41,045 research outputs found
Optical and X-ray Properties of CAL 83: I. Quasi-periodic Optical and Supersoft Variability
We have studied the long-term (~ years) temporal variability of the prototype
supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHO and
OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of
~1 mag on timescales of ~450 days, and spends typically ~200 days in the
optical low state. Combined with archival XMM-Newton X-ray observations these
represent the most extensive X-ray/optical study to date of this system, and
reveal in much greater detail that the X-ray light curve is anti-correlated
with the optical behaviour. This is remarkably similar to the behaviour of the
"transient" SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale
of ~168 days, and also anti-correlate with the optical flux. We performed
simple blackbody fits to both high and low state X-ray spectra, and find that
the blackbody temperature and luminosity decrease when the optical counterpart
brightens. We interpret these long-term variations in terms of the limit-cycle
model of Hachisu & Kato (2003a), which provides further support for these
systems containing massive (~1.3 Msun) white dwarfs. In addition, we have
refined their orbital periods in the MACHO and OGLE-III light curves to values
of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951,
respectively.Comment: 9 pages, 8 figures, 3 tables, accepted for publication in MNRA
Spectroscopic Identification of the Infrared Counterpart to GX5-1
Using CGS4 on UKIRT, we have obtained a 1.95-2.45 micron infrared spectrum of
the primary candidate counterpart to the bright Z LMXB GX5-1. IR photometry by
Naylor, Charles, & Longmore (1992) and the astrometry of Jonker et al. (2000)
had previously identified this star as the most likely counterpart to GX5-1.
The spectrum presented here clearly shows Brackett gamma and He lines in
emission, for the first time confirming the identity of the counterpart.
Similar to our previous spectroscopy of the Z source LMXBs Sco X-1 and Sco X-2
(Bandyopadhyay et al. 1999), the K-band spectrum of GX5-1 shows emission lines
only. We briefly discuss the implications of this spectrum for the nature of
the Z sources.Comment: accepted for publication as a Letter in MNRA
Simultaneous X-ray and optical observations of the flaring X-ray source, Aquila A-1
During the summer of 1978 the recurrent transient X-ray source, Aquila X-1, underwent its first major outburst in two years. The results of extensive observations at X-ray and optical wavelengths throughout this event, which lasted for approximately two months are presented. The peak X-ray luminosity was approximately 1.3 times that of the Crab and exhibited spectral dependent flickering on timescales approximately 5 minutes. The observations are interpreted in terms of a standard accretion disk model withparticular emphasis on the similarities to Sco X-1 and other dward X-ray systems, although the transient nature of the system remains unexplained. It was found that Aquila X-1 can be described adequately by the semi-detached Roche lobe model and yields a mass ratio of less than or approximate to 3.5
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