Full-Field Per-ObsId Event List (evt3.fits)
The full-field event file consists of a single FITS format event file for each observation that results from catalog processing. The observation event file has been reprocessed through acis_process_events or hrc_process_events, as appropriate, to apply the latest instrument calibrations and the standard event status and event grade (ACIS only) filters. In addition, the destreak algorithm has been applied to the ACIS-S4 CCD. Good time intervals have been revised to eliminate periods of background flares.
The good time intervals (GTIs) associated with full-field event data are included as additional FITS HDUs (CXC Data Model blocks) in the full-field FITS event file. For an event file containing ACIS data, there is a GTI for each ACIS CCD included in the full-field observation; there is a single GTI for an event file containing HRC data.
![[NOTE]](../../imgs/note.png)
The evt3.fits file is similar to the evt2.fits file from the Chandra Data Archive, but has different GTIs due to the filtering of background flares.
The full-field event FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_evt3.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, and 〈c〉 is the cycle. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.
Example
An example per-obsid evt3 file from release 2.0 is:
unix% dmlist acisf14031_000N020_evt3.fits blocks
--------------------------------------------------------------------------------
Dataset: acisf14031_000N020_evt3.fits
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Block Name Type Dimensions
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Block 1: PRIMARY Null
Block 2: EVENTS Table 15 cols x 176229 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
In this case, the observation was with ACIS-I, and has data for the four ACIS-I chips and two ACIS-S chips (S3 and S2). The observation is from stack acisfJ0518378m691337_001.
unix% dmkeypar acisf14031_000N020_evt3.fits STACK_ID echo+ acisfJ0518378m691337_001
This particular observation can be viewed with ds9 using a command similar to the following, which creates the following figure:
unix% ds9 acisf14031_000N020_evt3.fits \
-bin filter 'energy=500:7000' -bin factor 8 -scale log
Per-Obsid event file
![[The ds9 image viewer shows the image data, with the central ACIS-I array and - partly visible - the two ACIS-S chips above them (to the North).]](imgs/obsid14031-evt3.png)