X-RAY POLARIZATION FROM ACCRETING BLACK HOLES: THE THERMAL STATE

Journal Article · Thu Aug 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/701/2/1175; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21319571

Schnittman, Jeremy D

We present new calculations of X-ray polarization from black hole (BH) accretion disks in the thermally dominated state, using a Monte Carlo ray-tracing code in full general relativity. In contrast to many previously published studies, our approach allows us to include returning radiation that is deflected by the strong-field gravity of the BH and scatters off of the disk before reaching a distant observer. Although carrying a relatively small fraction of the total observed flux, the scattered radiation tends to be highly polarized and in a direction perpendicular to the direct radiation Agol and Krolik. For moderately large spin parameters (a/M {approx}> 0.9), this scattered returning radiation dominates the polarization signal at energies above the thermal peak, giving a net rotation in the polarization angle of 90 deg. We show how these new features of the polarization spectra from BHs in the thermal state may be developed into a powerful tool for measuring BH spin and probing the gas flow in the innermost disk. In addition to determining the emission profile, polarization observations can be used to constrain other properties of the system such as BH mass, inclination, and distance. New instruments currently under development should be able to exploit this tool in the near future.

• OSTI ID: 21319571
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 701; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
GAS FLOW
GENERAL RELATIVITY THEORY
GRAVITATION
INCLINATION
MONTE CARLO METHOD
ROTATION