Titill: | The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25 |
Höfundur: |
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Útgáfa: | 2018-06-18 |
Tungumál: | Enska |
Umfang: | L21 |
Háskóli/Stofnun: | Háskóli Íslands University of Iceland |
Svið: | Verkfræði- og náttúruvísindasvið (HÍ) School of Engineering and Natural Sciences (UI) |
Deild: | Raunvísindastofnun (HÍ) Science Institute (UI) |
Birtist í: | The Astrophysical Journal Letters;860(2) |
ISSN: | 2041-8205 2041-8213 (eISSN) |
DOI: | 10.3847/2041-8213/aaca3f |
Efnisorð: | Dust extinction; Galaxies; Gamma-ray burst; Stjarneðlisfræði; Gammageislar; Vetrarbrautir |
URI: | https://hdl.handle.net/20.500.11815/800 |
Tilvitnun:Zafar, T., Heintz, K. E., Fynbo, J. P. U., Malesani, D., Bolmer, J., Ledoux, C., . . . Xu, D. (2018). The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25. The Astrophysical Journal Letters, 860(2), L21. doi:10.3847/2041-8213/aaca3f
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Útdráttur:The ultraviolet (UV) extinction feature at 2175 Å is ubiquitously observed in the Galaxy but is rarely detected at high redshifts. Here we report the spectroscopic detection of the 2175 Å bump on the sightline to the γ-ray burst (GRB) afterglow GRB 180325A at z = 2.2486, the only unambiguous detection over the past 10 years of GRB follow-up, at four different epochs with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT)/X-shooter. Additional photometric observations of the afterglow are obtained with the Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We construct the near-infrared to X-ray spectral energy distributions (SEDs) at four spectroscopic epochs. The SEDs are well described by a single power law and an extinction law with R V ≈ 4.4, A V ≈ 1.5, and the 2175 Å extinction feature. The bump strength and extinction curve are shallower than the average Galactic extinction curve. We determine a metallicity of [Zn/H] > −0.98 from the VLT/X-shooter spectrum. We detect strong neutral carbon associated with the GRB with equivalent width of W r(λ 1656) = 0.85 ± 0.05. We also detect optical emission lines from the host galaxy. Based on the Hα emission-line flux, the derived dust-corrected star formation rate is ~46 ± 4 M ⊙ yr−1 and the predicted stellar mass is log M */M ⊙ ~ 9.3 ± 0.4, suggesting that the host galaxy is among the main-sequence star-forming galaxies.
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