Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM

M. Tanga, P. Schady, A. Gatto, J. Greiner, M.~G.~H. Krause, R. Diehl, S. Savaglio, S. Walch

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2−3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.
Original languageEnglish
Pages (from-to)A24
JournalAstronomy & Astrophysics
Volume595
DOIs
Publication statusPublished - 1 Oct 2016

Keywords

  • gamma-ray burst: general, X-rays: ISM, ultraviolet: ISM, galaxies: irregular, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies

Cite this

Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM. / Tanga, M.; Schady, P.; Gatto, A.; Greiner, J.; Krause, M.~G.~H.; Diehl, R.; Savaglio, S.; Walch, S.

In: Astronomy & Astrophysics, Vol. 595, 01.10.2016, p. A24.

Research output: Contribution to journalArticle

Tanga, M. ; Schady, P. ; Gatto, A. ; Greiner, J. ; Krause, M.~G.~H. ; Diehl, R. ; Savaglio, S. ; Walch, S. / Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM. In: Astronomy & Astrophysics. 2016 ; Vol. 595. pp. A24.
@article{547532bd7b3c4b0fabd5434db326978e,
title = "Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM",
abstract = "Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2−3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.",
keywords = "gamma-ray burst: general, X-rays: ISM, ultraviolet: ISM, galaxies: irregular, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies",
author = "M. Tanga and P. Schady and A. Gatto and J. Greiner and M.~G.~H. Krause and R. Diehl and S. Savaglio and S. Walch",
year = "2016",
month = "10",
day = "1",
doi = "10.1051/0004-6361/201527961",
language = "English",
volume = "595",
pages = "A24",
journal = "Astronomy & Astrophysics",
issn = "0004-6361",
publisher = "Springer Verlag",

}

TY - JOUR

T1 - Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM

AU - Tanga, M.

AU - Schady, P.

AU - Gatto, A.

AU - Greiner, J.

AU - Krause, M.~G.~H.

AU - Diehl, R.

AU - Savaglio, S.

AU - Walch, S.

PY - 2016/10/1

Y1 - 2016/10/1

N2 - Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2−3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.

AB - Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2−3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.

KW - gamma-ray burst: general, X-rays: ISM, ultraviolet: ISM, galaxies: irregular, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies

U2 - 10.1051/0004-6361/201527961

DO - 10.1051/0004-6361/201527961

M3 - Article

VL - 595

SP - A24

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

ER -