The true nature of the progenitor to GRBs remains elusive; one characteristic that would constrain our understanding of the GRB mechanism considerably is gamma-ray polarimetry measurements of the ...initial burst flux. We present a method that interprets the prompt GRB flux as it Compton scatters off the Earth's atmosphere, based on detailed modelling of both the Earth's atmosphere and the orbiting detectors. The BATSE mission aboard the CGRO monitored the whole sky in the 20 keV–1 MeV energy band continuously from April 1991 until June 2000. We present the BATSE Albedo Polarimetry System (BAPS), and show that GRB 930131 and GRB 960924 provide evidence of polarisation in their prompt flux that is consistent with degrees of polarisation of $\Pi>35$% and $\Pi>50$% respectively. While the evidence of polarisation is strong, the method is unable to strongly constrain the degree of polarisation beyond a systematics based estimation. Hence the implications on GRB theory are unclear, and further measurements essential.
SAX J1818.6–1703 has been characterized as a supergiant fast X-ray transient system on the basis of several INTEGRAL/IBIS detections since the original BeppoSAX Wide Field Camera detection. Using ...IBIS/ISGRI, Swift/BAT and archival observations, we show that, in fact, SAX J1818.6–1703 exhibits emission on a period of 30 ± 0.1 d, with a high degree of recurrence. SAX J1818.6–1703 is therefore the second supergiant fast X-ray transient shown to exhibit periodic outbursts, but with a considerably shorter period than the other known system, IGR J11215–5952.
IGR J18483−0311 is an X-ray pulsar with transient X-ray activity, belonging to the new class of high-mass X-ray binaries called supergiant fast X-ray transients. This system is one of the two members ...of this class, together with IGR J11215−5952, where both the orbital (18.52 d) and spin period (21 s) are known. We report on the first complete monitoring of the X-ray activity along an entire orbital period of a supergiant fast X-ray transient. These Swift observations, lasting 28 d, cover more than one entire orbital phase consecutively. They are a unique data set, which allows us to constrain the different mechanisms proposed to explain the nature of this new class of X-ray transients. We applied the new clumpy wind model for blue supergiants developed by Ducci et al. to the observed X-ray light curve. Assuming an eccentricity of e= 0.4, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging from 1018 g to 5 × 1021 g.
The unidentified source IGR J16328--4726 was covered with INTEGRAL observations for a long period (~9.8 Ms) and was undetectable for most of the time while showing a very recurrent micro-activity ...with a duration from tens of minutes to several hours. We report the discovery of two strong outbursts started at 53420.65 MJD and 54859.99 MJD, respectively, the first with a duration of ~1 hr and the second with a lower limit on the duration of ~3.5 hr. Furthermore, the sources have been detected in nine other short pointings with significance between 4 Delta *s and 5 Delta *s as well as in one of the revolutions (during the exposure ~130 ks) at a significance level of ~7 Delta *s. The stronger outburst spectrum is well described by a power-law model with a photon index of ~2.0 and a flux of ~3.3 X10--10 erg cm--2 s--1 in the 20-50 keV energy band. The weaker outburst and revolution spectra show the same spectral shape and different fluxes. The combined timing and spectral properties observed during the outburst, the recurrent nature of this transient source, the Galactic plane location, a dynamic range >170 in the 0.3-10 keV band and >165 in the 20-50 keV, and the presence of an IR star in the error circle of a Swift X-ray Telescope pointing are suggesting this source as a member of the class of the supergiant fast X-ray transients.
Aims.We communicate the detection of soft (20–200 keV) γ-rays from the pulsar and pulsar wind nebula of PSR J1846-0258 and aim to identify the component of the system which is responsible for the ...γ-ray emission. Methods.We combine spectral information from the INTEGRAL γ-ray mission with archival data from the Chandra X-ray Observatory to pinpoint the source of soft γ-ray emission. Results.Our analysis shows that the soft γ-rays detected from PSR J1846-0258 include emission from both the pulsar and the pulsar wind nebula, but the measured spectral shape is dominated by the pulsar wind nebula. We discuss PSR J1846-0258 in the context of rotation-powered pulsars with high magnetic field strengths and review the anomalously high fraction of spin-down luminosity converted into X- and γ-ray emission in light of a possible overestimate of the distance to this pulsar.
In this Letter we present the result of the cross correlation between the fourth INTEGRAL/IBIS soft gamma-ray catalog, in the range 20-100 keV, and the Fermi LAT bright source list of objects ...emitting in the 100 MeV-100 GeV range. The main result is that only a minuscule part of the more than 720 sources detected by INTEGRAL and the population of 205 Fermi LAT sources are detected in both spectral regimes. This is in spite of the mCrab INTEGRAL sensitivity for both galactic and extragalactic sources and the breakthrough, in terms of sensitivity, achieved by Fermi at MeV-GeV energies. The majority of the 14 Fermi LAT sources clearly detected in the fourth INTEGRAL/IBIS catalog are optically identified active galactic nuclei (10) complemented by two isolated pulsars (Crab and Vela) and two high-mass X-ray binaries (LS I +61{sup 0}303 and LS 5039). Two more possible associations have been found: one is 0FGL J1045.6-5937, possibly the counterpart at high energy of the massive colliding wind binary system Eta Carinae, discovered to be a soft gamma ray emitter by recent INTEGRAL observations and 0FGL J1746.0-2900 coincident with IGR J17459-2902, but still not identified with any known object at lower energy. For the remaining 189 Fermi LAT sources no INTEGRAL counterpart was found and we report the 2sigma upper limit in the energy band 20-40 keV.
Context. The fast X-ray transient IGR J16479-4514 is known to display flares typically lasting a few hours. Recently, its counterpart has been identified with a supergiant star, therefore the source ...can be classified as a member of the newly discovered class of Supergiant Fast X-ray Transients (SFXTs); specifically, it is the one with the highest duty cycle. Aims. Characterize the quiescent X-ray behaviour of the source and compare its broad band spectrum to those during fast X-ray flares. Methods. We analysed IBIS and JEM-X data with OSA 5.1, along with archival Swift/XRT data. Results. We present results from a long-term monitoring of IGR J16479-4514 with detailed spectral and timing information on 19 bright fast X-ray flares, 10 of which are newly discovered. We also report the first results on the quiescent X-ray emission. The typical luminosity value (~1034 erg s-1) is about 2 orders of magnitude greater than what is typical of SFXTs, while its broad band X-ray spectrum has a shape very similar to the shape during fast X-ray transient activity, i.e. a rather steep power law with $\Gamma \sim2.6$. Conclusions. IGR J16479-4514 is characterised by a quiescent X-ray luminosity higher than what is typical of other known SFXTs but lower than persistent emission from classical SGXBs. We suggest that this source is a kind of transition object between these two systems, supporting the idea that there is a continuum of behaviour between the class of SFXTs and that of classical persistent SGXBs.
In this paper, we present INTEGRAL observations of seven active galactic nuclei (AGNs): two newly discovered type 1 Seyferts, IGR J18027−1455 and J21247+5058 and five well-known Seyferts, NGC 6814 ...(type 1.5), Cygnus A (type 2), MCG-05-23-16 (type 2), ESO 103-G035 (type 2) and GRS 1734-292. For IGR J18027−1455 and J21247+5058, only INTEGRAL/IBIS data were available, while broad-band spectra are presented and discussed for the remaining five sources for which either BeppoSAX or ASCA data were used in conjunction with INTEGRAL measurements. In the cases of NGC 6814 and GRS 1734-292, data taken in different periods indicate variability in the flux: in the case of NGC 6814 by a factor of 16 over a period of about 10 years. Although limited in size, our sample can be used to investigate the parameter space of both the photon index and cut-off energy. The mean photon index is 1.8, while the cut-off energy ranges from 30–50 keV to greater than 200 keV; in the particular case of MCG-05-23-16, ESO 103-G035 and GRS 1734-292, the cut-off energy is well constrained at or below 100 keV. We have also tested an enlarged sample, which includes INTEGRAL data of three more AGNs, against the correlation found by a number of authors between the photon index and the cut-off energy but have found no evidence for a relation between these two parameters. Our analysis indicates that there is a diversity in cut-off energies in the primary continuum of Seyfert galaxies.
Using data collected with the BeppoSAX, INTEGRAL and Swift satellites, we report and discuss the results of a study on the X-ray emission properties of the X-ray source 1ES 1210-646, recently ...classified as a high-mass X-ray binary through optical spectroscopy. This is the first in-depth analysis of the X-ray spectral characteristics of this source. We found that the flux of 1ES 1210-646 varies by a factor of ~3 on a timescale of hundreds of seconds and by a factor of at least 10 among observations acquired over a time span of several months. The X-ray spectrum of 1ES 1210-646 is described using a simple powerlaw shape or, in the case of INTEGRAL data, with a blackbody plus powerlaw model. Spectral variability is found in connection with different flux levels of the source. A strong and transient iron emission line with an energy of ~6.7 keV and an equivalent width of ~1.6 keV is detected when the source is found at an intermediate flux level. The line strength seems to be tied to the orbital motion of the accreting object, as this feature is only apparent at the periastron. Although the X-ray spectral description we find for the 1ES 1210-646 emission is quite atypical for a high-mass X-ray binary, the multiwavelegth information available for this object leads us to confirm this classification. The results presented here allow us instead to definitely rule out the possibility that 1ES 1210-646 is a (magnetic) cataclysmic variable as proposed previously and, in a broader sense, a white dwarf nature for the accretor is disfavoured. X-ray spectroscopic data actually suggest a neutron star with a low magnetic field as the accreting object in this system.
Context. The combination of compact objects, short period variability and peculiar chemical composition of the ultra compact X-ray binaries make up a very interesting laboratory to study accretion ...processes and thermonuclear burning on the neutron star surface. Improved large optical telescopes and more sensitive X-ray satellites have increased the number of known ultra compact X-ray binaries allowing their study with unprecedented detail. Aims. We analyze the average properties common to all ultra compact bursters observed by INTEGRAL from ~0.2 keV to ~150 keV. Methods. We have performed a systematic analysis of the INTEGRAL public data and Key-Program proprietary observations of a sample of the ultra compact X-ray binaries. In order to study their average properties in a very broad energy band, we combined INTEGRAL with BeppoSAX and SWIFT data whenever possible. For sources not showing any significant flux variations along the INTEGRAL monitoring, we build the average spectrum by combining all available data; in the case of variable fluxes, we use simultaneous INTEGRAL and SWIFT observations when available. Otherwise we compared IBIS and PDS data to check the variability and combine BeppoSAX with INTEGRAL /IBIS data. Results. All spectra are well represented by a two component model consisting of a disk-blackbody and Comptonised emission. The majority of these compact sources spend most of the time in a canonical low/hard state, with a dominating Comptonised component and accretion rate $\dot {M}$ lower than ~ 10-9 ${M_{\odot}}/$yr, not depending on the model used to fit the data.
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