21,115 research outputs found
NuSTAR and Swift observations of Swift J1357.2-0933 during an early phase of its 2017 outburst
We present a detailed spectral analysis of Swift and NuSTAR observations of
the very faint X-ray transient and black hole system Swift J1357.2-0933 during
an early low hard state of its 2017 outburst. Swift J1357.2-0933 was observed
at 0.02% of the Eddington luminosity (for a distance of 2.3 kpc and a
mass of 4 M). Despite the low luminosity, the broadband X-ray
spectrum between 0.3 and 78 keV requires the presence of a disk blackbody
component with an inner disk temperature of T 0.06 keV
in addition to a thermal Comptonization component with a photon index of
{\Gamma} 1.70. Using a more physical model, which takes strong
relativistic effects into account, and assuming a high inclination of
70, which is motivated by the presence of dips in optical light curves,
we find that the accretion disk is truncated within a few RISCO from the black
hole, independent of the spin.Comment: 11 pages, 5 figures, accepted for publication in Ap
Peculiar outbursts of an ultra luminous source likely signs of an aperiodic disc-wind
The metal rich globular cluster RZ 2109 in the massive Virgo elliptical
galaxy NGC 4472 (M49) harbours the ultra luminous X-ray source XMMU
122939.7+075333. Previous studies showed that this source varies between bright
and faint phases on timescales of just a few hours. Here, we report the
discovery of two peculiar X-ray bursting events that last for about 8 and 3.5
hours separated by about 3 days. Such a recurring X-ray burst-like behaviour
has never been observed before. We argue that type-I X-ray bursts or super
bursts as well as outburst scenarios requiring a young stellar object are
highly unlikely explanations for the observed light curve, leaving an aperiodic
disc wind scenario driven by hyper-Eddington accretion as a viable explanation
for this new type of X-ray flaring activities.Comment: 7 pages, 2 figures, accepted by Ap
The Discovery of Quasisoft and Supersoft Sources in External Galaxies
We apply a uniform procedure to select very soft sources from point sources
observed by Chandra in 4 galaxies. This sample includes one elliptical galaxy
(NGC 4967), 2 face-on spirals (M101 and M83), and an interacting galaxy (M51).
We have found very soft X-ray sources (VSSs) in every galaxy. Some of these fit
the criteria for canonical supersoft sources (SSSs), while others are somewhat
harder. These latter have characteristic values of kT < 300 eV; we refer to
them as quasisoft sources (QSSs). We found a combined total of 149 VSSs in the
4 galaxies we considered; 77 were SSSs and 72 were QSSs. (See the paper for the
original long abstract)Comment: 20 pages, 6 figures. Accepted for publication in Ap
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