Low-rate accretion onto isolated stellar-mass black holes

Abstract

Abstract. Magnetic field behaviour in a spherically-symmetric accretion flow for parameters typical of single black holes in the Galaxy is discussed. It is shown that in the majority of Galaxy volume, accretion onto single stellar-mass black holes will be spherical and have a low accretion rate (10 −6 −10 −9 of the Eddington rate). An analysis of plasma internal energy growth during the infall is performed. Adiabatic heating of collisionless accretion flow due to magnetic adiabatic invariant conservation is 25% more efficient than in the standard non-magnetized gas case. It is shown that magnetic field line reconnections in discrete current sheets lead to significant nonthermal electron component formation. In a framework of quasi-diffusion acceleration, the "energy-radius" electron distribution is computed and the function describing the shape of synchrotron radiation spectrum is constructed. It is shown that nonthermal electron emission leads to formation of a hard (UV, X-ray, up to gamma), highly variable spectral component in addition to the standard synchrotron optical component first derived by Shvartsman generated by thermal electrons in the magnetic field of accretion flow. For typical interstellar medium parameters, a black hole at 100 pc distance will be a 16-25 m optical source coinciding with the highly variable bright X-ray counterpart, while the variable component of optical emission will be about 18-27 m . The typical time scale of the variability is 10 −4 s, with relative flare amplitudes of 0.2-6% in various spectral bands. Possible applications of these results to the problem of search for single black holes are discussed.

XMM-NEWTONANDCHANDRAOBSERVATIONS OF THE EJECTA-DOMINATED MIXED-MORPHOLOGY GALACTIC SUPERNOVA REMNANT G352.7–0.1

“…The remaining option would be an isolated black hole, which can be difficult to detect because of the very low accretion rate (assuming Bondi-Hoyle accretion) inside the rarefied hot gas filling the interior of the SNR (Beskin & Karpov 2005).…”

Search for the event horizon by means of optical observations with high temporal resolution

“…We placed the upper limit on the variability of the emission from the position of the object on the level of B < 21.5 m (3σ) over the 10 −5 -1 s time scales. The combination of the I-band Hubble data (I < 20 m ) and XMM-Newton (flux ¡ 10 −14 erg/s/cm 2 ) with our theoretical estimations for possible models (Beskin & Karpov 2005) allow us to rule out the first model (see Fig. 4).…”

Pre-low-mass X-ray binaries containing a black hole: investigating a detection mechanism

“…somewhat larger than the canonical maximum neutron star mass value of 3M , and 10 M , which is the most probable mass of a single black hole (see e.g. [18] and references therein). Systems are considered with either an Mdwarf secondary star or a K-dwarf secondary star (dwarf stars in this spectral-type range have been observed in LMXBs containing a black hole, see e.g.…”

“…[16][17][18]; gives the conversion efficiency of gravitational potential energy to radiation associated with disc accretion onto a black hole, and is taken to be 0.5 following [16,17]; η converts the bolometric accretion luminosity to an X-ray luminosity in a specific energy range, and is taken to be 0.8 for a representative range of 0.3 -7 keV following [17]; and other parameters as for Equation 3. The next step was to identify suitable values for the remaining parameters in these accretion rate and luminosity calculations.…”