A very-high-energy component deep in the Gamma-ray Burst afterglow
Abstract
Gamma-ray bursts (GRBs) are brief flashes of gamma rays, considered to be the most energetic explosive phenomena in the Universe. The emission from GRBs comprises a short (typically tens of seconds) and bright prompt emission, followed by a much longer afterglow phase. During the afterglow phase, the shocked outflow -- produced by the interaction between the ejected matter and the circumburst medium -- slows down, and a gradual decrease in brightness is observed. GRBs typically emit most of their energy via gamma-rays with energies in the kiloelectronvolt-to-megaelectronvolt range, but a few photons with energies of tens of gigaelectronvolts have been detected by space-based instruments. However, the origins of such high-energy (above one gigaelectronvolt) photons and the presence of very-high-energy (more than 100 gigaelectronvolts) emission have remained elussive. Here we report observations of very-high-energy emission in the bright GRB 180720B deep in the GRB afterglow -ten hours after the end of the prompt emission phase, when the X-ray flux had already decayed by four orders of magnitude. Two possible explanations exist for the observed radiation: inverse Compton emission and synchrotron emission of ultrarelativistic electrons. Our observations show that the energy fluxes in the X-ray and gamma-ray range and their photon indices remain comparable to each other throughout the afterglow. This discovery places distinct constraints on the GRB environment for both emission mechanisms, with the inverse Compton explanation alleviating the particle energy requirements for the emission observed at late times. The late timing of this detection has consequences for the future observations of GRBs at the highest energies.
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Cite
@article{arxiv.1911.08961,
title = {A very-high-energy component deep in the Gamma-ray Burst afterglow},
author = {H. Abdalla R. Adam F. Aharonian F. Ait Benkhali E. O. Anguener M. Arakawa and C. Arcaro and C. Armand and H. Ashkar and M. Backes and V. Barbosa Martins and M. Barnard Y. Becherini and D. Berge and K. Bernloehr and E. Bissaldi and R. Blackwell and M. Boettcher and C. Boisson and J. Bolmont and S. Bonnefoy and J. Bregeon and M. Breuhaus and F. Brun and P. Brun and M. Bryan and M. Buechele and T. Bulik and T. Bylund and M. Capasso and S. Caroff and A. Carosi and S. Casanova and M. Cerruti and T. Chand and S. Chandra and A. Chen and S. Colafrancesco and M. Curylo and I. D. Davids and C. Deil and J. Devin and P. deWilt and L. Dirson and A. Djannati-Atai and A. Dmytriiev and A. Donath and V. Doroshenko and J. Dyks and K. Egberts and G. Emery and J. -P. Ernenwein and S. Eschbach and K. Feijen and S. Fegan and A. Fiasson and G. Fontaine and S. Funk and M. Fuessling and S. Gabici and Y. A. Gallant and F. Gate and G. Giavitto and L. Giunti and D. Glawion and J. F. Glicenstein and D. Gottschall and M. -H. Grondin and J. Hahn and M. Haupt and G. Heinzelmann and G. Henri and G. Hermann and J. A. Hinton and W. Hofmann and C. Hoischen and T. L. Holch and M. Holler and D. Horns and D. Huber and H. Iwasaki and M. Jamrozy and D. Jankowsky and F. Jankowsky and A. Jardin-Blicq and I. Jung-Richardt and M. A. Kastendieck and K. Katarzynski and M. Katsuragawa and U. Katz and D. Khangulyan and B. Khelifi and J. King and S. Klepser and W. Kluzniak and N. Komin and K. Kosack and D. Kostunin and M. Kreter and G. Lamanna and A. Lemiere and M. Lemoine-Goumard and J. -P. Lenain and E. Leser and C. Levy and T. Lohse and I. Lypova and J. Mackey and J. Majumdar and D. Malyshev and V. Marandon and A. Marcowith and A. Mares and C. Mariaud and G. Marti-Devesa and R. Marx and G. Maurin and P. J. Meintjes and A. M. W. Mitchell and R. Moderski and M. Mohamed and L. Mohrmann and C. Moore and E. Moulin and J. Muller and T. Murach and S. Nakashima and M. de Naurois and H. Ndiyavala and F. Niederwanger and J. Niemiec and L. Oakes and P. O Brien and H. Odaka and S. Ohm and E. de Ona Wilhelmi and M. Ostrowski and I. Oya and M. Panter and R. D. Parsons and C. Perennes and P. -O. Petrucci and B. Peyaud and Q. Piel and S. Pita and V. Poireau and A. Priyana Noel and D. A. Prokhorov and H. Prokoph and G. Puehlhofer and M. Punch and A. Quirrenbach and S. Raab and R. Rauth and A. Reimer and O. Reimer and Q. Remy and M. Renaud and F. Rieger and L. Rinchiuso and C. Romoli and G. Rowell and B. Rudak and E. Ruiz-Velasco and V. Sahakian and S. Sailer and S. Saito and D. A. Sanchez and A. Santangelo and M. Sasaki and R. Schlickeiser and F. Schuessler and A. Schulz and H. M. Schutte and U. Schwanke and S. Schwemmer and M. Seglar-Arroyo and M. Senniappan and A. S. Seyffert and N. Shafi and K. Shiningayamwe and R. Simoni and A. Sinha and H. Sol and A. Specovius and M. Spir-Jacob and L. Stawarz and R. Steenkamp and C. Stegmann and C. Steppa and T. Takahashi and T. Tavernier and A. M. Taylor and R. Terrier and D. Tiziani and M. Tluczykont and C. Trichard and M. Tsirou and N. Tsuji and R. Tuffs and Y. Uchiyama and D. J. van der Walt and C. van Eldik and C. van Rensburg and B. van Soelen and G. Vasileiadis and J. Veh and C. Venter and P. Vincent and J. Vink and H. J. Voelk and T. Vuillaume and Z. Wadiasingh and S. J. Wagner and R. White and A. Wierzcholska and R. Yang and H. Yoneda and M. Zacharias and R. Zanin and A. A. Zdziarski and A. Zech and A. Ziegler and J. Zorn and N. Zywucka and F. de Palma and M. Axelsson and O. J. Roberts},
journal= {arXiv preprint arXiv:1911.08961},
year = {2019}
}
Comments
Preprint version of Nature paper. Contacts: E.Ruiz-Velasco, F. Aharonian, E.Bissaldi, C.Hoischen, R.D Parsons, Q.Piel, A.Taylor, D.Khangulyan