Part 2: Analysis of 3C454.3 Using iLat

See:

Introduction to the Standard Analysis of LAT Data

iLat Tutorial - Part 1: Setup

Step-by-step procedure:
iLat Tutorial - Part 2: Analysis of 3C454.3 Using iLat

HELP:

List of iLat Commands
(iLat Help file as of 11/07/2008)

iLat Tutorial – Part 2:
Analysis of 3C454.3 Using iLat

Notice: The Fermi code has not been released to the public and is for use by members of the LAT Collaboration only!

Getting started:

After performing the steps in Part 1: Setup, launch iLat from the command line by entering:

chuckp@noric06 $ iLat

A message similar to the following will be displayed:

TUnixSystem::SetDisplay:0: RuntimeWarning: DISPLAY not set, setting it to isoc-chuckp.slac.stanford.edu:0.0
Session Log file: iLat.history

and, after delay of ~30 seconds, or so, the following message will be displayed, followed by an iLat prompt:

**************************************************
* W E L C O M E *
* T O *
* iLat (interactive LAT analysis Tools) *
* version: v0r0p0 June 2008 *
* Started by G. Tosti *
* Based on script by J. Chiang *
* Contributors: GRB Analysis by N. Omodei *
**************************************************
Session started by user: tramacer Date: 2008-10-02T15:35:03.142719
To access shell commands prefix the command with "$"
Type "py" to access python interpreter
Type "quit" to exit
Type "help" to view the list of commands

Note: Commands used in this tutorial are shown to the right of the iLat prompts in the highlighted lines below; explanatory notes follow each command, and links to popup examples are included as appropriate.

ILAT>setwd ./

To set your working directory.

Getting LAT Data – Option 1:

ILAT>setdcdir /Data/Flight/Level1/LPA

To set the data repository.

ILAT>getdcft 243756000.0 243842400.0 ft1.fits ft2.fits

See: Example_01.

To get ft1 and ft2 data: Tstart(MET) Tstop(MET) ft1-file-name ft2-file-name.

Optionally, you could use the following command:

ILAT>getdcft 2008-09-22 06:00:00 2008-09-23 06:00:00 ft1-a.fits ft2-a.fits

Note: You can use "convmet" and "convdate" to switch from MET to DATE and viceversa.

ILAT>$ls

ft1.fits ft1list.list ft2.fits ft2list.list

ILAT>setevtcl 2

See: Example_02.

To select the DIFFUSE class events.
Refer to: 'Summary of response function sets'
and to Performance Plots.

Go to: Parameters Setting and Model Definition.

Getting LAT Data – Option 2:

ILAT>getastroft2 243756000.0 243842400.0 ft2.fits

Parameters:
243756000.0	=	Tstart(MET)
243842400.0	=	Tstop(MET)
ft2.fits	=	name of FT2 file.

ILAT>getastroft1 243756000.0 243842400.0 100 300000 343.4906163 16.1482111 25 2 ft1_diffuse.fits

Parameters:
243756000.0	=	Tstart(MET)
243842400.0	=	Tstop(MET)
100	=	minimum event energy
300000	=	maximum event energy
343.6566	=	RA	In this case, it is: 3C454.3
16.1494	=	DEC
25	=	photon extraction radius (in degrees)
2	=	event class selection (2 = diffuse).
ft1_diffuse.fits	=	name of FT1 file after event class selection.

ILAT>$ls

Note that the diffuse file has been created:

ft1.fits ft1_diffuse.fits ft1list.list ft2.fits ft2list.list

Parameters Setting and Model Definition

ILAT>setft1 ft1_diffuse.fits

To use the ft1 file with the DIFFUSE class selected.

ILAT>setft2 ft2.fits

See: Example_03.

To set the ft2 file.

ILAT>setirfs P6_V1_DIFFUSE

Note: You must set the irf according to the evtclass selection. Refer to: 'Summary of response function sets'

ILAT>setene 100 300000

Set energy boundaries in MeV.

Note: setene does not change the initial ft1 file, but it will affect subsequent analysis steps.

ILAT>setroi 343.6566 16.1494 15 25

Parameters:
343.6566	=	RA	In this case, it is: 3C454.3
16.1494	=	DEC	In this case, it is: 3C454.3
15	=	Radius (in degrees) in which photons are extracted.
25	=	Radius (in degrees) where pgwave will look for sources.

Note: setroi does not change the original ft1 file, but it will affect subsequent analysis steps.

ILAT>xmlmodel 0.5

See: Example_04.

We run a source detection for the ROI, looking for the sources therein and generating from them a corresponding xml model file to use in the likelihood analysis.

Notes:

Before you run xmlmodel, you can use the setgalmodel command to select the diffuse model.

Please use the recommended Galactic diffuse emission model. (See Diffuse Model for Analysis of LAT Data.)

The pgwave threshold of source significance for the xml model file can be set using the setfindsrc command.

The parameter 0.5 (as in xmlmodel 0.5) sets pixel resolution; in this case 1 pixel = 0.5^o.

ILAT>$ls

See: Example_05.

ILAT>$cat region_0000_pgw_map.list

See: Example_06.

To see the content of the PGWave detection.

Also see:

ds9 rendition of the Counts Map and PGWave Results (region_0000_pgw_map.fits)

ILAT>$cat region_0000.xml

See: Example_07.

To look at the content of the xml model file (that will be used by the likelihood).

Note: It is important to check the results of the PGWave count map and data to ensure that the inputs you will use when running the likelihood analysis are good and that there are no surprises that may lead to confusing results (e.g., two photon sources within the roi when only one is expected, the possibility of which increases with the length of the exposure).

Performing Likelihood

ILAT>ltcube

See: Example_08.

To generate the livetime cube.

ILAT>diffuse

See: Example_09.

Note: The diffuse command calculates diffuse responses for Galactic diffuse and Extragalactic (isotropic) sources.

ILAT>expmap

See: Example_10.

To generate exposure map for Likelihood analysis.

Refer to: Likelihood Tutorial: Make an Exposure Map.

ILAT> $ls

See: Example_11.

ILAT>setulike region_0000_evt.fits expCube_0000.fits expMap_0000.fits region_0000.xml

To set ROI, exposure map, and XML model.

Note: The command line shown above has wrapped.

ILAT>ulike 3C454-like-results.dat

See: Example_12.

To run the likelihood and store the results in the file 3C454-like-results.dat; the model for the source is PowerLaw2. Refer to: Likelihood Tutorial: PowerLaw2.

Also see:

Counts Spectra