We present first results from the spectral and temporal analysis of an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The timing properties of this hard state black hole show considerable variability, even though the state does not change. This has previously been noted for the power spectral density, but is probably even more pronounced for the time lags. From an anal...

We compare the evolution of spectral shape with luminosity in GRS 1915+105 with that of ‘normal’ black holes. The pathological time variability of GRS 1915+105 does not indicate that it belongs in a different class to all the other objects. At comparable fraction of Eddington luminosity its spectra and (more importantly) time variability behaviour are similar to that seen in the ‘normal’ black ...

We present high time-resolution multicolour observations of the quiescent soft X-ray transient XTEJ1118+480 obtained with ULTRACAM. Superimposed on the double-humped continuum g ′ and i -band lightcurves are rapid flare events which typically last a few minutes. The power density spectrum of the lightcurves can be described by a broken power–law model with a break frequency at ∼2mHz or a power–...

We study the emergence of string instabilities in D dimensional black hole spacetimes (Schwarzschild and Reissner Nordstrøm), and De Sitter space (in static coordinates to allow a better comparison with the black hole case). We solve the first order string fluctuations around the center of mass motion at spatial infinity, near the horizon and at the spacetime singularity. We find that the time ...

Rapid variability of the TeV emission in several blazars implies a central black hole mass MBH < 10M⊙, appreciably smaller than the values estimated from the MBH −Lbulg relation, and Doppler factors for the γ-ray emitting fluid much larger than those associated with radio patterns. We discuss the conditions in the central engine required to account for the short timescales and large luminositie...

The black hole candidate GRS 1915+105 exhibits a rich variety of variability. Assuming that the earlier paradigm of black hole accretion which includes a shock is applicable for this system as well, one can classify these variabilities into four classes. We present light curves of these classes and discuss the basis of our

Fast variability studies of accreting black holes in the Galaxy offer us a unique opportunity to measure the spins of black holes and test the strong-field behavior of general relativity. In this review, I summarize the arguments often used in attempts of measuring the spins of black holes, concentrating on their theoretical foundations. I also argue that X-ray studies of accreting black holes ...

We present the second XMM-Newton observation (85ks) of the narrow-line Seyfert 1 galaxy (NLS1) I Zw 1 and describe its mean spectral and timing characteristics. On average, I Zw 1 is ∼ 35 per cent dimmer in 2005 than in the shorter (20 ks) 2002 observation. Between the two epochs the intrinsic absorption column density diminished, but there were also subtle changes in the continuum shape. Consi...

This paper investigates the challenging problem of encoding the knowledge and reasoning processes involved in the common sense manipulation of physical objects. In particular we provide a formalisation of a domain involving rigid objects, holes and a string within a reasoning about actions and change framework. Therefore, this work investigates the formalisation and reasoning about flexible obj...

We use the microlensing variability observed for nine gravitationally lensed quasars to show that the accretion disk size at 2500Å is related to the black hole mass by log(R2500/cm) = (15.6± 0.2) + (0.54± 0.28) log(MBH/10M⊙). This scaling is consistent with the expectation from thin disk theory (R ∝ M BH), but it implies that black holes radiate with relatively low efficiency, log(η) = −1.29 ± ...