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SPI image of the Galactic Centre in the 40-100 keV band. The sources in white belong to our monitoring program. Other sources are marked in yellow for orientation.
Source publication
Early results from the INTEGRAL Core Program, for a sample of eight persistently bright neutron star low mass X-ray binaries in the energy range from 5 keV to 200 keV are presented. It is shown that INTEGRAL efficiently detects sources and that spectra may be obtained up to several hundreds of keV by combining data from three of the four INTEGRAL i...
Contexts in source publication
Context 1
... energy range, the spectrum of GX 9+1 derived from the SPI data might therefore be affected. In the case of GX 3+1, two faint sources, SLX 1735-269 and SAX J1747.0-2858, are at 2.2 • and 2.3 • angular separation, respectively. As both sources are weak compared to GX 3+1, significant effects on the spec- tral extraction of GX 3+1 are unlikely. Fig. 2 shows an im- age extracted from the SPI data in the 40-100 keV region. In the very dense region of the Galactic Centre, the extraction of sources seems to fail, while for more isolated sources, like e.g. GS 1826-24 and GX 13+1, the results are consistent with the ISGRI data (see Fig. 3). For spectral extraction twenty loga- rithmic ...
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... to ISGRI. The spectrograph can then be used to derive high energy spec- tra based on longer observations. Though the spectrum is in this case an average over the different stages of the LMXRB cycle, it can reveal high energy tails, as seen in Fig. 4 up to ∼ 150 keV. This capability is also seen in the high energy (40 -100 keV) image as shown in Fig. ...
Citations
... This so-called Core Programme mostly consisted of a deep survey of the central radian of the Galaxy and frequent scans of the Galactic plane. Early results of these campaigns were reported by ; Paizis et al. (2003); Del ; Rodriguez et al. (2003). In particular, Paizis et al. (2003), using a sample of 8 bright NS LMXBs (Atoll and Z sources), demonstrated the ability of the JEM-X , IBIS/ISGRI Lebrun et al., 2003) and SPI instruments aboard INTEGRAL to perform broad-band (from ~ 5 to several hundred keV) X-ray spectroscopy of Galactic X-ray binaries, confirming prelaunch expectations. ...
... Early results of these campaigns were reported by ; Paizis et al. (2003); Del ; Rodriguez et al. (2003). In particular, Paizis et al. (2003), using a sample of 8 bright NS LMXBs (Atoll and Z sources), demonstrated the ability of the JEM-X , IBIS/ISGRI Lebrun et al., 2003) and SPI instruments aboard INTEGRAL to perform broad-band (from ~ 5 to several hundred keV) X-ray spectroscopy of Galactic X-ray binaries, confirming prelaunch expectations. carried out a systematic analysis of IBIS/ ISGRI 15-60 keV maps of the ~ 35 ∘ × 25 ∘ central region of the Galaxy using deep observations (2 Ms total time) performed in August and September 2003 (as part of the Guest Observer Programme, complementing the Core Programme). ...
Seventeen years of hard X-ray observations with the instruments of the INTEGRAL observatory, with a focus on the Milky Way and in particular on the Galactic Centre region, have provided a unique database for exploration of the Galactic population of low-mass X-ray binaries (LMXBs). Our understanding of the diverse energetic phenomena associated with accretion of matter onto neutron stars and black holes has greatly improved. We review the large variety of INTEGRAL based results related to LMXBs. In particular, we discuss the spatial distribution of LMXBs over the Galaxy and their X-ray luminosity function as well as various physical phenomena associated with Atoll and Z sources, bursters, symbiotic X-ray binaries, ultracompact X-ray binaries and persistent black hole LMXBs. We also present an up-to-date catalogue of confirmed LMXBs detected by INTEGRAL, which comprises 166 objects. Last but not least, the long-term monitoring of the Galactic Centre with INTEGRAL has shed light on the activity of Sgr A* in the recent past, confirming previous indications that our supermassive black hole experienced a major accretion episode just ∼ 100 years ago. This exciting topic is covered in this review too.
We have analyzed a long-term database for Sco X-1 obtained with the telescope
IBIS onboard the INTEGRAL satellite in order to study the hard X-ray behavior
of Sco X-1 from 20 up to 200 keV. Besides the data used for producing of the
INTEGRAL catalog of sources, this is the longest (412 ks) database of IBIS on
Sco X-1 up to date. The production of hard X-ray tails in low-mass X-ray
binaries is still a matter of debate. Since most of the fits to the high-energy
part of the spectra are done with powerlaw models, the physical mechanism for
the hard X-ray tail production is unclear. The purpose of this study is to
better constrain those possible mechanisms. Our main result shows a strong
correlation between the fluxes in the thermal and nonthermal part of Sco X-1
spectra. We thus suggest that Comptonization of lower energy photons is the
mechanism for producing hard X-ray tails in Sco X-1.
We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE,made during INTEGRAL’s performance verification phase in 2002 November and December. Consistent with earlier results, the 3−250 keV data are well described by Comptonization spectra from a Compton corona with a temperature of kT ∼ 50−90 keV and an optical depth of τ ∼ 1.0−1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Ω/2π ∼ 0.2−0.3. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated detectors, with the remaining issues being mainly related to the flux calibration of INTEGRAL. Martinez Nuñez, Silvia, Silvia.Martinez@uv.es
We consider possible of effects of out-flowing plasma on the high-energy continuum spectra of accretion powered compact objects. We have developed an analytical formulation for the emergent spectrum of such systems, and performed model fitting on several Galactic X-ray binaries. Notably, Cyg X-3, is which is widely believed to be characterized by hot, dense circumstellar winds, provides a useful test case, Data from INTEGRAL and RXTE are included in our analysis. We further consider the possibility that the distortion of the power-law continuum above 10 keV may in some cases be explained by these spectral softening effects.
A number of recent lines of evidence point towards the presence of hot, out-flowing plasma from the central regions of compact Galactic and extragalactic X-ray sources. Additionally, it has long been noted that many of these sources exhibit an ``excess'' continuum component, above 10 keV, usually attributed to Compton Reflection from a static medium. Motivated by these facts, as well as by recent observational constraints on the Compton reflection models - specifically apparently discrepant variability timescales for line and continuum components in some cases -- we consider possible effects of out-flowing plasma on the high-energy continuum spectra of accretion powered compact objects. We present a general formulation for photon downscattering diffusion which includes recoil and Comptonization effects due to divergence of the flow. We then develop an analytical theory for the spectral formation in such systems that allows us to derive formulae for the emergent spectrum. Finally we perform the analytical model fitting on several Galactic X-ray binaries. Objects which have been modeled with high-covering-fraction Compton reflectors, such as GS1353-64 are included in our analysis. In addition, Cyg X-3, is which is widely believed to be characterized by dense circumstellar winds with temperature of order 10^6 K, provides an interesting test case. Data from INTEGRAL and RXTE covering the 3-300 keV range are used in our analysis. We further consider the possibility that the widely noted distortion of the power-law continuum above 10 keV may in some cases be explained by these spectral softening effects. Comment: 16 pages, 5 figures, accepted for publication in the Astrophysical Journal and scheduled for 1 December 2004, vol 616 issue
The possible identification by INTEGRAL of the EGRET source 3EG J1736-2908 with the active galactic nucleus GRS 1734-292 is discussed. The latter was discovered in 1990 and later identified with a Seyfert 1 galaxy. At the time of the compilation of the 3rd EGRET Catalog, it was not considered as a possible counterpart of the source 3EG J1736-2908, which remained unidentified. A detailed multiwavelength study of the EGRET error circle is presented, by including archival radio, soft- and hard-X observations, suggesting that GRS 1734-292 could be a likely counterpart of 3EG J1736-2908, even though this poses very interesting questions about the production mechanisms of gamma-rays with energies greater than 100 MeV. Comment: 6 pages, 3 figures. Accepted for publication on A&A Main Journal
Our collaboration is responsible for the study of a sample of 72 low mass X-ray binaries (LMXRB) using the INTEGRAL Core Programme data. In this paper we describe the monitoring programme we have started and the current variability and spectral results on a sample of 8 persistently bright LMXRBs hosting a neutron star (Z and Atoll sources). Current results show that among our sample of sources there seems to be no important difference in the variability of Z sources with respect to Atolls and the first colour-colour and hardness intensity diagrams built in the "traditional" energy bands display the expected patterns. Z sources seem to be harder than the bright Atolls of our sample (above 20 keV) and present no evident cut-off until about 50 keV. A hint of a non-thermal hard tail is seen in Sco X-1 with ISGRI and SPI, similarly to what was previously detected by D'Amico et al. (2001) with RXTE. These results, even if preliminary, show the importance of such a programme and the potential underlying it to understand these sources as a class.
The primary objective of the study of unidentified EGRET sources with INTEGRAL is to locate with a few arcminute accuracy the hard X-ray / soft gamma-ray counterparts within the EGRET error circle or to determine upper limits on their emission in the INTEGRAL energy range. The INTEGRAL Galactic Plane Scan (GPS) and Galactic Centre Deep Exposure (GCDE) data have been analysed and cross-correlated with the EGRET 3^rd Catalogue to search for counterparts of EGRET sources. The IBIS detection of a source within the EGRET error circle of 3EG J1736-2908 is presented and its possible identification with the active galaxy GRS 1734-292 is discussed. Finally, preliminary results on the cross-correlation between EGRET unidentified sources and the first data from the IBIS survey of the Galactic Centre are presented.
Theory and observations favor stable helium burning as the most important means to produce fuel for superbursts on neutron star surfaces. However, all known superbursters exhibit unstable burning as well. This ambiguity prompted us to search for superbursts in data from the BeppoSAX Wide Field Cameras of ten luminous LMXBs, most of which do not exhibit normal type-I X-ray bursts. We found no superbursts and determine a lower limit on the recurrence time which varies between 30 and 76 days (90% confidence). All recurrence time limits except one are longer than the observed recurrence time for GX 17+2. This difference can be understood if the mass accretion rate in GX 17+2 is several tens of percent higher than in the other sources; alternatively, the accreted material in GX 17+2 might be hydrogen deficient, leading to larger carbon yields than in the other sources. We compare our results to the latest models of superbursts. As our search method is indiscriminate of the burst ignition scenario, the recurrence time limits may also be applied to other bursts of similar duration and brightness. Comment: 8 pages, 2 figures. Accepted for publication in A&A
We present the study of one year of INTEGRAL data on the neutron star low mass X-ray binary GX 5-1. Thanks to the excellent angular resolution and sensitivity of INTEGRAL, we are able to obtain a high quality spectrum of GX 5-1 from ~5 keV to ~100 keV, for the first time without contamination from the nearby black hole candidate GRS 1758-258 above 20 keV. During our observations, GX 5-1 is mostly found in the horizontal and normal branch of its hardness intensity diagram. A clear hard X-ray emission is observed above ~30 keV which exceeds the exponential cut-off spectrum expected from lower energies. This spectral flattening may have the same origin of the hard components observed in other Z sources as it shares the property of being characteristic to the horizontal branch. The hard excess is explained by introducing Compton up-scattering of soft photons from the neutron star surface due to a thin hot plasma expected in the boundary layer. The spectral changes of GX 5-1 downward along the "Z" pattern in the hardness intensity diagram can be well described in terms of monotonical decrease of the neutron star surface temperature. This may be a consequence of the gradual expansion of the boundary layer as the mass accretion rate increases. Comment: 10 pages, 17 figures, accepted for publication in A&A
