M. Molina

The Third 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 data set is based on more than 40 Ms of high-quality observations performed during the first 3.5 yr 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 that can only be revealed with longer exposure times.

INTEGRAL IBIS Extragalactic Survey: Active Galactic Nuclei Selected at 20-100 keV*

Analysis of INTEGRAL Core Program and public Open Time observations performed up to April 2005 provides a sample of 62 active galactic nuclei in the 20-100 keV band above a flux limit of ∼ 1.5×10 erg cm s. Most(42) of the sources in the sample are Seyfert galaxies, almost equally divided between type 1 and 2 objects, 6 are blazars and 14 are still unclassified. Excluding the blazars, the average redshift of our sample is 0.021 while the mean luminosity is Log(L) = 43.45. We find that absorption is present in 65% of the objects with 14% of the total sample due to Compton thick active galaxies. In agreement with both Swift/BAT team results and 2-10 keV studies, the fraction of absorbed objects decreases with the 20-100 keV luminosity. All Seyfert 2s in our sample are absorbed as are 33% of Seyfert 1s. The present data highlight the capability of INTEGRAL to probe the extragalactic gamma-ray sky and to find new and/or absorbed active galaxies. Subject headings: surveys — galaxies: active — gamma rays: observations Based on observations obtained with the ESA science mission INTEGRAL IASF-Bologna/INAF, via P. Gobetti 101, 40129 Bologna, Italy; bassani@iasfbo.inaf.it, malizia@iasfbo.inaf.it, stephen@iasfbo.inaf.it School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK; molinam@astro.soton.ac.uk, ajb@astro.soton.ac.uk, ajd@astro.soton.ac.uk IASF-Roma/INAF, via del Fosso del Cavaliere 100, I-00133 Roma, Italy; bazzano@rm.iasf.cnr.it, derosa@rm.iasf.cnr.it, ubertini@rm.iasf.cnr.it CEA Saclay/DSM/DAPNIA/Sap, 91191 Gif Sur Yvette, France; flebrun@cea.fr, fil@discovery.saclay.cea.fr, belanger@hep.saclay.cea.fr INTEGRAL Science Data Center, Chemin D’Écogia 16, 1290 Versoix, Switzerland; roland.walter@obs.unige.chAnalysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL) Core Programme and public open-time observations performed up to 2005 April provides a sample of 62 active galactic nuclei in the 20-100 keV band above a flux limit of ~1.5 × 10-11 ergs cm-2 s-1. Most (42) of the sources in the sample are Seyfert galaxies, almost equally divided between type 1 and type 2 objects; six are blazars, and 14 are still unclassified. Excluding the blazars, the average redshift of our sample is 0.021, while the mean luminosity is log L = 43.45. We find that absorption is present in 65% of the objects, with 14% of the total sample due to Compton-thick active galaxies. In agreement with both Swift BAT team results and 2-10 keV studies, the fraction of absorbed objects decreases with the 20-100 keV luminosity. All Seyfert 2s in our sample are absorbed, as are 33% of Seyfert 1s. The present data highlight the capability of INTEGRAL to probe the extragalactic gamma-ray sky and to find new and/or absorbed active galaxies.

First high-energy observations of narrow-line Seyfert 1s with INTEGRAL/IBIS

Narrow-line Seyfert 1 (NLS1) galaxies are very interesting objects which display peculiar properties when compared to their broad-line analogues (BLS1). Although well studied in many wavebands, their behaviour at >10 keV is poorly studied and yet important to discriminate between models invoked to explain the complexity observed in the X-ray band. Here, we present for the first time high-energy observations (17–100 keV) of five NLS1 galaxies (three bona fide and two candidates) detected by INTEGRAL/Imager on Board INTEGRAL Satellite (IBIS) and provide for all of them a broad-band spectral analysis using data obtained by Swift/XRT below 10 keV. The combined INTEGRAL spectrum is found to be steeper (?= 2.6 ± 0.3) than those of classical Seyfert 1 objects. This is due to a high-energy cut-off, which is required in some individual fits as in the average broad-band spectrum. The location of this high-energy cut-off is at lower energies (E? 60 keV) than typically seen in classical type 1 active galactic nuclei (AGNs); a reflection component may also be present but its value (R < 0.8) is compatible with those seen in standard Seyfert 1s. We do not detect a soft excess in individual objects but only in their cumulative spectrum. Our results suggest a lower plasma temperature for the accreting plasma which combined to the high accretion rates (close to the Eddington rate) points to different nuclear conditions in broad and NLS1 galaxies, likely related to different evolutionary stages.

The broad-band XMM-Newton and INTEGRAL spectra of bright type 1 Seyfert galaxies

Aims. The 0.5–150 keV broad-band spectra of a sample of nine bright type 1 Seyfert galaxies are analyzed here. These sources have been discovered/detected by INTEGRAL and subsequently observed with XMM-Newton for the first time with high sensitivity below 10 keV. The sample, although small, is representative of the population of type 1 AGN which are now being observed above 20 keV. Methods. The intrinsic continuum has been modeled using three different parameterizations: a power-law model, an exponential cutoff power-law and an exponential cut-off power-law with a Compton reflection component. In each model the presence of intrinsic absorption, a soft component and emission line reprocessing features has also been tested. Results. A simple power-law model is a statistically good description of most of the spectra presented here; an FeK line, fully and/or partial covering absorption and a soft spectral component are detected in the majority of the sample sources. The average photon index (� Γ� = 1.7 ± 0.2) is consistent, within errors, with the canonical spectral slope often observed in AGN although the photon index distribution peaks in our case at flat Γ (∼1.5) values. For four sources, we find a significantly improved fit when the power-law is exponentially cut-off at an energy which is constrained to be below ∼150 keV. The Compton reflection parameter could be estimated in only two objects of the sample and in both cases is found to be R > 1.

INTEGRAL observations of active galactic nuclei obscured by the Galactic plane

In this paper we present INTEGRAL observations of 7 AGNs: two newly discovered type 1 Seyferts, IGR J18027-1455 and IGR J21247+5058, and five well known Seyferts, NGC 6814 (type 1.5), Cyg A (Type 2), MCG-05-23-16 (type 2), ESO 103-G035 (type2) and GRS1734-292. For IGR J18027-1455 and IGR J21247+5058 only INTEGRAL/IBIS data were available, while broadband spectra are presented and discussed for the remaining 5 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 68 14 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 3 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 diversit y in cut-off energies in the primary continuum of Seyfert galaxies.

A broad‐band spectral analysis of eight radio‐loud type 1 active galactic nuclei selected in the hard X‐ray band

Starting from a complete sample of type 1 active galactic nuclei (AGN) observed by INTEGRAL in the 20–40 keV band, we have selected a set of eight AGN which can be classified as radio-loud objects according to their 1.4 GHz power density, radio-to-hard X-ray flux density ratio and radio morphology. The sample contains six broad-line radio Galaxies and two candidate ones. Most of the objects in our sample display a double-lobe morphology, both on small and large scales. For all the objects, we present broad-band (1–110 keV) spectral analysis using INTEGRAL observations together with archival XMM–Newton, Chandra, Swift/XRT and Swift/BAT data. We constrain the primary continuum (photon index and cut-off energy), intrinsic absorption and reprocessing features (iron line and reflection) in most of the objects. The sources analysed here show remarkable similarities to radio-quiet type 1 AGN with respect to most of the parameters analysed; we only find marginal evidence for weaker reprocessing features in our objects compared to their radio-quiet counterparts. Similarly, we do not find any correlation between the spectral parameters studied and the source core dominance or radio to 20–100 keV flux density ratios, suggesting that what makes our objects radio loud has no effect on their high-energy characteristics.

THE TWO INTEGRAL X-RAY TRANSIENTS IGR J17091–3624 AND IGR J17098–3628: A MULTIWAVELENGTH 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. We present here the results obtained from the analysis of multiwavelength 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-Newton and Swift/X-ray Telescope (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.

Broad-band X-ray spectrum of the newly discovered broad-line radio galaxy IGR J21247+5058

In this paper, we present radio and high-energy observations of the INTEGRAL source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic plane. Archival Very Large Array radio data indicate that IGR J21247+5058 can be classified as an Faranoff-Riley type II Broad-Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low-energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler boosting of the base of the jet. The high-energy broad-band spectrum was obtained by combining XMM-Newton and Swift/X-Ray Telescope (XRT) observation with INTEGRAL/Image on Board Integral Satellite (IBIS) data. The 0.4-100-keV spectrum is well described by a power law, with slope r = 1.5, characterized by complex absorption due to two layers of material partially covering the source and a high-energy cut-off around 70-80 keV. Features such as a narrow iron line and a Compton reflection component, if present, are weak, suggesting that reprocessing of the power-law photons in the accretion disc plays a negligible role in the source.

Is the INTEGRAL IBIS Source IGR J17204?3554 a Gamma-Ray-emitting Galaxy Hidden behind the Molecular Cloud NGC 6334?

We report on the identification of a soft gamma-ray source, IGR J172043554, detected with IBIS, the Imager on Board the INTEGRALSatellite. The source has a 20–100 keV flux of ∼3 #10 11 ergs cm 2 s 1 and is spatially coincident with NGC 6334, a molecular cloud located in the Sagittarius arm of the Milky Way. Diffuse X-ray emission has been reported from this region by ASCA and interpreted as coming from five far-infrared cores located in the cloud. However, the combined ASCA spectrum with a 9 keV temperature was difficult to explain in terms of emission from young pre–main-sequence stars known to be embedded in the star-forming regions. Detection of gamma rays makes this interpretation even more unrealistic and suggests the presence of a highenergy source in or behind the cloud. Follow-up observations with Swift and archival Chandra data allow us to disentangle the NGC 6334 enigma by locating an extragalactic object with the proper spectral characteristics to explain the gamma-ray emission. The combined Chandra-IBIS spectrum is well fitted by an absorbed power law with G p 1.2 0.1, NH p (1.4 0.1) #10 23 cm 2 , and an unabsorbed 2–10 keV flux of 0.5 #10 11 ergs cm 2 s 1 . This column density is in excess of the Galactic value, implying that we are detecting a background galaxy concealed by the molecular cloud and further hidden by material located either in the galaxy itself or between IGR J172043554 and the cloud. Subject headings: galaxies: active — gamma rays: observations — ISM: clouds — X-rays: general Online material: color figures

An unexpected outburst from A0535+262

A0535+262 is a transient Be/X-ray binary system which was in a quiescent phase from 1994‐ 2005. In this paper we report on the timing and spectral properties of the INTEGRAL detection of the source in October 2003. The source is detected for∼6000 seconds in the 18‐100 keV energy band at a luminosity of∼3.8× 10 35 ergs s −1 ; this is compatible with the high end of the range of luminosities expected for quiescent emission. The system is observed to be outside of the centrifugal inhibition regime and pulsati ons are detected with periodicity, P=103.7± 0.1 seconds. An examination of the pulse history of the source shows that it had been in a constant state of spin-down since it entered the quiescent phase in 1994. The rate of spin-down implies the consistent presence of an accretion disk supplying torques to the pulsar. The observations show that the system is still activ e and highly variable even in the absence of recent Type I or Type II X-ray outbursts.