High-energy astrophysics - II. Compact binary stars

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Hubble Space Telescope Observations of the Black Hole X-ray Transient GRO J0422+32 Near Quiescence

We present HST/FOS ultraviolet and optical spectroscopy of the black hole X-ray transient GRO J0422+32 shortly before the system reached quiescence. We find that the accretion spectrum from 2500-9000A can be very well fit by a self-absorbed synchrotron model, with superposed HI and MgII emission lines. The explanations we suggest for this spectrum are that it is either due to active coronal regions above a geometrically thin accretion disc, or that the disc is evaporated into an advective flow.Comment: 7 pages with 7 postscript figures included, uses mn.sty. Accepted for publication in MNRA

Black hole hunting in the Andromeda Galaxy

We present a new technique for identifying stellar mass black holes in low mass X-ray binaries (LMXBs), and apply it to XMM-Newton observations of M31. We examine X-ray time series variability seeking power density spectra (PDS) typical of LMXBs accreting at a low accretion rate (which we refer to as Type A PDS); these are very similar for black hole and neutron star LMXBs. Galactic neutron star LMXBs exhibit Type A PDS at low luminosities (~10^36--10^37 erg/s) while black hole LMXBs can exhibit them at luminosities >10^38 erg/s. We propose that Type A PDS are confined to luminosities below a critical fraction of the Eddington limit, $l_c$ that is constant for all LMXBs; we have examined asample of black hole and neutron star LMXBs and find they are all consistent with $l_c$ = 0.10+/-0.04 in the 0.3--10 keV band. We present luminosity and PDS data from 167 observations of X-ray binaries in M31 that provide strong support for our hypothesis. Since the theoretical maximum mass for a neutron star is \~3.1 M_Sun, we therefore assert that any LMXB that exhibits a Type A PDS at a 0.3--10 keV luminosity greater than 4 x 10^37 erg/s is likely to contain a black hole primary. We have found eleven new black hole candidates in M31 using this method. We focus on XMM-Newton observations of RX J0042.4+4112, an X-ray source in M31 and find the mass of the primary to be 7+/-2 M_Sun, if our assumptions are correct. Furthermore, RX J0042.4+4112 is consistently bright in \~40 observations made over 23 years, and is likely to be a persistently bright LMXB; by contrast all known Galactic black hole LMXBs are transient. Hence our method may be used to find black holes in known, persistently bright Galactic LMXBs and also in LMXBs in other galaxies.Comment: 6 Pages, 6 figures. To appear in the conference proceedings of "Interacting Binaries: Accretion, Evolution and Outcomes" (Cefalu, July 4-10 2004

Doppler Tomography of Dwarf Nova IY UMa during Quiescence

Quiescent Doppler tomography of the newly discovered deeply-eclipsing SU UMa system IY UMa reveals properties of the region where the accretion stream from the donor impacts the edge of the disc. A very strong bright spot is produced and the Keplerian disc emission in the impact region is disrupted or obscured. The differing properties of Halpha, Hbeta and He I emission will allow physical parameters of the converging flow region to be studied.Comment: 6 pages, 5 figures. To appear in Proceedings of Astro-Tomography Workshop, Brussels, July 2000, Eds. H. Boffin, D. Steeghs, Springer-Verlag Lecture Notes in Physic

Doppler Tomography of XTE J2123-058 and Other Neutron Star LMXBs

We describe Doppler tomography obtained in the 1998 outburst of the neutron star low mass X-ray binary (LMXB) XTE J2123-058. This analysis, and other aspects of phase-resolved spectroscopy, indicate similarities to SW Sex systems, except that anomalous emission kinematics are seen in HeII, whilst phase 0.5 absorption is confined to H alpha. This separation of these effects may provide tighter constraints on models in the LMXB case than is possible for SW Sex systems. We will compare results for other LMXBs which appear to show similar kinematics and discuss how models for the SW Sex phenomenon can be adapted to these systems. Finally we will summarise the limited Doppler tomography performed on the class of neutron star LMXBs as a whole, and discuss whether any common patterns can yet be identified.Comment: 8 pages, 5 postscript figures. To appear in Proceedings of Astro-Tomography Workshop, Brussels, July 2000, Eds. H. Boffin, D. Steeghs, Springer-Verlag Lecture Notes in Physic