X-ray spectral components observed in the afterglow of GRB 130925A

Eric C. Bellm, Nicolas M. Barrière, Varun Bhalerao, Steven E. Boggs, S. Bradley Cenko, Finn Erland Christensen, William W. Craig, Karl Forster, Chris L. Fryer, Charles J. Hailey, Fiona A. Harrison, Assaf Horesh, Chryssa Kouveliotou, Kristin K. Madsen, Jon M. Miller, Eran O. Ofek, Daniel A. Perley, Vikram R. Rana, Stephen P. Reynolds, Daniel SternJohn A. Tomsick, William W. Zhang

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We have identified spectral features in the late-time X-ray afterglow of the unusually long, slow-decaying GRB 130925A using NuSTAR, Swift/X-Ray Telescope, and Chandra. A spectral component in addition to an absorbed power law is required at >4σ significance, and its spectral shape varies between two observation epochs at 2 × 105 and 106 s after the burst. Several models can fit this additional component, each with very different physical implications. A broad, resolved Gaussian absorption feature of several keV width improves the fit, but it is poorly constrained in the second epoch. An additive blackbody or second power-law component provide better fits. Both are challenging to interpret: the blackbody radius is near the scale of a compact remnant (108 cm), while the second power-law component requires an unobserved high-energy cutoff in order to be consistent with the non-detection by Fermi/Large Area Telescope.
Original languageEnglish
Article numberL19
JournalThe Astrophysical Journal Letters
Issue number2
Number of pages5
Publication statusPublished - 2014


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