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Register a new userChandra Observations of Eight Sources Discovered by INTEGRAL
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We report on 0.3-10 keV observations with the Chandra X-ray Observatory of eight hard X-ray sources discovered within 8 degrees of the Galactic plane by the INTEGRAL satellite. The short (5 ks) Chandra observations of the IGR source fields have yielded very likely identifications of X-ray counterparts for three of the IGR sources: IGR J14091-6108, IGR J18088-2741, and IGR J18381-0924. The first two have very hard spectra in the Chandra band that can be described by a power-law with photon indices of Gamma = 0.6+/-0.4 and -0.7(+0.4)(-0.3), respectively (90% confidence errors are given), and both have a unique near-IR counterpart consistent with the Chandra position. IGR J14091-6108 also displays a strong iron line and a relatively low X-ray luminosity, and we argue that the most likely source type is a Cataclysmic Variable (CV), although we do not completely rule out the possibility of a High Mass X-ray Binary. IGR J18088-2741 has an optical counterpart with a previously measured 6.84 hr periodicity, which may be the binary orbital period. We also detect five cycles of a possible 800-950 s period in the Chandra light curve, which may be the compact object spin period. We suggest that IGR J18088-2741 is also most likely a CV. For IGR J18381-0924, the spectrum is intrinsically softer with Gamma = 1.5(+0.5)(-0.4), and it is moderately absorbed, nH = (4+/-1)e22 cm-2. There are two near-IR sources consistent with the Chandra position, and they are both classified as galaxies, making it likely that IGR J18381-0924 is an Active Galactic Nucleus (AGN). For the other five IGR sources, we provide lists of nearby Chandra sources, which may be used along with further observations to identify the correct counterparts, and we discuss the implications of the low inferred Chandra count rates for these five sources.
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The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has detected in excess of 1000 sources in the ~20-100 keV band during its surveys of the sky over the past 17 years. We obtained 5 ks observations of 15 unclassified IGR sources with the Chandra X-ray Observatory in order to localize them, to identify optical/IR counterparts, to measure their soft X-ray spectra, and to classify them. For 10 of the IGR sources, we detect Chandra sources that are likely (or in some cases certain) to be the counterparts. IGR J18007-4146 and IGR J15038-6021 both have Gaia parallax distances, placing them at 2.5+0.5-0.4 and 1.1+1.5-0.4 kpc, respectively. We tentatively classify both of them as intermediate polar-type Cataclysmic Variables. Also, IGR J17508-3219 is likely to be a Galactic source, but it is unclear if it is a Dwarf Nova or another type of transient. For IGR J17118-3155, we provide a Chandra localization, but it is unclear if the source is Galactic or extragalactic. Based on either near-IR/IR colors or the presence of extended near-IR emission, we classify four sources as Active Galactic Nuclei (IGR J16181-5407, IGR J16246-4556, IGR J17096-2527, and IGR J19294+1327), and IGR J20310+3835 and IGR J15541-5613 are AGN candidates. In addition, we identified an AGN in the INTEGRAL error circle of IGR J16120-3543 that is a possible counterpart.
With respect to the recent INTEGRAL/IBIS 9-year Galactic Hard X-ray Survey (Krivonos et al. 2012), we use archival Swift/XRT observations in conjunction with multi-wavelength information to discuss the counterparts of a sample of newly discovered objects. The X-ray telescope (XRT, 0.3-10 keV) on board Swift, thanks to its few arcseconds source location accuracy, has been proven to be a powerful tool with which the X-ray counterparts to these IBIS sources can be searched for and studied. In this work, we present the outcome of this analysis by discussing four objects (SWIFT J0958.0-4208, SWIFT J1508.6-4953, IGR J17157-5449, and IGR J22534+6243) having either X-ray data of sufficient quality to perform a reliable spectral analysis or having interesting multiwaveband properties. We find that SWIFT J1508.6-4953 is most likely a Blazar, while IGR J22534+6243 is probably a HMXB. The remaining two objects may be contaminated by nearby X-ray sources and their class can be inferred only by means of optical follow-up observations of all likely counterparts.
Here, we report on observations of two hard X-ray sources that were originally discovered with the INTEGRAL satellite: IGR J04059+5416 and IGR J08297-4250. We use the Chandra X-ray Observatory to localize the sources and then archival near-IR images to identify the counterparts. Both sources have counterparts in the catalog of extended 2 Micron All-Sky Survey sources, and the counterpart to IGR J04059+5416 has been previously identified as a galaxy. Thus, we place IGR J04059+5416 in the class of Active Galactic Nuclei (AGN), and we suggest that IGR J08297-4250 is also an AGN. If this identification is correct, the near-IR images suggest that the host galaxy of IGR J08297-4250 may be merging with a smaller nearby galaxy. For IGR J04059+5416, the 0.3-86 keV spectrum from Chandra and INTEGRAL is consistent with an absorbed power-law with a column density of N_H = 3.1(+2.0)(-1.5)e22 cm-2 and a photon index of Gamma = 1.4+/-0.7, and we suggest that it is a Seyfert galaxy. For IGR J08297-4250, the photon index is similar, Gamma = 1.5+/-0.8, but the source is highly absorbed (N_H = 6.1(+10.1)(-4.3)e23 cm-2).
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.
We take advantage of the high sensitivity of the IBIS/ISGRI telescope and the improvements in the data analysis software to investigate the nature of the still poorly known X-ray source AX J1910.7+0917, and search for close-by previously undetected objects. We analyze all publicly available INTEGRAL data of AX J1910.7+0917, together with a number of archival observations that were carried out in the direction of the source with Chandra, XMM-Newton, and ASCA. In the IBIS/ISGRI field-of-view around AX J1910.7+0917, we discovered three new sources: IGR J19173+0747, IGR J19294+1327 and IGR J19149+1036; the latter is positionally coincident with the Einstein source 2E 1912.5+1031. For the first two sources, we also report the results of follow-up observations carried out with Swift/XRT. AX J1910.7+0917 features a clear variability in the X-rays. Its spectrum can be well described with an absorbed (N_H~6x10^(22) cm^(-2)) power-law ({Gamma}~1.5) model plus an iron line at ~6.4 keV. We also obtained a refined position and report on possible infrared counterparts. The present data do not allow for a unique classification of the sources. Based on the property of its X-ray emission and the analysis of a likely infrared counterpart, we investigate different possibilities for the nature of AX J1910.7+0917.
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