57 research outputs found
IGR J17445-2747 - yet another X-ray burster in the Galactic bulge
The discovery of a type I X-ray burst from the faint unidentified transient
source IGR J17445-2747 in the Galactic bulge by the JEM-X telescope onboard the
INTEGRAL observatory is reported. Type I bursts are believed to be associated
with thermonuclear explosions of accreted matter on the surface of a neutron
star with a weak magnetic field in a low-mass X-ray binary. Thus, this
observation allows the nature of this source to be established.Comment: 8 pages, 5 figure
Discovery of a pulse-phase-transient cyclotron line in the X-ray pulsar GROJ2058+42
We report the discovery of absorption features in the X-ray spectrum of the
transient X-ray pulsar GROJ2058+42. The features are detected around ,
and keV in both NuSTAR observations carried out during the
source type II outburst in spring 2019. The most intriguing property is that
the deficit of photons around these energies is registered only in the narrow
phase interval covering around 10% of the pulsar spin period. We interpret
these absorption lines as a cyclotron resonant scattering line (fundamental)
and two higher harmonics. The measured energy allow us to estimate the magnetic
field strength of the neutron star as G.Comment: 7 pages, 5 figures, accepted to ApJ
Hard X-rays and QPO in Swift J1727.8-1613: the rise and plateau of the 2023 outburst
We report on the detection of type-C quasi-periodic oscillations during the
initial stages of the outburst of Swift J1727.8-1613 in 2023. Using data of the
INTEGRAL observatory along with the data of the SRG/ART-XC and Swift/XRT
telescopes the fast growth of the QPO frequency was traced. We present a hard
X-ray lightcurve that covers the initial stages of the 2023 outburst - the fast
rise and plateau - and demonstrate that the QPO frequency was stable during the
plateau. The switching from type-C to type-B QPO was detected with the
beginning of the source flaring activity. We have constructed a broad-band
spectrum of Swift J1727.8-1613 and found an additional hard power-law spectral
component extending at least up to 400 keV. Finally, we have obtained an upper
limit on the hard X-ray flux at the beginning of the optical outburst and
estimated the delay of the X-ray outburst with respect to the optical one.Comment: Submitted to MNRAS Letter
X-ray emission from Westerlund 2 detected by SRG/ART-XC and Chandra: search for radiation of TeV leptons
We present the results of current observations of the young compact cluster
of massive stars Westerlund 2 with the Mikhail Pavlinsky ART-XC telescope
aboard the Spectrum-Roentgen-Gamma (SRG) observatory which we analysed together
with the archival Chandra data. In general, Westerlund 2 was detected over the
whole electromagnetic spectrum including high-energy gamma rays, which revealed
a cosmic ray acceleration in this object to the energies up to tens of TeV. The
detection of Westerlund 2 with ART-XC allowed us to perform a joint spectral
analysis together with the high resolution Chandra observations of the diffuse
emission from a few selected regions in the vicinity of the Westerlund 2 core
in the 0.4 - 20 keV range. To fit the Westerlund 2 X-ray spectrum above a few
keV one needs either a non-thermal power-law emission component, or a hot
plasma with temperatures 5 keV. Our magnetohydrodynamic modeling of the
plasma flows in Westerlund 2 shows substantially lower electron temperatures in
the system and thus the presence of the non-thermal component is certainly
preferable. A kinetic model of the particle acceleration demonstrated that the
non-thermal component may originate from the synchrotron radiation of multi-TeV
electrons and positrons produced in Westerlund 2 in accordance with the TeV
photons detection from the source. However, the inverse Compton radiation of
mildly relativistic electrons could explain the non-thermal emission as well.Comment: 10 pages, 6 figures, submitted to MNRA
Discovery of a Pulse-phase-transient Cyclotron Line in the X-Ray pulsar GRO J2058+42
We report the discovery of absorption features in the X-ray spectrum of the transient X-ray pulsar GRO J2058+42. The features are detected around similar to ~10, similar to ~20, and similar to ~30 keV in both NuSTAR observations carried out during the source type II outburst in spring 2019. The most intriguing property is that the deficit of photons around these energies is registered only in the narrow phase interval covering around 10% of the pulsar spin period. We interpret these absorption lines as a cyclotron resonant scattering line (fundamental) and two higher harmonics. The measured energy allow us to estimate the magnetic field strength of the neutron star as similar to ~10(12) G
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