Search Publications
The EXOSAT Data on GX 339-4: Further Evidence for an ``Intermediate'' State
Méndez, Mariano; van der Klis, Michiel
We have studied the fast timing and spectral behavior of the black hole candidate (BHC) GX 339-4 using all 1-20 keV EXOSAT ME data: the 1983 July, 1984 March, 1984 May, and 1985 April observations. In 1985 April, GX 339-4 was in a weak low state (0.03 × 10-9 ergs cm-2 s-1, 2-10 keV). The X-ray spectrum was a hard p…
On the Relationship between the Periodic and Aperiodic Variability of Accreting X-Ray Pulsars
Stella, Luigi; Lazzati, Davide
Besides the narrow peaks originating from the periodic signal, the power spectra of accreting X-ray pulsars display continuum components usually increasing toward low frequencies; these arise from the source aperiodic variability. Most studies up to the present have adopted the view that the periodic and aperiodic variations are independent. Howev…
Evidence for an Anomalous State in the Black Hole Candidate 4U 1630-47
Kuulkers, Erik; van der Klis, Michiel; Parmar, Arvind N.
We have reanalyzed two EXOSAT medium-energy observations during part of the 1984 X-ray outburst of the black hole candidate transient system 4U 1630-47. One observation (May 10) shows fast-timing properties (on timescales shorter than ~250 s) typical of those of other black hole candidates in their high states. The power spectrum shows a power law…
A Transition Disk Model Fit for the Broadband X-Ray Spectrum of Cygnus X-1
Rao, A. R.; Misra, R.; Melia, F. +1 more
The broadband (2-500 keV) data for Cygnus X-1 from observations by EXOSAT, OSSE, and the XMPC balloon, have been fitted to the transition disk model. In this model the emission is from the inner region of an accretion disk where the temperature is a rapidly varying function of radius and the radiative mechanism is saturated Comptonization. We fit …
The Long-Term Periodic Oscillation of the NGC 4151 Nucleus
Lyuty, V. M.; Kotov, V. A.; Haneychuk, V. I. +3 more
The hypothesis that the luminosity of the nucleus of the Seyfert 1 galaxy NGC 4151 varies with a period of P0 ~ 160.0101 minutes is revised. In 1987-1994 a series of photometric observations of the NGC 4151 has been carried out in the U and V filters at several instruments. In the total sample of 27 nights, the U data of 15 nights showe…