Suzaku observation of IGR J16318-4848

📝 Abstract

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 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) keV. The absorbing column is 1.95(3)x10e24 cm-2. Consistent with earlier work, strong fluorescent emission lines of Fe Kalpha, Fe Kbeta, and Ni Kalpha are observed. Despite the large absorbing column, 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 3.4x10e-10 erg cm-2 s-1, the source exhibits significant variability on timescales of hours.

💡 Analysis

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 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) keV. The absorbing column is 1.95(3)x10e24 cm-2. Consistent with earlier work, strong fluorescent emission lines of Fe Kalpha, Fe Kbeta, and Ni Kalpha are observed. Despite the large absorbing column, 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 3.4x10e-10 erg cm-2 s-1, the source exhibits significant variability on timescales of hours.

📄 Content

arXiv:0912.0254v1 [astro-ph.HE] 1 Dec 2009 Astronomy & Astrophysics manuscript no. 10811 c⃝ESO 2018 November 6, 2018 Suzaku observation of IGR J16318−4848 Laura Barrag´an1, J¨orn Wilms1, Katja Pottschmidt2,3, Michael A. Nowak4, Ingo Kreykenbohm1, Roland Walter5, and John A. Tomsick6 1 Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universit¨at Erlangen-N¨urnberg, Sternwartstraße 7, 96049 Bamberg, Germany 2 CRESST, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA 3 NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771, USA 4 MIT Kavli Institute for Astrophysics and Space Research, 77, Massachusetts Avenue, 37-241, Cambridge, MA 02139, USA 5 INTEGRAL Science Data Centre, Geneva Observatory, University of Geneva, Chemin d’´Ecogia 16, 1290 Versoix, Switzerland 6 Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450, USA Received: — / Accepted: — ABSTRACT 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 (χ2 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 cutoffat 20.5(6) keV. The absorbing column is NH = 1.95(3) × 1024 cm−2. Consistent with earlier work, strong fluorescent emission lines of Fe Kα, Fe Kβ, and Ni Kα are observed. Despite the large NH, 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 × 10−10 erg cm−2 s−1, the source exhibits significant variability on timescales of hours. Key words. stars: individual (IGR J16318−4848) – binaries: general – X-rays: binaries

1. Introduction IGR J16318−4848 was detected on 2003 Jan. 29 during a scan of the Galactic plane by the IBIS/ISGRI soft gamma- ray detector onboard the International Gamma Ray Laboratory (INTEGRAL; Courvoisier et al., 2003; Walter et al., 2003). The source was the first and most extreme example of a number of highly absorbed Galactic X-ray binaries discovered with INTEGRAL. Due to the strong absorption, which can exceed an equivalent hydrogen column of 1024 cm−2, these sources are extremely faint in the soft X-rays and had not been detected by earlier missions (Rodriguez et al., 2003; Patel et al., 2004; Kuulkers, 2005). Right after its discovery, a re-analysis of archival ASCA data by Murakami et al. (2003) revealed a highly photoabsorbed source (NH = 4 × 1023 cm−2) coincident with the position given by INTEGRAL. The data also suggested an iron emission line at 6.4 keV. These results were confirmed by various sub- sequent studies (e.g. Schartel et al., 2003; de Plaa et al., 2003; Revnivtsev et al., 2003; Walter et al., 2003). Matt & Guainazzi (2003) detected intense Fe Kα, Fe Kβ, and Ni Kα emission lines in the spectrum. Based on the interstellar absorption to- ward the system, which is two orders of magnitude lower than the measured NH, Revnivtsev (2003), Filliatre & Chaty (2004), and Lutovinov et al. (2005) also suggested that much of the X- ray absorption is intrinsic to the compact object. In an optical study of the system, Filliatre & Chaty (2004) proposed that IGR J16318−4848 is a High Mass X-ray Binary Send offprint requests to: L. Barrag´an, (e-mail: laura.barragan@sternwarte.uni-erlangen.de) (HMXB) with an sgB[e] star as the mass donor surrounded by a dense and absorbing circumstellar material (see also Revnivtsev, 2003; Moon et al., 2007). This dense stellar wind results in sig- nificant photoabsorption within the binary system. Based on the optical data, Filliatre & Chaty (2004) suggest a distance be- tween 0.9 and 6.2 kpc for the system. A likely location for the source is in the Norma-Cygnus arm (Revnivtsev, 2003; Walter et al., 2004), which would place it at a distance of 4.8 kpc (Filliatre & Chaty, 2004). In this Paper, we describe the results of follow-up observa- tions of IGR J16318−4848 obtained with the Suzaku satellite, the instruments on which are uniquely suited to study Compton- thick absorption. In Sect. 2 we describe the data reduction. Section 3 is devoted to a presentation of the results of the spectral and temporal analysis. We discuss our results in Sect. 4.
2. Data analysis We observed IGR J16318−4848 with Suzaku from 2006 August 14 until 2006 August 17 for a total net exposure of 97 ks (Suzaku sequence number 401094010). We used the stan- dard procedures to reduce the data from the X-Ray Imaging Spectrometer (XIS, Koyama et al., 2007) and the Hard X- Ray Detector (HXD, Takahashi et al., 2007). For t

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