Very high energy gamma-ray observation of the peculiar transient event Swift J1644+57 with the MAGIC telescopes and AGILE

¹ IFAE, Edifici Cn., Campus UAB, 08193 Bellaterra, Spain
² INAF National Institute for Astrophysics, 00136 Rome, Italy
³ Università di Siena, and INFN Pisa, 53100 Siena, Italy
⁴ Universidad Complutense, 28040 Madrid, Spain
⁵ Technische Universität Dortmund, 44221 Dortmund, Germany
⁶ Max-Planck-Institut für Physik, 80805 München, Germany
⁷ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁸ University of Łódź, 90236 Lodz, Poland
⁹ Depto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
¹⁰ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹¹ ETH Zurich, 8093 Zurich, Switzerland
¹² Universität Würzburg, 97074 Würzburg, Germany
¹³ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040 Madrid, Spain
¹⁴ Università di Udine, and INFN Trieste, 33100 Udine, Italy
¹⁵ Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
¹⁶ Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, 10000 Zagreb, Croatia
¹⁷ Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
¹⁸ Università dell’Insubria, Como, 22100 Como, Italy
¹⁹ Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
²⁰ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
²¹ Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan
²² Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²³ Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
²⁴ Università di Padova and INFN, 35131 Padova, Italy
²⁵ INAF/Osservatorio Astronomico and INFN, 34143 Trieste, Italy
²⁶ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²⁷ ICREA, 08010 Barcelona, Spain
²⁸ Now at École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
²⁹ Supported by INFN Padova  
³⁰ Now at: DESY, Zeuthen, Germany
³¹ Now at: Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland
³² Also at Instituto de Fisica Teorica, UAM/CSIC, 28049 Madrid, Spain
³³ Università di Trieste, and INFN Trieste, 34127 Trieste, Italy
³⁴ Agenzia Spaziale Italiana (ASI) Science Data Center, 00044 Frascati, and INAF-Oar, 00040 Monteporzio Catone, Italy

Received: 30 January 2013
Accepted: 15 February 2013

Abstract

Context. On March 28, 2011, the BAT instrument on board the Swift satellite detected a new transient event that in the very beginning was classified as a gamma ray burst (GRB). However, the unusual X-ray flaring activity observed from a few hours up to days after the onset of the event made a different nature seem to be more likely. The long-lasting activity in the X-ray band, followed by a delayed brightening of the source in infrared and radio activity, suggested that it is better interpreted as a tidal disruption event that triggered a dormant black hole in the nucleus of the host galaxy and generated an outflowing jet of relativistic matter.

Aims. Detecting a very high energy emission component from such a peculiar object would be enable us to constrain the dynamic of the emission processes and the jet model by providing information on the Doppler factor of the relativistic ejecta .

Methods. The MAGIC telescopes observed the peculiar source Swift J1644+57 during the flaring phase, searching for gamma-ray emission at very-high energy (VHE, E > 100 GeV), starting observations nearly 2.5 days after the trigger time. MAGIC collected a total of 28 h of data during 12 nights. The source was observed in wobble mode during dark time at a mean zenith angle of 35°. Data were reduced using a new image-cleaning algorithm, the so-called sum-cleaning, which guarantees a better noise suppression and a lower energy threshold than the standard analysis procedure.

Results. No clear evidence for emission above the energy threshold of 100 GeV was found. MAGIC observations permit one to constrain the emission from the source down to 100 GeV, which favors models that explain the observed lower energy variable emission. Data analysis of simultaneous observations from AGILE, Fermi and VERITAS also provide negative detection, which additionally constrain the self-Compton emission component.