We analyzed the data obtained by the SPI telescope onboard the INTEGRAL observatory to search for short transient events with a duration from 1 ms to a few tens of seconds. An algorithm for ...identifying gamma-ray events against the background of a large number of charged particle interactions with the detector has been developed. The classification of events was made. Apart from the events associated with cosmic gamma-ray bursts (GRBs) confirmed by other space experiments and the activity of known soft gamma repeaters (for example, SGR 1806-20), previously unreported GRBs have been found. GRB candidates and short gamma-ray events probably associated with the activity of known SGRs and AXPs have been selected. The spectral evolution of 28 bright GRBs from the catalog has been studied extensively. A new method for investigating the spectral evolution is proposed. The energy dependence of the spectral lag for bursts with a simple structure of their light curves and for individual pulses of multipulse events is shown to be described by a logarithmic function,
lag
∼
A
log(
E
). It has been established that the parameter
A
depends on the pulse duration, with the dependence being universal for all of the investigated GRBs. No negative spectral lags have been detected for bursts with a simple structure of their light curves.
A number of new X-ray sources (IGR J17091-3624, IGR/XTE J17391-3021, IGR J17464-3213 (=XTE J17464-3213 = H 1743-322), IGR J17597-2201, SAX/IGR J18027-2017) have been observed with the INTEGRAL ...observatory during ultra deep exposure of the Galactic Center region in August-September 2003. Most of them were permanently visible by INTEGRAL at energies higher than ∼20 keV, but IGR/XTE J17391-3021 was observed only during its flaring activity with a flux maximum of ~120 mCrab. IGR J17091-3624, IGR J17464-3213 and IGR J17597-2201 were detected up to ∼100–150 keV. In this paper we present the analysis of INTEGRAL observations of these sources to determine the nature of these objects. We conclude that all of them have a galactic origin. Two sources are black hole candidates (IGR J17091-3624 and IGR J17464-3213), one (IGR J17597-2201) is an LMXB neutron star binary (presumably an X-ray burster) and two other sources (IGR J17391-3021 and SAX/IGR J18027-2017) are neutron stars in high mass binaries; one of them (SAX/IGR J18027-2017) is an accreting X-ray pulsar.
We study the cosmic X-ray background (CXB) intensity variations on large angular scales using the slew data from the RXTE observatory. We detect intensity variations up to ~2% on angular scales of ...20-40°. These variations are partly correlated with the local large-scale structure, which allowed us to estimate the emissivity of the local Universe in the energy band 2-10 keV at (8±4)$\times$1038 h75 erg s-1 Mpc-3. The spectral energy distribution of the large-angular-scale variations is hard and is compatible with that of the CXB, which implies that normal galaxies and clusters of galaxies, whose spectra are typically much softer, do not contribute more than 15% to the total X-ray emissivity of the local Universe. Most of the observed CXB anisotropy (after exclusion of point sources with fluxes $\ga$10-11 erg s-1 cm-2) can be attributed to low-luminosity AGNs.
The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in ...2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module.
The models and results of the experimental studies of the characteristics of objects that are new for domestic instrumentation are presented: an X-ray mirror system and a CdTe strip semiconductor ...detector that are used in the first Russian ART-XC reflecting X-ray telescope. This telescope is a part of the Spektr-RG international space observatory, which started to the L2 libration point in July 2019.
SGR 1806-20 has been observed for more than 2 years with the INTEGRAL satellite. In this period the source went from a quiescent state into a very active one culminating in a giant flare on December ...27, 2004. Here we report on the properties of all the short bursts detected with INTEGRAL before the giant flare. We derive their number-intensity distribution and confirm the hardness-intensity correlation for the bursts found by Goetz et al. (2004a, A&A, 417, L45). Our sample includes a very bright outburst that occurred on October 5, 2004, during which over one hundred bursts were emitted in 10 minutes, involving an energy release of 3 x 1042 erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model.
The analysis of hard X-ray INTEGRAL observations (2003–2008) of superaccreting Galactic microquasar SS433 at precessional phases of the source with the maximum disc opening angle is carried out. It ...is found that the shape and width of the primary X-ray eclipse are strongly variable, suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I component and the wind–wind collision region. The independence of the observed hard X-ray spectrum on the accretion disc precessional phase suggests that hard X-ray emission (20–100 keV) is formed in an extended, hot, quasi-isothermal corona, probably heated by interaction of relativistic jet with inhomogeneous wind outflow from the precessing supercritical accretion disc. A joint modelling of X-ray eclipsing and precessional hard X-ray variability of SS433 revealed by INTEGRAL by a geometrical model suggests the binary mass ratio q=mx/mv≃ 0.25–0.5. The absolute minimum of joint orbital and precessional χ2 residuals is reached at q≃ 0.3. The found binary mass ratio range allows us to explain the substantial precessional variability of the minimum brightness at the middle of the primary optical eclipse. For the mass function of the optical star fv= 0.268 M⊙ as derived from Hillwig & Gies data, the obtained value of q≃ 0.3 yields the masses of the components mx≃ 5.3 M⊙, mv≃ 17.7 M⊙, confirming the black hole nature of the compact object in SS433.
We present the analysis of serendipitous sources in a deep, 500 ks, hard X-ray observation of the Coma Cluster region with the IBIS instrument on board INTEGRAL. In addition to the Coma Cluster, the ...final 20-50 keV image contains 12 serendipitous sources with statistical significance >4 s. We use these data (after correcting for expected number of false detections) to extend the extragalactic source counts in the 20-50 keV energy band down to a limiting flux of 1.0 x 10 super(-11) ergs s super(-1) cm super(-2) ( 1 mcrab). This is a more than a factor of 10 improvement in sensitivity compared to the previous results in this energy band obtained with the HEAO 1 A-4 instrument. The derived source counts are consistent with the Euclidean relation N(> f) 8 f super(3/2). A large fraction of identified serendipitous sources are low-redshift, z < 0.02, active galactic nuclei (AGNs), mostly of Seyfert 1 type. The surface density of hard X-ray sources is (1.4 c 0.5) x 10 super(-2) deg super(-2) above a flux threshold of 10 super(-11) ergs s super(-1) cm super(-2). These sources directly account for 63% of the cosmic X-ray background in the 20-50 keV energy band. Given the low redshift depth of our sample, we expect that similar sources at higher redshifts account for a significant fraction of the hard X-ray background. Our field covers only 3% of the sky; a systematic analysis of other extragalactic INTEGRAL observations can produce much larger source samples and is, therefore, critically important.
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 × 10
29
erg s
−1
M
⊙
−1
in the 2–20 keV band and
L
20–100 keV
∼ 8 × 10
27
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.
We analyze the images of the Sagittarius Arm tangent obtained with the IBIS telescope of the INTEGRAL observatory in the energy range 18-120 keV during its observations in the spring of 2003. We ...detected 28 sources at a statistically significant level with fluxes above 1.4 mCrab in the energy range 18-60 keV. Of these sources, 16 were previously identified as binaries of various classes in our Galaxy, 3 were identified as extragalactic objects, 2 were identified as pulsars in supernova remnants, and 7 sources were of an unknown nature. These observations revealed three new sources. A statistically significant flux in the energy range 60-120 keV was recorded from 13 sources.PUBLICATION ABSTRACT
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