Last modified: December 2022

AHELP for CIAO 4.15


Context: Tools::ACIS


Create a combined GTI file for multiple ACIS chips


multi_chip_gti  infile i0_gti i1_gti i2_gti i3_gti s0_gti s1_gti s2_gti
s3_gti s4_gti s5_gti outfile [tmpdir] [verbose] [clobber]


There are situations - such as filtering out background flares - when it is necessary to filter the ACIS chips either individually, or in groups (e.g. front-illuminated versus back-illuminated). The result of this is a set of separate good-time interval (GTI) files. The multi_chip_gti script combines these separate files into a single GTI file, which can then be used to filter the event file.

This is for ACIS data only since HRC data does not make use of multiple GTIs.


% multi_chip_gti infile=635_repro_evt.fits i0=acis-0.gti i1=acis-1.gti
i2=acis-2.gti s2=acis-6.gti out=new_635.gti mode=h clob+

Combines the GTI files for 5 different chips into a single file that can then be used to filter the event file.

% dmcopy "635_repro_evt.fits[@new_635.gti]" 635_no_flares.gti
% dmlist 635_no_flare.gti header,clean | grep ONTIME
ONTIME                   58034.3591358210 [s]       Sum of GTIs
ONTIME3                  58034.3591358210 [s]       Sum of GTIs
ONTIME2                  55333.5180784310 [s]       Sum of GTIs
ONTIME1                  45436.7591483740 [s]       Sum of GTIs
ONTIME0                  61300.0 [s]                Sum of GTIs
ONTIME6                  65477.6000949590 [s]       Sum of GTIs


name type ftype def min max reqd
infile file input       yes
i0_gti file input       yes
i1_gti file input       yes
i2_gti file input       yes
i3_gti file input       yes
s0_gti file input       yes
s1_gti file input       yes
s2_gti file input       yes
s3_gti file input       yes
s4_gti file input       yes
s5_gti file input       yes
outfile file output       yes
tmpdir file         no
verbose integer   1 0 5  
clobber boolean   no      

Detailed Parameter Descriptions

Parameter=infile (file required filetype=input)

Input event file (optional)

The infile is used to determine the order of the GTIs. Since the keywords ONTIME, LIVETIME, and EXPOSURE are computed from the first GTI, preserving the order may be important.

Parameter=i0_gti (file required filetype=input)

The input GTI file for ACIS-I0 aka ACIS=0.

Leave parameter blank or set to 'none' if no GTI file for this chip.

Parameter=i1_gti (file required filetype=input)

The input GTI file for ACIS-I1 aka ACIS=1.

Parameter=i2_gti (file required filetype=input)

The input GTI file for ACIS-I2 aka ACIS=2.

Parameter=i3_gti (file required filetype=input)

The input GTI file for ACIS-I3 aka ACIS=3.

Parameter=s0_gti (file required filetype=input)

The input GTI file for ACIS-S0 aka ACIS=4.

Parameter=s1_gti (file required filetype=input)

The input GTI file for ACIS-S1 aka ACIS=5.

Parameter=s2_gti (file required filetype=input)

The input GTI file for ACIS-S2 aka ACIS=6.

Parameter=s3_gti (file required filetype=input)

The input GTI file for ACIS-S3 aka ACIS=7.

Parameter=s4_gti (file required filetype=input)

The input GTI file for ACIS-S4 aka ACIS=8.

Parameter=s5_gti (file required filetype=input)

The input GTI file for ACIS-S5 aka ACIS=9.

Parameter=outfile (file required filetype=output)

The output GTI file name.

Parameter=tmpdir (file not required)

The name of the temporary directory for intermediate files.

Parameter=verbose (integer default=1 min=0 max=5)

Amount of tool chatter

Parameter=clobber (boolean default=no)

Overwrite the output file if it already exists?


The ONTIME, EXPOSURE, and LIVETIME keywords are computed from the first GTI (or more precisely in datamodel terminology from the first subspace component). Files that are retrieved from the Chandra archive come with the GTIs ordered such that the 1st GTI is for the chip with the target location (RA_TARG, DEC_TARG). When a filter file is applied using the "@" syntax, the order of the filters in that file can re-order the GTI blocks which then may change the meaning of these keywords.

When an infile is specified, this script tries to preserve the order of the GTIs as best as possible. The first GTI in the infile should be the same; however, the order of the other extensions may be different.

About Contributed Software

This script is not an official part of the CIAO release but is made available as "contributed" software via the CIAO scripts page. Please see this page for installation instructions - such as how to ensure that the parameter file is available.


There are no known bugs for this tool.

See Also

lc_clean, lc_sigma_clip, lightcurves
acis_detect_afterglow, acis_streak_map, acisreadcorr, axbary, deflare, destreak, dmcopy, glvary, gti_align, monitor_photom, multi_chip_gti, pfold