Generating the Good Time Interval (GTI) File

Examination of the lightcurve shows that there are two noisy sections, one between 9.6405e7 and 9.6413e7 seconds, and another between 9.6422e7 and 9.6425e7 seconds. Both show rates well in excess of the normal background count rate of $\sim$ 0.05 count/second. There are two procedures that make the GTI file (gtibuild and tabgtigen) that, when applied to the event file in another run of rgsproc, will excise these sections.

The first method, using gtibuild, requires a text file as input. This file can be made on your local machine and uploaded to your Hera account by right-clicking and dragging the file from your local directory to the remote directory. In the first two columns, refer to the start and end times (in seconds) that you are interested in, and in the third column, indicate with either a + or - sign whether that region should be kept or removed. In the example case, then, we would write in our ASCII file (named r1_gti.txt):

9.6405e7 9.6413e7 -
9.6422e7 9.6425e7 -

and proceed to the task gtibuild.

To make the GTI with gtibuild in the GUI:

1)

Call gtibuild in the Hera GUI.

2)

Enter the name of the text file and the output GTI table (here, r1_gti.fits).

3)

Click ``Run''.

To make the GTI with gtibuild in the Command Window, type:

gtibuild file=r1_gti.txt table=r1_gti.fits

where

file - intput text file
table - output gti table

The task tabgtigen applies a filtering expression to the event file, limiting either the rates or the times, to produce the GTI.

To make the GTI with tabgtigen in the GUI:

1)

Call the tabgtigen task.

2)

Next to ``Name of input data set'', enter the name of the lightcurve file, r1_ltcrv.fits.

3)

Directly below, enter the name of the output file, r1_gti.fits.

4)

Next to ``Booleam expression controlling the GTI creation'', enter the filtering expression. Since the nominal count rate is about 0.05 count/sec, we will set the upper limit to 0.2 count/sec: RATE$<$0.2

5)

Click ``Run''.

To make the GTI with tabgtigen in the Command Window, type:

tabgtigen table=r1_ltcrv.fits gtiset=r1_gti.fits expression='RATE$<$0.2'

where

table - the lightcurve file
gtiset - output gti table
expression - the filtering criteria. Since the nominal count rate is 0.05 about count/sec, we have set the upper limit to 0.2 count/sec.