Jeffrey E. McClintock

Compact Stellar X-Ray Sources: Black hole binaries

4.1.1 Scope of this review We focus on 18 black holes with measured masses that are located in X–ray binary systems. These black holes are the most visible representatives of an estimated ∼300 million stellar–mass black holes that are believed to exist in the Galaxy (van den Heuvel 1992; Brown & Bethe 1994; Timmes et al. 1996; Agol et al. 2002). Thus the mass of this particular form of dark matter, assuming ∼10M⊙ per black hole, is ∼4% of the total baryonic mass (i.e., stars plus gas) of the Galaxy (Bahcall 1986; Bronfman et al. 1988). Collectively this vast population of black holes outweighs the Galactic–center black hole, SgrA, by a factor of ∼1000. These stellar–mass black holes are important to astronomy in numerous ways. For example, they are one endpoint of stellar evolution for massive stars, and the collapse of their progenitor stars enriches the universe with heavy elements (Woosley et al. 2002). Also, the measured mass distribution for even the small sample of 18 black holes featured here are used to constrain models of black hole formation and binary evolution (Brown et al. 2000a; Nelemans & van den Heuvel 2001; Fryer & Kalogera 2001). Lastly, some black hole binaries appear to be linked to the hypernovae believed to power gamma–ray bursts (Israelian et al. 1999; Brown et al. 2000b; Orosz et al. 2001). This review is focused on the X–ray timing and spectral properties of these 18 black holes, plus a number of black hole candidates, with an eye to their importance to physics as potential sites for tests of general relativity (GR) in the strongest possible gravitational fields. There are now several current areas of research that probe phenomena in these systems that are believed to occur very near the event horizon. These X–ray phenomena include quasi–periodic oscillations (QPOs) at high frequency (40–450 Hz) observed from seven systems, relativistically broadened iron lines from the inner accretion disk, and thermal disk emission from near the innermost stable circular orbit allowed by GR. We also comment on evidence for the existence of the event horizon, which is based on a comparison of black–hole and neutron–star binaries and on models for advective accretion flows. The black hole binaries featured here are mass–exchange binaries that contain an accreting black hole primary and a nondegenerate secondary star. They comprise about 10% of all bright X–ray binaries. For background on X–ray binaries, see Chapter 1, and references therein. For comprehensive reviews on black hole binaries, see

Parameters for the soft X-ray transient 4U 1543-47: Evidence for a black hole

Spectroscopic observations of the soft X-ray transient 4U 1543-47 reveal a sinusoidal radial velocity curve with a period of P=1.123±0.008 days and an amplitude of K=124±4 km sec−1. The resulting mass function is f(M)=0.22±0.02 M⊙. The V and I light curves exhibit two waves per orbital cycle with amplitudes about 0.08 mag. We modeled the light curves as ellipsoidal variations in the secondary star and found that the formal 3σ limits on the inclination from a simultaneous fit to the V and I light curves are 24°⩽i⩽36° for Q=M1/M2⩾1. However, there are systematic effects in the data that the model does not account for, so the above constraints should be treated with caution. We argue that the secondary star is still on the main sequence with a mass in the range 2.3⩽M2⩽2.6 M⊙. This mass range, the 3σ inclination range (24°⩽i⩽36°), and the 3σ mass function range (0.16⩽f(M)⩽0.28 M⊙) imply a primary mass in the range 2.7⩽M1⩽7.5 M⊙. Thus the mass of the compact object in 4U 1543-47 is likely to be in excess of ≈3...

A Black Hole of > 6 Solar Masses in the X-ray Nova XTE J1118+480

Observations of the quiescent X-ray nova XTE J1118+480 with the new 6.5 m Multiple Mirror Telescope have revealed that the velocity amplitude of the dwarf secondary is 698 ± 14 km s-1 and the orbital period of the system is 0.17013 ± 0.00010 days. The implied value of the mass function, f(M) = 6.00 ± 0.36 M☉, provides a hard lower limit on the mass of the compact primary that greatly exceeds the maximum allowed mass of a neutron star (~3 M☉). Thus, we conclude that the compact primary is a black hole. Among the 11 dynamically established black hole X-ray novae, the large mass function of XTE J1118+480 is rivaled only by that of V404 Cyg. We estimate that the secondary supplies 34% ± 8% of the total light at 5900 A and that its spectral type is in the range from K5 V to M1 V. A double-humped I-band light curve is probably due to ellipsoidal modulation, although this interpretation is not entirely secure because of an unusual 12 minute offset between the spectroscopic and photometric ephemerides. Assuming that the light curve is ellipsoidal, we present a provisional analysis that indicates that the inclination of the system is high and the mass of the black hole is correspondingly modest (M1 10 M☉). The broad Balmer emission lines (FWHM = 2300-2900 km s-1) also suggest a high inclination. For the range of spectral types given above, we estimate a distance of 1.8 ± 0.6 kpc.