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High-Level LAT Simulations

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GLAST LAT Project. DC2 Workshop, SLAC, 1 3 March 2006 1. High-Level LAT Simulations ... sources and can attenuate according to redshift and its own idea of the ... – PowerPoint PPT presentation

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Title: High-Level LAT Simulations


1
High-Level LAT Simulations S. W.
Digel Stanford Linear Accelerator Center M.
Razzano INFN and University of Pisa
2
High-level LAT simulations
  • This is short-hand for what some call a Fast
    Monte Carlo
  • The science tools include an observation
    simulator (gtobssim, by Jim Chiang) that uses
    the instrument response functions (hence
    high-level) to generate simulated data, rather
    than instrument-level interaction simulation,
    reconstruction, and classification (Gleam)
  • gtobssim uses the same event generator
    (scheduler) as Gleam, and can read the same
    source specifications (although it simulates only
    gamma rays).
  • Can use the same pointing history, too (more
    later)
  • Advantages of gtobssim
  • Easier to use than Gleam much, much faster (DC2
    gamma rays 10 CPU hours in gtobssim, 500 hours
    in Gleam)
  • Response functions are by construction perfect

Ask me why all the tools start with gt DC2
Gleam run including (resampled) background was
20,000 CPU hours
3
gtobssim as a science tool
  • Well, the obvious application is to be able to
    make a data set for which you know the truth
  • For DC2, consider following Francescos advice to
    simulate a region of the DC2 sky that you are
    studying
  • Some applications include evaluating
    sensitivities running multiple trials of some
    simulation
  • Or you could evaluate effects of different
    observing strategies, if you could make up your
    own FT2 file (although this is not a goal of DC2)

4
Defining a gtobssim simulation
  • Basically, you need a source model and a
    pointing/attitude/livetime history
  • The source models are defined as XML file(s) see
    later
  • The pointing history is an FT2 file. gtobssim
    pays attention to the livetime of each interval
    and enforces those livetime fractions in the
    simulation
  • gtobssim will run without a pointing history file
  • In this case you get a default orbit of some kind
    with idealized rocking, (probably) no SAA
    outages, and a uniform livetime fraction that you
    specify
  • The resulting FT2 equivalent is then also written
    to a file
  • gtorbsim can do this for you if all you want is a
    phony FT2 file

5
Source model specifications
  • First question Can the source model files be
    the same as gtlikelihood uses? No
  • Example source specification for a point source
  • N.B. this is not really Vela
  • (The SourcePop source is available for defining
    point sources in bulk)
  • General rule fluxes are integrated over the
    energy range specified and are in m-2 s-1
  • This is a source from the Flux package, one of
    the originals by Toby. Most of the new sources
    are SpectrumClass (by Jim unless otherwise
    noted - in the genericSources package) and have a
    simpler but less readable specification

ltsource name"vela" flux"0.00928"gt    ltspectrum
escale"MeV"gt        ltparticle name"gamma"gt
ltpower_law emin"30.0" emax"100000.
gamma"1.62"/gt lt/particlegt            
ltcelestial_dir ra"128.73" dec"-45.2"/gt
        lt/spectrumgt     lt/sourcegt
If broken power-law, ebreak and gamma2 tags are
accepted
6
More on source model specifications
  • Example generic source from the Workbook
  • Want to know what those parameters are? See the
    workbook
  • Options Extended sources
  • GaussianSource (2-dim gaussian power-law)
  • MapSource (2-dim image power-law spectrum)
  • MapCube (3-dim image 2 spatial one spectral)
  • Isotropic (power-law)

ltsource name"periodic_source"gt ltspectrum
escale"MeV"gt ltSpectrumClass
name"PeriodicSource" params"0.1, 2.1, 1e3, 1,
0.75, 30., 2e5"/gt ltgalactic_dir
l"0" b"0"/gt lt/spectrumgt lt/sourcegt
7
More on source model specifications (2)
  • Options Time-varying sources
  • SimpleTransient Point source with power-law
    spectrum and a finite on time
  • Transient template Like above but light curve
    can be specified in detail
  • SpectralTransient Point source with broken
    power-law spectrum and detailed light curve can
    handle multiple sources and can attenuate
    according to redshift and its own idea of the
    Extragalactic Background Light
  • PeriodicSource Point source with power-law
    spectrum and sinusoidal variation of flux
  • GRBobs (Nicola Omodei) GRB simulator (Valerie
    described how this tells GBM simulation software
    about a given burst)

8
More on time-varying sources (3)
  • More time-varying sources
  • Pulsar Specified p and pdot, lightcurve in an
    ASCII file, power-law spectrum does not
    decorrect arrival times
  • PulsarSpectrum (Max Razzano) detailed pulsar
    simulator

9
And nowcreate your pulsar!(I)
Part A Adding the pulsar general parameters to
a Datalist
Every pulsar to be simulated must be inserted in
a DataList file, containing the pulsar general
parameters that not depend on specific model
(i.e. total flux, ephemerides, etc..)
All the DataList files that PulsarSpectrum can
manage must be specified in a default file named
PulsarDataList.txt, located in the /data
directory.
2 - Add a line with myDataList.txt in the
PulsarDataList.txt file
10
And nowcreate your pulsar!(II)
Part B Creating a pulsar entry in a XML file
The remaining pulsar parameters must be defined
in a XML file. Part of them depend on the model
you want to use.
Here En1E6, E08E6, g1.6, b1.7 (out of page)
Lightcurve option 2 random generated 3
takes from a profile (named NAMETimeProfile.txt
and located in the /data directory)
For more informations, please see at
http//glast.pi.infn.it/soft/Pulsar/psrpisa.htm
11
PulsarSpectrum footnote on /data directory
  • This is in the ST/celestialSources/Pulsar/vXrYpZ/
    data directory, or C\Glast\ScienceTools-vXrYpZ\co
    de\celestialSources\Pulsar\v1r1p10\data
  • Alternatively you may define an environment
    variable PULSARDATA that points to where the
    pulsar definition files are.
  • If you want that output files are redirected to a
    directory different from the current one, you
  • This will contain the various log and ROOT 2d
    histogram files that PulsarSpectrum writes
  • Except for the file SimPulsars_Spin.txt, which
    has the timing information formatted so that
    gtpulsardb can ingest it this is how you go from
    simulation to analysis with pulsars
  • To create a D4-formatted fits file
  • Gtppulsardb SimPulsars_Spin.txt and enter a name
    for the output file.

12
About time
  • As far as the time-dependent sources are
    concerned, time is expressed in MET, Mission
    Elapsed Time, which is the number of seconds
    elapsed since midnight, January 1, 2001
    (MJD51910).
  • Right now is approximately 162985200
  • Yes, MET is inconvenient to use directly
  • The start_date parameter of gtobssim allows you
    to specify your own reference date, so that the
    source specifications can be made with
    conveniently small time offsets
  • No, I am not entirely sure right now that we are
    handling UTC (earth rotation-based) vs. TT
    (Terrestrial Time, absolute time, constant offset
    from GPS time) conversion carefully enough at the
    leap second level

13
Walk through the parameter file (1)
xml_source_file,f,a,"none",,,"File of flux-style
source definitions" source_list,fr,a,"source_names
.txt",,,"File containing list of source
names" scfile,f,a,"none",,,"Pointing history
file" sctable,s,h,"SC_DATA",,,"Spacecraft data
extension" outfile_prefix,s,a,"test",,,"Prefix
for output files" evtable,s,h,"EVENTS",,,"Event
data extension" simulation_time,r,a,86400,1,4e7,"
Simulation time (seconds)" livetime_frac,r,h,0.9,,
,"Livetime fraction" start_time,r,h,0,,,Simulation
start time (seconds wrt start_date) use_as_numeve
nts,b,h,no,,,Use simulation time as number of
events max_simulation_time,r,h,3.155e8,,,Maximum
simulation time (seconds) start_date,s,a,"2001-01-
01 000000",,,"Simulation start date"
Any parameter with an h is hidden (not
prompted for)
  • xml_source_file can be a file that is a list of
    other XML files, too none means use the
    default libraries
  • source_list is the file that lists the sources to
    be included from the libraries
  • scfile is the FT2 file
  • If you want to you can simulate by of events
    (instead of time)

14
Walk through the parameter file (2)
use_acceptance_cone,b,a,no,,,"Apply acceptance
cone?" ra,r,a,0,-360,360,"RA of cone center
(degrees)" dec,r,a,0,-90,90,"Dec of cone center
(degrees)" radius,r,a,20,0,180,"Acceptance cone
radius (degrees)" emin,r,h,30,20,2e5,"Minimum
event energy (MeV)" emax,r,h,200000,20,2e5,"Maximu
m event energy (MeV)" rspfunc,s,a,"DC2",DC2DC1A
G25,,"Response functions" max_effarea,r,h,1.21,,,"
Maximum effective area value" max_numrows,i,h,200
000,,,"Maximum number of rows in FITS
files" random_seed,i,a,293049,,,"Random number
seed" chatter, i, h, 2, 0, 4, "Output
verbosity" clobber, b, h, yes, , ,
"Overwrite existing output files" debug,
b, h, no, , , "Activate debugging mode" gui,
b, h, no, , , "GUI mode activated" mode,
s, h, "ql", , , "Mode of automatic
parameters"
  • An acceptance cone and energy range can be
    specified if you want to, and the maximum number
    of events per file
  • Setting gui to yes will tell the science tools to
    prompt for the parameter files values via a GUI

15
Tips and tricks
  • The output event summary (FT1) files from
    gtobssim have an additional column called
    MC_SRC_ID
  • For each event, this identifies the particular
    source that produced it the mapping is in the
    ltprefixgt_srcIds.txt file that gtobssim writes
  • Yes, we wont have this in real life, but it is
    extremely useful for studying algorithms
  • Of course you can also filter on this column with
    the fselect FTOOL
  • What is more, most (eventually all) of the
    science tools that use FT1 files as input will
    accept an ASCII file with a list of event files
    gtbin requires _at_ as the prefix
  • So, for example, you can keep your large,
    relatively time consuming Galactic diffuse model
    FT1 files separate from an additional component
    that you are generating

16
More on using gtobssim
  • Read the User Workbook
  • The section with descriptions of each of the
    sources and their parameters will be updated
    soon. It currently does not include steady point
    sources and some other useful sources
  • The workbook also contains a useful worked
    example
  • Also, Francesco Longo has regenerated the
    Checkout 3 sky model using the DC2 response
    functions, and the input and output files will be
    made available

17
ObsSim GUI
  • Also by Jim Chiang
  • Nice interface for defining models and running
    gtobssim
  • Can also communicate with ds9
  • Not 100 working under Windows at the moment
  • Most useful if you want to pick and choose within
    a library that you have already defined (or has
    already been defined for you)
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