the microquasar GRS 1915+105 in quiescence, should its current 16-year-long outburst end during the 10th Chandra observing cycle. This system has never been observed in quiescence: its properties suggest that its quiescent X-ray flux would be rather high (~ 10^34 erg/s), allowing a measurement of the spectrum and a test of models for quiescent emission in black-hole binaries. In addition, it will be possible to detect a fossil jet similar to that detected in the black hole candidate 4U 1755-33.

Proposal Number: 10400234

Title: Precise Localization of Neutron Star Soft X-Ray Transients

PI Name: Deepto Chakrabarty

We propose to observe four neutron star soft X-ray transients (NS SXTs) in outburst to obtain accurate source positions, continuing a successful multi-cycle program in place since Cycle 6. These positions will allow reobservation of this sources in the X-ray, optical, and infrared bands in order to study their quiescent emission. This program will increase the number of known SXTs with good positions, providing a more uniform sample for future work. We will only trigger our program for sources in crowded or obscured fields where a position from another instrument (e.g., Swift) is not sufficiently constraining.

Proposal Number: 10400238

Title: ToO observation of a bright Galactic transient discovered by GLAST and Swift

PI Name: Isabelle Grenier

We propose a TOO observation of one bright Galactic transient detected by the GLAST large area telescope, and followed by a Swift-XRT detection. Our goal is to determine the nature of an event similar to the intense, non-blazar, transient that EGRET has detected near the Galactic plane once in its lifetime. The lack of a radio-loud blazar counterpart and of a spacially coincident X-ray binary indicates either a new manifestation of a non-blazar active galaxy lying behind the Milky Way, capable of producing massive gamma-ray flares, or a new facet of Galactic compact objects. A significant XRT detection of an X-ray counterpart will trigger the proposed 30 ks Chandra observation to locate precisely this counterpart, to constrain the X-ray decay time, and to measure the source spectrum.

Proposal Number: 10400252

Title: Chandra observations of newly discovered, nearby, globular clusters in the Galaxy

PI Name: EDWARD CACKETT

We propose short, 10 ksec Chandra observations of two recently discovered nearby (~1.5 kpc) globular clusters FSR 1767 and FSR 584. We will determine their X-ray source population and confirm their globular cluster nature. As they are the two closest globular clusters to the Sun, their proximity gives us an unprecedented look. If we discover any quiescent low-mass X-ray binaries, they will be some of the very closest known to us, enabling a study of their properties in unrivaled detail, especially because of the known distance and reddening.

Proposal Number: 10400273

Title: Understanding the nature of high inclination low mass X-ray binaries: broad-band and line spectra from A1744-361

PI Name: Tod Strohmayer

We propose to observe the transient, dipping neutron star low mass X-ray binary (LMXB) system A1744-361 during an outburst with the CHANDRA HETGS, and contemporaneously with RXTE. This will be the first observation of A1744-361 with a high resolution spectral instrument. With these observations we will: 1) search for narrow absorption lines for the first time from A1744-361; 2) measure the profile of its broad iron emission line; 3) unambiguously determine the binary orbital period and source position; 4) search for kHz QPOs and burst oscillations. These studies will allow us to further understand the ionized plasma in the immediate environs of A1744-361, and dippers in general. These goals rely on the unique capabilities of CHANDRA (high spectral and angular resolution) and RXTE.

Proposal Number: 10400329

Title: Crustal cooling in the neutron star KS 1731-260

PI Name: EDWARD CACKETT

We propose a 60 ksec observation of the quasi-persistent neutron-star low-mass X-ray transient KS~1731-260 in quiescence. The long outbursts of this source heated the neutron star crust out of thermal equilibrium with the core. We have tracked the cooling of the neutron star crust in this object since it went into quiescence. Empirical fits to the data are not yet conclusive as to whether cooling has ceased or may continue. Furthermore, recent theoretical work motivated by our observations predict that the cooling may continue if the neutrino emissivity in the core is high. Our proposed observation will determine whether cooling has continued further constraining models for the neutron star crust and core, and will test whether residual accretion is important.

Proposal Number: 10400350

Title: X-ray Column Density Towards The Low Mass X-ray Binary 4U 1608-522

PI Name: Feryal Ozel

We request a 25~ks observation of the low-mass X-ray binary 4U 1608-522 with Chandra HETG in order to measure the interstellar extinction towards the source using absorption edges in its spectrum. The measurement of the column density is critical for two reasons. First, we will employ the independent grating measurement when fitting continuum X-ray spectra of the source to determine the temperature of the neutron star surface. Second, we will employ the extinction measurement to determine the distance to the source using a technique that makes use of red clump stars in the field of view of the source, which we have already extracted from the 2MASS archival data. The ultimate goal is to determine the mass and radius of the neutron star in this binary to a high accuracy.

Proposal Number: 10400384

Title: Following a black hole candidate X-ray transient to quiescence

PI Name: Peter Jonker

There is increasing evidence that the quiescent state of BH X-ray binaries is different from the canonical hard state. Our recent Chandra campaigns on BH transient decays suggest that the spectral hardening in the hard state decay stops. This transition has so far not been resolved with enough SN to fully quantify it, but there are strong indications that the spectrum softens during the subsequent decay. We also find evidence that the decay rate varies between sources. Both the decay and spectral evolution can provide important constraints for jet-dominated and ADAF models. We now request 4 instead of 6 simultaneous Chandra/VLA TOO observations. The early part of the decay can be covered with approved Swift ToO and existing radio proposals.

Proposal Number: 10400393

Title: Looking at the quiescence of the unique system GRB 070610/Swift J195509.6+261406

PI Name: Nanda Rea

We propose for a 68ks ACIS-S observation aimed at determining the nature of the unique system GRB 070610/Swift J195509.6+261406. This very peculiar system, discovered as a long gamma-ray burst (GRB 070610), is most likely a low mass X-ray binary (LMXB) hosting either a neutron star (NS) or a black hole (BH). This is the only LMXB associated with a typical long-duration GRB. The discovery of this source challenges the current picture of long GRBs being all due to cosmological objects. Very deep X-ray observations of this system in its quiescent state are needed in order to disentangle the nature of the system, in particular of its compact object, and then study the expected rate of GRBs with LMXB origin.

Proposal Number: 10400405

Title: Crust cooling of bright neutron star transients with long recurrence times

PI Name: Nathalie Degenaar

We propose a series of three Chandra ToO observations of a bright neutron star X-ray transient with a long recurrence time (many years), as soon as the system returns to quiescence following its accretion outburst. Monitoring the thermal relaxation of the accretion-heated neutron star as it cools down in quiescence, allows us to probe various properties of the neutron star crust and core. By comparing these with results of transients that undergo accretion episodes of years to decades, we aim at probing possible physical differences induced by widely different outburst durations. In addition, we will test the recent theoretical conjecture that additional heating occurs in the outer layers of the neutron star crust.

Proposal Number: 10400425

Title: Photospheric radius-expansion bursts at high spectral resolution

PI Name: Duncan Galloway

It has been predicted that strong (a few hundred~eV EW) photoionisation edges might be present in the X-ray spectra at the peak of photospheric radius-expansion thermonuclear bursts. We propose to search for such features in bursts from sources uniquely known to exhibit frequent radius-expansion bursts. These observations will result in detection of up to 30 thermonuclear bursts, also providing a high signal-to-noise low-flux state spectrum, as well as allowing a detailed comparison of recurrence time and energetics with numerical ignition models. Detection of discrete features from the burst spectra may lead to highly-sought constraints on the compactness and hence the neutron-star equation of state.

Proposal Number: 10400447

Title: Crust Cooling of HETE J1900.1-2455 and Swift J1626.6-5156

PI Name: Nathalie Degenaar

We propose Chandra ToO observations of the two neutron star quasi-persistent X-ray binaries HETE J1900.1-2455 and Swift J1626.6-5156 in quiescence. Currently, both sources exhibit an outburst phase that started about 2.5 years ago. By studying the thermal relaxation of the neutron star crust following such a prolonged accretion episode, we can deduce stellar parameters such as the thermal conductivity and distribution of heating sources in the crust, as well as the neutrino emission mechanism operating in the core. Our targets are the only two quasi-persistent X-ray binaries that are known to exhibit X-ray pulsations and have high inferred magnetic fields. We want to explore the observational effects of strong magnetic fields on the thermal evolution of transiently accreting neutron stars.

Proposal Number: 10400448

Title: Bright edge-on LMXB transients to map ionized disk atmospheres

PI Name: Laurence Boirin

With the discovery of Fe XXV and Fe XXVI lines in several binaries viewed close to the disk plane, XMM and Chandra have revealed the existence of a highly-ionized atmosphere above the accretion disk. We have further demonstrated that the spectral changes during dips from dipping LMXBs, both in the lines and in the continuum could be explained by a decrease in the ionization level of this plasma. We want to investigate the presence of such a highly ionized plasma in four other binaries viewed close to the disk plane should these currently quiet transient sources turn on. We wish to constrain the plasma properties (location in binary, stationary or outflow) as a function of binary parameters (inclination, period) and luminosity.

Proposal Number: 10400459

Title: Deep search for the pulsars powering the TeV emission of LS I 61+303 and LS 5039

PI Name: Nanda Rea

We propose to observe with Chandsra ACIS in Continuous Clocking mode the two TeV emitters High Mass X-ray binaries LS I 61+303 and LS 5039, for 95 and 71ks, respectively. Aim of these Chandra observations is to address the long-standing puzzle on the nature of the compact objects hosted by these two TeV binaries, searching with unprecedented sensitivity for X-ray pulsations from these putative young rotational powered pulsars. As a nice by product we will also study the one-dimensional X-ray angular distribution searching (or, in the case of LS I 61+303, confirming with higher significance) for extended X-ray emission.

Proposal Number: 10400463

Title: Taking the temperature of the superburster 4U 1608-522 after an outburst

PI Name: Laurens Keek

Superbursts are rare thermonuclear flashes from accreting neutron stars. One condition for ignition is a sufficiently high temperature of the neutron star crust, which is heated during accretion. Most superbursts take place when the neutron star was accreting continuously above 10% of the Eddington limit for more then 10 years. In 2005 a superburst was observed from the transient system 4U 1608-522, when accretion started 55 days earlier. Crustal heating models predict a significantly lower temperature than the superburst models require. If the superburst models are correct in their prediction of a high temperature, crustal cooling is observable after an accretion outburst. We propose to observe 4U 1608-522 two times for 30 ks triggered after an outburst, to measure the cooling rate.

Proposal Number: 10400480

Title: Quasi-persistent neutron-star X-ray binaries in quiescence

PI Name: Rudy Wijnands

We propose to observe the next (quasi-)persistent neutron-star low-mass X-ray binary that turns off and becomes quiescent. This will provide an excellent opportunity to study the effects of prolonged accretion on the neutron-star properties (i.e., crust and core and thus the properties of ultra-dense matter) and the quiescent properties of low-mass X-ray binaries. Two follow-up observations taken several months later will provide important information about the time evolution of the quiescent properties. In particular, if indeed the quiescent X-rays are emitted by the crust, we will be able to study its evolution in time,thus setting strong constraints on the crust cooling models and the exact structure of the crust.

Proposal Number: 10400502

Title: ToO Observations of New Galactic Gamma-ray Transients Discovered with GLAST

PI Name: Dirk Pandel

The EGRET instrument on board CGRO discovered a unique transient event near the Galactic plane. The nature of this gamma-ray transient could never be established, and no clear counterpart at other wavelengths could be identified. The transient appears to represent a currently unknown class of gamma-ray emitting objects in the Galaxy. The GLAST gamma-ray observatory is expected to discover many new transient gamma-ray sources. Here we propose ToO observations of bright gamma-ray transients discovered by GLAST in the Galactic plane that are not associated with known blazars. The Chandra observations will enable us to precisely locate the transients for multi-wavelength follow-up observations, to determine their X-ray to gamma-ray flux ratio, and to measure their X-ray spectrum.

Proposal Number: 10400562

Title: Precise Chandra position determinations of compact binary candidates-faint persistent INTEGRAL sources in the bulge

PI Name: Mikhail Revnivtsev

Deep observations of the Galactic Center/Galactic bulge region with the INTEGRAL satellite have provided a statisticaly well-defined sample of faint persistent sources, the majority of which may be X-ray binaries with extremely low mass optical companions feeding the compact object via Roche lobe overflow. The optical emission of these low mass binary system should be extremely faint. Therefore, to make secure associations of an optical object with these X-ray sources, we require very accurate astrometric positions. We propose to obtain ``snapshot'' observations of a sample of such sources with the CHANDRA Observatory to obtain the best possible astrometric positions which will allow us to pursue follow up optical studies of this extremely rare class of objects. (Abridged)

Proposal Number: 10400572

Title: Variability in Quiescent Neutron Star Binaries in Dense Globular Clusters

PI Name: Craig Heinke

We propose to re-observe four rich globular clusters (Terzan 5, NGC 6388, NGC 6266, and NGC 6440), which have been previously observed by Chandra and found to contain 5 or more quiescent neutron star binaries with L_X>10^32 ergs/s. Our goal is to measure the years-timescale spectral and luminosity variability of the quiescent neutron star X-ray binaries seen in these clusters. Detecting variability in the thermal component of quiescent X-ray binaries would prove that accretion continues into quiescence, and that the thermal component can be produced by accretion. This study surveys seventeen quiescent X-ray binaries with sufficient sensitivity to draw strong conclusions about low-level accretion and the nature of the thermal component.

Proposal Number: 10400588

Title: Validating Neutron Star Radius Measurements

PI Name: Deepto Chakrabarty

Spectral analysis of non radius-expansion X-ray bursts and transient neutron star in quiescence were both used to estimate the NSs radii for different sources. The validities of the methods need to be verified by performing the radius measurements on the same source with different methods respectively. Transient type-I X-ray bursters are excellent candidates for testing the consistency between the methods, since they were detected in both bursts and quiescence. Out of 3 candidates: Cen X-4, Aql X-1 and 4U 1608-52, 4U 1608-52 turns out to be the best one due to the lack of archival RXTE burst data for Cen X-4 and the previous reported significant luminosity and temperature variability for Aql X-1 in quiescence. Therefore, we propose a 20 ks Chandra/ACIS-S observation of 4U 1608-52.

Proposal Number: 10400599

Title: The brightest unidentified Galactic sources of the new H.E.S.S. survey

PI Name: Omar Tibolla

In a survey of the Galactic plane performed in 2007, the High Energy Stereoscopic System(H.E.S.S.) discovered many new sources and most of them are still unidentified. We propose to use the Chandra X-ray Observatory to perform follow-up observations on two of the brightest newly discovered sources, HESS J1507-622 and HESS J1741-302, to identify the possible X-ray counterparts. Both sources have no clear positional counterparts: HESS J1507-622 does not show any counterpart at all, whereas an offset PWN is one of the possible explanations for HESS J1741-302. The aim is to obtain morphological and spectral information on the possible counterparts in order to understand the emission mechanisms of these 2 sources: the predicted X-ray flux is sufficient for detailed studies of these objects.

Proposal Number: 10400649

Title: Completing the Galactic Bulge Survey: categorising the plethora of faint X-ray sources in the Galactic Bulge

PI Name: Peter Jonker

We propose to image an area of 6x1 degrees centered on the Galactic Center at |b|=1.5 degrees: the Galactic Bulge Survey. 50% of this area will be observed in AO9. We here propose to complete the survey. These regions have been selected because of their lower extinction and crowding in the optical and near-infrared than in the Galactic Center area, while still having a high density of X-ray sources. We will detect a plethora of faint X-ray sources that will constrain binary evolution models by way of a number count and by identifying predicted X-ray binary types that so far have eluded identification. We expect to find (quiescent) eclipsing neutron star and black hole LMXBs. These are important for neutron star and black hole mass measurements.

Proposal Number: 10400745

Title: Hot on the Trail of Circinus X-1: The first X-ray jet from an accreting neutron star

PI Name: Sebastian Heinz

We propose to observe the pc-scale X-ray jet of the accreting neutron star Circinus X-1 during the source's current ultra-deep minimum state to obtain a high-fidelity image of the jet and determine the emission mechanism and spectral parameters of the jet. This will allow us to measure the jet power and to probe the physics of jet formation in neutron stars, and to investigate the interaction of powerful, ultra-relativistic jets from microquasars with the ISM. Reaching our science goals will require a 100ksec ACIS-S target-of-opportunity observation.

Proposal Number: 10400827

Title: The cooling neutron star in the super-Eddington accretor XTE J1701-462

PI Name: Jeroen Homan

Observing the cooling of neutron stars that are reheated by accretion provides new insights into neutron star structure. A detailed and efficient study of this cooling requires the use of Chandra. Here we propose to continue our ongoing monitoring campaign of the neutron star binary XTE J1701-462, a unique system that accreted at super- and near Eddington luminosities for more than 1.5 years before recently returning to quiescence. Our goal is to study the cooling of the surprisingly hot neutron star and also the evolution of the enigmatic non-thermal spectral component in unprecedented detail. Our ongoing strategy of frequent observations (every ~2.5 months) is necessary to test the most recent cooling models. We therefore request five ACIS-S observations for a total of 323 ks.

Proposal Number: 10400907

Title: Extended emission of microquasar LS 5039

PI Name: Gordon Garmire

Previous ACIS observations of LS 5039 have provided evidence of extended emission which consists of variable and possibly moving knots and a more compact asymmetric structure near the microquasar. However, the observations were either very short or the source was imaged very far off-axis. The poor statistics and the very broad off-axis PSF make it difficult to distinguish between intrinsically extended emission and emission produced by unresolved point sources. In a deeper, on-axis observation we will resolve these ambiguities, understand the nature of the variable knots, measure their motion, and study the asymmetric extended emission in the vicinity of LS 5039. This will help to understand the nature of LS 5039 and the mechanisms responsible for its high-energy emission.

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