X-ray reflection spectroscopy of black hole binary XTE J1550-564: exploring accretion evolution with improved sensitivity
Abstract
Black hole binaries exhibit a wealth of astrophysical phenomena as they go into outburst, evolving through two principal spectral states: hard and soft. Since BHB accretion flows evolve on such short timescales (typical duty cycles are on the order of years to decades) we can track the structural changes to their accretion flows in realtime with a multitude of ground and space based observatories across the electromagnetic spectrum. One useful technique for probing the accretion flows of BHBs is to model the X-ray reflection spectrum, a signature of the reflection of the primary continuum off the accretion disc. The characteristic relativistically broadened Iron K-alpha line and Compton reflection hump allow us to constrain the black hole spin, inner disc radius, and other key properties of the accretion disc such as the abundance of iron and the inclination of the disc with respect to the line of sight. Such modeling depends on high sensitivity spectral observations in order to distinguish these reflection features and therefore constrain key physical parameters. I present ongoing reflection modeling of newly calibrated RXTE PCA-and-HEXTE X-ray spectra of the BHB XTE J1550-564, covering multiple outburst cycles across all spectral states, using the most-up-date X-ray reflection spectroscopic code, relxill. The archival dataset includes 517 spectra with a total exposure of 971 ks, making use of 876 million PCA (3-45 keV) counts and 114 million HEXTE (20-200) counts. We utilize the drastically improved calibration of RXTE's PCA and HEXTE (cluster B) instruments-using the publicly available recalibration tools pcacorr and hexBcorr-which allows us to increase the data precision by up to an order of magnitude over previous studies, and reduces instrumental features typically present in the residuals. The goal is to track key physical parameters of XTE J1550-564 (black hole spin, inner disc radius, iron abundance) as it evolves through its spectral states. We optimize the prominence of reflection features in the spectrum (such as the iron line and Compton reflection hump) by combining multiple spectra in groups according to spectral hardness and intensity, and employ Markov Chain Monte Carlo techniques to explore the statistical landscape and constrain key model parameters. This work is part of a broader campaign to systematically analyze several bright black holes. With the increased instrument sensitivity we will be able to better constrain the evolution of the inner disc radii of a number of BHBs during multiple outbursts, as well as their black hole spins, building a more complete picture of the physics of black hole accretion.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.689C