Search results for "x-rays"
showing 10 items of 445 documents
Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
2016
In this paper, we report on the analysis of the peculiar X-ray variability displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80 ks-long joint NuSTAR and XMM-Newton observation performed during the source outburst in 2015. The light curve of the source was characterized by a flaring-like behavior, with typical rise and decay time scales of ~120 s. The flares are accompanied by a remarkable spectral variability, with the X-ray emission being generally softer at the peak of the flares. A strong quasi periodic oscillation (QPO) is detected at ~8 mHz in the power spectrum of the source and clearly associated with the flaring-like behavior. This feature has the strongest po…
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
2008
We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=…
Black-Hole Accretion Discs and Jets at Super-Eddington Luminosity
2004
Super-Eddington accretion discs with 3 and 15 dot M_E around black holes with mass 10 M_sun are examined by two-dimensional radiation hydrodynamical calculations extending from the inner disc edge to 5*10^4 r_g and lasting up to \sim 10^6 r_g/c. The dominant radiation-pressure force in the inner region of the disc accelerates the gas vertically to the disc plane, and jets with 0.2 -- 0.4$c$ are formed along the rotational axis. In the case of the lower accretion rate, the initially anisotropic high-velocity jet expands outward and becomes gradually isotropic flow in the distant region. The mass-outflow rate from the outer boundary is as large as \sim 10^{19} -- 10^{23} g s^{-1}, but it is v…
On the nature of the soft γ-ray emission in the hard state of the black hole transient GRS 1716-249
2020
The black hole transient GRS 1716-249 was monitored from the radio to the gamma-ray band during its 2016-2017 outburst. This paper focuses on the Spectral Energy Distribution (SED) obtained in 2017 February-March, when GRS 1716-249 was in a bright hard spectral state. The soft gamma-ray data collected with the INTEGRAL/SPI telescope show the presence of a spectral component which is in excess of the thermal Comptonisation emission. This component is usually interpreted as inverse Compton emission from a tiny fraction of non-thermal electrons in the X-ray corona. We find that hybrid thermal/non-thermal Comptonisation models provide a good fit to the X/gamma-ray spectrum of GRS 1716-249. The …
New insights on the puzzling LMXB 1RXS J180408.9-342058: the intermediate state, the clocked type-I X-ray bursts and much more
2019
1RXS J180408.9--342058 is a low mass X-ray binary hosting a neutron star, which shows X-ray activity at very different mass-accretion regimes, from very faint to almost the Eddington luminosity. In this work, we present a comprehensive X-ray study of this source using data from the Neil Gehrels Swift Observatory, NuSTAR and INTEGRAL/JEM-X. In order to follow the spectral evolution, we analysed the 2015 outburst using Swift data and three Nustar observations. Besides the canonical hard and soft spectral states, we identified the rarely observed intermediate state. This was witnessed by the appeareance of the accretion disk emission in the spectrum (at $kT_{\rm disk}$ $\sim$0.7 keV) and the s…
Beating Darwin-Bragg losses in lab-based ultrafast x-ray experiments
2017
The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this work. (C) 2017 Author(s). Funding Agencies|Knut and Alice Wallenberg Foundation; ERC [226136]; Finnish Funding Agency for Technology and Innovation TEKES; Academy of Finland [260880]; NIST Innovations in Measurement Science program; DOE Office of Basic Energy Sciences
Activity from the Be/X-ray binary system V0332+53 during its intermediate-luminosity outburst in 2008
2015
Aims: We present a study of the Be/X-ray binary system V 0332+53 with the main goal of characterizing its behavior mainly during the intermediate-luminosity X-ray event on 2008. In addition, we aim to contribute to the understanding of the global behavior of the donor companion by including optical data from our dedicated campaign starting on 2006. Methods: V 0332+53 was observed by RXTE and Swift during the decay of the intermediate-luminosity X-ray outburst of 2008, as well as with Suzaku before the rising of the third normal outburst of the 2010 series. In addition, we present recent data from the Spanish ground-based astronomical observatories of El Teide (Tenerife), Roque de los Muchac…
In-flight calibration of the ROSAT HRI ultraviolet sensitivity
2000
Comparing measured and estimated count rates of a few selected sample stars, we confirm the validity and provide the in-flight calibration of the ROSAT HRI UV/visible effective area model in Zombeck et al. The count rate estimates for Betelgeuse derived with this model are in agreement with the measured HRI upper limit. This result is also confirmed in an erratum by Berghöfer et al. aimed at revising their previous calculation, which was overestimated by more than 2 orders of magnitude. Adopting this ROSAT HRI UV/visible effective area model and measured UV/visible spectra of a set of sample stars covering the range of Teff 3000-40,000 K, we have built the calibration curves to estimate UV/…
INTEGRAL/RXTE Observations of Cygnus X-1
2003
We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with earlier results, the 3-250 keV data are well described by Comptonization spectra from a Compton corona with a temperature of kT~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Omega/2pi~0.2-0.3. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated de…
Long-term optical and X-ray variability of the Be/X-ray binary H 1145-619: Discovery of an ongoing retrograde density wave
2017
Multiwavelength monitoring of Be/X-ray binaries is crucial to understand the mechanisms producing their outbursts. H 1145-619 is one of these systems, which has recently displayed X-ray activity. We investigate the correlation between the optical emission and the X-ray activity to predict the occurrence of new X-ray outbursts from the inferred state of the circumstellar disc. We have performed a multiwavelength study of H 1145-619 from 1973 to 2017 and present here a global analysis of its variability over the last 40 years. We have used optical spectra from the SAAO, SMARTS and SALT telescopes and optical photometry from INTEGRAL/OMC and ASAS. We also used X-ray observations from INTEGRAL/…