F. Brun

Limits on the TeV gamma-ray afterglow of fast radio bursts with H.E.S.S.

We here present the H.E.S.S. follow-up of Fast Radio Bursts (FRBs), millisecond-long, very strong radio pulses of yet unknown origin. The SUPERB (SUrvey for Pulsars and Extragalactic Radio Bursts) project at the Parkes radio observatory is able to detect these enigmatic events almost in real-time which allows triggering follow-up observations covering the full electromagnetic spectrum. The H.E.S.S. gamma-ray observatory is taking active part in this endeavor. Here we focus on data taken within hours of FRB 150418, which allow us to derive the first limits on gamma-ray afterglow emission of FRBs. Based on the identification of the potential host galaxy of this burst we are able to discuss absorption effects due to the extragalactic background light (EBL) and derive intrinsic, energy dependent limits on the gamma-ray afterglow.

Discovery of gamma-ray emission from the extragalactic pulsar wind nebula N157B with the High Energy Stereoscopic System

We present the significant detection of the first extragalactic pulsar wind nebula (PWN) detected in gamma rays, N157B, located in the large Magellanic Cloud (LMC). Pulsars with high spin-down luminosity are found to power energised nebulae that emit gamma rays up to energies of several tens of TeV. N157B is associated with PSRJ0537-6910, which is the pulsar with the highest known spin-down luminosity. The High Energy Stereoscopic System telescope array observed this nebula on a yearly basis from 2004 to 2009 with a dead-time corrected exposure of 46 h. The gamma-ray spectrum between 600 GeV and 12 TeV is well-described by a pure power-law with a photon index of 2.8 \pm 0.2(stat) \pm 0.3(syst) and a normalisation at 1 TeV of (8.2 \pm 0.8(stat) \pm 2.5(syst)) \times 10^-13 cm^-2s^-1TeV^-1. A leptonic multi-wavelength model shows that an energy of about 4 \times 10^49erg is stored in electrons and positrons. The apparent efficiency, which is the ratio of the TeV gamma-ray luminosity to the pulsars spindown luminosity, 0.08% \pm 0.01%, is comparable to those of PWNe found in the Milky Way. The detection of a PWN at such a large distance is possible due to the pulsars favourable spin-down luminosity and a bright infrared photon-field serving as an inverse-Compton-scattering target for accelerated leptons. By applying a calorimetric technique to these observations, the pulsars birth period is estimated to be shorter than 10 ms.