* Astronomy

Title: Discovery of the broad-lined Type Ic SN 2013cq associated with the very energetic GRB 130427A
Authors: D. Xu, A. de Ugarte Postigo, G. Leloudas, T. Kruhler, Z. Cano, J. Hjorth, D. Malesani, J. P. U. Fynbo, C. C. Thoene, R. Sanchez-Ramirez, S. Schulze, P. Jakobsson, L. Kaper, J. Sollerman, D. J. Watson, A. Cabrera-Lavers, C. Cao, H. Flores, J. Gorosabel, S. M. Hu, B. Milvang-Jensen, M. Sparre, L. P. Xin, T. M. Zhang, W. K. Zheng, Y. C. Zou

Long-duration gamma-ray bursts (GRBs) at z < 1 are in most cases found to be accompanied by bright, broad-lined Type Ic supernovae (SNe Ic-BL). The highest-energy GRBs are mostly located at higher redshifts, where the associated SNe are hard to detect observationally. Here we present early and late observations of the optical counterpart of the very energetic GRB 130427A. Despite its moderate redshift z = 0.3399±0.0002, GRB 130427A is at the high end of the GRB energy distribution, with an isotropic-equivalent energy release of Eiso ~ 9.6x10^53 erg, more than an order of magnitude more energetic than other GRBs with spectroscopically confirmed SNe. In our dense photometric monitoring, we detect excess flux in the host-subtracted r-band light curve, consistent with what expected from an emerging SN, ~0.2 mag fainter than the prototypical SN 1998bw. A spectrum obtained around the time of the SN peak (16.7 days after the GRB) reveals broad undulations typical of SNe Ic-BL, confirming the presence of a SN, designated SN 2013cq. The spectral shape and early peak time are similar to those of the high expansion velocity SN 2010bh associated with GRB 100316D. Our findings demonstrate that also high-energy long-duration GRBs, commonly detected at high redshift, can be associated with SNe Ic-BL, pointing to a common progenitor mechanism.

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Title: High energy emission of GRB 130427A: evidence for inverse Compton radiation
Authors: Yi-Zhong Fan, P.H.T. Tam, Fu-Wen Zhang, Yun-Feng Liang, Hao-Ning He, Bei Zhou, Rui-Zhi Yang, Zhi-Ping Jin, Da-Ming Wei

A nearby super-luminous burst GRB 130427A was simultaneously detected by five gamma-ray space telescopes (Swift, Fermi-GBM/LAT, Konus-Wind, SPI-ACS/INTEGRAL and AGILE) and by three RAPTOR full-sky persistent monitors. The isotropic gamma-ray energy release is of ~ 10^{54} erg and the absence of a jet break in the X-ray afterglow lightcurve up to t>7 days suggests an intrinsic energy release of > 10^{52} erg, rendering it the most powerful explosion among the GRBs with a redshift z\leq 0.5. The emission above 100 MeV lasted about one day and four photons are at energies greater than 40 GeV. We show that the count rate of 100 MeV-100 GeV emission may be mainly accounted for by the forward shock synchrotron radiation and the inverse Compton radiation likely dominates at GeV-TeV energies. In particular, an inverse Compton radiation origin is established for the ~ (95.3,~47.3,~41.4) GeV photons arriving at t ~ (243,~256.3,~610.6) s after the trigger of Fermi-GBM. Interestingly, the external-inverse-Compton-scattering of the prompt emission (the second episode, i.e., t ~120-260 s) by the forward-shock-accelerated electrons is expected to produce a few gamma-rays with a typical energy ~ 10 GeV, while five photons above 10 GeV were detected in the same time interval. A possible unified model for the prompt soft gamma-ray, optical and GeV emission of GRB 130427A, GRB 080319B and GRB 090902B is outlined. Implication of the null detection of >1 TeV neutrinos from GRB 130427A by IceCube is discussed.

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