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The Palermo Swift-BAT hard X-ray catalogue. II. Results after 39 months of sky survey
Aims: We present the Palermo Swift-BAT hard X-ray catalogueobtained from the analysis of data acquired during the first 39 monthsof the Swift mission. Methods: We developed a dedicated softwareto perform the data reduction, mosaicking, and source detection of theBAT survey data. We analyzed the BAT dataset in three energy bands(14-150 keV, 14-30 keV, 14-70 keV), obtaining a list of 962 detectionsabove a significance threshold of 4.8 standard deviations. Theidentification of the source counterparts was pursued using threestrategies: cross-correlation with published hard X-ray catalogues,analysis of field observations of soft X-ray instruments, andcross-correlation with SIMBAD databases. Results: The surveycovers 90% of the sky down to a flux limit of 2.5×10-11 erg cm-2 s-1 and 50% ofthe sky down to a flux limit of 1.8 ×10-11 ergcm-2 s-1 in the 14-150 keV band. We derived acatalogue of 754 identified sources, of which ˜69% areextragalactic, ˜27% are Galactic objects, and ˜4% arealready known X-ray or gamma ray emitters, whose nature has yet to bedetermined. The integrated flux of the extragalactic sample is ˜1%of the cosmic X-ray background in the 14-150 keV range.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A48
| Strömgren H? Photometry of O and B Stars in Norma
This investigation presents a study of the Galactic structure toward theNorma section of the Milky Way. The field studied is located between325° and 335° Galactic longitude and -8° to 8° Galactic latitude. New observations in the uvby? system are combined with all uvby? data currently available to collate a sample of 130 O and B stars. A uniform procedure is applied to obtain the color excesses and stellardistances for all of the stars in the sample. The sample is magnitudelimited to about V=9.5 mag and contains the brightest stars of the openclusters NGC 6087 and Ly 6, the field 2158 of Loden, the OB associationNor OB1, and stars located in the directions of R 103 and R 105. Theintrinsically luminous stars in the field studied appear to be closer tothe Sun than it has previously been thought. At about 860 pc, themajority of the stars in the sample delineate a segment consistent withthe location of the Sagittarius-Carina arm as suggested in the four-armmodel representation of the grand design of the Milky Way. A small partof the sample defines the near edge of the Scutum-Crux arm at about 1.75kpc.
| Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from theInternational Gamma-Ray Astrophysics Laboratory (INTEGRAL) andSwift-Burst Array Telescope Galactic plane surveys. All the sources havea large neutral hydrogen column density and show properties consistentwith being supergiant X-ray binaries or supergiant fast X-ray transients(SFXTs), adding to the growing list of heavily absorbed XBs discoveredby INTEGRAL. Two of the sources in our sample are approximately constantflux sources, one source shows periodic variation and one sourceexhibits a short, bright X-ray outburst. The periodicity is transient,suggesting it is produced by a neutron star in an elliptical orbitpassing through a stellar wind, possibly one which is significantlyclumpy. We analyze the flaring source in several segments to look forspectral variation and discuss the implications of the findings for thenature of the source. We conclude that all four sources in our samplecan be identified as highly absorbed high mass X-ray binaries. Thisconfirms the previous identification of IGR16195-4945 and IGR16465-4507as such and reports new identifications in the cases of IGR16493-4348and SWJ2000.6+3210. We report SWJ2000.6+3210 as a newly identifiedtransient X-ray pulsar and confirm previous reports of SFXT flaringbehavior in IGR16195-4945.
| Chandra Localizations and Spectra of INTEGRAL Sources in the Galactic Plane
We report on the results of observations of hard X-ray sources in theGalactic plane with the Chandra X-Ray Observatory. The hard X-ray``IGR'' sources were discovered by the INTEGRAL satellite, and the goalsof the Chandra observations are to provide subarcsecond localizations toobtain optical and infrared counterparts and to provide constraints ontheir 0.3-10 keV spectra. We obtained relatively short, ~5 ks,observations for 20 IGR sources and find a bright Chandra source inINTEGRAL error circles in 12 cases. In 11 of these cases, across-correlation with optical and/or infrared source catalogs yields acounterpart, and the range of J-band magnitudes is 8.1-16.4. Also, infour cases, the Chandra X-ray spectra show evidence for absorbingmaterial surrounding the compact object with a column density of localmaterial in excess of 5×1022 cm-2. Weconfirm that IGR J00234+6141 is a cataclysmic variable and IGRJ14515-5542 is an active galactic nucleus (AGN). We also confirm thatIGR J06074+2205, IGR J10101-5654, IGR J11305-6256, and IGR J17200-3116are high-mass X-ray binaries (HMXBs). Our results (along with follow-upoptical spectroscopy reported elsewhere) indicate that IGR J11435-6109is an HMXB and IGR J18259-0706 is an AGN. We find that IGR J09026-4812,IGR J18214-1318, and IGR J18325-0756 may be HMXBs. In cases where we donot find a Chandra counterpart, the flux upper limits place interestingconstraints on the luminosities of black hole and neutron star X-raytransients in quiescence.
| INTEGRAL and Swift/XRT observations of the SFXT IGR J16479-4514: from quiescence to fast flaring activity
Context: The fast X-ray transient IGR J16479-4514 is known to displayflares typically lasting a few hours. Recently, its counterpart has beenidentified with a supergiant star, therefore the source can beclassified as a member of the newly discovered class of Supergiant FastX-ray Transients (SFXTs); specifically, it is the one with the highestduty cycle. Aims: Characterize the quiescent X-ray behaviour ofthe source and compare its broad band spectrum to those during fastX-ray flares. Methods: We analysed IBIS and JEM-X data with OSA5.1, along with archival Swift/XRT data. Results: We presentresults from a long-term monitoring of IGR J16479-4514 with detailedspectral and timing information on 19 bright fast X-ray flares, 10 ofwhich are newly discovered. We also report the first results on thequiescent X-ray emission. The typical luminosity value (~1034erg s-1) is about 2 orders of magnitude greater than what istypical of SFXTs, while its broad band X-ray spectrum has a shape verysimilar to the shape during fast X-ray transient activity, i.e. a rathersteep power law with ? ˜2.6. Conclusions: IGRJ16479-4514 is characterised by a quiescent X-ray luminosity higher thanwhat is typical of other known SFXTs but lower than persistent emissionfrom classical SGXBs. We suggest that this source is a kind oftransition object between these two systems, supporting the idea thatthere is a continuum of behaviour between the class of SFXTs and that ofclassical persistent SGXBs.
| Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. II. The environment of the companion star
Context: The INTEGRAL mission has led to the discovery of a new type ofsupergiant X-ray binaries (SGXBs), whose physical properties differ fromthose of previously known SGXBs. Those sources are in the course ofbeing unveiled by means of multi-wavelength X-rays, optical, near- andmid-infrared observations, and two classes are appearing. The firstclass consists of obscured persistent SGXBs and the second is populatedby the so-called supergiant fast X-ray transients (SFXTs). Aims:We report here mid-infrared (MIR) observations of the companion stars oftwelve SGXBs from these two classes in order to assess the contributionof the star and the material enshrouding the system to the totalemission. Methods: We used data from observations we carried outat ESO/VLT with VISIR, as well as archival and published data, toperform broad-band spectral energy distributions of the companion starsand fitted them with a combination of two black bodies representing thestar and a MIR excess due to the absorbing material enshrouding thestar, if there was any. Results: We detect a MIR excess in theemission of IGR J16318-4848, IGR J16358-4726, and perhaps IGRJ16195-4945. The other sources do not exhibit any MIR excess even whenthe intrinsic absorption is very high. Indeed, the stellar winds ofsupergiant stars are not suitable for dust production, and we show thatthis behaviour is not changed by the presence of the compact object.Concerning IGR J16318-4848 and probably IGR J16358-4726, the MIR excesscan be explained by their sgB[e] nature and the presence of anequatorial disk around the supergiant companion in which dust can beproduced. Moreover, our results suggest that some of the supergiantstars in those systems could exhibit an absorption excess compared toisolated supergiant stars, this excess being possibly partly due to thephotoionisation of their stellar wind in the vicinity of theiratmosphere. We also show that the differences in behaviour between theobscured SGXBs and the SFXTs in the high-energy domain do not exist fromoptical-to-MIR wavelength. Supergiant stars in SFXTs could neverthelessbe most of the time less absorbed than supergiant stars in obscuredSGXBs, due to the geometry of the systems. At last, our results confirma very dense cocoon of material around the compact object as theextinction in the X-ray domain is generally several orders of magnitudehigher than the extinction in the visible.Based onobservations carried out at the European Southern Observatoryunder programmes ID 075.D-0773 and 077.D-0721.
| Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. I. The nature of the companion star
Context: The INTEGRAL hard X-ray observatory has revealed an emergingpopulation of highly obscured X-ray binary systems throughmulti-wavelength observations. Previous studies have shown that many ofthese sources are high-mass X-ray binaries hosting neutron starsorbiting around luminous and evolved companion stars. Aims: Tobetter understand this newly-discovered population, we have selected asample of sources for which an accurate localisation is available toidentify the stellar counterpart and reveal the nature of the companionstar and of the binary system. Methods: We performed anintensive study of a sample of thirteen INTEGRAL sources, throughmulti-wavelength optical to NIR photometric and spectroscopicobservations, using EMMI and SofI instruments at the ESO NTT telescope.We performed accurate astrometry and identified candidate counterpartsfor which we give the optical and NIR magnitudes. We detected manyspectral lines allowing us to determine the spectral type of thecompanion star. We fitted with stellar black bodies the mid-infrared tooptical spectral energy distributions of these sources. From thespectral analysis and SED fitting we identified the nature of thecompanion stars and of the binary systems. Results: Throughspectroscopic analysis of the most likely candidates we found thespectral types of IGR J16320-4751, IGR J16358-4726, IGR J16479-4514, IGRJ17252-3616, IGR J18027-2016: They all host OB type supergiant companionstars, with IGR J16358-4726 likely hosting an sgB[e]. Our spectra alsoconfirm the supergiant O and B nature of IGR J17391-3021 and IGRJ19140+0951. From SED fitting we found that IGR J16418-4532 is a (likelyOB supergiant) HMXB, IGR J16393-4643 a (likely BIV-V star) HMXB, and IGRJ18483-0311 a likely HMXB system. Through accurate astrometry, werejected the proposed counterparts of IGR J17091-3624 and IGRJ17597-2201, and we discovered two new candidate counterparts for eachsource, both suggesting an LMXB from SED fitting. We confirm the AGNnature of IGR J16558-5203. Finally, we report that NIR fields of foursources of our sample exhibit large-scale regions of absorption. Conclusions: The majority of these systems are high-mass X-raybinaries hosting supergiant companion stars. We therefore confirm thatINTEGRAL reveals a dominant class of obscured and short-livedhigh-energy binary systems, and we suggest an association of thesesystems with regions of the Galaxy exhibiting large-scale absorption.Stellar population models should take these systems into account forrealistic estimates of high-energy binary systems in our Galaxy.Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere, Chile (ESO Programme073.D-0339) (PI S. Chaty). Table 8 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/484/783
| Probing clumpy stellar winds with a neutron star
Context: INTEGRAL, the European Space Agency's γ-ray observatory,tripled the number of super-giant high-mass X-ray binaries (sgHMXB)known in the Galaxy by revealing absorbed and fast transient (SFXT)systems. Aims: In these sources, quantitative constraints on thewind clumping of the massive stars could be obtained from the study ofthe hard X-ray variability of the compact accreting object. Methods: Hard X-ray flares and quiescent emission of SFXT systems havebeen characterized and used to derive wind clump parameters. Results: A large fraction of the hard X-ray emission is emitted in theform of flares with a typical duration of 3 ks, frequency of 7 days andluminosity of 1036 erg/s. Such flares are most probablyemitted by the interaction of a compact object orbiting at 10Rast with wind clumps (1022-23 g) representing alarge fraction of the stellar mass-loss rate. The density ratio betweenthe clumps and the inter-clump medium is 102-4 in SFXTsystems. Conclusions: The parameters of the clumps and of theinter-clump medium, derived from the SFXT flaring behavior, are in goodagreement with macro-clumping scenario and line driven instabilitysimulations. SFXT have probably a larger orbital radius than classicalsgHMXB.
| INTEGRAL/IBIS all-sky survey in hard X-rays
We present results of an all-sky hard X-ray survey based on almost fouryears of observations with the IBIS telescope onboard the INTEGRALobservatory. The dead time-corrected exposure of the survey is ~33 Ms.Approximately 12% and 80% of the sky has been covered to limiting fluxeslower than 1 and 5 mCrab, respectively. Our catalog of detected sourcesincludes 403 objects, 316 of which exceed a 5σ detection thresholdon the time-averaged map of the sky, and the rest were detected invarious subsamples of exposures. Among the identified sources, 219 areGalactic (90 low-mass X-ray binaries, 76 high-mass X-ray binaries, 21cataclysmic variables, 6 coronally active stars, and other types) and137 are extragalactic, including 130 active galactic nuclei (AGNs) and 3galaxy clusters. We derived number-flux functions of AGNs and Galacticsources. The log N-log S relation of non-blazar AGNs is based on 68sources located at Galactic latitudes |b| > 5°, where the surveyis characterized by high identification completeness, with fluxes higherthan S_lim = 1.1 × 10-11 erg s-1cm-2(~0.8 mCrab) in the 17-60 keV energy band. The cumulativeAGN number-flux function can be described by a power law with a slope of1.62 ± 0.15 and normalization of (5.7±0.7) ×10-3 sources per deg2 at fluxes > 1.43 ×10-11 erg s-1 cm-2(>1 mCrab). ThoseAGNs with fluxes higher than S_lim make up ~1% of the cosmic X-raybackground at 17-60 keV. We present evidence of strong inhomogeneity inthe spatial distribution of nearby (⪉70 Mpc) AGNs, which reflectsthe large-scale structure in the local Universe.Based on observations with INTEGRAL, an ESA project with the instrumentsand science data center funded by ESA member states (especially the PIcountries: Denmark, France, Germany, Italy, Switzerland, Spain), CzechRepublic, and Poland, and with the participation of Russia and the USA.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/775
| HESS J1616-508: likely to be powered by PSR J1617-5055
HESS J1616-508 is one of the brightest emitters in the TeV sky. Recentobservations with the IBIS/ISGRI telescope onboard the INTEGRALspacecraft have revealed that a young, nearby and energetic pulsar, PSRJ1617-5055, is a powerful emitter of soft ?-rays in the 20-100 keVdomain. In this paper, we present an analysis of all available data fromthe INTEGRAL, Swift, BeppoSAX and XMM-Newton telescopes with a view toassessing the most likely counterpart to the High Energy StereoscopicSystem (HESS) source. We find that the energy source that fuels theX/?-ray emissions is derived from the pulsar, both on the basis ofthe positional morphology, the timing evidence and the energetics of thesystem. Likewise the 1.2 per cent of the pulsar's spin-down energy lossneeded to power the 0.1-10 TeV emission is also fully consistent withother HESS sources known to be associated with pulsars. The relativesizes of the X/?-ray and very high energy sources are consistentwith the expected lifetimes against synchrotron and Compton losses for asingle source of parent electrons emitted from the pulsar. We find thatno other known object in the vicinity could be reasonably considered asa plausible counterpart to the HESS source. We conclude that there isgood evidence to assume that the HESS J1616-508 source is driven by PSRJ1617-5055 in which a combination of synchrotron and inverse-Comptonprocesses combine to create the observed morphology of a broad-bandemitter from keV to TeV energies.
| The Third IBIS/ISGRI Soft Gamma-Ray Survey Catalog
In this paper we report on the third soft gamma-ray source catalogobtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRALsatellite. The scientific data set is based on more than 40 Ms ofhigh-quality observations performed during the first 3.5 yr of CoreProgram and public IBIS/ISGRI observations. Compared to previousIBIS/ISGRI surveys, this catalog includes a substantially increasedcoverage of extragalactic fields, and comprises more than 400high-energy sources detected in the energy range 17-100 keV, includingboth transients and faint persistent objects that can only be revealedwith longer exposure times.Based on observations with INTEGRAL, an ESA project with instruments andscience data center funded by ESA member states (especially the PIcountries: Denmark, France, Germany, Italy, Switzerland, Spain), CzechRepublic, and Poland, and with the participation of Russia and the USA.
| A description of sources detected by INTEGRAL during the first 4 years of observations
Context: In its first 4 years of observing the sky above 20 keV,INTEGRAL-ISGRI has detected 500 sources, around half of which are new orunknown at these energies. Follow-up observations at other wavelengthsrevealed that some of these sources feature unusually large columndensities, long pulsations, and other interesting characteristics. Aims: We investigate where new and previously-known sources detected byISGRI fit in the parameter space of high-energy objects, and we use theparameters to test correlations expected from theoretical predictions.For example, the influence of the local absorbing matter on periodicmodulations is studied for Galactic High-Mass X-ray Binaries (HMXBs)with OB supergiant and Be companions. We examine the spatialdistribution of different types of sources in the Milky Way usingvarious projections of the Galactic plane, in order to highlightsignatures of stellar evolution and to speculate on the origin of thegroup of sources whose classifications are still uncertain. Methods:Parameters that are available in the literature, such as positions,photoelectric absorption (NH), spin and orbital periods, anddistances or redshifts, were collected for all sources detected byISGRI. These values and their references are provided online. Results:ISGRI has detected similar numbers of X-ray Binaries and Active GalacticNuclei (AGN). The former group contains new members of the class ofHMXBs with supergiant stellar companions. Usually, this type of objectpresents strong intrinsic absorption which leads to a peak emission inan energy range that ISGRI is ideally suited to detect. Thanks to theseadditional systems, we are able to show that HMXBs are generallysegregated in plots of intrinsic NH versus the orbital periodof the system and versus the spin period of the pulsar, based on whetherthe companion is a Be or an OB supergiant star. We also find a tentativebut expected anti-correlation between NH and the orbitalperiod, and a possible and unexpected correlation between theNH and the spin period. While only a handful of new Low-MassX-ray Binaries (LMXBs) have been discovered, there are many sources thatremain unclassified and they appear to follow a spatial distributiontypical of Galactic sources (especially LMXBs) rather than extragalacticsources.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Identifications of Four INTEGRAL Sources in the Galactic Plane via Chandra Localizations
Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite isuncovering large numbers of 20-100 keV ``IGR'' sources. We presentresults from Chandra, INTEGRAL, optical, and IR observations of four IGRsources: three sources in the Norma region of the Galaxy (IGRJ16195-4945, IGR J16207-5129, and IGR J16167-4957) and one that iscloser to the Galactic center (IGR J17195-4100). In all four cases, onerelatively bright Chandra source is seen in the INTEGRAL error circle,and these are likely to be the soft X-ray counterparts of the IGRsources. They have hard 0.3-10 keV spectra with power-law photon indicesof Γ=0.5-1.1. While many previously studied IGR sources show highcolumn densities (NH~1023-1024cm-2), only IGR J16195-4945 has a column density that couldbe as high as 1023 cm-2. Using optical and IR skysurvey catalogs and our own photometry, we have obtained identificationsfor all four sources. The J-band magnitudes are in the range 14.9-10.4,and we have used the optical/IR spectral energy distributions (SEDs) toconstrain the nature of the sources. Blackbody components withtemperature lower limits of >9400 K for IGR J16195-4945 and>18,000 K for IGR J16207-5129 indicate that these are very likelyhigh-mass X-ray binaries (HMXBs). However, for IGR J16167-4957 and IGRJ17195-4100, low extinction and the SEDs indicate later spectral typesfor the putative companions, suggesting that these are not HMXBs.
| A Comprehensive Search for Gamma-Ray Lines in the First Year of Data from the INTEGRAL Spectrometer
We have carried out an extensive search for gamma-ray lines in the firstyear of public data from the spectrometer (SPI) on the INTEGRAL mission.INTEGRAL has spent a large fraction of its observing time in theGalactic plane with particular concentration in the Galactic center (GC)region (~3 Ms in the first year). Hence the most sensitive searchregions are in the Galactic plane and center. The phase space of thesearch spans the energy range 20-8000 keV and line widths from 0 to 1000keV (FWHM). It includes both diffuse and pointlike emission. We havesearched for variable emission on timescales down to ~1000 s. Diffuseemission has been searched for on a range of different spatial scalesfrom ~20° (the approximate field of view of the spectrometer) up tothe entire Galactic plane. Our search procedures were verified by therecovery of the known gamma-ray lines at 511 and 1809 keV at theappropriate intensities and significances. We find no evidence for anypreviously unknown gamma-ray lines. The upper limits range from afew×10-5 to a few×10-2 cm-2s-1 depending on line width, energy, and exposure; regions ofstrong instrumental background lines were excluded from the search.Comparison is made between our results and various prior predictions ofastrophysical lines.
| Unveiling Supergiant Fast X-Ray Transient Sources with INTEGRAL
Supergiant high-mass X-ray binaries (SGXBs) are believed to be rareobjects, as stars in the supergiant phase have a very short lifetime andto date only about a dozen of them have been discovered. They are knownto be persistent and bright X-ray sources. INTEGRAL is changing thisclassical picture, as its observations are revealing the presence of anew subclass of SGXBs that have been labeled supergiant fast X-raytransients (SFXTs), since they are strongly characterized by fast X-rayoutbursts lasting less than a day, typically a few hours. We report onIBIS detections of newly discovered fast X-ray outbursts from 10sources, four of which have been recently optically identified assupergiant high-mass X-ray binaries. For one of them in particular, IGRJ11215-5952, we observe fast X-ray transient behavior for the firsttime. The remaining six sources (IGR J16479-4514, IGR J16418-4532, IGRJ16195-4945=AX J161929-4945, XTE J1743-363, AX J1749.1-2733, and IGRJ17407-2808) are still unclassified; however, they can be consideredcandidate SFXTs because of their similarity to the known SFXTs.
| GMRT observations of the field of INTEGRAL X-ray sources. II
We conducted low-frequency radio observations with the Giant MetrewaveRadio Telescope (GMRT) of the 40 new hard X-ray sources discovered bythe INTEGRAL satellite. This survey was conducted in order to studyradio emissions from these sources, to provide precise position, and toidentify new microquasar candidates. Our observations show that 24 ofthe X-ray sources have radio candidates within the INTEGRAL errorcircle. Based on the radio morphology, variability, and informationavailable from different wavelengths, we categorize them as seventeenGalactic sources (4 unresolved, 7 extended, 6 extended sources indiffuse regions) and seven extragalactic sources (2 unresolved, 5extended). A detailed account of seventeen of these sources waspresented in an earlier paper. Based on the radio data for the remainingsources at 0.61 GHz and on the available information from NVSS, DSS,2MASS, and NED, we have identified possible radio counterparts for thehard X-ray sources. The three unresolved sources, i.e., IGR J17303-0601,IGR J17464-3213, and IGR J18406-0539, are discussed in detail. Thesesources have been associated with compact sources that are variable inradio and X-rays. The remaining fourteen sources have an extended radiomorphology and either are diffuse Galactic regions or have anextragalactic origin.
| Optical Spectroscopy of the IGR J16195-4945 Candidate Counterpart
On 2005 October 5, we observed the candidate optical counterpart of theINTEGRAL source IGR J16195-4945 with the EMMI spectrograph attached tothe ESO 3.5m NTT in La Silla, Chile (see Tomsick et al. 2006; astro-ph/0603810 v2 and references therein for the details about this likelyHigh-Mass X-ray Binary). The Chandra position of IGR J16195-4945coincides with the infrared source 2MASS J16193220-4944305 (Ks =11.00).
| The Second IBIS/ISGRI Soft Gamma-Ray Survey Catalog
In this paper we report the second soft gamma-ray source catalogobtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRALsatellite. The scientific data set is based on more than 10 Ms ofhigh-quality observations performed during the first 2 years of CoreProgram and public IBIS/ISGRI observations, and covers ~50% of the wholesky. The main aim of the first survey was to scan systematically, forthe first time at energies above 20 keV, the whole Galactic plane toachieve a limiting sensitivity of ~1 mcrab in the central radian. Thetarget of the second year of the INTEGRAL mission lifetime was to expandas much as possible our knowledge of the soft gamma-ray sky, with thesame limiting sensitivity, to at least 50% of the whole sky, mainly byincluding a substantial coverage of extragalactic fields. This catalogcomprises more than 200 high-energy sources detected in the energy range20-100 keV, including new transients not active during the first year ofoperation, faint persistent objects revealed with longer exposure time,and several Galactic and extragalactic sources in sky regions notobserved in the first survey. The mean position error for all thesources detected with significance above 10 σ is ~40", enough toidentify most of them with a known X-ray counterpart and to unveil thenature of most of the strongly absorbed ones, even though they are verydifficult to detect in X-rays.Based on observations with INTEGRAL, an ESA project with instruments andscience data center funded by ESA member states (especially the PIcountries: Denmark, France, Germany, Italy, Switzerland, Spain), CzechRepublic, and Poland, and with the participation of Russia and the USA.
| INTEGRAL insight into the inner parts of the Galaxy. High mass X-ray binaries
Since its launch INTEGRAL has devoted a significant fraction of itsobserving time to the Galactic plane region. We present the results ofINTEGRAL observations of the inner spiral arms of the Galaxy (Norma,Scutum and Sagittarius) with attention to high mass X-ray binaries. Theincreased sensitivity of the survey and possibility to detect absorbedsources significantly enlarged our sample of HMXBs in comparison withprevious studies. For some absorbed sources we present for the firsttime high quality broadband (1-100 keV) energy spectra. We confirmpulsations of the X-ray flux of IGR J16358-4726, discovered by CHANDRA,and report discovery of pulsations with a period of 228±6 s fromIGR J16465-4507. We confirm that the Galactic high mass X-ray binarydistribution is significantly different from the distribution of lowmass X-ray binaries concentrated in the Galactic Center. A largefraction of detected high mass X-ray binaries are absorbed sources.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| The soft X-ray counterpart of the newly discovered INTEGRAL source IGR J16195-4945
The INTEGRAL satellite, during its regular scanning observations of theGalactic plane, has discovered several new X-ray sources emitting above20 keV. The nature of the great majority of them is still unknown. Herewe report on the likely low energy counterpart, observed with ASCA in1994 and 1997, of one of these sources, IGR J16195-4945. The ASCA sourceis faint (F2-10 keV˜10-11 ergcm-2 s-1), highly absorbed(N_H˜1023 cm-2) and has a rather hardspectrum (photon index ˜ 0.6). These spectral properties aresuggestive of a neutron star in a High Mass X-ray Binary. Our analysisof all the public INTEGRAL data of IGR J16195-4945 shows that thissource is variable and was in a high state with a 20-40 keV flux of˜17 mCrab in two occasions in March 2003.
| The First IBIS/ISGRI Soft Gamma-Ray Galactic Plane Survey Catalog
We report the first high-energy survey catalog obtained with the IBISgamma-ray imager on board INTEGRAL. The analysis has been performed onthe first-year Core Program ISGRI data comprising both Galactic PlaneScan and Galactic Centre Deep Exposure pointings for a total exposuretime exceeding 5 Ms. This initial survey has revealed the presence of~120 sources detected with the unprecedented sensitivity of ~1 mcrab inthe energy range 20-100 keV. Each source is located to an accuracybetween 1' and 3', depending on its brightness. The outstanding IBIScapability to locate soft γ-ray emitters has allowed us toidentify most of the detected sources with already known Galactic X-raybinary systems, while 28 of the objects are of unknown nature.Based on observations with INTEGRAL, an ESA project with instruments andscience data centre funded by ESA member states (especially the PIcountries: Denmark, France, Germany, Italy, Switzerland, and Spain), theCzech Republic and Poland, and with the participation of Russia and theUS.
| 14 New Unidentified INTEGRAL Sources
We report the detection of 14 new unidentified hard X-ray sources by theIBIS/ISGRI instrument onboard INTEGRAL. The sources have been detectedin all-sky mosaics built from data of the INTEGRAL core programaccumulated between February 27 and October 19, 2003.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Determination of R_V towards galactic O stars
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 35 O stars. The results arecombined with measurements from the literature for 60 stars to study thebehaviour of RV with heliocentric distance. RV isthe single basic parameter which characterizes the interstellarextinction from the near-infrared to the far-UV spectral region. Theabsolute extinction AV, from which RV is derived,is best determined by optical and near-infrared photometry (Cardelli etal. \cite{r3}). We consider important the derivation of RVwith the same technique in the direction of as many as possible galacticO stars.
| Faint X-Ray Sources Resolved in the ASCA Galactic Plane Survey and Their Contribution to the Galactic Ridge X-Ray Emission
The X-ray emission from the central region of the Galactic plane,|l|<~45° and |b|<~0.4d, was studied in the 0.7-10 keV energyband with a spatial resolution of ~3' with the Advanced Satellite forCosmology and Astrophysics (ASCA) observatory. We developed a newanalysis method for the ASCA data to resolve discrete sources from theextended Galactic ridge X-ray emission (GRXE). We successfully resolved163 discrete sources with an X-ray flux down to 10-12.5 ergscm-2 s-1 and determined the intensity variationsof the GRXE as a function of the Galactic longitude with a spatialresolution of about 1°. The longitudinal intensity variation in theenergy band above 4 keV, for which there is little absorption in theGalactic plane, shows a large enhanced feature within |l|<~30°.This suggests a strong enhancement of X-ray emissivity of the GRXEinside the 4 kpc arm of the Galaxy. Searches for identifications of theresolved X-ray sources with cataloged X-ray sources and optical starsshow that the 66% are unidentified. Spectral analysis of each sourceshows that a large number of the unidentified sources have hard X-rayspectra obscured by the Galactic interstellar medium. We classified thesources into several groups by the flux, the hardness and the softnessof the spectra, and performed further detailed analysis for the spectrasummed within each group. Possible candidates of X-ray origins of theseunidentified sources are discussed based on the grouping spectralanalysis. Also, we derived the logN-logS relations of the resolvedsources in the energy bands below and above 2 keV separately. ThelogN-logS relation of the Galactic X-ray sources above 2 keV wasobtained for the first time with this study. It is represented by apower-law with an index of -0.79+/-0.07 after correction for thecontribution of extragalactic X-ray sources. This flat power-lawrelation suggests that the spatial distribution of the X-ray sourcesshould have an armlike structure in which the solar system is included.The integrated surface brightness of the resolved sources is about 10%of the total GRXE in both energy bands. The approximately 90% of theemission remaining is still unresolved.
| Observations of OB-stars at the former Leiden Southern Station
About 700 stars, mostly OB-stars, were observed by the author at theformer Leiden Southern Station at Hartebeespoortdam, South Africa, inthe observing seasons 1965, 1968, 1969, 1974, 1977, 1978. Observationswere made in the five channels of the Walraven photometric system. Dueto weathering of the telescope mirror the W channel gave no reliableresults for the faintest stars (m = 11 mag); in these cases the U-Wcolour index is not given. The change in sensitivity in the V channel,supposedly having occurred in 1968, was not recognised. Table~5 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/527
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.Table~1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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