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Distribution of High-mass X-Ray Binaries in the Milky Way
Observations of the high-energy sky, particularly with the INTEGRALsatellite, have quadrupled the number of supergiant X-ray binariesobserved in the Galaxy and revealed new populations of previously hiddenhigh-mass X-ray binaries (HMXBs), raising new questions about theirformation and evolution. The number of detected HMXBs of different typesis now high enough to allow us to carry out a statistical analysis oftheir distribution in the Milky Way. For the first time, we derive thedistance and absorption of a sample of HMXBs using a spectral energydistribution fitting procedure, and we examine the correlation with thedistribution of star-forming complexes (SFCs) in the Galaxy. We showthat HMXBs are clustered with SFCs with a typical cluster size of 0.3± 0.05 kpc and a characteristic distance between clusters of 1.7± 0.3 kpc. Furthermore, we present an investigation of theexpected offset between the position of spiral arms and HMXBs, allowingus to constrain age and migration distance due to supernova kick for 13sources. These new methods will allow us to assess the influence of theenvironment on these high-energy objects with unprecedented reliability.
| Clustering between High-mass X-Ray Binaries and OB Associations in the Milky Way
We present the first direct measurement of the spatial cross-correlationfunction of high-mass X-ray binaries (HMXBs) and active OB star-formingcomplexes in the Milky Way. This result relied on a sample containing 79hard X-ray-selected HMXBs and 458 OB associations. Clustering betweenthe two populations is detected with a significance above 7? fordistances <1 kpc. Thus, HMXBs closely trace the underlyingdistribution of the massive star-forming regions that are expected toproduce the progenitor stars of HMXBs. The average offset of 0.4± 0.2 kpc between HMXBs and OB associations is consistent withbeing due to natal kicks at velocities of the order of 100 ± 50km s-1. The characteristic scale of the correlationfunction suggests an average kinematical age (since the supernova phase)of ~4 Myr for the HMXB population. Despite being derived from a globalview of our Galaxy, these signatures of HMXB evolution are consistentwith theoretical expectations as well as observations of individualobjects.
| Finding Persistent Sources with the BeppoSAX/Wide Field Camera: An In-depth Analysis
During the operational life of the Italian/Dutch X-ray satellite(1996-2002), BeppoSAX, its two Wide Field Cameras (WFCs) performedobservations that covered the full sky at different epochs. Although themajority of analysis performed on BeppoSAX WFC data concentrated on thedetection of transient sources, we have now applied the same techniquesdeveloped for the INTEGRAL/IBIS survey to produce the same work with theBeppoSAX WFC data. This work represents the first unbiased source listcompilation produced from the overall WFC data set optimized for faintpersistent source detection. This approach recovered 182 more sourcescompared to the previous WFC catalog reported in Verrecchia et al. Thecatalog contains 404 sources detected between 3 and 17 keV, 10 of whichare yet to be seen by the new generation of telescopes.
| INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey. II. Catalog of sources
This paper is the second in a series devoted to the hard X-ray (17-60keV) whole sky survey performed by the INTEGRAL observatory over sevenyears. Here we present a catalog of detected sources that includes 521objects, 449 of which exceed a 5? detection threshold on thetime-averaged map of the sky, and 53 were detected in various subsamplesof exposures. Among the identified sources with known and suspectednature, 262 are Galactic (101 low-mass X-ray binaries, 94 high-massX-ray binaries, 37 cataclysmic variables, and 30 of other types) and 221are extragalactic, including 217 active galactic nuclei (AGNs) and 4galaxy clusters. The extragalactic (|b|>5°) and Galactic (|b|<5°) persistently detected source samples have high identificationcompleteness (respectively ~96% and ~93%) and are valuable forpopulation studies.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, Spain), CzechRepublic, and Poland, and with the participation of Russia and theUSA.Table 2 is also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/523/A61
| The catalog of variable sources detected by INTEGRAL. I. Catalog and techniques
Context. During its 6 years of operation, INTEGRAL/ISGRI has detectedmore than 500 sources. Many of these sources are variable. Taking intoaccount that nearly half of INTEGRAL/ISGRI sources are new and many ofthem remain unidentified, the variability properties of the sources canprovide additional constraints to help us to classify and identify theunknown sources. Aims: To study the variability properties of thesources detected by INTEGRAL/ISGRI, we develop a method to quantify thevariability of a source. We describe here our techniques and compile acatalog of the sources that fit our criteria of variability. Methods: We use the natural time binning of INTEGRAL observations calledScience Window (? 2000 s) and test the hypothesis that the detectedsources are constant using a ?^2 all-sky map in three energy bands(20-40, 40-100, 100-200 keV). We calculate an intrinsic variance of theflux in individual pixels and use it to define the fractionalvariability of a source. The method is sensitive to the sourcevariability on timescales of one Science Window and higher. Weconcentrate only on the sources that were already reported to bedetected by INTEGRAL. Results: We present a catalog of 202sources found to be significantly variable. For the catalog sources, wegive the measure of variability and fluxes with corresponding errors inthe 20-40, 40-100 and 100-200 keV energy bands, and we present somestatistics about the population of variable sources. The description ofthe physical properties of the variable sources will be given in aforthcoming paper.Table 3 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A68
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| The 22 Month Swift-BAT All-Sky Hard X-ray Survey
We present the catalog of sources detected in the first 22 months ofdata from the hard X-ray survey (14-195 keV) conducted with the BurstAlert Telescope (BAT) coded mask imager on the Swift satellite. Thecatalog contains 461 sources detected above the 4.8? level withBAT. High angular resolution X-ray data for every source from Swift-XRTor archival data have allowed associations to be made with knowncounterparts in other wavelength bands for over 97% of the detections,including the discovery of ~30 galaxies previously unknown as activegalactic nuclei and several new Galactic sources. A total of 266 of thesources are associated with Seyfert galaxies (median redshift z ~ 0.03)or blazars, with the majority of the remaining sources associated withX-ray binaries in our Galaxy. This ongoing survey is the first uniformall-sky hard X-ray survey since HEAO-1 in 1977. Since the publication ofthe nine-month BAT survey we have increased the number of energychannels from four to eight and have substantially increased the numberof sources with accurate average spectra. The BAT 22 month catalog isthe product of the most sensitive all-sky survey in the hard X-ray band,with a detection sensitivity (4.8?) of 2.2 ×10-11 erg cm-2 s-1 (1 mCrab) over mostof the sky in the 14-195 keV band.
| 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
| The Fourth IBIS/ISGRI Soft Gamma-ray Survey Catalog
In this paper, we report on the fourth soft gamma-ray source catalogobtained with the IBIS gamma-ray imager on board the INTEGRAL satellite.The scientific data set is based on more than 70 Ms of high-qualityobservations performed during the first five and a half years of theCore Program and public observations. Compared to previous IBIS surveys,this catalog includes a substantially increased coverage ofextragalactic fields, and comprises more than 700 high-energy sourcesdetected in the energy range 17-100 keV, including both transients andfaint persistent objects that can only be revealed with longer exposuretimes. A comparison is provided with the latest Swift/BAT surveyresults.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, Spain), CzechRepublic, and Poland, and with the participation of Russia and the USA.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| 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
| A probable accretion-powered X-ray pulsar in IGR J00370+6122
Serendipitous and dedicated observations with the Rossi X-ray TimingExplorer (RXTE) and the International Gamma-Ray Astrophysics Laboratory(INTEGRAL) were analyzed to study the transient high-mass X-ray binaryIGR J00370+6122, in particular to search for an accretion-powered pulsaras companion to the optically identified (Reig et al. 2005, A&A,440, 637) B0.5 II-III donor star. Highly variable fluxes were measuredin the RXTE data during outbursts of up to 2.2 × 10-10erg cm-2 s-1 (3-20 keV; averaged over 1 h). Duringa 1-h time span with RXTE flaring activity was detected with anoscillating signal repeating 7 times. Epoch folding reveals a 346± 6 s period. We propose that this is the period of the putativepulsar. This measurement puts the source in the wind-fed accretionregion of the P_orb (=15.7 d) versus P_pulse “Corbet”diagram. The 3 to 60 keV flare spectrum was modeled with an absorbedpower law and the absorption column was found to be 15-20 times largerthan the interstellar value and the value obtained for the opticalcounterpart, suggesting an accretor embedded in the wind of the donorstar.
| 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.
| Three new hard X-ray sources in the Cassiopeia/Perseus region discovered by INTEGRAL
In an ultra-deep INTEGRAL exposure (4.1 Ms) on the Cassiopeia region,resulting from the combination of observations performed betweenDecember 12, 2003 and January 10, 2006 (INTEGRAL revolutions 142-396),two new hard X-ray sources have been detected: IGR J00335+6126 and IGRJ00254+6822. A deep 1.9 Ms INTEGRAL mosaic centered on gamma-ray binaryLS I+61 303 using observations performed between March 3, 2003 and July4, 2006 (INTEGRAL revolutions 47 and 454) revealed the presence of apreviously unknown hard X-ray source, IGR J02501+5440.
| 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.
| 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.
| INTEGRAL survey of the Cassiopeia region in hard X rays
We report on the results of a deep 1.6 Ms INTEGRAL observation of theCassiopeia region performed from December 2003 to February 2004. Elevensources were detected with the imager IBIS-ISGRI at energies above 20keV, including three new hard X-ray sources. Most remarkable is thediscovery of hard X-ray emission from the anomalous X-ray pulsar 4U0142+61, which shows emission up to ~150 keV with a very hard power-lawspectrum with photon index Γ = 0.73 ± 0.17. We derived fluxupper limits for energies between 0.75 MeV and 30 MeV using archivaldata from the Compton telescope COMPTEL. In order to reconcile the veryhard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upperlimits, the spectrum has to bend or break between ~75 keV and ~750 keV.1E 2259+586, another anomalous X-ray pulsar in this region, was notdetected. INTEGRAL and COMPTEL upper limits are provided. The newINTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGRJ00370+6122 is a new supergiant X-ray binary with an orbital period of15.665 ± 0.006 days, derived from RXTE All-Sky Monitor data.Archival BeppoSAX Wide-Field Camera data yielded four more detections.IGR J00234+6144 still requires a proper identification. Other sourcesfor which INTEGRAL results are presented are high-mass X-ray binaries 2S0114+650, γ Cas, RX J0146.9+6121 and 4U 2206+54, intermediatepolar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each ofthese sources the hard X-ray spectra are fitted with different modelsand compared with earlier published results.
| A Systematic Search for Periodicities in RXTE ASM Data
We present the results of a systematic search in 8.5 yr of Rossi X-RayTiming Explorer All-Sky Monitor data for evidence of periodicities. Thesearch was conducted by application of the Lomb-Scargle periodogram tothe light curves of each of 458 actually or potentially detected sourcesin each of four energy bands (1.5-3, 3-5, 5-12, and 1.5-12 keV). Awhitening technique was applied to the periodograms before evaluation ofthe statistical significance of the powers. We discuss individualdetections with a focus on relatively new findings.
| 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.
| Identification of the optical counterparts of high-mass X-ray binaries through optical photometry and spectroscopy
We present the results of our search for optical counterparts tohigh-mass X-ray transient sources discovered by various X-ray missions.We obtained CCD images of the X-ray fields through BVR and Hαfilters to identify early-type stars in the R-Hα versus B-Vcolour-colour diagram. We also obtained medium-resolution spectroscopyof the candidates in order to confirm the presence of Hα emissionand perform spectral classification. We report on the discovery of theoptical counterparts to two X-ray sources: XTEJ1858+034 and IGR J01363+6610, and thefollow-up observations of another two, newly identified by our group:SAX J2103.5+4545 and GRO J2058+42.For another source, IGR J00370+6122, we present thefirst detailed optical spectral analysis. The optical photometry andspectroscopy reveal B-type companions in all five sources; GROJ2058+42, SAX J2103.5+4545 and IGRJ01363+6610 are positively identified with Be/X-ray binaries,IGR J00370+6122 with a supergiant X-ray binary, whilethe nature of the XTE J1858+034 is uncertain. We alsostudy the relationship between the optical and X-ray emission duringquiescent states.
| Radio observations of BD +60 73 = IGR J00370+6122
We report Very Large Array (VLA) D-configuration observations ofrecently discovered High Mass X-ray Binary IGR J00370+6122 = BD +60 73(ATEL #281, #282, #285). Data taken by the VLA Summer Students on 9 July2004, from 16:58 to 18:58 UT, show no detections at the frequencieslisted below with the nominal flux densities measured at the position ofBD +60 73. 1.46 GHz: 0.34 +/- 0.23 mJy/beam 4.86 GHz:0.055 +/- 0.044 mJy/beam 8.46 GHz: 0.081 +/- 0.033mJy/beam 22.46 GHz: 0.44 +/- 0.20 mJy/beam Errorbars are 1 sigma.
| Bd +60 73 = Igr J00370+6122
A classification spectrum of BD +60 73, reported to be the opticalcounterpart to IGR J00370+6122 (ATel #281), was taken on the night of2003 July 7th with the 2.5-m Issac Newton telescope at La Palma. Thederived spectral type is BN0.5II-III, where the composite luminosityclass indicates an intermediate luminosity. The Nitrogen enhancement ismoderately high, with numerous NII lines being rather stronger thancorresponds to the spectral type.
| Optical Identification of 1RXS J003709.6+612131 with BD+60 73
Further to the association of 1RXS J003709.6+612131 with the V=9.7 B1Ibstar BD+60 73 (ATel #281): This X-ray source has been previouslyidentified with BD+60 73, with a probability of a unique identificationof 99.7% (Rutledge et al 2000 ). The probability was derived usingstatistical association.
| IGR J00370+6122 - A new high-mass X-ray binary
We report the discovery of a new variable hard X-ray source, IGRJ00370+6122, in a 1.2 Ms INTEGRAL observation of the Cassiopeia regionin Dec 2003. The source was found twice while analyzing the data instretches of ~200 ks. It has a maximum significance of 11.2 sigma in anINTEGRAL IBIS/ISGRI map for the 20-60 keV energy band between MJD53000.29 and 53002.86.
| 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.
| 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.
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| A spectral survey of early-type stars in the region of Cassiopeia using an objective prism
Not Available
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