Bellm, Eric C.13; Barrière, Nicolas M.14; Bhalerao, Varun5; Boggs, Steven E.14; Cenko, S. Bradley15; Christensen, Finn Erland1; Craig, William W.14; Forster, Karl13; Fryer, Chris L.16; Hailey, Charles J.17; Harrison, Fiona A.13; Horesh, Assaf18; Kouveliotou, Chryssa19; Madsen, Kristin K.13; Miller, Jon M.20; Ofek, Eran O.18; Perley, Daniel A.13; Rana, Vikram R.13; Reynolds, Stephen P.21; Stern, Daniel13; Tomsick, John A.14; Zhang, William W.19
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 California Institute of Technology4 University of California at Berkeley5 Inter-University Center for Astronomy and Astrophysics6 NASA Goddard Space Flight Center7 Los Alamos National Laboratory8 Columbia University9 Weizmann Institute of Science10 NASA Marshall Space Flight Center11 University of Michigan12 North Carolina State University13 California Institute of Technology14 University of California at Berkeley15 NASA Goddard Space Flight Center16 Los Alamos National Laboratory17 Columbia University18 Weizmann Institute of Science19 NASA Marshall Space Flight Center20 University of Michigan21 North Carolina State University
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.