Time delay of the PeV gamma ray burst after the October 1985 radio flare of Cygnus X-3

Abstract

Cygnus X-3 remains a puzzling and controversial source of ultra-high-energy radiation, E≳O.l PeV (1 PeV = 10¹⁵eV). At these energies the radiation is variable^1–3, with periodicity 4.8 h and a prominent peak at phase ∼0.2 during 1976–1980 and at phase ∼0.6 after 1984. There are outstanding difficulties in explaining both the phase diagram of the radiation and also the high luminosity in particles, L_p = 10⁴⁰ erg s⁻¹. In existing data, TeV and sometimes PeV radiation has been seen episodically; such an episode is connected with the radio flare of Cyg X-3 in October 1985, when PeV radiation with no phase structure was seen. The PeV pulse was detected⁵ 3–5 days after the radio flare. It was suggested⁶ that this delay could be explained by introducing a massless free gluon as an intermediary, but here I propose a more natural explanation in which gamma-photons of PeV energy are absorbed by radio radiation inside the source. After a delay, the gamma radiation emerges as the radio flux diminishes and absorption decreases.