3. Overview of proposal preparation, submission and selection
Proposers/ guest observers will have to submit proposals to ISRO by the deadline given in the ISSDC website using AstroSat Proposal Processing System (APPS) software. APPS is available online through http://www.issdc.gov.in. APPS is not downloadable and cannot be used off-line. An APPS proposer’s guide will be made available in ISSDC and ASC websites which elaborates on the proposal submission procedure. A summary is provided in this section.
3.1 Proposal preparation pre-requisites
Depending on the scientific requirement, proposals to AstroSat can be submitted for observation with a single or more instruments. Proposals are to be made as per APPS proposer’s guide and this procedures document. Proposers can refer to redbook for the list of observed targets.
AstroSat proposals will require the following information at the minimum.
- Source coordinates, source angular size if extended, V magnitude, 2-10 keV flux, estimated count rates for different instruments, exposure times, UVIT bright source list, Astroviewer output for feasibility of observations of the target in pdf format. (use AstroSat tools listed in section 3.3)
- Instrument configuration parameters such as instrument mode, filter, etc. (Ref. Handbook)
- Scientific and technical justification.
3.2 APPS Instructions
Instructions to fill various entries within APPS to prepare proposals are available online. APPS proposer’s guide can also be referred for this purpose. Queries on APPS can be mailed to firstname.lastname@example.org for proposal preparation and submission. Queries will be answered on best effort basis.
3.3 Proposal Preparation Tools
Proposers can use the following tools in order to prepare an AstroSat proposal.
- Astroviewer (http://issdc.gov.in/astroviewer/index.html) to determine Astrosat visibility period for a target of interest.
- PIMMS (http://astrosat-ssc.iucaa.in:8080/WebPIMMS_ASTRO/index.jsp) 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.
- AstroSat Schedule viewer (https://astro.issdc.gov.in:9321/MCAP/) to check Tentative/Confirmed Target Schedule of Astrosat.
- Spectral simulation tools such as X-ray Spectral fitting package (XSPEC ; https://heasarc.gsfc.nasa.gov/xanadu/xspec/), Interactive Spectral Interpretation System (ISIS ; http://space.mit.edu/CXC/ISIS/), Modelling and fitting package (Sherpa ; http://cxc.harvard.edu/sherpa4.4/) 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 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 proposer 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 proposer 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.
- RAM angle (+ROLL and velocity vector) > 12˚
- Terminator (+ROLL and Bright Earth Limb) > 12˚
- Sun Angle (+ROLL and SUN) > 65˚
- 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://astrosat-ssc.iucaa.in:8080/WebPIMMS_ASTRO/index.jsp) 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 1.6.1 (4 July 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 to be done for UVIT observations
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, v 1.0, 15 November 2016) for mandatory checks to be done for UVIT observations.
3.4 Preparing an ASTROSAT proposal
Proposers will need to register into the APPS before they can prepare proposals. Proposers may go through the APPS help document regarding submission of proposals.
3.5 Proposal handling in APPS
The receipt of each incoming proposal will be automatically acknowledged. At the end of submission date, the APPS will forward them to the ATAC for scientific review, while performing some assessments and preparing overall statistics on the response. ATAC is already constituted by Chairman, ISRO.
The ATAC will assign priorities to each proposal as A, B and C (and, as needed, grade individual observations within a proposal). The ATAC may ask some proposers to reduce the observing time or the number of targets in a proposal. Such proposals will be made available for revision to the PIs. The proposers will be able to submit a revised proposal before the set deadline only for changes recommended by the ATAC. Such partially allocated proposals, if not revised before the deadline, will be excluded from the list of successful proposal.
The technical feasibility of making the observations will be conducted by AstroSat Technical Committee (ATC) with support from Mission operations team.
One of the parameters used to plan which observations will be carried out during a particular orbit, is the priority of the observations as allocated by the ATAC and ATC. However, for operational reasons, no guarantee can be given that a particular observation will in fact be executed, regardless of its grade.