REINSTATING THE M31 X-RAY SYSTEM RX J0042.3+4115 AS A BLACK HOLE X-RAY BINARY AND COMPELLING EVIDENCE FOR AN EXTENDED CORONA
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland, MD 21218 (United States)
The M31 X-ray source RX J0042.3+4115 was originally identified as a black hole (BH) binary because it displayed characteristic low-state variability at conspicuously high luminosities; unfortunately, this variability was later found to be artificial. However, analysis of 84 Chandra ACIS observations, a Hubble Space Telescope Advanced Camera for Surveys (ACS)/WFC observation, and a 60 ks XMM-Newton observation has supplied new evidence that RX J0042.3+4115 is indeed a BH binary. The brightest optical star within 3{sigma} of the position of RXJ0042.3+4115 had a F435W ({approx}B) magnitude of 25.4 {+-} 0.2; M{sub B} > -0.4, hence we find a low-mass donor likely. RX J0042.3+4115 was persistently bright over {approx}12 years. Spectral fits revealed characteristic BH binary states: a low/hard state at 2.08 {+-} 0.08 Multiplication-Sign 10{sup 38} erg s{sup -1} and a steep power-law state at 2.41 {+-} 0.05 Multiplication-Sign 10{sup 38} erg s{sup -1} (0.3-10 keV). The high-luminosity low state suggests a {approx}20 M{sub Sun} primary; this is high, but within the range of known stellar BH masses. The inner disk temperature during the steep power-law state is 2.24 {+-} 0.15 keV, high but strikingly similar to that of GRS 1915+105, the only known Galactic BH binary with a low-mass donor to be persistently bright. Therefore, RX J0042.3+4115 may be an analog for GRS 1915+105; however, other mechanisms may account for its behavior. We find compelling evidence for an extended corona during the steep power-law state, because compact corona models where the seed photons for Comptonization are tied to the inner disk temperature are rejected.
- OSTI ID:
- 22004429
- Journal Information:
- Astrophysical Journal, Vol. 743, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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