排序方式： 共有11条查询结果，搜索用时 968 毫秒
1.
We report the detection of series of close type I X-ray bursts consisting of two or three events with a recurrence time much shorter than the characteristic (at the observed mean accretion rate) time of matter accumulation needed for a thermonuclear explosion to be initiated on the neutron star surface during the JEM-X/INTEGRAL observations of several X-ray bursters. We show that such series of bursts are naturally explained in the model of a spreading layer of accreting matter over the neutron star surface in the case of a sufficiently high (? ? 1 × 10?9 M ⊙ yr?1) accretion rate (corresponding to a mean luminosity L tot ? 1 × 1037erg s?1). The existence of triple bursts requires some refinement of the model—the importance of a central ring zone is shown. In the standard model of a spreading layer no infall of matter in this zone is believed to occur. 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.
When analyzing the archival data of the INTEGRAL observatory, we detected an intense X-ray burst recorded on April 16, 2005, by the JEM-X and IBIS/ISGRI telescopes from the weak and poorly studied source AX J1754.2-2754. Analysis of its time profiles and spectra allows this event to be attributed to type I X-ray bursts associated with thermonuclear explosions on the surfaces of neutron stars and the source itself to X-ray bursters. Peculiarities of the X-ray emission observed at the initial evolutionary phase of the burst point to a dramatic expansion and a corresponding cooling of the neutron star photosphere that took place at this time under the action of radiation pressure. Assuming the luminosity of the source at this phase to be the Eddington one, we have estimated the distance to the burst to be d = 6.6 ± 0.3 kpc (for a hydrogen atmosphere of the neutron star) and d = 9.2 ± 0.4 kpc (for a helium atmosphere). 相似文献
4.
While analyzing the archival data of the INTEGRAL observatory, we detected and localized a cosmic gamma-ray burst recorded on April 28, 2006, by the IBIS/ISGRI and SPI telescopes in their fields of view. Since the burst was not revealed by the INTEGRAL burst alert system (IBAS), information about its coordinates was not distributed in time and no search for its afterglow was conducted. The burst was recorded by the KONUS/WIND and RHES SI satellites. Its 20–200-keV fluence was 2.3 × 10?6 erg cm?2, the peak flux was 3.6 × 10?7 erg cm?2 s?1 (3.9 phot. cm?2 s?1). The burst had a complex multipeaked profile and stood out among typical bursts by an increase in its hardness with time. At the flux peak, the spectrum was characterized by a photon index α ? ?1.5 and a peak energy E p ? 95 keV. The burst lasted for ～12 s, after which its afterglow decaying as a power law with an index γ ～ ?4.5 was observed at energies 15–45 keV. The spectral hardness decreased noticeably during the afterglow. 相似文献
5.
The results of observations of the transient X-ray burster KS 1731-260 with the ART-P telescope onboard the GRANAT observatory are presented. The observations were performed in 1990–1991 at the initial stage of the source’s 12-yr activity period when no studies were conducted by other X-ray observatories. The flux from KS 1731-260 is shown to have systematically decreased, forming a separate initial “minioutburst” of the source with a duration of ～2.5 yr. The decrease in flux was accompanied by an increase in the spectral hardness of KS 1731-260 and an enhancement of its burst activity; two X-ray bursts were detected in the last observing sessions when the flux decreased by 40–60%. Their analysis showed that they occurred in a medium with an appreciable hydrogen abundance; i.e., the enrichment efficiency of the material in the lower atmospheric layers of the neutron star during quasi-steady hydrogen burning was low. The BDLE model that was suggested by Grebenev et al. (2006) to describe the radiation spectra of weakly magnetized accreting neutron stars has been used for the first time to analyze the continuum radiation spectrum of the source. This model incorporates two spectral components associated with the radiation from the boundary layer formed at the place of contact between the accretion disk and the neutron star surface and with the radiation from the accretion disk proper. The model satisfactorily fits the observed radiation spectra of the source and allow such parameters of the binary system as the accretion disk inclination, the bolometric luminosity (accretion rate), and the temperature of the outer boundary layer to be estimated. The boundary layer radiation for KS 1731-260 is shown to have originated in an exponential atmosphere of moderate optical depth for Thomson scattering under conditions where comptonization had no time to form the Wien spectrum, but only modified the thermal plasma radiation spectrum. 相似文献
6.
Pozanenko A. S. Minaev P. Yu. Grebenev S. A. Chelovekov I. V. 《Astronomy Letters》2019,45(11):710-727
The results of observations of the gravitational-wave (GW) event S190425z recorded by the LIGO/Virgo detectors with the anti-coincidence shield (ACS) of the SPI gamma-ray spectrometer onboard the INTEGRAL observatory are presented. With a high probability (>99%) it was associated with a neutron star (NS) merger in a close binary system. This is only the second event of such a type in the history of gravitational-wave observations (after GW170817). A weak gamma-ray burst, GRB190425, consisting of two pulses ～0.5 and ～5.9 s after the NS merger in the event S190425z with an a priori significance of 3.5 and 4.4σ (taken together 5.5σ) was detected by SPI-ACS. Analysis of the SPI-ACS count rate history recorded on these days (a total of ～125 ks of observations) has shown that the rate of random occurrence of two close spikes with the characteristics of GRB190425 does not exceed 6.4 × 10?5 s?1 (i.e., such events occur by chance, on average, every ～4.3 hours). Note that the time profile of GRB190425 has much in common with the profile of GRB170817A accompanying the event GW170817, that both NS mergers were the nearest (≤150 Mpc) of all the events recorded by the LIGO/Virgo detectors, and that no significant excesses of the gamma-ray flux above the background were detected in any of ～30 black hole merger events recorded to date by these detectors. No bursts of hard radiation were detected in the field of view of the SPI and IBIS/ISGRI gamma-ray telescopes onboard INTEGRAL. This, along with the absence of detection of gamma-ray emission from GRB190425 by the GBM gamma-ray burst monitor of the Fermi observatory suggesting its occultation by the Earth, allows the localization region for the source of this GWevent to be reduced significantly. The parameters Eiso and Ep for GRB190425 are estimated and compared with those for GRB170817A.
相似文献7.
The excess of the rate of type I X-ray bursts over that expected when the matter fallen between bursts completely burns out in a thermonuclear explosion which is observed in bursters with a high persistent luminosity (4 × 1036 ? LX ? 2 × 1037 erg s?1) is explained in terms of the model of a spreading layer of matter coming from the accretion disk over the neutron star surface. In this model the accreting matter settles to the stellar surface mainly in two high-latitude ring zones. Despite the subsequent spreading of matter over the entire star, its surface density in these zones turns out to be higher than the average one by 2–3 orders of magnitude, which determines the predominant ignition probability. The multiple events whereby the flame after the thermonuclear explosion in one ring zone (initial burst) propagates through less densematter to another zone and initiates a second explosion in it (recurrent burst) make a certain contribution to the observed excess of the burst rate. However, the localized explosions of matter in these zones, after which the burning in the zone rapidly dies out without affecting other zones, make a noticeably larger contribution to the excess of the burst rate over the expected one. 相似文献
8.
I. V. Chelovekov A. A. Lutovinov S. A. Grebenev R. A. Sunyaev 《Astronomy Letters》2005,31(10):681-694
We present the results of our study of the emission from the transient burster MX 0836-42 using its observations by the INTEGRAL and RXTE X-ray and gamma-ray observatories in the period 2003–2004. The source’s broadband X-ray spectrum in the energy range 3–120 keV has been obtained and investigated for the first time. We have detected 39 X-ray bursts from this source. Their analysis shows that the maximum 3–20-keV flux varies significantly from burst to burst, F ～ (0.5–1.5) × 10?8 erg cm?2 s?1. Using the flux at the maximum of the brightest detected burst, we determined an upper limit for the distance to the source, D ? 8 kpc. 相似文献
9.
I. V. Chelovekov S. A. Grebenev I. A. Mereminskiy A. V. Prosvetov 《Astronomy Letters》2017,43(12):781-795
We present the results of our analysis of the JEM-X/INTEGRAL data obtained from January 2003 to January 2015 aimed at searching for type I X-ray bursts from known and new bursters. Such bursts are caused by thermonuclear explosions on the surface of a neutron star. We have searched for bursts in the records of the count rate of the JEM-X detectors in the 3–20 keV energy band. We have separately reconstructed and analyzed the light curves of 104 X-ray bursters known to date based on the JEM-X data. A similar search for bursts was previously carried out in the 15–25 keV data from the IBIS/ISGRI telescope onboard the INTEGRAL observatory obtained in 2003–2009. We have continued to analyze the data from this telescope up until the observations in January 2015. The joint catalog of bursts detected by the two instruments includes 2201 events; their basic parameters are given. The large size of the sample of bursts makes it one of the most representative of the existing one and allows various statistical studies of bursts to be performed. In particular, we have constructed the dependence of the mean rate of type I bursts from bursters on the luminosity (accretion rate), revealed an appreciable burst rate from sources with a near-Eddington luminosity, and investigated the population of multiple bursts with a recurrence time much shorter than the time it takes for a critical mass of matter required for the initiation of an explosion to be accumulated on the neutron star surface. Almost all of the detected bursts are associated with already known bursters,we have found only one previously unknown burster, IGRJ17380-3749, in the archival data, and one more known, but poorly studied source, AX J1754.2-2754, has been identified as a burster. Several similar sources have previously been identified as bursters directly during the INTEGRAL observations. 相似文献
10.
Details of the discovery (in February 2004) and results of subsequent (in 2004–2009) INTEGRAL observations of the transient
X-ray burster IGR J17380-3749 (IGR J17379-3747) are presented. Over the period of its observations, the INTEGRAL observatory
recorded two hard X-ray flares and one type I X-ray burst from the source, which allowed the nature of IGR J17380-3749 to
be determined. The burster radiation spectrum during the flares was hard—a power law with a photon index α = 1.8–2.0 or bremsstrahlung corresponding to a plasma with a temperature kT = 90–140 keV. The spectral shape at the flare peaks turned out to be the same, despite a more than twofold difference in
flux (the peak flux recorded in the energy range 18–100 keV reached ∼20 mCrab). The upper limit on the flux from the source
in its quiescent (off) state in the range of 18–40 keV was 0.15 mCrab (3σ). 相似文献