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1.
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. 相似文献
2.
To find X-ray bursts from sources within the field of view of the IBIS/INTEGRAL telescope, we have analyzed all the archival
data of the telescope available at the time of writing the paper (the observations from January 2003 to April 2009). We have
detected 834 hard (15–25 keV) X-ray bursts, 239 of which were simultaneously recorded by the JEM-X/INTEGRAL telescope in the
standard X-ray energy range. More than 70% of all bursts (587 events) have been recorded from the well-known X-ray burster
GX 354-0. We have found upper limits on the distances to their sources by assuming that the Eddington luminosity limit was
reached at the brightness maximum of the brightest bursts. 相似文献
3.
During the observation of the Galactic-center field by the INTEGRAL observatory on September 9, 2003, the IBIS/ISGRI gamma-ray telescope detected a short (several-hours-long) intense (～380 mCrab at the peak) outburst of hard radiation from the X-ray transient SAX J1818.6-1703. Previously, this source was observed only once in 1998 during a similar short outburst. We present the results of our localization, spectral and timing analyses of the object and briefly discuss the possible causes of the outburst. The release time of the bulk of the energy in such an outburst is appreciably shorter than the accretion (viscous) time that characterizes the flow of matter through a standard accretion disk. 相似文献
4.
We present observations of the X-ray burster A1742-294 near the Galactic center with the ART-P telescope onboard the Granat observatory. The shape of its persistent spectra was described well by the model of bremsstrahlung from optically thin plasma, and it remained essentially unchanged over ～2.5 years of observations. We show that the mean interval between X-ray bursts from the source is several times shorter than assumed previously and that the burst profile itself depends on the flux during the burst. We analyze in detail the strong X-ray burst detected from this source on October 18, 1990, and construct the evolution curves of its luminosity and radiation temperature. 相似文献
5.
In 2003?C2012, the INTEGRAL observatory has performed long-term observations of the Large Magellanic Cloud (LMC). At present, this is one of the deepest hard X-ray (20?C60 keV) surveys of extragalactic fields in which more than 20 sources of different natures have been detected. We present the results of a statistical analysis of the population of high-mass X-ray binaries in the LMC and active galactic nuclei (AGNs) observed in its direction. The hard X-ray luminosity function of high-mass X-ray binaries is shown to be described by a power law with a slope ?? 1.8, that in agreement with the luminosity function measurements both in the LMC itself, but made in the soft X-ray energy band, and in other galaxies. At the same time, the number of detected AGNs toward the LMC turns out to be considerably smaller than the number of AGNs registered in other directions, in particular, toward the source 3C 273. The latter points to the nonuniformity of the distribution of matter in the local Universe. 相似文献
6.
The possibility of investigating the sky region near the Galactic center with instruments of the INTEGRAL orbital astrophysical gamma-ray observatory by the method of its occultation by the Earth and the Moon is considered. Existing engineering constraints on the observing conditions, such as the admissible orientation of the INTEGRAL satellite relative to the direction to the Sun and the performance of measurements only outside the Earth??s radiation belts, are taken into account. Long time intervals during which the lunar occultation center passes at angular distances of less than 2° from the Galactic center have been found. Such events occur under the adopted constraints two or three times per year without any correction of the INTEGRAL satellite orbit. The orbit can be corrected to reduce the angular distance between the Moon and the Galactic center in occultation events. The required velocity impulses do not exceed several meters per second. The possibility of the Galactic center being occulted by the Earth has been analyzed. In this case, to perform measurements, the admissible (in radiation exposure) height of the working segment of the orbit should be reduced to 25 000 km, which can be problematic. At the same time, part of the Galaxy??s equatorial region is shadowed by the Earth for a time long enough to carry out the corresponding experiments. 相似文献
7.
P. Yu. Minaev S. A. Grebenev A. S. Pozanenko S. V. Molkov D. D. Frederiks S. V. Golenetskii 《Astronomy Letters》2012,38(10):613-628
The detection of GRB 070912 recorded in the field of view of the SPI, IBIS/ISGRI, and JEMX telescope on September 12, 2007, at 07h32m19s (UT) when analyzing the INTEGRAL archival data is reported. The burst is one of the well-localized events closest to the direction toward the Galactic center (less than from the source Sgr A*) over the entire history of burst observations. Since it was not promptly revealed by the INTEGRAL Burst Alert System (IBAS), no information about its coordinates was disseminated and no search for optical and soft X-ray afterglows was conducted. The 3–200 keV fluence was 2.8 × 10?6 erg cm?2 and the peak flux was 1.8 × 10?7 erg cm?2 s?1 (1.9 ph cm?2 s?1). The burst was also observed in the KONUS/WIND experiment in the background mode, although it was not included in the list of recorded bursts. GRB 070912 is among a limited number of events for which a broadband (3 keV-2 MeV) spectrum of X-ray and gamma-ray emission has been obtained and their evolution from the first instants to complete decay has been traced. It shows how the fast evolution of its spectrum gives rise to absorption features at energies of ～100 keV.Within the first seconds after the onset of the burst, its spectrum was a power law with a photon index of ～0.8, but it exhibited a noticeable deficit of photons at energies below 20 keV. Such an initial deficit (a delay in appearance) of X-ray photons can be explained by their “high-latitude” origin relative to the line of sight. The spectrum rapidly softened and at the decay phase was well described by a blackbody (or Wien) law. This allows the distance (redshift) to the burst source to be estimated. 相似文献
8.
S. A. Grebenev 《Astronomy Letters》2013,39(10):661-664
The discovery of a new X-ray source, IGR J18175-2419, that flared up for a short (～1 h) time on September 26, 2012, by the INTEGRAL observatory is reported. The results of the source’s localization and the spectral/timing analysis of its X-ray emission are presented. The source may turn out to be yet another representative of the population of fast X-ray transients, which is the focus of attention due to the identification of their optical counterparts with early-type supergiants. 相似文献
9.
Observations of the X-ray pulsar Vela X-1 with the ART-P telescope onboard the Granat Observatory are presented. Variability on a time scale of several thousand seconds was detected; intensity variations are shown to be accompanied by changes in the source’s spectrum. The hardness was also found to be highly variable on a scale of one pulsation period. The source’s spectrum exhibits an absorption feature at energy ～7 keV, which is apparently attributable to cyclotron scattering/absorption in the neutron-star magnetic field. Weak persistent emission was detected during an X-ray eclipse, which probably resulted from the scattering of pulsar emission in the stellar wind from an optical star. 相似文献
10.
We present the results of our comparative timing and spectral analysis of the high and low (off) states in the X-ray pulsar Her X-1 based on data from the ART-P telescope onboard the Granat observatory. A statistically significant (several mCrab) persistent flux with a simple power-law spectrum was detected during the low state. The spectral slope changed from observation to observation by almost a factor of 2. Pulsations were detected only during the high state of the source, when its flux was a factor of ～25 larger than the low-state flux. The spectral shape of Her X-1 in its high state was complex, with the parameters depending on pulse phase. 相似文献