ISRO

3.3 Proposal Preparation Tools

Proposers can use the following tools in order to prepare an AstroSat proposal. 

PIMMS (http://103.230.165.218:9001/exptimecalc/) to estimate source count rates.

  • UVIT Exposure Time Calculator (http://uvit.iiap.res.in/Software/etc) to estimate required exposure time for an astronomical source.
  • UVIT Bright Source Warning Tool (http://uvit.iiap.res.in/Software/bswt to set filters of the VIS channel for ensuring: a) safety of the detector against overexposure, b) adequacy of signal from stars in the field for tracking drift of the S/C.
  • Spectral simulation tools such as X-ray Spectral fitting package (XSPEC), Integrated Spectrographic Innovative Software (ISIS), Modelling and fitting package (Sherpa) which are available online.

 

3.3.1   ASTROVIEWER - Tool to aid Celestial Source Viewing

The tool gives the view periods of a selected celestial source for a prolonged period of one year maximum.  Also, the view periods that satisfy all the constraints are provided orbit-wise so that the proposer/ Guest Observer can plan their observations more accurately and also season-wise. For UVIT payload users, view duration timings during eclipse that satisfies all envisaged constraints are available in a separate file as UVIT is expected to observe only in eclipse.  The Tool has been designed to use the latest orbit information available on a daily basis and provides the various constraint angle characteristics in graphical plots so that GO can visualize the situation while planning for observations. The view period of the selected source is stored orbit wise and is made available in tabular form for the GO to use.  Since the ram angle constraint for certain sources are on and off due to the closeness to the orbit inclination, this output contains flags ‘0’ for satisfying the constraint and ‘1’ for violating the constraint in the table.  A Graphical User Interface program allows the user to interact remotely and obtain the required details. Additional information like Eclipse and occult Entry/Exit is also made available. 

Geometrical Constraints

  • RAM angle (+ROLL and velocity vector) > 12˚
  • Terminator (+ROLL and Bright Earth Limb)  > 12˚
  • Sun Angle (+ROLL and SUN)  > 45˚ (may be  higher  depending on mission  requirement)
  • Angle b/w +YAW and SUN > 90˚
  • Angle b/w Star Sensor and SUN > 50˚  Angle b/w +ROLL and Albedo > 12˚

3.3.2       Portable Interactive Multi-Mission Simulator (PIMMS) The AstroSat PIMMS package (downloadable from http://astrosat-ssc.iucaa.in or accessed online at http://103.230.165.218:9001/exptimecalc/) is an implementation of the Portable Interactive Multi-Mission Simulator package, originally distributed from NASA/GSFC High Energy Astrophysics Science Archive Research Centre (HEASARC).  This implementation includes the effective area of AstroSat X-ray instruments and can be used to estimate source count rates in LAXPC, SXT, CZTI and SSM for a variety of input spectral models.  A user manual is distributed with the downloadable version, and online help is available for the WebPIMMS version.

Response files:  Response Matrix files and estimated background spectra are provided for LAXPC, SXT and CZTI payloads at the website http://astrosat-ssc.iucaa.in.  These may be used to carry out spectral simulations for X-ray sources, for example with the fakeit command in HEASOFT XSPEC.

3.3.3       UVIT Exposure Time Calculator (ETC)

Help Page: http://uvit.iiap.res.in/Software/etc/Help Present Version: 2.0.0 (03 May, 2016) The UVIT Exposure Time Calculator (ETC) will help assess the feasibility of an observation. It calculates the expected count rate from a source in various UVIT filters, followed by either i) The Signal-to-Noise Ratio (SNR) achieved for a given observation time, or ii) The time required to reach a given SNR. Users may choose from a range of astronomical sources/spectra such as a star, black-body, galaxy, power law, etc. or choose to upload their own source spectrum. 3.3.4       Bright Source Warning Tool (BSWT) Help Page: http://uvit.iiap.res.in/Software/bswt/Help Present Version 1.5.0 (30 March 2016) Aim of the tool is to inform the proposer whether the region of the sky around a science target is safe / unsafe for UVIT to take observations. The program scans for stars brighter than the safety threshold and lists out the count rates of these bright stars in all the 10 filters in the FUV and NUV telescopes. This program identifies all the bright stars within 20 arcmin radius of the target object.  See also guidelines document at the same website. Please note that as per the latest process used by UVIT this output is only used to check for filters of VIS (320-550 nm) channel; the checks for NUV/FUV filters are not made with this list.  Hence the following mandatory checks are necessary. 

 

Mandatory checks for successful observation with UVIT

The UVIT is not designed to observe very bright sources and the presence of a bright source in the UVIT field of observation can cause “Bright Object Trigger” in the hardware that would switch OFF all three detectors. In addition, the presence of an ultra-bright source near the UVIT field of view will scatter excessive radiation beyond the allowed limit. One of the UVITs, the VIS channel is primarily used for the spacecraft tracking. It is the proposers’ responsibility to ensure smooth tracking during their proposed observations. Hence the proposers need to exercise extra caution in preparing a proposal for UVIT observations. It is strongly recommended that the proposers follow the guideline described in detail in the document (ref:http://uvit.iiap.res.in/sites/uvit.iiap.res.in/files/Guidelines_for_proposal_submission_3.pdf) for mandatory checks to be done for UVIT observations.