# ctobssim¶

Simulate event list(s).

## Synopsis¶

This tool simulates event list(s) using the instrument characteristics specified by the instrument response function(s) and an input model. The simulation includes photon events from astrophysical sources and background events from an instrumental background model.

By default, ctobssim creates a single event list. ctobssim queries a pointing direction, the radius of the simulation region, a time interval, an energy interval, an instrumental response function, and an input model. ctobssim uses a numerical random number generator for the simulations with a seed value provided by the hidden seed parameter. Changing this parameter for subsequent runs will lead to different event samples.

ctobssim performs a safety check on the maximum photon rate for all model components to avoid that the tool locks up and requests huge memory resources, which may happen if a mistake was made in setting up the input model (for example if an error in the flux units is made). The maximum allowed photon rate is controlled by the hidden maxrate parameter, which by default is set to 1e6.

ctobssim can also generate multiple event lists if an observation definition file is specified on input using the hidden inobs parameter. In that case, simulation information will be gathered from the file, and for each observation an event list will be created.

For each event file, the simulation parameters will be written as data selection keywords to the FITS header. These keywords are mandatory for any unbinned maximum likelihood analysis of the event data.

## General parameters¶

inobs [file]
Input event list or observation definition XML file. If provided (i.e. the parameter is not blank or NONE), the pointing definition and eventually the response information will be extracted from the input file for event simulation.
inmodel [file]
Input model XML file.
caldb [string]
Calibration database.
irf [string]
Instrumental response function.
(edisp = no) [boolean]
Apply energy dispersion?
outevents [file]
Output event list or observation definition XML file.
(prefix = sim_events_) [string]
Prefix for event list in observation definition XML file.
(startindex = 1) [integer]
Start index of event list in observation definition XML file.
(seed = 1) [integer]
Integer seed value to be used for Monte Carlo simulations. Keep this parameter at the same value for repeatable simulations, or increment this value for subsequent runs if non-repeatable simulations are required.
ra [real]
Right Ascension of CTA pointing (J2000, in degrees).
dec [real]
Declination of CTA pointing (J2000, in degrees).
rad [real]
tmin [time]
Start time (UTC string, JD, MJD or MET in seconds).
tmax [time]
Stop time (UTC string, JD, MJD or MET in seconds).
(mjdref = 51544.5) [real]
Reference Modified Julian Day (MJD) for simulated events. The times in seconds for each event are counted from this reference time on.
emin [real]
Lower energy limit of simulated events (in TeV).
emax [real]
Upper energy limit of simulated events (in TeV).
(deadc = 0.95) [real]
(maxrate = 1.0e6) [real]
Maximum photon rate for source models. Source models that exceed this maximum photon rate will lead to an exception as very likely the specified model normalisation is too large (probably due to the a misinterpretation of units). Note that ctools specifies intensity units per MeV.

## Standard parameters¶

(nthreads = 0) [integer]
Number of parallel processes (0=use all available CPUs).
(publish = no) [boolean]
Specifies whether the event list(s) should be published on VO Hub.
(chatter = 2) [integer]
Verbosity of the executable:

chatter = 0: no information will be logged

chatter = 1: only errors will be logged

chatter = 2: errors and actions will be logged

chatter = 3: report about the task execution

chatter = 4: detailed report about the task execution

(clobber = yes) [boolean]
Specifies whether existing files should be overwritten.
(debug = no) [boolean]
Enables debug mode. In debug mode the executable will dump any log file output to the console.
(mode = ql) [string]
Mode of automatic parameters (default is ql, i.e. “query and learn”).
(logfile = ctobssim.log) [string]
Name of log file.