Abstract
ABSTRACT We revisit the well-studied outburst of the low-mass X-ray binary (LMXB) system V404 Cygni, and claims of γ-ray excesses observed with the Fermi-LAT instrument. Upon analysing an 11.5 yr data set with the 8-yr LAT point source catalogue and 8-yr background models, we find no evidence to suggest that there is high energy γ-ray emission during the outburst period (or at any other time) from V404 Cygni. This is due to the proximity of V404 Cygni to the γ-ray emitting blazar B2023+336, a luminous source approximately 0.3○ away, which causes source confusion at the position of V404 Cygni, the luminous γ-ray background, and the use of older background models and catalogues in previous studies.
Highlights
1.1 X-ray binaries and γ -ray emissionV404 Cygni is an X-ray binary system that lies on the Galactic plane (Kitamoto et al 1989)
We provide an independent analysis of the reported V404 Cygni γ -ray excesses, and of the nearby blazar B2023+336
We find that there is an 9.25 per cent chance of finding these six γ -ray excesses by chance, indicating a strong possibility that there is no γ -ray emission from V404 Cygni shown in the Xing 20 fig. 3 light curve that cannot be accounted for with either source confusion with B2023+336 or by considering the effect of apparently significant bins arising by chance
Summary
V404 Cygni ( known as GS 2023+338) is an X-ray binary system that lies on the Galactic plane (Kitamoto et al 1989) It consists of a K-type star with a mass slightly below 1 M (Wagner et al 1992) and a black hole companion of mass 9 M (Khargharia, Froning & Robinson 2010); this stellar mass means that V404 Cygni is considered a low-mass X-ray binary (LMXB). Jets are seen from microquasars in a variety of states as described by the hardnessintensity cycle (Fender, Belloni & Gallo 2004), including compact jets in the low-hard X-ray state (Tomsick et al 2008) It is from these jets that the particle acceleration required for γ -ray emission takes place, with evidence to suggest that γ -rays are produced when a jet forms at the transition between the hard and soft state, and from the hard state compact jet (Zdziarski et al 2017). The first and arguably best studied is SS 433, which is a unique
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