98 research outputs found
Studying temporal variability of GRS1739-278 during the 2014 outburst
We report a discovery of low-frequency quasi periodic oscillation at 0.3-0.7
Hz in the power spectra of the accreting black hole GRS1739-278 in the
hard-intermediate state during its 2014 outburst based on the
and Swift/XRT data. The QPO frequency strongly evolved with the source flux
during the NuSTAR observation. The source spectrum became softer with rising
QPO frequency and simultaneous increasing of the power-law index and decreasing
of the cut-off energy. In the power spectrum, a prominent harmonic is clearly
seen together with the main QPO peak. The fluxes in the soft and the hard X-ray
bands are coherent, however, the coherence drops for the energy bands separated
by larger gaps. The phase-lags are generally positive (hard) in the 0.1-3 Hz
frequency range, and negative below 0.1 Hz. The accretion disc inner radius
estimated with the relativistic reflection spectral model appears to be . In the framework of the relativistic precession model, in
order to satisfy the constraints from the observed QPO frequency and the
accretion disc truncation radius, a massive black hole with M is required.Comment: 15 pages, 12 figures; accepted for publication in MNRA
Study of the X-ray Pulsar IGR J21343+4738 based on NuSTAR, Swift, and SRG data
We present the results of our study of the X-ray pulsar IGR J21343+4738 based
on NuSTAR, Swift, and SRG observations in the wide energy range 0.3 - 79 keV.
The absence of absorption features in the energy spectra of the source, both
averaged and phase-resolved ones, has allowed us to estimate the upper and
lower limits on the magnetic field of the neutron star in the binary system,
G, respectively. The spectral
and timing analyses have shown that IGR J21343+4738 has all properties of a
quasi-persistent X-ray pulsar with a pulsation period of s and
a luminosity erg s. The analysis of the
long-term variability of the object in X-rays has confirmed the possible
orbital period of the binary system days previously detected in the
optical range.Comment: 8 pages, 4 figures, 1 tabl
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
- …