MAGIC observation of the GRB 080430 afterglow

¹ IFAE, Edifici Cn., Campus UAB, 08193, Bellaterra, Spain
² ETH Zurich, 8093, Switzerland
³ INAF National Institute for Astrophysics, 00136 Rome, Italy
⁴ Universidad Complutense, 28040 Madrid, Spain
⁵ Technische Universität Dortmund, 44221 Dortmund, Germany
⁶ Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
⁷ Università di Padova and INFN, 35131 Padova, Italy
⁸ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁹ University of Łódź, 90236 Lodz, Poland
¹⁰ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
¹¹ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹² Max-Planck-Institut für Physik, 80805 München, Germany
¹³ Università di Siena, and INFN Pisa, 53100 Siena, Italy
¹⁴ Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
¹⁵ Universität Würzburg, 97074 Würzburg, Germany
¹⁶ Depto. de Astrofisica, Universidad, 38206 La Laguna, Tenerife, Spain
¹⁷ Università di Udine, and INFN Trieste, 33100 Udine, Italy
¹⁸ Supported by INFN Padova
¹⁹ Institut de Ciències de l'Espai (IEEC-CSIC), 08193 Bellaterra, Spain
²⁰ Now at: Max-Planck-Institut für Kernphysik, 69029 Heidelberg, Germany
²¹ Now at: Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
²² Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
²³ Croatian MAGIC Consortium, Institute R. Boskovic, University of Rijeka and University of Split, 10000 Zagreb, Croatia
²⁴ University of California, Davis, CA-95616-8677, USA
²⁵ Deceased
²⁶ Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²⁷ INAF/Osservatorio Astronomico and INFN, 34143 Trieste, Italy
²⁸ ICREA, 08010 Barcelona, Spain
²⁹ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy

Received: 13 October 2009
Accepted: 17 April 2010

Abstract

Context. Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment.

Aims. Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies.

Methods. We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRB 080430 at energies above about 80 GeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes.

Results. We obtained an upper limit of F_{95% CL} = 5.5 × 10^-11 erg cm^-2 s^-1 for the very-high energy emission of GRB 080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z ≲ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.