Name of the Speaker(s): Wolfgang Kundt
Institution: Bonn University
Title of the communication: THE (STELLAR-MASS) BLACK-HOLE CANDIDATES (BHCs)
Preliminary abstract (12 lines max.):
are observationally defined as the class of (> 15) binary X-ray sources whose compact component has a mass exceeding several M(sun). Their best-known repre- sentatives are Cyg X-1, LMC X-1, A 0620-00, Nova Muscae, and the superluminal jet sources GRS 1915+105 and GRO J1655-40. The properties of the BHCs differ remarkably little from those of establish- ed neutron-star sources: they show often: (1) polarized optical emission, (2) high-low state bimodality, (3) Li absorption (like in Cen X-4), (4) X-ray dip- ping, (5) X-ray intensity flickering and QPO (like the LMXBs of high neutron- star spinrate), (6) formation of radio jets (i.e. of relativistic pair plasma), and (7) transient period lengthening (like during 'superhumps' of the cataclys- mic variables). Moreover, the BH interpretation is hard put by the following further proper- ties: (8) their X-ray lightcurves tend to peak near the Eddington luminosity of (no more than) one solar mass, and (9) mostly fall below some 10^32 erg/s dur- ing quiescence, (in conflict with accretion-disk theory). (10) The spectral power during high state can peak above 1 MeV, (with an equivalent black-body area of <10^2 cm^2 !). And an extended, variable, luminous windzone is signal- led by (11) strong (Balmer) emission lines, (12) noisy LOS line velocities, and (13) noisy optical light curves which even during quiescence (of A 0620-00 & Nova Muscae) lack reflection symmetry about the two orbital minima. Due to the Eddington hurdle, disks around neutron stars differ from those around white dwarfs in being able to store almost all the matter transferred from their companion, occasionally as much as several M(sun). Once the disk mass approaches stellar values, a compact binary can appear first as a super- Eddington source, then as a 'supersoft (X-ray) source', and finally as a BHC.