Non-quiescent X-ray emission from neutron stars and black holes

Two types of bursting behavior are observed in X-ray binaries. Short X-ray bursts lasting seconds, and X-ray outbursts lasting weeks to months. The short bursts are believed to be thermonuclear explosions on the surface of neutron stars (type I X-ray bursts). The long outbursts occur in sources known as soft X-ray transients (SXTs) and result due to instabilities in accreting matter onto either a neutron star or black hole.; Type I X-ray bursts provide a tool for probing surfaces of neutron stars. Requiring a surface for the burning has led authors to use X-ray bursts to rule out the existence of a black hole (where an event horizon exists not a surface) for systems which exhibit type I X-ray bursts. Distinguishing between neutron stars and black holes has been a problem for decades.; Narayan and Heyl have developed a theoretical framework to convert suitable upper limits on type I X-ray bursts from accreting black hole candidates (BHCs) into evidence for an event horizon. We survey 2101.2 ks of data from the USA X-ray timing experiment and 5142 ks of data from the Rossi X-ray Timing Explorer (RXTE) experiment to obtain the first constraint of this type. 1122 ks of neutron star data yield a population averaged mean burst rate of 1.7 ± 0.4 × 10−5 bursts s−1, while 6081 ks of BHC data yield a 95% confidence level upper limit of 4.9 × 10−7 bursts s−1. Applying the framework of Narayan and Heyl we calculate regions of luminosity where the neutron stars are expected to burst and the BHCs would be expected to burst if they had a similar surface. In this luminosity region 464 ks of neutron star data yield an averaged mean burst rate of 4.1 ± 0.9 × 10−5 bursts s−1, and 1512 ks of BHC data yield a 95% confidence level upper limit of 2.0 × 10−6 bursts s−1 and a strong limit that BHCs do not burst with a rate similar to the rate of neutron stars in these regions. This gives evidence that BHCs do not have surfaces.; We also analyzed SXT behavior. In particular, 4U 1630–47, was analyzed throughout its 1999 outburst using USA and RXTE data. This source is assumed to be a BHC in a low-mass X-ray binary system. Despite the length of time devoted to studying this source, there is still little known about it. (Abstract shortened by UMI.)...