Talk detail

Participant	Wang, Xiangyu
Institution	Department of Astronomy, Nanjing University - 163 Xianlin Avenue - Nanjing - Jaingsu - China

Session	GB2	Accepted	Yes	Order	8	Time	17:20	15'
Talk	Oral abstract	Title	Measuring the bulk Lorentz factors of gamma-ray bursts with Fermi-LAT
Coauthors	Qing-Wen Tang, Fang-Kun Peng, Xiang-Yu Wang, Pak-Hin Thomas Tam
Abstract	Gamma-ray bursts (GRBs) are powered by ultra-relativistic jets. The value of the Lorentz factor of the relativistic bulk motion can be obtained if a spectral cutoff due to pair-production absorption is detected. With the good spectral coverage of the Large Area Telescope (LAT) on Fermi, measurements of such cutoff become possible, and two cases (GRB 090926A and GRB 100724B) have been reported to have high-energy cutoffs or breaks. We systematically search for such high energy spectral cutoffs/breaks from the LAT and the Gamma-ray burst monitor (GBM) observations of the prompt emission of GRBs detected since August 2011. Six more GRBs are found to have cutoff-like spectral feature at energies of ¡« 10−500 MeV. Assuming that these cutoffs are caused by pair-production absorption within the source, the bulk Lorentz factors of these GRBs are obtained. We further find that the Lorentz factors are correlated with the isotropic gamma-ray luminosity of the bursts, indicating that more powerful GRB jets move faster.
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Session	HE2	Accepted	Yes	Order	13	Time	18:15	15'
Talk	Oral abstract	Title	Hypernova remnants in star-forming galaxies as the origin of IceCube PeV neutrinos
Coauthors	Ruo-Yu Liu, Xiang-Yu Wang, Susumu Inoue, Roland Crocker, Felix Aharonian
Abstract	We argue that the excess of sub-PeV/PeV neutrinos recently reported by IceCube could plausibly originate through pion-production processes in the same sources responsible for cosmic rays (CRs) with energy above the second knee around 10^18 eV. The pion-production efficiency for escaping CRs that produce PeV neutrinos is required to be ≳ 0.1 in such sources. On the basis of current data, we identify semirelativistic hypernova remnants as possible sources that satisfy the requirements. By virtue of their fast ejecta, such objects can accelerate protons to EeV energies, which, in turn, can interact with the dense surrounding medium during propagation in their host galaxies to produce sufficient high-energy neutrinos via proton-proton (pp) collisions. Their accompanying gamma-ray flux can remain below the diffuse isotropic gamma-ray background observed by the Fermi Large Area Telescope.
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