INTEGRAL high energy behaviour of 4U 1812-12

The low mass X-ray binary system 4U 1812-12 was monitored with the INTEGRAL observatory in the period 2003-2004 and with BeppoSAX on April 20, 2000. We report here on the spectral and temporal analysis of both persistent and burst emission. The full data set confirms the persistent nature of this burster, and reveals the presence of emission up to 200 keV. The persistent spectrum is well described by a comptonization (CompTT) model plus a soft blackbody component. The source was observed in a hard spectral state with a 1-200 keV luminosity of 2*10^(36) ergs/s and L/LEdd~1% and no meaningful flux variation has been revealed, as also confirmed by a 2004 RXTE observation. We have also detected 4 bursts showing double peaked profiles and blackbody spectra with temperatures ranging from 1.9 to 3.1 keV.Comment: 6 pages, 4 figures. Accepted for publication by A&

The two INTEGRAL X-ray transients IGR J17091--3624 and IGR J17098--3628: a multi-wavelength long term campaign

IGR J17091-3624 and IGR J17098-3628 are two X-ray transients discovered by INTEGRAL and classified as possible black hole candidates (BHCs). We present here the results obtained from the analysis of multi-wavelength data sets collected by different instruments from 2005 until the end of 2007 on both sources. IGR J17098-3628 has been regularly detected by INTEGRAL and RXTE over the entire period of the observational campaign; it was also observed with pointed observations by XMM and Swift/XRT in 2005 and 2006 and exhibited flux variations not linked with the change of any particular spectral features. IGR J17091-3624 was initially in quiescence (after a period of activity between 2003 April and 2004 April) and it was then detected again in outburst in the XRT field of view during a Swift observation of IGR J17098--3628 on 2007 July 9. The observations during quiescence provide an upper limit to the 0.2-10 keV luminosity, while the observations in outburst cover the transition from the hard to the soft state. Moreover, we obtain a refined X-ray position for IGR J17091-3624 from the Swift/XRT observations during the outburst in 2007. The new position is inconsistent with the previously proposed radio counterpart. We identify in VLA archive data a compact radio source consistent with the new X-ray position and propose it as the radio counterpart of the X-ray transient.Comment: Accepted for publication in Ap

The first outburst of the black hole candidate MAXI J1836-194 observed by INTEGRAL, Swift, and RXTE

MAXI J1836-194 is a transient black-hole candidate discovered in outburst by MAXI on 30 August 2011. We report on the available INTEGRAL, Swift, and RXTE observations performed in the direction of the source during this event before 55 864 MJD. Combining the broad band (0.6-200 keV) spectral and timing information obtained from these data with the results of radio observations, we show that the event displayed by MAXI J1836-194 is another example of "failed" outburst. During the first ~20 days after the onset of the event, the source underwent a transition from the canonical low/hard to the hard intermediate state, while reaching the highest X-ray flux. In the ~40 days following the peak of the outburst, the source displayed a progressive spectral hardening and a decrease of the X-ray flux, thus it entered again the low/hard state and began its return to quiescence.Comment: Accepted for A&A Letters on 22 Dec. 201

The peculiar 2011 outburst of the black hole candidate IGR J17091−3624, a GRS 1915+105-like source?

We report on the long-term monitoring campaign of the black hole candidate IGR J17091−3624 performed with INTEGRAL and Swift during the peculiar outburst started on 2011 January. We have studied the two-month spectral evolution of the source in detail. Unlike the previous outbursts, the initial transition from the hard to the soft state in 2011 was not followed by the standard spectral evolution expected for a transient black hole binary. IGR J17091−3624 showed pseudo-periodic flare-like events in the light curve, closely resembling those observed from GRS 1915+105. We find evidence that these phenomena are due to the same physical instability process ascribed to GRS 1915+105. Finally, we speculate that the faintness of IGR J17091−3624 could be not only due to the high distance of the source but also due to the high inclination angle of the syste

Five new INTEGRAL unidentified hard X-Ray sources uncovered by Chandra

The IBIS imager on board INTEGRAL, with a sensitivity better than a mCrab in deep observations and a point source location accuracy of the order of few arcminutes, has localized so far 723 hard X-ray sources in the 17--100 keV energy band, of which a fraction of about 1/3 are still unclassified. The aim of this research is to provide sub-arcsecond localizations of the unidentified sources, necessary to pinpoint the optical and/or infrared counterpart of those objects whose nature is so far unknown. The cross-correlation between the new IBIS sources published within the fourth INTEGRAL/IBIS Survey catalogue and the CHANDRA/ACIS data archive resulted in a sample of 5 not yet identified objects. We present here the results of CHANDRA X-ray Observatory observations of these five hard X-ray sources discovered by the INTEGRAL satellite. We associated IGR J10447-6027 with IR source 2MASSJ10445192-6025115, IGR J16377-6423 with the cluster CIZA J1638.2-6420, IGR J14193-6048 with the pulsar with nebula PSR J1420-6048 and IGR J12562+2554 with the Quasar SDSSJ125610.42+260103.5. We suggest that the counterpart of IGR J12288+0052 may be an AGN/QSO type~2 at a confidence level of 90%.Comment: ApJ accepte

The 3rd IBIS/ISGRI soft gamma-ray survey catalog

In this paper we report on the third soft gamma-ray source catalog obtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRAL satellite. The scientific dataset is based on more than 40 Ms of high quality observations performed during the first three and a half years of Core Program and public IBIS/ISGRI observations. Compared to previous IBIS/ISGRI surveys, this catalog includes a substantially increased coverage of extragalactic fields, and comprises more than 400 high-energy sources detected in the energy range 17-100 keV, including both transients and faint persistent objects which can only be revealed with longer exposure times.Comment: Accepted for publication in ApJ Suppl.; 11 pages; 4 figures Minor changes to conten

3-200 keV spectral states and variability of the INTEGRAL Black Hole binary IGR J17464-3213

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studied with the three main instruments onboard INTEGRAL. The data, collected with unprecedented sensitivity in the hard X-Ray range, show a quite hard Comptonised emission from 3 keV up to 150 keV during the rising part of the source outburst, with no thermal emission detectable. A few days later, a prominent soft disk multicolour component appears, with the hard tail luminosity almost unchanged: 10-9 erg*cm-2*s-1. Two months later, during a second monitoring campaign near the end of the outburst, the observed disk component was unchanged. Conversely, the Comptonised emission from the central-hot part of the disk reduced by a factor of 10. We present here its long term behaviour in different energy ranges and the combined JEM-X, SPI and IBIS wide band spectral evolution of this source.Comment: 12 pages, 4 figures, accepted for pubblication in AP

Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a Comptonised accreting ms pulsar ?

We report the discovery of a high-energy transient with the IBIS/ISGRI detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934, was first detected on 2nd December 2004 in the routine monitoring of the IBIS/ISGRI 20--60 keV images. The observations were conducted during Galactic Plane Scans, which are a key part of the INTEGRAL Core Programme observations. After verifying the basic source behaviour, the discovery was announced on 3rd December. The transient shows a hard Comptonised spectrum, with peak energy release at about 20 keV and a total luminosity of ~ 0.9E36 erg/s in the 5--100 keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of the discovery of IGR J00291+5934, a number of observations were made by other instruments. We summarise the results of those observations and, together with the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of accreting X-ray millisecond pulsars.Comment: Accepted for publication as an A&A Letter 24/01/2005. 5 pages, 2 figure

INTEGRAL/IBIS search for e-e+ annihilation radiation from the Galactic Center Region

Electron-positron annihilation radiation from the Galactic Center region has been detected since the seventies, but its astrophysical origin is still a topic of a scientific debate. We have analyzed data of the gamma-ray imager IBIS/ISGRI onboard of ESA's INTEGRAL platform in the e$^{-}$e$^{+}$ line. During the first year of the missions Galactic Center Deep Exposure no evidence for point sources at 511 keV has been found in the ISGRI data; the $2 \sigma$ upper limit for resolved single point sources is estimated to be $1.6\times 10^{-4} ph cm^{-2} s^{-1}$.Comment: 6 pages, 3 figures; Cospar 2004. To be published in: Advances in Space Researc