FAQ

 

Q. Who can download AstroSat data from Astrobrowse?

Ans: During the lock-in period, the Principal investigator of the proposal can download data from the Astrobrowse link (https://astrobrowse.issdc.gov.in/astro_archive/archive/Home.jsp). After the data lock-in period, the data become publicly available and any registered user can download.

 

Q. Where can a user find a readme file for software tools for processing AstroSat data?

Ans: All the software related to AstroSat data analysis is available on this website. There are detailed readme files available for all the tools in the detector related software pipelines. http://astrosat-ssc.iucaa.in/?q=data_and_analysis.

 

Q. When will be the next workshop for analyzing AstroSat data?

Ans: Please visit the ASSC webpage upcoming workshop notification for the next workshop for analyzing AstroSat data (http://astrosat-ssc.iucaa.in/?q=workshops).

 

Q. Where can one find a list of all the accepted proposals for AstroSat?

Ans: All the accepted AstroSat proposals with proposal Id and Abstract are available in AstroSat Proposal Redbook at the site https://issdc.gov.in/astro.html.

 

Q. Where can one look for AstroSat call for proposals?

Ans: A proposer can visit the site https://issdc.gov.in/astro.html for the latest updates/deadlines on AstroSat call for proposals.

 

Q. What does Q, L1, and L2 mean in the Astrobrowse source query page?

Ans: Q represents quality information, L1 represents Level 1 tar data sets and L2 represents Level 2 tar data sets.

 

Q. I am unable to convert Level1 data to Level2 data products. Can I use Level2 data products available at Astrobrowse page for scientific purposes?

Ans: Yes, one can use Level2 data products for scientific purposes. Instrument POC teams provide processed Level2 data from Level 1 data of the same observation.

 

Q. How to modify header files of AstroSat data for using barycenter code?

Ans: To modify the header keywords to enable barycenter correction in the data, a Python script and a C code are available in the link http://astrosat-ssc.iucaa.in/?q=data_and_analysis. After running one of these on the event file as per the instructions provided in the corresponding readme file, use as1bary code available in the same ASSC page for barycenter correction.

 

Q. What is the usage of as1bary code for barycenter correction of AstroSat data?

Ans: Usage of the barycenter correction code is : as1bary - i orbitfile -f eventfile -ra RAdeg -dec Decdeg -ref FK5.

 

Q. Whether there are any quick look images for the sources observed with AstroSat?

 Ans: For SXT data, the quick look report is available at http://www.tifr.res.in/~astrosat_sxt/HTMLOUTDIR/input.html.  For CZTI,  the quick look reports may be viewed at http://www.iucaa.in/~astrosat/czti_dqr/.

 

Q. Unable to compile SXT pipeline in Ubuntu 16.04 and 18.04 LTS.

Ans: To successfully install SXT pipeline in Ubuntu >14.04 LTS version, please downgrade gcc and g++ to version 4.8.

 

Q. How to resolve the error “PIL library missing” during the installation of sxtpipeline?

Ans: Some Linux systems show this compilation error. If you encounter this, then please follow the steps given in solution 1 and solution 2 provided at the end of the link https://www.tifr.res.in/~astrosat_sxt/sxtpipeline.html

Further, during the installation of SXT pipeline please comment out in the .bashrc file the commands entered for software related to other AstroSat instruments.

 

Q. Can “Laxpcsoft” software analyse level2 FITS event files?

Ans: “Laxpcsoft” routines are designed to work on the Level 1 LAXPC FITS files disseminated from Astrobrowse. This applies to the software having individual routines to extract spectra, lightcurves, power spectra, energy and frequency-dependent time-lag, dynamic power spectra, flux resolved spectroscopy, faint source background estimation, as well as the software having a single routine to extract spectra, lightcurve and background.

 

Q. Whether there is any log of sources observed by AstroSat, if yes, where to find it?

Ans: Catalogue of all AstroSat observations may be obtained by accessing the AstroSat Schedule Viewer: https://webapps.issdc.gov.in/MCAP/.  One could also use the AstroSat Observation Finder tool at http://astrosat-ssc.iucaa.in:8080/ObservationFinder.

 

Q. LaxpcSoft error “fcreate: not found” while running laxpc_make_stdgti filterfiles command.

Ans : Please initialize heasoft (heainit) before using LaxpcSoft commands to generate user-defined good time interval files.

 

Q. Problems while configuring LAXPCsoft in MAC-OS . While configuring (./Configure), the error “libcfitsio.a not found” is encountered. Even though the libcfitsio.a file is copied from heasoft to the present location, compilation still fails.

Ans : Please use mac specific Configure_curl file to compile, and the first line in it has to be commented out to avoid issues with the location of the libcfitsio.a file. Copy the libcfitsio.a file from the heasoft folder into the LAXPCsoftware directory, and then configure.

 

Q. There are two different versions of the SXT Event Merger Tool for merging different orbits in SXT data. Which is preferred?

Ans: There are two event merger tools SXTEVTMERGERTOOL (python based) and SXTPYJULIAMERGER_v01 (Julia based). The preferred event merger tool is SXTPYJULIAMERGER_v01.

 

Q. Using CZTbindata command on the cleaned event files for a specific bin size, for example 1 sec., one finds that the program fails to generate the output light curves.

Ans: To generate the light curve at a required binning, say 1 sec, using the CZTI pipeline, the bin size of the livetime file should be less than or equal to the intended bin size of the light curve.

 

Q. The observation time of a few observations of the same source are overlapping in consecutive orbits. How is it possible? How to correct it?

Ans: The Orbit Id associated with AstroSat data files refer to the orbit when the data were telemetered to the ground and not that during which the data were acquired on board. While generating Level 1 products at ISSDC a slight overlap is maintained between successive files in order to prevent potential data loss. The analysis software developed for all AstroSat instruments remove these overlaps while generating merged products using data from multiple orbits.

 

Q. Are the preliminary lightcurves of the sources observed with AstroSat (LAXPC, SXT and CZTI) accessible?

Ans: Quick look light curves from LAXPC, SXT and CZTI instruments are available at:

LAXPC    : https://www.tifr.res.in/~astrosat_laxpc/laxpclog/lc-hdr.html

SXT          : https://www.tifr.res.in/~astrosat_sxt/HTMLOUTDIR/input.html

CZTI        : http://www.iucaa.in/~astrosat/czti_dqr/

 

Q. Is any schedule available for AstroSat observations?

Ans: Schedule for AstroSat observations is available at : https://webapps.issdc.gov.in/MCAP/

 

Q. How much is the dead-time of LAXPC?

Ans: The dead-time LAXPC is estimated to be 42 micro sec (https://ui.adsabs.harvard.edu/abs/2017ApJS..231...10A).

 

Q . Are there different response matrices for SXT fast window mode (FW) and Photon counting mode (PC) data?

Ans: There a single response matrix sxt_pc_mat_g0to12.rmf available from the SXT instrument team for both FW and PC mode data.

 

Q. The command laxpc_make_event aborts with the message “please update the file gaina8.dat”.

Ans: The user needs to have a version of the file gaina8.dat which includes the date of observation of the data being analysed.  The latest version of gaina8.dat can be downloaded by navigating to “LAXPC Gain Record” on the webpage http://astrosat-ssc.iucaa.in/?q=laxpcData.

 

Q. How to obtain the required orbit file of AstroSat for barycenter correction?

Ans: An orbit file generator tool for AstroSat is available at http://astrosat-ssc.iucaa.in:8080/orbitgen/.

 

Q. LAXPCsoft tar file was downloaded from the ASSC AstroSat webpage. Upon untarring the GTI_make_V1_15Jun17 folder is found to be empty. How to overcome this issue?

Ans: Please issue commands in a unix terminal command line to untar the files. The package provided at http://astrosat-ssc.iucaa.in/?q=laxpcData has no empty folder.

 

APPS and proposal related Queries

 

Q. How to update affiliation in APPS account?

Ans: To update details like affiliation, please login at https://apps.issdc.gov.in/apps/auth/login.jsp webpage. Then go to the change profile option and edit the necessary details.

 

Q. While trying to  generate astroviewer output for a source with Declination less than 5 deg, the generated plots show all the parameters of the spacecraft to be above the lower limit. But the pdf file of the duration does not show any value for visibility and eclipse. For these it mention as "no time all the attitude constraints were met for this source for the given period". This pdf file only shows values for occult duration.

Ans: Sources in the declination band between -6 and +6 degrees are not visible with AstroSat as they violate the RAM angle constraint.

 

Q. The astroviewer tool shows an error "Special characters not allowed for celestial object", while checking visibility of the source.

Ans: Special Characters and +/- symbols in the source name are not allowed in the input fields of the Astroviewer tool.

 

Q. Why do we keep getting proposals rejected when it is a famous source like GRS 1915+105 or Cygnus X-1?

Ans:

1. If the proposed source is already well observed with AstroSat, then it should be clearly demonstrated why the existing observations are not sufficient to meet the proposed science goal.

2. Feasibility of meeting the required goals must be demonstrated through simulations. For example, for the detection of a QPO, the proposed duration should be the minimum required to achieve the desired level of significance.  Arguments must be provided to justify the necessary significance level.

3. Spectral simulation is mandatory to check if a particular feature is visible with the requested exposure time and instrument of interest.

4. There may be other proposals already accepted for the target, for which observations have not yet been carried out.  The list of such proposals may be obtained from the redbook or the AstroSat schedule viewer.

 

Q. Why do we need to simulate the spectrum and what is the impact of exposure time criteria? What are the common mistakes?

Ans:

Common mistakes in AO proposals:

 

1. Source too weak--not enough counts. In requesting attractively low integration times, many

proposers fall short of accumulating enough counts to achieve their scientific objectives, e.g.,

constraining the abundance of a distant cluster.

What to do?: perform a simulation.

 

2. Source too weak--background ignored. Backgrounds should not be neglected for weak

sources. As well as contributing additional noise, background often has the effect of

shortening the useable passband. Detection of iron K line may be impossible even with long integration times.

What to do?: perform a simulation with background.

 

3.Source too bright. AstroSat cannot observe arbitrarily bright sources.

What to do?: Check the restrictions on respective instruments in the AstroSat Handbook.

 

4. Look for similar observations that are already published or with data available online and reproduce the levels achievable to check the feasibility of the science case.

 

5. While simulating, one has to consider that the total stare time is always greater than the total observing time. It is essential to keep this in mind while estimating the observing time for covering specific temporal durations such as orbital periods.

 

Observing time must be optimised to that required for detecting a required spectral feature, say, a cyclotron line.

Methodology : Xspec or ISIS X-ray spectral fitting software can be used to simulate the known cyclotron line of the source in different exposure time, and the requirement of exposure time can be studied depending on the significance of line detection requirement, errors on parameters and noise in the hard X-rays.

 

Q. LAXPC light curve simulations: What should be the criteria or justification of identifying a QPO or interpretation of simulation?

Ans: The event file for LAXPC is simulated using this software simul.f available at the ASSC webpage. The simulated event file can be used to construct simulated energy-dependent

lightcurves, power spectra, energy, and frequency-dependent time-lags using the laxpc data analysis software.

Example: If proposal requires justification of simulation to detect presence of QPO in hard X-ray> 30 keV

Proposers can used LAXPC light curve simulation tool to generate energy dependent simulated QPO and justify required exposure to detect the significant hard X-ray QPO >30 keV with a 3 sigma detection limit, or the Q-factor (nu/delta nu)  >2 to claim it as a QPO.

So the methodology will be to simulate energy-dependent lightcurve with different exposures and rule out with lower limit or upper limit such that in less than the requested time it will not be possible to probe the science interest of high energy QPO detection at energies greater than 30 keV.

Supporting scientific justification with temporal simulation adds important strength to the proposal.

 

Q. Whether a light curve simulator can simulate the spin period of a pulsar candidate?

Ans: Yes, the light curve simulator for LAXPC can be used to simulate thre spin period of a pulsar.

 

Q. If we have two different sources of interest that have trigger criteria, for example, 0.5 Crab in flux to trigger the observation of the source and we want to observe the source with a 15 days gap, what is the suitable proposal type? Whether it is anticipated ToO or monitoring proposal?

Ans: This type of proposal is more suitable for anticipated ToO because there are proper trigger criteria, and monitoring or such sources may be carried out with follow up ToO proposal.

Moreover, the trigger criteria should be selected appropriately, and it is better to propose one source in a proposal or clear priority among the sources of interest should be mentioned.

 

 

Q. AVIS or Astroviewer tool, whether both are admissible for technical justification requirement?

Ans: Yes, output file of either tool is acceptable for technical justification. Astroviewer output gives the details about source visibility with AstroSat, occultation time and UVIT eclipse time. Other criteria for search remain the same like the default value of RAM, ROM etc. angles.

AVIS tool, on the other hand, gives plot and text output of the AstroSat visibility of the source for the instruments SXT, LAXPC, CZTI, and UVIT seperately unlike Astroviewer output.

 

Q. Reason for the values chosen as default for Astroviewer output?

Ans: Avoidance of ram-angle, Sun, and bright-Earth for safety: In order to avoid any damage to the coating of the primary mirror, due to atomic oxygen, a minimum angle of 12O is kept between the ram direction and the roll-axis, i.e., the axis of UVIT. In order to avoid damage/UV-assisted contamination due to radiation from Sun/bright-Earth/ Moon, a minimum angle of 45O/12O/15O is kept between the axis and Sun/ bright-Earth/Moon at all times even if UVIT is not observing.

AstroSat is normally operated with an additional Sun and Anti-Sun Angle constraint of 65 deg in order to achieve the best thermal control.

 

Q. Is it ok to propose an anticipated ToO for monitoring requirements?

Ans: It is recommended to write a follow up ToO proposal instead of monitoring anticipated ToO.

 

Q. If UVIT is not configured/ not required for the science case, so whether BSWT output is mandatory to be attached to the proposal?

Ans: If UVIT is not configured or required for the science proposal, then it is not mandatory to upload

the UVIT bright source warning tools output in the proposal submission page.

In the recent proposal cycles a combined output of THEIA and GAIA tool should be attached instead of BSWT output for the required documentation of safety check of UVIT.

 

Q. To increase the stare time, whether one can use UVIT as a primary instrument so that longer stare time is achieved with the secondary instruments.

Ans: If the source is brighter then 0.5 counts/sec in full field of UVIT then partial fields can be used to obtain the desired science case but proposers should take into account the exposure time calculation for each orbit the total data for FUV and NUV images

((Number of FUV frames + Number of NUV frames) * 32000 + Time of exposure * 500000) < 1010 bits/orbit. This imposes a limiting criteria of exposure time request with UVIT as the primary instrument.

 

Q. Whether it is advisable to write a proposal with LAXPC as a primary instrument and SXT in Fast Window mode or SXT Photon Counting mode as a secondary instrument?

Ans: There is an offset between the SXT pointing and the pointing of LAXPC, CZTI, and UVIT as available in the AstroSat handbook. These offsets are of the order of a few arcmins. Therefore, the proposers should use the PC mode when SXT is not the primary instrument. This is because the source may be out of the SXT FoV for the FW mode in this case.

 

Q. Whether for spectral simulation ISIS and XSPEC are equally acceptable? Is there any advantage of using ISIS over XSPEC?

Ans: Both XSPEC and ISIS X-ray spectral fitting softwares can be used to perform simulations for AstroSat proposal, but ISIS with astrosat.sl will automatically load response and background, and it gives estimates of count rate in SXT, LAXPC, CZTI, and UVIT.

Walkthrough of spectral simulation and detection of the iron line hands-on session for justification of requested observation time is available at http://astrosat-ssc.iucaa.in/?q=workshops under the title “Workshop on technical aspects of AstroSat proposal submission”.

 

Q. There is a conflict on the estimated count rate from LAXPC using webpimms web-based tool and simulated/real spectrum in the same energy band. What is the reason?

Ans: Webpimms web-based tool can be used for estimation of approximate count rate from the AstroSat’s LAXPC instrument.

 

Q. If any bright source is present in the field of view, which will be harmful in different UVIT filters, if it says that some filters are safe, whereas some filters are unsafe, can one propose the observation with safe filters of UVIT?

Ans: If among all the filters, one filter in UVIT is safe to observe, then we can still observe with UVIT as a primary instrument.

        The field should be checked in  TD1 catalogue and counts should be calculated for selected filters for safe limits. The absence of sources in 20 arc min radius is taken as presence of a source with a flux of 2 x 10-13 erg/sec/cm2/A and the count-rate for this flux in various UVIT filters are given in Table 3 of http://uvit.iiap.res.in/Software/gaia/docs/gaia_procedure_1.0.pdf

 

Q. If GALEX NUV/FUV images are NOT available and the field is above the +/- 30 deg galactic latitude then whether we can still propose from UVIT.

Ans: The field 28 arc min around target of interest should be checked in  TD1 catalogue and counts should be calculated for selected filters for safe limits. The absence of sources in 20 arc min radius is taken as presence of a source with a flux of 2 x 10-13 erg/sec/cm2/A and the count-rate for this flux in various UVIT filters are given in Table 3 of http://uvit.iiap.res.in/Software/gaia/docs/gaia_procedure_1.0.pdf.

 

Q. In case the field lies in any of the bright areas (within ±30 degree Galactic latitude or LMC or SMC) whether UVIT observations are permissible?

Ans: No within ±30 degree Galactic latitude or LMC or SMC any exposure of UVIT FUV/NUV exposures are not permissible.  However for individual target fields UVIT Safety Check ToO may be proposed to determine whether they are safe to observe, before making a regular proposal for those targets.

 

Q. Whether the estimated count rate from webpimms and/or ISIS simulation tool (astrosat.sl) is sufficient for UVIT safety check?

Ans: No, the count rate estimated from web-based webpimms tool of AstroSat and/or ISIS simulation tool (astrosat.sl) is model dependent, and low energy absorption can profoundly affect the count rate. So the proposers are strongly advised to use the UVIT simulator instead of webpimms for the estimation of count rate.

 

 

Q. A user has 5 targets (type 2 AGN), 3 of the targets have only partial coverage from GALEX. However all of them are beyond the 30 degree galactic latitude. Is it ok?

Ans: Check TD1 catalogue for the probable presence of bright source in the field of view of 28 arc min around the target of interest. Further, if the offset is small, the proposer can shift the source co-ordinate and check manually from the GALEX catalogue.

 

Q.  My source is not safe in the FUV-CAF2-1 filter and FUV-Baf2. But safe in other filters like FUVCaF2-2, FUV Silica Sapphire, Is this ok?

Ans: Yes, you can configure UVIT for safe filters.

 

Q. Is the NUV working? If not, are we still required to configure it? If NUV works later, will I have access to NUV data? So I better configure it.

Ans: Currently NUV channel of UVIT is not functional. Still proposer can configure it so that in future if it becomes functional the data will be accessible to the Principle Investigator of the proposal.

 

Q. How do I check for the scattered light from outside the main FOV ?

Ans: The output of THEIA and GAIA web based tool for safety check of UVIT filters should be generated for LAXPC as a primary instrument. This will give a output FOV ~28 arc min around the  target of interest, which is good enough for checking the bright source effect that can possibly contribute due to scattered light.

Q. My primary instrument is UVIT, and hence the exposure time is based on it. But since I also have the possibility to get X-ray, which all are the absolutely important parameters that I need to configure? We are looking for hard X-ray mainly.

Ans: If your science justification is based on UVIT as primary instrument and if the science case will also require secondary instruments (X-ray) then it is advisable to configure the X-ray instruments.

Q. How to estimate the probability of the recurrence of the transient black hole binary or neutron star binary for a AToO proposal?

Ans: We can calculate the duty cycle using previously known recurrence rate of outburst and duration of the outburst from the X-ray binary source. That fraction is the probability of such outburst being captured within a given time. Suppose the recurrence time is 2 years and the cycle duration is only half a year then the probability is 1/4.

 

Please send your queries to

 

astrosathelp@iucaa.in