The properties of the 2175 angstrom extinction feature discovered in GRB afterglows

Tayyaba Zafar; Darach Jafar Watson; Árdís Elíasdóttir; Johan Peter Uldall Fynbo; Thomas Christian Krühler; P. Schady; Georgios Leloudas; P. Jakobsson; Christina Thöne; D.A. Perley; J. Bloom; J. Greiner

doi:10.1088/0004-637X/753/1/82

The properties of the 2175 angstrom extinction feature discovered in GRB afterglows

Tayyaba Zafar, Darach Jafar Watson, Árdís Elíasdóttir, Johan Peter Uldall Fynbo, Thomas Christian Krühler, P. Schady, Georgios Leloudas, P. Jakobsson, Christina Thöne, D.A. Perley, J. Bloom, J. Greiner

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52 Citations (Scopus)

Abstract

The unequivocal, spectroscopic detection of the 2175Å bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB070802 and GRB080607). In this work, we analyze in detail the detections of the 2175Å extinction bump in the optical spectra of two further GRB afterglows: GRB080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB080605 and GRB080805 at two epochs are fit well with a single power law with a derived extinction of A_V = 0.52^+0.13 _{- 0.16} and 0.50^+0.13 _{- 0.10}, and 2.1^+0.7 _{- 0.6} and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB080805 is not well constrained, the extinction curve of GRB080605 has an unusual very steep far-UV rise together with the 2175Å bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175Å bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A _bump) for GRB afterglows is weaker for a given A_V than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.

Original language	English
Journal	Astrophysical Journal
Volume	753
Issue number	1
Pages (from-to)	82
ISSN	0004-637X
DOIs	https://doi.org/10.1088/0004-637X/753/1/82
Publication status	Published - 1 Jul 2012

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@article{af036805882248dd8c5833d5a32a7d3f,

title = "The properties of the 2175 angstrom extinction feature discovered in GRB afterglows",

abstract = "The unequivocal, spectroscopic detection of the 2175{\AA} bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB070802 and GRB080607). In this work, we analyze in detail the detections of the 2175{\AA} extinction bump in the optical spectra of two further GRB afterglows: GRB080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB080605 and GRB080805 at two epochs are fit well with a single power law with a derived extinction of AV = 0.52+0.13 - 0.16 and 0.50+0.13 - 0.10, and 2.1+0.7 - 0.6 and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB080805 is not well constrained, the extinction curve of GRB080605 has an unusual very steep far-UV rise together with the 2175{\AA} bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175{\AA} bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A bump) for GRB afterglows is weaker for a given AV than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.",

author = "Tayyaba Zafar and Watson, {Darach Jafar} and {\'A}rd{\'i}s El{\'i}asd{\'o}ttir and Fynbo, {Johan Peter Uldall} and Kr{\"u}hler, {Thomas Christian} and P. Schady and Georgios Leloudas and P. Jakobsson and Christina Th{\"o}ne and D.A. Perley and J. Bloom and J. Greiner",

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doi = "10.1088/0004-637X/753/1/82",

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T1 - The properties of the 2175 angstrom extinction feature discovered in GRB afterglows

AU - Zafar, Tayyaba

AU - Watson, Darach Jafar

AU - Elíasdóttir, Árdís

AU - Fynbo, Johan Peter Uldall

AU - Krühler, Thomas Christian

AU - Schady, P.

AU - Leloudas, Georgios

AU - Jakobsson, P.

AU - Thöne, Christina

AU - Perley, D.A.

AU - Bloom, J.

AU - Greiner, J.

PY - 2012/7/1

Y1 - 2012/7/1

N2 - The unequivocal, spectroscopic detection of the 2175Å bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB070802 and GRB080607). In this work, we analyze in detail the detections of the 2175Å extinction bump in the optical spectra of two further GRB afterglows: GRB080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB080605 and GRB080805 at two epochs are fit well with a single power law with a derived extinction of AV = 0.52+0.13 - 0.16 and 0.50+0.13 - 0.10, and 2.1+0.7 - 0.6 and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB080805 is not well constrained, the extinction curve of GRB080605 has an unusual very steep far-UV rise together with the 2175Å bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175Å bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A bump) for GRB afterglows is weaker for a given AV than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.

AB - The unequivocal, spectroscopic detection of the 2175Å bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB070802 and GRB080607). In this work, we analyze in detail the detections of the 2175Å extinction bump in the optical spectra of two further GRB afterglows: GRB080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB080605 and GRB080805 at two epochs are fit well with a single power law with a derived extinction of AV = 0.52+0.13 - 0.16 and 0.50+0.13 - 0.10, and 2.1+0.7 - 0.6 and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB080805 is not well constrained, the extinction curve of GRB080605 has an unusual very steep far-UV rise together with the 2175Å bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175Å bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A bump) for GRB afterglows is weaker for a given AV than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.

U2 - 10.1088/0004-637X/753/1/82

DO - 10.1088/0004-637X/753/1/82

M3 - Journal article

SN - 0004-637X

VL - 753

SP - 82

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

ER -

The properties of the 2175 angstrom extinction feature discovered in GRB afterglows

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