Probing the ambient medium of GRB 090618 with XMM-Newton observations

📝 Abstract

Long Gamma-ray Bursts (GRBs) signal the death of massive stars. The afterglow emission can be used to probe the progenitor ambient through a detailed study of the absorption pattern imprinted by the circumburst material as well as the host galaxy interstellar medium on the continuum spectrum. This has been done at optical wavelengths with impressive results. Similar studies can in principle be carried out in the X-ray band, allowing us to shed light on the material metallicity, composition and distance of the absorber. We start exploiting this route through high resolution spectroscopy XMM-Newton observations of GRB 090618. We find a high metallicity absorbing medium (Z> 0.2 Zsun) with possible enhancements of S and Ne with respect to the other elements (improving the fit at a level of >3.4 sigma). Including the metallicity effects on the X-ray column density determination, the X-ray and optical evaluations of the absorption are in agreement for a Small Magellanic Cloud extinction curve.

💡 Analysis

Long Gamma-ray Bursts (GRBs) signal the death of massive stars. The afterglow emission can be used to probe the progenitor ambient through a detailed study of the absorption pattern imprinted by the circumburst material as well as the host galaxy interstellar medium on the continuum spectrum. This has been done at optical wavelengths with impressive results. Similar studies can in principle be carried out in the X-ray band, allowing us to shed light on the material metallicity, composition and distance of the absorber. We start exploiting this route through high resolution spectroscopy XMM-Newton observations of GRB 090618. We find a high metallicity absorbing medium (Z> 0.2 Zsun) with possible enhancements of S and Ne with respect to the other elements (improving the fit at a level of >3.4 sigma). Including the metallicity effects on the X-ray column density determination, the X-ray and optical evaluations of the absorption are in agreement for a Small Magellanic Cloud extinction curve.

📄 Content

arXiv:1106.6001v1 [astro-ph.HE] 29 Jun 2011 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 20 November 2018 (MN LATEX style file v2.2) Probing the ambient medium of GRB 090618 with XMM-Newton observations S. Campana1,⋆, P. D’Avanzo1, D. Lazzati2, S. Covino1,3, G. Tagliaferri1, N. Panagia4 1 INAF-Osservatorio Astronomico di Brera, Via Bianchi 46, I–23807, Merate (Lc), Italy 2 Department of Physics, NC State University, 2401 Stinson Drive, Raleigh, NC 27695-8202, USA 3 INAF/TNG Fundaci´on Galileo Galilei, Rambla Jos´e Ana Fern´andez P´erez, 7, 38712 Bre˜na Baja, Tenerife, Spain 4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD21218, USA 20 November 2018 ABSTRACT Long Gamma–ray Bursts (GRBs) signal the death of massive stars. The afterglow emission can be used to probe the progenitor ambient through a detailed study of the absorption pattern imprinted by the circumburst material as well as the host galaxy interstellar medium on the continuum spectrum. This has been done at optical wavelengths with impressive results. Similar studies can in principle be carried out in the X–ray band, allowing us to shed light on the material metallicity, composition and distance of the absorber. We start exploiting this route through high resolution spectroscopy XMM-Newton observations of GRB 090618. We find a high metallicity absorbing medium (Z >∼0.2 Z⊙) with possible enhancements of S and Ne with respect to the other elements (improving the fit at a level of > 3.4 σ). Including the metallicity effects on the X–ray column density determination, the X–ray and optical evaluations of the absorption are in agreement for a Small Magellanic Cloud extinction curve. Key words: gamma-rays: bursts – X–rays: general – X–ray: ISM 1 INTRODUCTION Tracking the evolution of metals from star-size scale to large- scale structures is a major step in understanding the evolu- tion of the Universe. Metals are produced in stellar interiors and then ejected in their environs through supernova (SN) explosions and stellar winds, thus enriching the interstellar medium (ISM) of their galaxy. So far, the study of metal en- richment in galaxies at high redshifts has been carried out mostly by observing galaxies along the line of sight of bright quasars. This technique is plagued by selection effects, e.g. radiation from quasars probes more probably halos of the in- tervening galaxies. Gamma-ray bursts (GRBs) are opening a completely new window in understanding the history of metals and galaxy formation, in particular at high redshift. This is because, for geometrical reasons, quasar sight lines should preferentially intersect the outer regions of the ISM in high−z galaxies. In contrast, GRBs originate within the densest regions of their host galaxies where massive stars are produced, probing denser environments (Prochaska et al. 2007). It is now recognized that long-duration GRBs are linked to collapse of massive stars, based on the association between (low−z) GRBs and (type Ic) core-collapse super- ⋆E-mail: sergio.campana@brera.inaf.it novae (Woosley & Bloom 2006 and references therein). In- deed, at least ∼75% of GRBs with known redshift show intrinsic (i.e. at the redshift of the host galaxy) X–ray ab- sorption larger than 3×1021 cm−2 (Campana et al. 2010; see also Stratta et al. 2005; Campana et al. 2006). In particular, more than 80% of GRBs show an intrinsic column density larger than 5 × 1021 cm −2 (Campana et al. 2010). Fur- thermore, the presence of absorption indicates a significant metal enrichment, because X–rays are effectively photoelec- trically absorbed only by metals. Metallicities larger than those derived from Damped Lyman Alpha (DLA) studies at the same redshift are also measured from optical studies of GRB. They indicate that the metal abundance can be as high as 10% of the solar one up to z = 6 (Savaglio 2006; Kawai et al 2006; Campana et al. 2007). Signatures for the presence of this material can be expected in the optical light curve of GRB afterglows showing up as flux enhancements in their light curves or as (variable) fine-structure transition lines in their spectra (Vreeswijk et al. 2007; D’Elia et al. 2009a, 2009b) as well as Lyα (Th¨one et al. 2011). The ob- servations of these features can set important constraints on the density and distance of the absorbing material located either in the star-forming region within which the progenitor formed or in the circumstellar environment of the progeni- 2 S. Campana et al. Table 1. XMM-Newton observation log. Instrument Start time Exp. time Net exp. time (hr after burst) (s) (s) MOS1 13:48:09 (5.33) 22615 – MOS2 13:48:08 (5.33) 22620 – pn 14:10:31 (5.70) 21034 12695 RGS1 13:47:24 (5.32) 22842 19675 RGS2 13:47:32 (5.32) 22789 19651 tor itself (Prochaska et al. 2006; Dessauges-Zavadsky et al. 2006; D’Elia et al. 2009a, 2009b). Metal abundance derived from optical spectroscopy can be underestimated because some of the metals can be locked in dust grains, the comp

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