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  • 1
    Publication Date: 2019-07-13
    Description: Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite is uncovering large numbers of 20-100 keV "IGR" sources. We present results from Chandra, INTEGRAL, optical, and IR observations of four IGR sources: three sources in the Norma region of the Galaxy(1GR J16195-4945,IGR J16207-5129, and IGR J16167-4957) and one that is closer to the Galactic center (IGR 5171 95-4100). In all four cases, one relatively bright Chandra source is seen in the INTEGRAL error circle, and these are likely to be the soft X-ray counterparts of the IGR sources. They have hard 0.3-10 keV spectra with power-law photon indices of Gamma = 0.5-1.1. While many previously studied IGR sources show high column densities (NH approx. 10(exp 23)-10(exp 24)/sq cm), only IGR J16195-4945 has a column density that could be as high as 10(exp 23)/sq cm. Using optical and IR sky survey catalogs and our own photometry, we have obtained identifications for 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) to constrain the nature of the sources. Blackbody components with temperature lower limits of 〉9400 K for IGR J16195-4945 and 〉18,000 K for IGR J16207-5129 indicate that these are very likely high-mass X-ray binaries (HMXBs). However, for IGR 516167-4957 and IGR J17195-4100, low extinction and the SEDs indicate later spectral types for the putative companions, suggesting that these are not HMXBs.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 647; Part 1; 1309-1322
    Format: text
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  • 2
    Publication Date: 2019-07-13
    Description: We present the results from analyses of Suzaku observations of the supergiant X-ray binaries IGR Jl6207-5129 and IGR Jl7391-3021. For IGR Jl6207-5129, we provide the first broadband (0.5-60 keV) spectrum from which we confirm a large intrinsic column density (N(sub H) = 16 X 10(exp 22)/square cm), and constrain the cutoff energy for the first time (E(sub c) 19 keV). We observed a prolonged (〉 30 ks) attenuation of the X-ray flux which we tentatively attribute to an eclipse of the probable neutron star by its massive companion. For IGR Jl739J-3021, we witnessed a transition from quiescence to a low-activity phase punctuated by weak flares whose peak luminosities in the 0.5-10 keV band are only a factor of 5 times that of the pre-flare emission. The weak flaring is accompanied by an increase in the absorbing column which suggests the accretion of obscuring clumps of wind. Placing this observation in the context of the recent Swift monitoring campaign, we now recognize that these low-activity epochs constitute the most common emission phase for this system, and perhaps in other supergiant fast X-ray transients (SFXTs) as well.
    Keywords: Astronomy
    Type: GSFC.CP.4731.2011 , 8th INTEGRAL Workshop "The Restless Gamma-ray Universe"; Sep 27, 2011 - Sep 30, 2011; Dublin; Ireland
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  • 3
    Publication Date: 2019-07-12
    Description: We report on the first Suzaku observation of IGR J16318-4848, the most extreme example of a new group of highly absorbed X-ray binaries that have recently been discovered by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). The Suzaku observation was carried out between 2006 August 14 and 17, with a net exposure time of 97 ks. The average X-ray spectrum of the source can be well described (chi-square (sub red)= 0.99) with a continuum model typical for neutron stars i.e., a strongly absorbed power law continuum with a photon index of 0.676(42) and an exponential cutoff at 20.5(6) keY. The absorbing column is N(sub H) = 1.95(3) X 10(exp 24)/square cm. Consistent with earlier work, strong fluorescent emission lines of Fe K-alpha, Fe K-beta, and Ni K-alpha are observed. Despite the large N(sub H), no Compton shoulder is seen in the lines, arguing for a non-spherical and inhomogeneous absorber. Seen at an average 5-60 keV absorbed flux of 3.4 x 10(exp -10) erg/square cm/second, the source exhibits significant variability on timescales of hours.
    Keywords: Astronomy
    Type: Astronomy and Astrophysics
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