Related papers: Witnessing the magnetospheric boundary at work in …
$Context$: Vela X-1 is the prototype of the classical sgHMXB systems. Recent continuous and long monitoring campaigns revealed a large hard X-rays variability amplitude with strong flares and off-states. This activity has been interpreted…
We present results from a 20 h RXTE observation of Vela X-1, ncluding a peculiar low state of a few hours duration, during which the pulsation of the X-ray emission ceased, while significant non-pulsed emission remained. This ``quiescent…
We present an in-depth analysis of the spectral and temporal behavior of a long almost uninterrupted INTEGRAL observation of Vela X-1 in Nov/Dec 2003. In addition to an already high activity level, Vela X-1 exhibited several very intense…
We elaborate on a recently proposed model for subsonic quasi-spherical accretion onto slowly rotating pulsars, in which accretion is mediated through a hot quasi-static shell above the neutron star magnetosphere. We show that under the same…
We investigate the spectral and temporal behavior of the high mass X-ray binary Vela X-1 during a phase of high activity, with special focus on the observed giant flares and off states. INTEGRAL observed Vela X-1 in a long almost…
Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high mass X-ray binaries hosting a supergiant donor. We have analyzed in a systematic way ten years of INTEGRAL data of Vela X-1 (22-50 keV) and we found that when…
In classical supergiant X-ray binaries (SgXBs), the Bondi-Hoyle-Lyttleton wind accretion was usually assumed, and the angular momentum transport to the accretors is inefficient. The observed spin-up/spin-down behavior of the neutron star in…
We present a detailed analysis of all archival INTEGRAL data of the accreting X-ray pulsar Vela X-1. We extracted lightcurves in several energy bands from 20 keV up to 60 keV. The lightcurves show that the source was found in very active as…
We have analyzed the time variability of the wide-band X-ray spectrum of Vela X-1, the brightest wind-fed accreting neutron star, on a short timescale of 2 ks by using {\it Suzaku} observations with an exposure of 100 ks. During the…
Results of GRANAT/ART-P observations of three X-ray pulsars in non-pulsing states are presented: 1) a statistically significant non-pulsing flux with a simple power-law spectrum was detected during the ``off''- state of Her X-1; 2) a…
We present a detailed pulse phase resolved spectral analysis of the persistent high mass X-ray binary pulsar Vela X-1 observed with Suzaku during June 2008. The pulse profiles exhibit both intensity and energy dependence with multiple peaks…
Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability and convenient physical parameters (close distance, high inclination, small orbital separation) which facilitate the observation and…
Vela X-1 is among the best studied and most luminous accreting X-ray pulsars. The supergiant optical companion produces a strong radiatively-driven stellar wind, which is accreted onto the neutron star producing highly variable X-ray…
RXTE ASM count rates from the X-ray pulsar Her X-1 began falling consistently during the late months of 2003. The source is undergoing another state transition similar to the anomalous low state of 1999. This new event has triggered…
We present the observations of the pulsar SMC X-1 with the ART-P telescope onboard the Granat observatory. We investigate the variability of the flux from the source on time scales of several tens of days. The intensity variation of the…
We report on the March-April 1997 BeppoSAX observations of Aql X-1, the first to monitor the evolution of the spectral and time variability properties of a neutron star soft X-ray transient from the outburst decay to quiescence. We observed…
We present RXTE monitoring of the eclipsing X-ray binary Hercules X-1 conducted over the short-high state of July 1998. This was one of the last major short-high states before the source entered an anomalous low-state of activity. A…
Results of a 1999 July 8-10 BeppoSAX observation during an anomalous low-state of Her X-1 are presented. The standard on-state power-law and blackbody continuum model is excluded at high confidence unless partial covering is included. This…
We report on the deepest X-ray observation of the narrow-line Seyfert 1 galaxy Mrk 335 in the low-flux state obtained with Suzaku. The data are compared to a 2006 high-flux Suzaku observation when the source was ~10-times brighter.…
We present results from four observations of the accreting X-ray pulsar Vela X-1 with RXTE in 1996 February. The light curves show strong pulse to pulse variations, while the average pulse profiles are quite stable, similar to previous…