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Absolute time calibration of LAXPC aboard AstroSat

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Abstract

The AstroSat mission carries several high-energy detectors meant for fast timing studies of cosmic sources. In order to carry out high precision multi-wavelength timing studies, it is essential to calibrate the absolute time stamps of these instruments to the best possible accuracy. We present here the absolute time calibration of the AstroSat LAXPC instrument, utilising the broad-band electromagnetic emission from the Crab Pulsar to cross calibrate against Fermi-LAT and ground based radio observatories Giant Metrewave Radio Telescope (GMRT) and the Ooty Radio Telescope (ORT). Using the techniques of pulsar timing, we determine the fixed timing offsets of LAXPC with respect to these different instruments and also compare the offsets with those of another AstroSat instrument, CZTI.

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Notes

  1. https://fermi.gsfc.nasa.gov/cgibin/ssc/LAT/LATDataQuery.cgi.

  2. We refer the median of the TOA errors as the “typical timing accuracy”

  3. http://psrchive.sourceforge.net/.

  4. https://bitbucket.org/psrsoft/tempo2/src/master/.

  5. https://fermi.gsfc.nasa.gov/cgibin/ssc/LAT/LATDataQuery.cgi.

  6. https://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/overview.html.

  7. http://www.jb.man.ac.uk/pulsar/crab.html.

  8. http://astrosat-ssc.iucaa.in/?q=data_and_analysis.

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Acknowledgements

We thank the anonymous referees for their valuable suggestions to improve the presentation of the paper. This publication made use of data from the Indian astronomy mission AstroSat, archived at the Indian Space Science Data Centre (ISSDC). The LAXPC data were processed at the Payload Operations Centre at TIFR Mumbai. The CZT Imager instrument was built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed and facilitated the project. We thank the staff of the Ooty Radio Telescope and the Giant Metrewave Radio Telescope for taking observations over such a large number of epochs. Both these telescopes are operated by National Centre for Radio Astrophysics of Tata Institute of Fundamental Research. PONDER backend, used in this work, was built with TIFR XII plan grants 12P0714 and 12P0716. BCJ acknowledges support for this work from DST-SERB grant EMR/2015/000515. BCJ and AB acknowledges the support of Department of Atomic Energy, Government of India, under projcet # 12-R&D-TFR-5.02-0200. AB acknowledges the support from the UK Science and Technology Facilities Council (STFC). Pulsar research at Jodrell Bank Centre for Astrophysics and Jodrell Bank Observatory is supported by a consolidated grant from STFC.

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Correspondence to Avishek Basu.

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This article is part of the Special Issue on “AstroSat: Five Years in Orbit”.

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Basu, A., Bhattacharya, D. & Joshi, B.C. Absolute time calibration of LAXPC aboard AstroSat. J Astrophys Astron 42, 61 (2021). https://doi.org/10.1007/s12036-021-09748-w

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