Publication: Statistics of VHE γ-rays in temporal association with radio giant pulses from the Crab pulsar
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2020-01-30
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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& x2004;> & x2004;100 GeV) gamma-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 gamma-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 gamma-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 gamma-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 gamma-ray emission and radio GPs reported so far.
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© ESO 2020. Artículo firmado por 146 autores. NL would like to thank Axel Jessner (MPIfR), Jean Eilek (NRAO), Maura McLaughlin (WVU), Ryan Lynch (GBO) and Vlad Kondratiev (ASTRON) for numerous helpful comments which improved the quality of the paper. We acknowledge Marina Manganaro (Croatian MAGIC Consortium) for her continuous help in preparing the manuscript. We would like to thank the anonymous referee for numerous comments which helped us to improve the quality of the manuscript. NL would also like to thank Ramesh Karuppusamy (MPIfR), Alex Kraus (MPIfR), Ralf Kisky (MPIfR), Jorg Barthel (MPIfR) and Thomas Wedel (MPIfR) for constant support during the observations with the Effelsberg radio telescope. NL gratefully acknowledges the support of this study by the ASTRON/JIVE Helena Kluyver female visitor program. This study is partly based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut fur Radioastronomie) at Effelsberg. Another part of this study was carried out with data taken with the Westerbork Synthesis Radio Telescope (WSRT). The Westerbork Synthesis Radio Telescope is operated by the ASTRON (Netherlands Institute for Radio Astronomy) with support from the Netherlands Foundation for Scientific Research (NWO). We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA201569210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA201571042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P, CSD2009-00064), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia "Severo Ochoa" SEV-20120234 and SEV-2015-0548, and Unidad de Excelencia "María de Maeztu" MDM2014-0369, by the Croatian Science Foundation (HrZZ) Project 09/176 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq and FAPERJ.