X-ray Light Curves (x-ray + light_curve)

Distribution by Scientific Domains

Selected Abstracts

Interpretation of the 1998 outburst of the unique X-ray transient CI Camelopardalis (XTE J0421+560)

ABSTRACT We present an analysis of the 1998 outburst of the peculiar X-ray binary and X-ray transient CI Cam (XTE J0421+560). We discuss the observations in the framework of several possible models and argue that this outburst can be explained by the thermal instability of the accretion disc, analogous to the outbursts of soft X-ray transients. Applying the model by King & Ritter and Shahbaz, Charles & King on the X-ray light curve, we obtain a realistic mass of the disc at the peak of outburst to be Mh(0) , 1.5 1023 g (the distance d= 5 kpc) or 3.8 1022 g (d= 2.5 kpc). The disc radius at this moment is then Rh(0) , 2.5 1010 cm (d= 5 kpc) or 1.6 1010 cm (d= 2.5 kpc), provided that the factor f (the ratio of the mass of the hot disc at that moment with respect to its maximum possible mass) is close to unity. Even if we take a quite low f= 0.05, we still obtain Rh(0) by only 2.7 times larger. The reddening in the outburst maximum and brighter peak absolute magnitude of CI Cam with respect to those of soft X-ray transients in outbursts can be explained if the disc in CI Cam heats up an extended envelope and/or a strong jet is formed. We thus bring firm arguments for Robinson, Ivans & Welsh's hypothesis. On the other hand, we bring the arguments against the mass transfer burst from the donor and the periastron passage of the compact object. [source]

3D models of radiatively driven colliding winds in massive O + O star binaries , III.

Thermal X-ray emission
ABSTRACT The X-ray emission from the wind,wind collision in short-period massive O + O star binaries is investigated. The emission is calculated from 3D hydrodynamical models which incorporate gravity, the driving of the winds, orbital motion of the stars and radiative cooling of the shocked plasma. Changes in the amount of stellar occultation and circumstellar attenuation introduce phase-dependent X-ray variability in systems with circular orbits, while strong variations in the intrinsic emission also occur in systems with eccentric orbits. The X-ray emission in eccentric systems can display strong hysteresis, with the emission softer after periastron than at corresponding orbital phases prior to periastron, reflecting the physical state of the shocked plasma at these times. Our simulated X-ray light curves bear many similarities to observed light curves. In systems with circular orbits the light curves show two minima per orbit, which are identical (although not symmetric) if the winds are identical. The maxima in the light curves are produced near quadrature, with a phase delay introduced due to the aberration and curvature of the wind collision region. Circular systems with unequal winds produce minima of different depths and duration. In systems with eccentric orbits the maxima in the light curves may show a very sharp peak (depending on the orientation of the observer), followed by a precipitous drop due to absorption and/or cooling. We show that the rise to maximum does not necessarily follow a 1/dsep law. Our models further demonstrate that the effective circumstellar column can be highly energy dependent. Therefore, spectral fits which assume energy-independent column(s) are overly simplified and may compromise the interpretation of observed data. To better understand observational analyses of such systems we apply Chandra and Suzaku response files, plus Poisson noise, to the spectra calculated from our simulations and fit these using standard xspec models. We find that the recovered temperatures from two- or three-temperature mekal fits are comparable to those from fits to the emission from real systems with similar stellar and orbital parameters/nature. We also find that when the global abundance is thawed in the spectral fits, subsolar values are exclusively returned, despite the calculations using solar values as input. This highlights the problem of fitting oversimplified models to data, and of course is of wider significance than just the work presented here. Further insight into the nature of the stellar winds and the wind,wind collision region in particular systems will require dedicated hydrodynamical modelling, the results of which will follow in due course. [source]

X-ray spectroscopy of the intermediate polar PQ Gem

Cynthia H. James
Abstract Using RXTE and ASCA data, we investigate the roles played by occultation and absorption in the X-ray spin pulse profile of the intermediate polar PQ Gem. From the X-ray light curves and phase-resolved spectroscopy, we find that the intensity variations are the result of a combination of varying degrees of absorption and the accretion regions rotating behind the visible face of the white dwarf. These occultation and absorption effects are consistent with those expected from the accretion structures calculated from optical polarization data. We can reproduce the changes in absorber covering fraction either from geometrical effects, or by considering that the material in the leading edge of the accretion curtain is more finely fragmented than in other parts of the curtain. We determine a white dwarf mass of , 1.2 using the RXTE data. [source]

No visible optical variability from a relativistic blast wave encountering a wind termination shock

H. J. Van Eerten
ABSTRACT Gamma-ray burst afterglow flares and rebrightenings of the optical and X-ray light curves have been attributed to both late-time inner engine activity and density changes in the medium surrounding the burster. To test the latter, we study the encounter between the relativistic blast wave from a gamma-ray burster and a stellar wind termination shock. The blast wave is simulated using a high-performance adaptive mesh relativistic hydrodynamic code, amrvac, and the synchrotron emission is analysed in detail with a separate radiation code. We find no bump in the resulting light curve, not even for very high density jumps. Furthermore, by analysing the contributions from the different shock wave regions we are able to establish that it is essential to resolve the blast wave structure in order to make qualitatively correct predictions on the observed output and that the contribution from the reverse shock region will not stand out, even when the magnetic field is increased in this region by repeated shocks. This study resolves a controversy in the recent literature. [source]

Recent discoveries of supersoft X-ray sources in M 31,

M. Henze
Abstract Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X-ray observations of M 31 with XMM-Newton and Chandra. We carried out a dedicated optical and X-ray monitoring program of CNe and SSSs in the central area ofM 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X-ray monitoring data we discovered the CN M3 1N 2007-11a, which shows a very short SSS phase of 29,52 days. Short SSS states (durations , 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007-11a, the optical and X-ray light curves suggest a binary containing a WD with MWD > 1.0 M,. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006-04a. The X-ray light curve of M31N 2006-04a shows short-time variability, which might indicate an orbital period of about 2 hours ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]