Search Publications
AB Dor: Coronal Imaging and Activity Cycles
Pandey, J. C.; Singh, Gurpreet
Using long-term X-ray observations, we present short-term and long-term X-ray variability analysis of the ultrafast rotating active star AB Dor. Flaring events are common in X-ray observations of AB Dor and occupy a substantial portion of the total observation time, averaging at around 57% ± 23%. The flare-free X-ray light curves show rotational m…
Self-organized Criticality in Stellar Flares
Güdel, Manuel; Aschwanden, Markus J.
Power-law size distributions are the hallmarks of nonlinear energy dissipation processes governed by self-organized criticality (SOC). Here we analyze 75 data sets of stellar flare size distributions, mostly obtained from the Extreme-Ultraviolet Explorer and the Kepler mission. We aim to answer the following questions for size distributions of ste…
A 33 Yr Constancy of the X-Ray Coronae of AR Lac and Eclipse Diagnosis of Scale Height
Drake, Jeremy J.; Huenemoerder, David P.; Ratzlaff, Peter +3 more
Extensive X-ray and EUV photometric observations of the eclipsing RS CVn system AR Lac were obtained over the years 1997-2013 with the Chandra X-Ray Observatory Extreme-Ultraviolet Explorer (EUVE). During primary eclipse, High Resolution Camera count rates decrease by ~40%. A similar minimum is seen during one primary eclipse observed by EUVE but …
Observations of the High-mass X-Ray Binary A 0535+26 in Quiescence
Fürst, Felix; Pottschmidt, Katja; Wilms, Jörn +7 more
We have analyzed three observations of the high-mass X-ray binary A 0535+26 performed by the Rossi X-Ray Timing Explorer (RXTE) three, five, and six months after the last outburst in 2011 February. We detect pulsations only in the second observation. The 3-20 keV spectra can be fit equally well with either an absorbed power law or absorbed thermal…
A Comparison of Broad Iron Emission Lines in Archival Data of Neutron Star Low-mass X-Ray Binaries
Reis, Rubens C.; Fabian, Andrew C.; Miller, Jon M. +2 more
Relativistic X-ray disklines have been found in multiple neutron star low-mass X-ray binaries, in close analogy with black holes across the mass scale. These lines have tremendous diagnostic power and have been used to constrain stellar radii and magnetic fields, often finding values that are consistent with independent timing techniques. Here, we…
A Study of the Long-Term Evolution of Quasi-Periodic Oscillations in the Accretion-Powered X-Ray Pulsar 4U 1626-67
Paul, Biswajit; Kumar, Brijesh; Kaur, Ramanpreet +1 more
We report here a study of the long-term properties of quasiperiodic oscillations (QPOs) in an unusual accreting X-ray pulsar, 4U 1626-67. This is a unique accretion-powered X-ray pulsar in which we have found the QPOs to be present during all sufficiently long X-ray observations with a wide range of X-ray observatories. In the present spin-down er…
Power Spectra of Black Holes and Neutron Stars as a Probe of Hydrodynamic Structure of the Source: Diffusion Theory and Its Application to Cygnus X-1 and Cygnus X-2 X-Ray Observations
Titarchuk, Lev; Shaposhnikov, Nikolai; Arefiev, Vadim
We present a model of Fourier power density spectrum (PDS) formation in accretion-powered X-ray binary systems derived from diffusion theory. Timing properties of X-ray emission are considered a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power Px of the resulting PDS is…
Recovery of the Orbital Parameters and Pulse Evolution of V0332+53 during a Huge Outburst
Torres, Diego F.; Zhang, Shu; Qu, Jin-Lu +1 more
The high-mass X-ray binary V0332+53 became active at the end of 2004, and the outburst was observed in hard X-rays by RXTE and INTEGRAL. Based on these hard X-ray observations, we measure the orbital parameters by fitting the Doppler-shifted spin periods. The derived orbital period and eccentricity are consistent with those obtained by Stella et a…
The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214
Kaaret, Philip; Gelino, Dawn M.; Tomsick, John A.
We report on X-ray and optical observations of the X-ray burster EXO 1747-214. This source is an X-ray transient, and its only known outburst was observed in 1984-1985 by the EXOSAT satellite. We reanalyzed the EXOSAT data to derive the source position, column density, and a distance upper limit using its peak X-ray burst flux. We observed the EXO…
4U 2206+54: An Unusual High-Mass X-Ray Binary with a 9.6 Day Orbital Period But No Strong Pulsations
Corbet, Robin H. D.; Peele, Andrew G.
Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor observations of the X-ray source 4U 2206+54, previously proposed to be a Be star system, show the X-ray flux to be modulated with a period of approximately 9.6 days. If the modulation is due to orbital variability, then this would be one of the shortest orbital periods known for a Be star X-ray so…