Abstract
The Large Area Proportional Counter (LAXPC) instruments onboard the AstroSat Observatory has observed the X-ray binary system Her X-1 during AstroSAT observing sessions AO2, AO3 and TO2. These include observations while Her X-1 is in different stages of its 35 day cycle: Low State, Turn-On to Main High State, peak of Main High State and early decline of Main High State. These observations also include a number of dips and one egress of neutron star eclipse. Here we present light curves and softness ratio analysis for these observations and discuss new features of the spectral changes with 35-day phase and orbital phase. We find a new phenomenon for dips during Main High State: about half of the dips show constant softness ratio as count rate decreases, which has not been seen before, and could be caused by highly ionized matter or very dense cold matter. The other half of the dips show the normal decrease of softness ratio as count rate decreases. These are caused by cold matter absorption and were previously known.
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Acknowledgements
This project is undertaken with the financial support of the Canadian Space Agency and of the Natural Sciences and Engineering Research Council of Canada. This publication uses data from the AstroSat mission of the Indian Space Research Institute (ISRO), archived at the Indian Space Science Data Center (ISSDC). LAXPC data were processed by the Payload Operation Centre at TIFR, Mumbai.
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This article is part of the Special Issue on “AstroSat: Five Years in Orbit”.
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Leahy, D.A., Chen, Y. Results from AstroSat LAXPC observations of Hercules X-1 (Her X-1). J Astrophys Astron 42, 44 (2021). https://doi.org/10.1007/s12036-020-09676-1
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DOI: https://doi.org/10.1007/s12036-020-09676-1