222 research outputs found
An X-Ray Dip in the X-Ray Transient 4U 1630-47
An x-ray dip was observed during a 1996 Rossi X-Ray Timing Explorer
observation of the recurrent x-ray transient 4U 1630-47. During the dip, the
2-60 keV x-ray flux drops by a factor of about three, and, at the lowest point
of the dip, the x-ray spectrum is considerably softer than at non-dip times. We
find that the 4U 1630-47 dip is best explained by absorption of the inner part
of an accretion disk, while the outer part of the disk is unaffected. The
spectral evolution during the dip is adequately described by the variation of a
single parameter, the column density obscuring the inner disk.Comment: 13 pages, 4 figures, Accepted for publication in Ap
SRG/ART-XC and NuSTAR observations of the X-ray pulsar GRO J1008-57 in the lowest luminosity state
We report results of the first broadband observation of the transient X-ray
pulsar GRO J1008-57 performed in the quiescent state. Observations were
conducted quasi-simultaneously with the Mikhail Pavlinsky ART-XC telescope on
board SRG and NuSTAR right before the beginning of a Type I outburst. GRO
J1008-57 was detected in the state with the lowest observed luminosity around
several erg s and consequently accreting from the cold
disk. Timing analysis allowed to significantly detect pulsations during this
state for the first time. The observed pulsed fraction of about 20\% is,
however, almost three times lower than in brighter states when the accretion
proceeds through the standard disk. We traced the evolution of the broadband
spectrum of the source on a scale of three orders of magnitude in luminosity
and found that at the lowest luminosities the spectrum transforms into the
double-hump structure similarly to other X-ray pulsars accreting at low
luminosities (X Persei, GX 304-1, A0535+262) reinforcing conclusion that this
spectral shape is typical for these objects.Comment: 8 pages, 5 figures, accepted to Ap
A Black Hole in the X-Ray Nova Velorum 1993
We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the
Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The
orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is
475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17
+/- 0.12 M_sun, is close to the conventional absolute limiting mass for a
neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than
80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4
M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6).
The primary star is therefore almost certainly a black hole rather than a
neutron star. The velocity curve of the primary from H-alpha emission has a
semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237
degrees (rather than 180 degrees) from that of the secondary star. The nominal
mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 =
0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun
is significantly below the typical value of ~ 7 M_sun found for black holes in
other low-mass X-ray binaries.
Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable
optical counterpart at R = 23.6 +/- 0.4 mag.Comment: 16 pages, 9 figures, added references, revised per. referee's
comments Accepted for publication in August 1999 issue of PAS
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
The Marshall Space Flight Center Development of Mirror Modules for the ART-XC Instrument aboard the Spectrum-Roentgen-Gamma Mission
The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Currently, four of the modules are being fabricated by the Marshall Space Flight Center (MSFC.) Each MSFC module consist of 28 nested Ni/Co thin shells giving an effective area of 65 sq cm at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of these modules to the IKI is scheduled for summer 2013. We present a status of the ART x-ray modules development at the MSFC
- âŚ