Two Bursts of Ultra-High Energy Gamma Rays Detected by the Baksan Air Shower Array
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ELEMENTARY PARTICLES AND FIELDS Experiment
Two Bursts of Ultra-High Energy Gamma Rays Detected by the Baksan Air Shower Array A. S. Lidvansky* Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, 117312 Russia Received July 10, 2019; revised July 10, 2019; accepted July 10, 2019
Abstract—During a Cygnus X-3 campaign many years ago the Carpet air shower array of the Baksan Neutrino Observatory had recorded two bursts from two different sources: from the Crab Nebula on February 23, 1989 and from Cygnus X-3 on October 14–16, 1985. The characteristics of the bursts were quite different, as well as types of the source objects. The first of these bursts was discussed in some detail after registration of regular flares of gamma rays with energies of several hundred MeV by the satellite gamma-ray telescopes FermiLAT and AGILE. The second burst was not discussed in recent time, and in this paper attention is attracted to it in connection with the new results of the Tibet ASγ collaboration. DOI: 10.1134/S1063778819660360
INTRODUCTION Recently [1] the Tibet ASγ Collaboration reported the detection of 100-TeV photons from the Crab Nebula. However, their statement “This is the first detection of photons with E > 100 TeV from an astrophysical source” (see abstract in [1]) is not fully true. It was claimed by some people that they had detected positive signals from different sources in this or even higher energy range. Among them are the two bursts recorded by the Carpet air shower array of the Baksan Neutrino Observatory from two different sources: from the Crab Nebula on February 23, 1989 and from Cygnus X-3 on October 14–16, 1985. In the 1980s the gamma ray astronomy of ultrahigh energies (Eγ > 1014 eV) was at a peak of activity in connection with the sensational data of the Kiel University group that reported about a signal detected from the X-ray source Cygnus X-3 in this energy range. Later it became clear that this result was obviously wrong, but it stimulated many experimental and theoretical works on the problem. A lot of experimental efforts (including specially constructed EAS array called Cygnus) were made and witty hypotheses put forward (like hypothetical new elementary particle cygnet and quark confinement violation). Among other results obtained in the course of the campaign for Cygnus X-3 observations there were two which are discussed here. First was a three-day excess of count rate in the source’s angular cell detected by the Baksan air shower array (BASA) on October 14–16, 1985 [2, 3]. *
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This event had occurred several days after a most powerful radio outburst in Cygnus X-3 (in fact the strongest for all previous history of observations). Another burst-like event was detected by the BASA three and a half years later from the Crab Nebula [4, 5]. Both these events are discussed below in some detail. CYGNUS X-3 OBSERVATIONS AND A RECORDED BURST Figures 1 and 2 summarize the general yield of Cygnus X-3 observations in DC mode for several years [2]. Since no energy reco
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