Statistics of VHE γ-rays in temporal association with radio giant pulses from the Crab pulsar

¹ ETH Zurich, 8093 Zurich, Switzerland
² Università di Udine, and INFN Trieste, 33100 Udine, Italy
³ Japanese MAGIC Consortium: ICRR, The University of Tokyo, 277-8582, Chiba, Japan; Department of Physics, Kyoto University, 606-8502, Kyoto, Japan; Tokai University, 259-1292 Kanagawa, Japan
⁴ National Institute for Astrophysics (INAF), 00136 Rome, Italy
⁵ Università di Padova and INFN, 35131 Padova, Italy
⁶ Croatian MAGIC Consortium: University of Rijeka, Department of Physics, 51000 Rijeka, University of Split – FESB, 21000 Split, University of Zagreb – FER, 10000 Zagreb, University of Osijek, 31000 Osijek and Rudjer Boskovic Institute, 10000 Zagreb, Croatia
⁷ Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Salt Lake, Sector-1, Kolkata 700064, India
⁸ Max-Planck-Institut für Physik, 80805 München, Germany
⁹ Centro Brasileiro de Pesquisas Físicas (CBPF), Urca, 22290-180 Rio de Janeiro (RJ), Brazil
¹⁰ Universidad Complutense, 28040 Madrid, Spain
¹¹ Inst. de Astrofísica de Canarias, 38200 La Laguna, and Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹² University of Łódź, Department of Astrophysics, 90236 Łódź, Poland
¹³ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹⁴ Humboldt University of Berlin, Institut für Physik Newtonstr. 15, 12489 Berlin, Germany
¹⁵ Also at Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
¹⁶ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra, Barcelona, Spain
¹⁷ Università di Siena, and INFN Pisa, 53100 Siena, Italy
¹⁸ Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁹ Universität Würzburg, 97074 Würzburg, Germany
²⁰ Finnish MAGIC Consortium: Tuorla Observatory and Finnish Centre of Astronomy with ESO (FINCA), University of Turku, Vaisalantie 20, 21500 Piikkiö, Astronomy Division, University of Oulu, 90014 Oulu, Finland
²¹ Departament de Física, and CERES-IEEC, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
²² Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
²³ Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA and Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA
²⁴ Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
²⁵ INAF-Trieste and Dept. of Physics & Astronomy, University of Bologna, Bologna, Italy
²⁶ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²⁷ ASTRON, PO Box 2, 7990 Dwingeloo, The Netherlands

Received: 1 June 2018
Accepted: 30 October 2019

Abstract

Aims. The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE, E >  100 GeV) γ-rays from the Crab pulsar.

Methods. We performed 16 h of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV we used the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes. We searched for a statistical correlation between the radio and VHE γ-ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHE γ-rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges, respectively.

Results. In the radio data sample, 99444 radio GPs were detected. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows, we find upper limits at a 95% confidence level on an increase in VHE γ-ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges, respectively. This puts upper limits on the flux increase during a radio GP between 12% and 2900% of the pulsed VHE flux, depending on the search window duration and phase cuts. This is the most stringent upper limit on a correlation between γ-ray emission and radio GPs reported so far.