On the Nature of Ultraluminous X-Ray Sources, Or What a Black Hole Should Look Like

Journal Article · Mon Sep 18 04:00:00 EDT 2006 · Submitted to Mon.Not.Roy.Astron.Soc.

OSTI ID:891858

Poutanen, Juri; Fabrika, Sergei; Butkevich, Alexey G; Abolmasov, Pavel

We derive the luminosity-temperature relation for the accreting black holes (BHs). At the accretion rates below the critical Eddington, the BHs are described by the standard Shakura-Sunyaev model resulting in the L {infinity} T{sup 4} {infinity} M relation. At super-Eddington rates, {dot m} = {dot M}/{dot M}{sub Edd} >> 1, a strong outflow forms within the spherization radius R{sub sp} {infinity} {dot M}. If the angular momentum of the outflowing matter is conserved and typical outflow velocities are of the order of Keplerian, the wind occupies 50-85 per cent of the sky as viewed from the BH, while the region around the rotation axis remains transparent. The bolometric luminosity in such a case is known to exceed the Eddington luminosity by a factor 1 + ln {dot m} and the observed luminosity is 2-7 times higher because of geometrical beaming. An edge-on observer sees only the soft emission from the extended envelope, with the photosphere radius exceeding R{sub sp} by orders of magnitude. The photosphere temperature follows the T{sub ph} {infinity} {dot M}{sup -3/4} or {dot M}{sup -1} relation depending on the velocity profile at R > R{sub sp} (constant velocity or a Keplerian profile). The resulting L-T{sub ph} dependence is consistent with that observed in the super-Eddington accreting BHs SS 433 and V4641 Sgr. A face-on observer has a direct view of the inner hot accretion disc which in stellar-mass BHs has temperature T{sub max} of a few keV. The effective temperature depends on radius as {infinity} R{sup -1/2} (up to the spherization radius) and the emitted spectrum is a power-law F{sub E} {infinity} E{sup -1} extending from {approx} 3T{sub max} down to the temperature at the spherization radius T{sub sp} {approx} {dot m}{sup -1/2} keV. It continues further as a power-law F{sub E} {infinity} E{sup 1/3} to the photospheric temperature T{sub ph}. We associate T{sub max} with a few keV spectral components and T{sub sp} with the soft, 0.1-0.2 keV components observed in the ultraluminous X-ray sources (ULX). The strong outflows combined with the large intrinsic X-ray luminosity of the central BH explain naturally the presence of the photoionized nebulae around ULX. An excellent agreement between the model and the observational data on ULX strongly argues in favour of ULX being super-critically accreting, stellar-mass BHs similar to SS 433, but viewed along the symmetry axis.

• Research Organization: Stanford Linear Accelerator Center (SLAC)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 891858
• Report Number(s): SLAC-PUB-12118; astro-ph/0609274
• Journal Information: Submitted to Mon.Not.Roy.Astron.Soc., Journal Name: Submitted to Mon.Not.Roy.Astron.Soc.
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANGULAR MOMENTUM
Astrophysics
ASTRO
BLACK HOLES
LUMINOSITY
NEBULAE
PHOTOSPHERE
ROTATION
SKY
SYMMETRY
VELOCITY
X-RAY SOURCES