Source Region Per-Observation Detections Events Files (regevt3.fits)

The source region events file consists of a single FITS format events file for each source region of each observation; it is the result of applying a rectangular SKY region filter to the corresponding full-field event file for the observation. The rectangular SKY region filter is equal in size to the background region of interest (ROI) corresponding to the detected source region.

The good time intervals (GTIs) associated with source region event data are included as additional FITS HDUs (CXC Data Model blocks) in the source region FITS event file. For an events file containing ACIS data, there is a GTI block for each ACIS CCD included in the source region; there is a single GTI block for an event file containing HRC data.

There will also be a MASK block, which contains the relevant region of the per-observation pixel mask. This allows users to find out how the area was spatially filtered (for example chip edges or read-out streaks).

The per-observation region events FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_〈r〉_regevt3.fits

where 〈i〉 is the instrument designation, 〈s〉 is the data source; 〈obs〉 is the observation identification; 〈obi〉 is the observation interval identification; 〈v〉 is the data product version number; 〈c〉 is the cycle; and 〈r〉 is the region ID, formatted as "rnnnn", where nnnn is the 4-digit region number, formatted with leading zeros. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.

Example

An example per-obsid source regevt3 file from release 2.1 is:

unix% dmlist acisf14031_000N028_r0016_regevt3.fits blocks
 
--------------------------------------------------------------------------------
Dataset: acisf14031_000N028_r0016_regevt3.fits
--------------------------------------------------------------------------------
 
     Block Name                          Type         Dimensions
--------------------------------------------------------------------------------
Block    1: PRIMARY                        Null        
Block    2: EVENTS                         Table        15 cols x 356      rows
Block    3: GTI3                           Table         2 cols x 1        rows
Block    4: GTI6                           Table         2 cols x 2        rows
Block    5: GTI7                           Table         2 cols x 1        rows
Block    6: GTI2                           Table         2 cols x 1        rows
Block    7: GTI1                           Table         2 cols x 2        rows
Block    8: GTI0                           Table         2 cols x 1        rows
Block    9: MASK                           Image      Byte(141x139)

This particular observation can be viewed with ds9 using a command similar to the following, which creates the following figure:

unix% ds9 acisf14031_000N028_r0016_regevt3.fits \
        -mask transparency 80 \
        -mask "acisf14031_000N028_r0016_regevt3.fits[MASK]" \
        -region "acisf14031_000N028_r0016_reg3.fits[ecf90regb]" \
        -pan to 4785 4142 -bin filter 'energy=500:7000' \
        -bin factor 1 -zoom 4

The region event file

The region event file

The observation event file for this source. In this case the mask can be seen to cover the full area of the event file, so there are no pixels excluded due to the per-observation pixel mask. The per-observation region is shown as the green ellipse (chosen is the broad-band ECF90 region).

Related Science Documents

• CSC: reg3; regexp3; regimg3.
• CSC (per observation): pixel mask
• CIAO: Extract Spectrum and Response Files for a Pointlike Source
• CIAO: Coadding Spectra and Responses