NuSTAR observations of GRB 130925A
ATel #5435; E. C. Bellm, F. A. Harrison, K. Forster, K. K. Madsen, V. Rana (Caltech), S. E. Boggs, J. Tomsick (U. C. Berkeley), J. M. Miller (Michigan), and S. B. Cenko (NASA/GSFC) on behalf of the NuSTAR collaboration
on 1 Oct 2013; 22:37 UT
Credential Certification: John A. Tomsick (jtomsick@ssl.berkeley.edu)
Subjects: X-ray, Gamma-Ray Burst
Referred to by ATel #: 5531
NuSTAR observed the unusual ultra-long GRB/TDE candidate GRB 130925A (GCN 15246) beginning 44.3 hours after the Swift trigger for a total of 39.2 ksec exposure time.
NuSTAR detects the source to >20 keV; the average 3-20 keV flux over the interval was 1.3E-12 erg/cm^-2/s^-1. The data may be fit with an absorbed power law with spectral index Gamma ~ 3.
NuSTAR observes a broad absorption feature centered near 6 keV. Simultaneous Swift-XRT spectra support the existence of this feature at lower SNR. An F-test of a Gaussian absorption feature fit to the combined data sets yields a detection significance of 5.5 sigma. Preliminary searches for features in the early-time XRT data have not identified any clear signatures; additional tests are ongoing.
Further observations are in progress; we encourage continued monitoring of this interesting event at all wavelengths.
We thank the NuSTAR Mission Operations Team for the rapid turnaround that enabled this observation.
