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1.
We present the results of measurements of the total X-ray flux from the Andromeda galaxy (M31) in the 3-100 keV band based on data from the RXTE/PCA, INTEGRAL/ISGRI, and SWIFT/BAT space experiments. We show that the total emission from the galaxy has a multicomponent spectrum whose main characteristics are specified by binaries emitting in the optically thick and optically thin regimes. The galaxy’s luminosity at energies 20–100 keV gives about 6% of its total luminosity in the 3–100 keV band. The emissivity of the stellar population in M31 is L 2–20 keV ～ 1.1 × 1029 erg s?1 M ⊙ ?1 in the 2–20 keV band and L 20–100 keV ～ 8 × 1027 erg s?1 M ⊙ ?1 in the 20–100 keV band. Since low-mass X-ray binaries at high luminosities pass into a soft state with a small fraction of hard X-ray emission, the detection of individual hard X-ray sources in M31 requires a sensitivity that is tens of times better (up to 10?13 erg s?1 cm?2) than is needed to detect the total hard X-ray emission from the entire galaxy. Allowance for the contribution from the hard spectral component of the galaxy changes the galaxy’s effective Compton temperature approximately by a factor of 2, from ～1.1 to ～2.1 keV.  相似文献   

2.
We present the results of our study of the X-ray spectrum for the source X-6 in the nearby galaxy M33 obtained for the first time at energies above 10 keV from the data of the NuSTAR orbital telescope. The archival Swift–XRT data for energy coverage below 3 keV have been used, which has allowed the spectrum of M33 X-6 to be constructed in the wide energy range 0.3–20 keV. The spectrum of the source is well described by the model of an optically and geometrically thick accretion disk with a maximum temperature of ~2 keV and an inner radius of ~5 cos?1/2θ km (where >θ is the unknown disk inclination angle with respect to the observer). There is also evidence for the presence of an additional hard component in the spectrum. The X-ray luminosity ofM33 X-6 measured for the first time in the wide energy range 0.3–20 keV is ~2 × 1038 erg s?1, with the luminosity in the hard 10–20 keV X-ray band being ~10% of the source’s total luminosity. The results obtained suggest that X-6 may be a Z-source, i.e., an X-ray binary with subcritical accretion onto a weakly magnetized neutron star.  相似文献   

3.
Balloon observations of the X-ray source Sco X-1 carried out in November 1978 have revealed a thermal spectrum withkT?7 keV in the 20–60 keV energy band. In addition, there was evidence of a high energy component, possibly variable, above ～50 keV. The spectral form of this component could not be determined but was hard with a 60 keV flux of ～10?4 photons (keV cm2 s)?1.  相似文献   

4.
We obtained constraints on the luminosity of the central source in SNR 1987 A using XMM-Newton and INTEGRAL data. XMM-Newton yields an upper limit on the SNR luminosity in the 2–10 keV energy band, LX ? 5 × 1034 erg s?1. Since the optical depth of the envelope is still large in the XMM-Newton energy band, this constraint carries no useful information about the luminosity of the central source. The optical depth is expected to be small in the hard (20–200 keV) X-ray band of the IBIS telescope aboard the INTEGRAL observatory. We detected no statistically significant emission from SNR 1987 A in the INTEGRAL data and obtained an upper limit of LX ? 1.1 × 1036 erg s?1 on the luminosity of the central source in the 20–60 keV band. We also obtained an upper limit on the mass of radioactive 44Ti, M(44Ti) ? 10?3M⊙.  相似文献   

5.
We present a preliminary analysis of multiple X-ray (0.1–2.5 keV) observations of HD 50896 andγ Velorum obtained with theROSAT satellite. For HD 50896, our 8 observations show variability at the 30% level on timescales of ～ 1 day, together with larger (× 1.7) epoch-changes, but no evidence for rapid variability. No phase-dependent modulation is apparent on the 3d.766 optical period. The mean PSPC spectrum gives kT = 0.28 keV, log N(H) = 20.6, and Lx = 3.8 × 1032 erg s?1, and implies that the observed X-rays have undergone little absorption in the WN5 wind. Forγ Velorum, we have 13 observations secured over several cycles in the 78d.5 binary period. At most binary phases, the X-ray emission is relatively constant, with kT ? 0.19 keV, log N(H) = 20.2, and Lx = 2.5 × 1031 erg s?1. Near orbital phase 0.5, the X-ray emission is enhanced by a factor of 4, due almost entirely to an additional harder component with kT ≥ 2 keV. We believe this is due to X-ray emission produced in the collision of the two stellar winds.  相似文献   

6.
ART-P/Granat observations of the X-ray burster SLX 1732-304 in the globular cluster Terzan 1 are presented. The X-ray (3–20 keV) fluxes from the source differed by more than a factor of 4 during the observing sessions on September 8 (F x ? 6.95 × 10?10 erg cm?2 s?1) and October 6, 1990 (F x ? 1.64 × 10?10 erg cm?2 s?1). The intensity variations of SLX 1732-304 were apparently accompanied by variations in its hardness: whereas the source in its high state had the spectrum with a distinct exponential cutoff typical of bright low-mass X-ray binaries, its low-state spectrum could be satisfactorily described by a simple power law with a photon index α?1.7. During the ART-P observation on September 8, a type I X-ray burst was detected from SLX 1732-304.  相似文献   

7.
We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the RXTE and INTEGRAL observatories in a wide X-ray (3–100 keV) energy band during its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic of the cyclotron resonance absorption line near the maximum of the X-ray flux from the source (luminosity range 5 × 1037–2 × 1038 erg s?1) is ～11 keV. When the pulsar luminosity falls below ～5 × 1037 erg s?1, the energy of the fundamental harmonic is displaced sharply toward the high energies, up to ～16 keV. Under the assumption of a dipole magnetic field configuration, this change in cyclotron harmonic energy corresponds to a decrease in the height of the emitting region by ～2 km, while other spectral parameters, in particular, the cutoff energy, remain essentially constant. At a luminosity ～7 × 1037 erg s?1, four almost equidistant cyclotron line harmonics are recorded in the spectrum. This suggests that either the region where the emission originates is compact or the emergent spectrum from different (in height) segments of the accretion column is uniform. We have found significant pulse profile variations with energy, luminosity, and time. In particular, we show that the profile variations from pulse to pulse are not reduced to a simple modulation of the accretion rate specified by external conditions.  相似文献   

8.
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.
The X-ray luminosity function of distant (3 < z < 5.1) type 1 quasars has been measured. A sample of distant high-luminosity (1045 erg s?1 ≤ LX,2?10 < 7.5×1045 erg s?1 in the 2–10 keV energy band) quasars from the catalog by Khorunzhev et al. (2016) compiled from the data of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey and the Sloan Digital Sky Survey (SDSS) has been used. This sample consists of 101 sources. Most of them (90) have spectroscopic redshifts zspec ? 3; the remaining ones are quasar candidates with photometric redshift estimates zphot ? 3. The spectroscopic redshifts of eight sources have been measured with the BTA and AZT-33IK telescopes. Owing to the record sky coverage area (?250 sq. deg at X-ray fluxes ~10?14 erg s?1 cm?2 in the 0.5–2 keVband) from which the sample was drawn, we have managed to obtain reliable estimates of the space density of distant X-ray quasars with luminosities LX,2?10 > 2×1045 erg s?1 for the first time. Their comoving space density remains constant as the redshift increases from z = 3 to 5 to within a factor of 2. The power-law slope of the X-ray luminosity function of distant quasars at its bright end (above the break) has been reliably constrained for the first time. The range of possible slopes for the quasar luminosity and density evolution model is γ2 = 2.72 ?0.12 +0.19 ± 0.21, where initially the lower and upper boundaries of γ2 with the remaining uncertainty in the detection completeness of X-ray sources in SDSS and subsequently the statistical error of the slope are specified.  相似文献   

10.
Detection of a new X-ray source and its identification with the Pleiades cluster is reported here. The new X-ray source has an X-ray luminosity of ～1032 ergs s?1 in the 0.15–3.0 keV energy band. The observed X-ray emission could be explained as integrated emission from a large number of stars in the cluster.  相似文献   

11.
A Fabry-Perot spectrometer was used to map the H II region around the O star ξ Per in the Hβ emission line. The angular size of the region is \(9_.^ \circ 1 \times 6_.^ \circ 0\). The region-boundary contour drawn at the double background level is centered on the star. The accuracy of our emission intensity measurements is 0.2 rayleigh. The proximity of the nebula NGC 1499 has virtually no effect on the measured emission measure toward the star. The star excitation parameter derived from observations corresponds to the spectral type O7.5 III and is U(Sp)=56.0±8.4 pc cm?2; the mean electron density in the region is ne=3.1±0.4 cm?3.  相似文献   

12.
We analyze the statistical properties of normal galaxies to be detected in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configuration and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be ≈10?14 erg s?1 in the 0.5–2 keV band. This will allow ～(1.5–2) × 104 normal galaxies with approximately the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in the survey are located within ～200–400 Mpc. A typical (most probable) galaxy will have a luminosity log L X ～ 40.5–41.0, will be located at a distance of ～70–90 Mpc, and will be either a star-forming galaxy with a star formation rate of ～20M ⊙ yr?1 whose X-ray emission is produced by ultraluminous X-ray sources (ULXs) or an elliptical galaxy with amass log M * ～ 11.3 emitting through to a hot interstellar gas. The galaxies within 35 Mpc will collectively contain ～102 ULXs with luminosities log L X > 40, ～80% of whichwill be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum luminosity of ULXs.  相似文献   

13.
We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5–10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n H L>4×1023 cm?2). The Kα line of neutral or weakly ionized iron with an equivalent width of ～2.5 keV dominates in the energy range 4–10 keV. There is also evidence for the presence of a second line at energy ～7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1–15 µm. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.  相似文献   

14.
Observational properties of two white-light flares (WLFs), on June 15, 1991, and June 26, 1999, are presented and compared. This is of particular interest, because the former was one of the most intense flares of X-ray class X12, while the latter was a compact flare of class M2.3. Significant differences between some flare parameters (GOES class, Hα classification, the number of WLF kernels and their location in the sunspot group, the size and duration of the WLF emission, and the peak flux density of the microwave emission) have been found. However, both these events had approximately the same powers of the emission per unit area in continuum near 658.0 nm: E = 1.5 × 107 and 1.1. × 107 erg cm?2 s?1 nm?1. There is generally a good temporal coincidence between the microwave and hard X-ray emissions and the WLF emission during the impulsive phase, but the light curve of the WLF emission on June 26, 1999, shows a stronger correlation with the X-ray emission in the energy range 14–23 keV. Both flares can be classified by their spectral characteristics as type I white-light flares.  相似文献   

15.
We have computed a spherically symmetric model for the interaction of matter ejected during the outburst of a classical nova with the stellar wind from its optical component. This model is used to describe the intense X-ray outburst (the peak 3–20 keV flux was ～2 Crab) of the binary system CI Camelopardalis in 1998. According to our model, the stellar wind from the optical component heated by a strong shock wave produced when matter is ejected from the white dwarf as the result of a thermonuclear explosion on its surface is the emission source in the standard X-ray band. Comparison of the calculated and observed time dependences of the mean radiation temperature and luminosity of the binary system during its outburst has yielded very important characteristics of the explosion. We have been able to measure the velocity of the ejected matter immediately after the onset of the explosion for the first time: it follows from our model that the ejected matter had a velocity of ～2700 km s?1 even on 0.1–0.5 day after the outburst onset and it flew with such a velocity for the first 1–1.5 day under an external force, possibly, the radiation pressure from the white dwarf. Subsequently, the matter probably became transparent and began to decelerate. The time dependence of the mean radiation temperature at late expansion phases has allowed us to estimate the mass of the ejected matter, ～10?7–10?6 M ⊙. The mass loss rate in the stellar wind required to explain the observed peak luminosity of the binary system during its outburst has been estimated to be \(\dot M\) ～ (1 ? 2) × 10?6 M ⊙ yr?1.  相似文献   

16.
New optical and X-ray observations of the supernova remnant (SNR) G78.2+2.1 are presented. CCD Hα observations with a Fabry-Perot interferometer attached to the 125-cm reflector at the Crimean Station of the Sternberg Astronomical Institute are used to obtain the radial-velocity field toward the SNR and in its vicinity. The brightness distribution and X-ray spectrum of the SNR are obtained from archival ROSAT and ASCA X-ray data. The X-ray image of G78.2+2.1 exhibits a shell structure (ΔR/R?0.3) and is generally similar to its radio image; a comparison with the radio map at ν=1.4 GHz constructed from archival VLA data reveals the coincidence of features on scales of several arcminutes at the eastern boundary of G78.2+2.1. Weak X-ray emission (an outer shell or a halo of size ?2°) has been identified for the first time far outside G78.2+2.1. The X-ray emission from G78.2+2.1 is shown to characterize a young adiabatic SNR [M X-ray ? 100 M ⊙, V s?103km s?1, t?(5–6)×103 years], which probably expands inside the cavity swept up by the progenitor's stellar wind. Searches for the corresponding radio structure are required to elucidate the nature of the outer X-ray shell or halo.  相似文献   

17.
Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E –(1.92±0.10) photons cm–2s–1 keV–1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E –(1.89±0.22) photons cm–2s–1 keV–1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of E –2, while below 20 keV the spectrum varies fromE –1.7 toE –5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.  相似文献   

18.
This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0–3 Å, 0–8 Å and 8–20 Å bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10?5 ergs cm?2 sec?1 in the main ionizing band of 0–3 Å. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this beingα r≈6×10?6 cm3 sec?1; furthermore ion production rates were estimated during SPA's at heights below the reference level.  相似文献   

19.
From the UCSD OSO-7 X-ray experiment data, we have identified 54 X-ray bursts with 5.1–6.6 keV flux greater than 103 photon cm?2 keV?1 which were not accompanied by visible Hα flare on the solar disk. By studying OSO-5 X-ray spectroheliograms, Hα activity at the limb and the emergence and disappearance of sunspot groups at the limb, we found 17 active centers as likely seats of the X-ray bursts beyond the limb. We present the analysis of 37 X-ray bursts and their physical parameters. We compare our results with those published by Datlowe et al. (1974a, b) for disk events. The distributions of maximum temperature, maximum emission measure, and characteristic cooling time of the over-the-limb events do not significantly differ from those of disk events. We show that of conduction and radiation, the former is the dominant cooling mechanism for the hot flare plasma. Since the disk and over-the-limb bursts are similar, we conclude that the scale height for X-ray emission in the 5–10 keV range is large and is consistent with that of Catalano and Van Allen (1973), 11000 km, for primarily 1–3 keV emission. Twenty-five or about 2/3 of the over-the-limb events had a non-thermal component. The distribution of peak 20 keV flux is not significantly different from that of disk events. However, the spectral index at the time of maximum flux is significantly different for events over the limb and for events near the center of the disk; the spectral index for over-the-limb events is larger by about δγ = 3/4. If hard X-ray emission came only from localized sources low in the chromosphere we would expect that hard X-ray emission, would be occulted over the limb; on the contrary, the observation show that the fraction of soft X-ray bursts which have a nonthermal component is the same on and off of the disk. Thus hard X-ray emission over extended regions is indicated.  相似文献   

20.
Results of 11-year-long X-ray INTEGRAL observations of the nucleus of Seyfert galaxy NGC 4945 in the 3–500 keV range were processed. A two-component spectrum model, which includes strong radiation absorption in the Compton-thick torus around the AGN “central engine” and secondary radiation reflected from the torus walls, was used in the analysis. The following primary spectrum parameters were determined based on the data accumulated throughout the entire exposure period: photon index Γ = 1.60 ± 0.07, exponential cutoff energy E c =157 -22 +29 keV, and column density of the medium that absorbs primary radiation N H,1 =5.0 -0.9 +1.0 × 1024 cm–2. The column density of the medium absorbing reflected radiation is two orders of magnitude lower. Both the X-ray flux in the ranges of 20–40, 40–60, and 60–100 keV and the shape of the X-ray spectrum of NGC 4945 vary. The spectrum shape variations may be induced by inhomogeneities of the absorbing medium surrounding the AGN. At the same time, there is some evidence for moderate spectrum variations in the highenergy region, which may be associated with changes in the “central engine.”  相似文献   

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