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Register a new userChandra Localizations and Spectra of INTEGRAL Sources in the Galactic Plane
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We report on the results of observations of hard X-ray sources in the Galactic plane with the Chandra X-ray Observatory. The hard X-ray IGR sources were discovered by the INTEGRAL satellite, and the goals of the Chandra observations are to provide sub-arcsecond localizations to obtain optical and infrared counterparts and to provide constraints on their 0.3-10 keV spectra. We obtained relatively short, ~5 ks, observations for 20 IGR sources and find a bright Chandra source in INTEGRAL error circles in 12 cases. In 11 of these cases, a cross-correlation with optical and/or infrared source catalogs yields a counterpart, and the range of J-band magnitudes is 8.1-16.4. Also, in 4 cases, the Chandra X-ray spectra show evidence for absorbing material surrounding the compact object with a column density of local material in excess of 5x10^22 cm^-2. We confirm that IGR J00234+6141 is a Cataclysmic Variable and IGR J14515-5542 is an Active Galactic Nucleus (AGN). We also confirm that IGR J06074+2205, IGR J10101-5645, IGR J11305-6256, and IGR J17200-3116 are High Mass X-ray Binaries (HMXBs). Our results (along with follow-up optical spectroscopy reported elsewhere) indicate that IGR J11435-6109 is 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 do not find a Chandra counterpart, the flux upper limits place interesting constraints on the luminosities of black hole and neutron star X-ray transients in quiescence.
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We report on 0.3-10 keV X-ray observations by the Chandra X-ray Observatory of the fields of 22 sources that were discovered as hard X-ray (20-100 keV) sources by the INTEGRAL satellite (IGR sources). The purpose of the Chandra observations is to localize the sources and to measure their soft X-ray spectra in order to determine the nature of the sources. We find very likely Chandra counterparts for 18 of the 22 sources. We discuss the implications for each source, considering previous results and new optical or IR identifications, and we identify or suggest identifications for the nature of 16 of the sources. Two of the sources, IGR J14003-6326 and IGR J17448-3232, are extended on arcminute scales. We identify the former as a pulsar wind nebula (PWN) with a surrounding supernova remnant (SNR) and the latter as a SNR. In the group of 242 IGR sources, there is only one other source that has previously been identified as a SNR. We confirm a previous identification of IGR J14331-6112 as an High-Mass X-ray Binary (HMXB), and we suggest that IGR J17404-3655, IGR J16287-5021, IGR J17354-3255, IGR J17507-2647, IGR J17586-2129, and IGR J13186-6257 are candidate HMXBs. Our results indicate or confirm that IGR J19267+1325, IGR J18173-2509, and IGR J18308-1232 are Cataclysmic Variables (CVs), and we suggest that IGR J15529-5029 may also be a CV. We confirm that IGR J14471-6414 is an Active Galactic Nucleus (AGN), and we also suggest that IGR J19443+2117 and IGR J18485-0047 may be AGN. Finally, we found Chandra counterparts for IGR J11098-6457 and IGR J18134-1636, but more information is required to determine the nature of these two sources.
The NuSTAR serendipitous survey has already uncovered a large number of Active Galactic Nuclei (AGN), providing new information about the composition of the Cosmic X-ray Background. For the AGN off the Galactic plane, it has been possible to use the existing X-ray archival data to improve source localizations, identify optical counterparts, and classify the AGN with optical spectroscopy. However, near the Galactic Plane, better X-ray positions are necessary to achieve optical or near-IR identifications due to the higher levels of source crowding. Thus, we have used observations with the Chandra X-ray Observatory to obtain the best possible X-ray positions. With eight observations, we have obtained coverage for 19 NuSTAR serendips within 12 deg of the plane. One or two Chandra sources are detected within the error circle of 15 of the serendips, and we report on these sources and search for optical counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical spectrum and detected the presence of hydrogen emission lines. The source is Galactic, and we argue that it is likely a Cataclysmic Variable. For the other sources, the Chandra positions will enable future classifications in order to place limits on faint Galactic populations, including high-mass X-ray binaries and magnetars.
Here we report on X-ray observations of ten 17-60 keV sources discovered by the INTEGRAL satellite. The primary new information is sub-arcsecond positions obtained by the Chandra X-ray Observatory. In six cases (IGR J17040-4305, IGR J18017-3542, IGR J18112-2641, IGR J18434-0508, IGR J19504+3318, and IGR J20084+3221), a unique Chandra counterpart is identified with a high degree of certainty, and for five of these sources (all but J19504), Gaia distances or proper motions indicate that they are Galactic sources. For four of these, the most likely classifications are that the sources are magnetic Cataclysmic Variables (CVs). J20084 could be either a magnetic CV or a High Mass X-ray Binary. We classify the sixth source (J19504) as a likely Active Galactic Nucleus (AGN). In addition, we find likely Chandra counterparts to IGR J18010-3045 and IGR J19577+3339, and the latter is a bright radio source and probable AGN. The other two sources, IGR J12529-6351 and IGR J18013-3222 do not have likely Chandra counterparts, indicating that they are transient, highly variable, or highly absorbed.
The results of optical identifications of five hard X-ray sources in the Galactic plane region from the INTEGRAL all-sky survey are presented. The X-ray data on one source (IGRJ20216+4359) are published for the first time. The optical observations were performed with 1.5-m RTT-150 telescope (TUBITAK National Observatory, Antalya, Turkey) and 6-m BTA telescope (Special Astrophysical Observatory, Nizhny Arkhyz, Russia). A blazar, three Seyfert galaxies, and a high-mass X-ray binary are among the identified sources.
We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed (NH > 1e22 1/cm^2) power law, with average spectral index Gamma = 1.9 +/- 0.3. A high energy exponential cut-off at Ec ~ 50 keV is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ~ 2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (NH from 17e22 to 33e22 1/cm^2) or by the presence of a cut-off at >~ 120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.
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