Results from AstroSat LAXPC Observations of Hercules X-1 (Her X-1)

TL;DR

This paper reports on AstroSat LAXPC observations of Her X-1, revealing new spectral dip phenomena during its 35-day cycle, enhancing understanding of the system's accretion and absorption processes.

Contribution

It presents new spectral features observed during different states of Her X-1, including a novel dip behavior indicating highly ionized or dense cold matter.

Findings

Discovery of dips with constant softness ratio during Main High state.

Identification of dips caused by highly ionized matter or dense cold matter.

Analysis of spectral changes with 35-day and orbital phases.

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.