Data organisation
Layout
The content of the 1dc.pre folder should be as follows:
caldb/
caldb/data
caldb/data/cta
caldb/data/cta/prod3b
caldb/data/cta/prod3b/caldb.indx
caldb/data/cta/prod3b/bcf
...
data/
data/baseline/
data/baseline/gc
data/baseline/gc/gc_baseline_000001.fits
data/baseline/gc/gc_baseline_000002.fits
...
models/
models/models_gc.xml
...
obs/
obs/obs_gc_baseline.xml
Instrument Response Functions
The caldb folder contains the :ref:`Instrument Response Functions <glossary_irf>` that are necessary for the analysis of the simulated CTA data. The folder contains the prod3b response that should be used for the :ref:`first CTA Data Challenge <glossary_1dc>`. In the pre-release, only the response functions for CTA South are available for a zenith angle of 20 deg. Specifically, the following response functions are available:
Response name Site Configuration Zenith Duration South_z20_50h South Baseline 20 deg 50 hours South_z20_5h South Baseline 20 deg 5 hours South_z20_0.5h South Baseline 20 deg 30 min South_TS_z20_50h South Threshold 20 deg 50 hours South_TS_z20_5h South Threshold 20 deg 5 hours South_TS_z20_0.5h South Threshold 20 deg 30 min
Warning
The 50 hours :ref:`Instrument Response Functions <glossary_irf>` were used for the simulation of the :ref:`first CTA Data Challenge <glossary_1dc>` data. Please use only these response functions for the analysis. If you use :ref:`Observation Definition Files <glossary_obsdef>` for the analysis (see below) the appropriate 50 hours response functions will be used automatically.
Event data
The data folder contains the calibrated, reconstructed and background reduced event data that were procuded for the :ref:`first CTA Data Challenge <glossary_1dc>` and that were stored into FITS files. Each event file contains the events for an :ref:`observation <glossary_obs>` (or run) of 30 minutes duration and comprises an :ref:`event list <glossary_eventlist>` and a :ref:`Good Time Intervals <glossary_gti>` binary table extension (see figure below).
Structure of an event file
The header of the EVENTS table contains information about the :ref:`observation <glossary_obs>` such as the start and stop date and time, the duration and livetime of the observation, and the pointing direction in Right Ascension and Declination (see figure below).
Header of an event list
Note
The pointing direction during an observation is fixed. The simulation has the following characteristics:
- Number of observations (and pointings): 1673
- Duration of each observation: 1800 sec
- Deadtime fraction: 5%
- Total exposure time of simulation: 836.5 hours
- Simulated event energies: 30 GeV - 120 TeV
- Maximum off-axis angle: 5 deg
- Start date of observations: 1/1/2021
Warning
Only the following header keywords in the EVENTS table have meaningful values:
- DSTYPx - Data sub-space type
- DSUNIx - Data sub-space unit
- DSVALx - Data sub-space value
- DSREFx - Data sub-space reference
- DATE_OBS - start date of observation (UTC)
- TIME_OBS - start time of observation (UTC)
- DATE_END - end date of observation (UTC)
- TIME_END - end time of observation (UTC)
- TSTART - start time of observation, counted from time reference (s)
- TSTOP - stop time of observation, counted from time reference (s)
- MJDREFI - integer part of time reference MJD (days)
- MJDREFF - fractional part of time reference MJD (days)
- TIMEUNIT - time unit
- TIMESYS - time system
- TIMEREF - time reference
- TELAPSE - elapsed time (s)
- ONTIME - exposure time (s)
- LIVETIME - livetime (s)
- DEADC - deadtime correction factor, livetime / exposure time
- TIMEDEL - time resolution
- RA_PNT - Right Ascension of pointing direction (deg)
- DEC_PNT - Declination of pointing direction (deg)
- RADECSYS - Coordinate system
- EQUINOX - Coordinate epoch
All remaining header keywords have arbitrary values and should not be used for the analysis.
Each row of the EVENTS table corresponds to a single event. Each event is characterised by
Column Meaning Unit EVENT_ID Event number in file unitless TIME Time stamp, countered from time reference s RA Reconstructed Right Ascension deg DEC Reconstructed Declination deg ENERGY Reconstructed energy TeV DETX Reconstructed camera X coordinate deg DETY Reconstructed camera Y coordinate deg
An example of an EVENTS table is shown below.
Content of an event list
Warning
The time stamps in the TIME column are not necessarily in ascending order.
Observation Definition Files
The file obs_gc_baseline.xml is a so called :ref:`Observation Definition File <glossary_obsdef>` that contains the information (or metadata) of a list of observations. The file is a plain ASCII files in XML format that can be inspected and manipulated by any text editor.
Models
The models folder contains the definitions of all source and background models that were used for simulating the data. The file models_gc.xml is a so called :ref:`Model Definition File <glossary_moddef>` that collects the definition of all model components used for the Galactic Centre Survey simulation. The other files in the folder are ASCII and FITS files containing spectral, temporal and spatial information that was used in the simulations.
Warning
The ASCII and FITS files should always reside in the same folder as the :ref:`model definition XML files <glossary_moddef>` since the latter reference the former.