15,837 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
X-ray Localization of the Globular Cluster G1 with XMM-Newton
We present an accurate X-ray position of the massive globular cluster G1 by
using XMM-Newton and the Hubble Space Telescope (HST). The X-ray emission of G1
has been detected recently with XMM-Newton. There are two possibilities for the
origin of the X-ray emission. It can be either due to accretion of the central
intermediate-mass black hole, or by ordinary low-mass X-ray binaries. The
precise location of the X-ray emission might distinguish between these two
scenarios. By refining the astrometry of the XMM-Newton and HST data, we
reduced the XMM-Newton error circle to 1.5". Despite the smaller error circle,
the precision is not sufficient to distinguish an intermediate-mass black hole
and luminous low-mass X-ray binaries. This result, however, suggests that
future Chandra observations may reveal the origin of the X-ray emission.Comment: 4 pages, 2 figures; accepted for publication in Ap
A NuSTAR Observation of the Gamma-ray Emitting Millisecond Pulsar PSR J1723-2837
We report on the first NuSTAR observation of the gamma-ray emitting
millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is
clearly detected and the simultaneous NuSTAR and Swift spectrum is well
described by an absorbed power-law with a photon index of ~1.3. We also find
X-ray modulations in the 3-10 keV, 10-20 keV, 20-79 keV, and 3-79 keV bands at
the 14.8-hr binary orbital period. All these are entirely consistent with
previous X-ray observations below 10 keV. This new hard X-ray observation of
PSR J1723-2837 provides strong evidence that the X-rays are from the
intrabinary shock via an interaction between the pulsar wind and the outflow
from the companion star. We discuss how the NuSTAR observation constrains the
physical parameters of the intrabinary shock model.Comment: Accepted for publication in ApJ. 5 pages, 3 figure
A journey from the hard to the soft state: How do QPOs evolve in the 2021 outburst of GX 339-4?
We investigated the snapshots of five NICER observations of the black hole
transient GX 339-4 when the source transited from the hard state into the soft
state during its outburst in 2021. In this paper, we focused our study on the
evolution of quasi-periodic oscillations (QPOs) and noise components using
power-density spectra. In addition, we derived hardness ratios comparing count
rates above and below 2 keV. The evolution from the hard to the soft state was
a somewhat erratic process showing several transitions between states that are
dominated by top-flat noise and can show type-C QPOs; those that are dominated
by red noise and can show type-B QPOs. From the parameters that we studied, we
only found a strong correlation between the hardness ratio and the type of QPO
observed. This implies that the appearance of type-B QPOs is related to a
change in the accretion geometry of the system that also reflects in altered
spectral properties. We also observed that the type-B QPO forms from or
disintegrates into a broad peaked feature when the source comes out of or goes
to the hard-intermediate state, respectively. This implies some strong
decoherence in the process that creates this feature.Comment: 6 pages, 5 figures, supplementary online material as appendices (13
pages), accepted for publication in MNRA
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