INTEGRAL observations of Her X-1

TL;DR

This study analyzes INTEGRAL data of Her X-1, revealing significant pulse profile changes, a strong spin-up within a 35-day cycle, and detailed cyclotron line variations, enhancing understanding of its X-ray spectral and timing behavior.

Contribution

First detailed INTEGRAL analysis showing pulse profile evolution, spin-up within a cycle, and phase-dependent cyclotron line variations in Her X-1.

Findings

Significant changes in pulse profiles during observations.

First measurement of strong spin-up within a 35-day cycle.

Cyclotron line parameters vary with pulse phase.

Abstract

Aims: We investigate the X-ray spectral and timing properties of the accreting X-ray pulsar Her X-1 observed with the INTEGRAL satellite in July-August 2005. Methods: The data analyzed in this work cover a substantial part of one main-on state of the source. The short-time scale pulse period development is measured. X-ray pulse profiles for different energy ranges and time intervals are constructed. Pulse-averaged and pulse-phase resolved broad band X-ray spectra are studied. Spectral changes during X-ray dips are explored. Results: The X-ray pulse profiles are found to change significantly during the period of observations. For the first time a strong spinup is measured within one 35 d cycle. Spectral characteristics observed during the X-ray dips are consistent with their interpretaion as due to partial covering as has been reported by several authors. The fundamental cyclotron absorption line is firmly observed in both pulse-averaged and pulse-phase resolved X-ray spectra. The energy, width, and the depth of the line are found to vary significantly with pulse phase.