Enhanced high-energy gamma-ray emission from the microquasar Cygnus X-3 detected by Fermi/LAT

ATel #10109; Alan Loh (LESIA, Paris Observatory) & Stephane Corbel (SAp-AIM, CEA, Paris Diderot University), on behalf of the Fermi Large Area Telescope Collaboration
on 22 Feb 2017; 13:23 UT
Credential Certification: Alan Loh (alan.loh.up7@gmail.com)

Tweet

Following the recent decrease of the hard X-ray emission from the high-mass X-ray binary Cygnus X-3 as seen by the Swift/Burst Alert Telescope (https://swift.gsfc.nasa.gov/results/transients/CygX-3/), the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed significant gamma-ray emission originating from the microquasar. Preliminary analysis of LAT data has unveiled a gamma-ray flare from Cyg X-3, with a flux (E > 100 MeV) of (1.6 +/- 0.3) x 10^-6 ph cm^-2 s^-1 (errors are statistical only) on MJD 57799 (~5 sigma significance over 24 hours). Integrating from MJD 57798 to MJD 57801 yields a detection significance of nearly 7 sigma with a corresponding flux of (1.1 +/- 0.3) x 10^-6 ph cm^-2 s^-1. The gamma-ray detection time interval matches the soft state of Cygnus X-3, while the source was likely reaching the so-called ultra-soft state as defined by Corbel et al. 2012, MNRAS 421, 2947. Multiple high-energy gamma-ray flares of Cyg X-3 have been previously detected by the LAT and AGILE since 2009 (Fermi/LAT Collaboration et al. 2009, Science 326, 1512, Tavani et al. 2009, Nature 462, 620) until recently (ATel#8591, ATel#9502), often when Cyg X-3 was in the soft state. The Swift/BAT and MAXI light curves may indicate that Cyg X-3 is currently in the ultra-soft state, where the radio emission from the jet is likely quenched. A major jet ejection event may therefore be coming in the next days, which would probably be associated with enhanced gamma-ray emission (see for e.g. Corbel et al. 2012). We thus strongly encourage multi-wavelength observations of Cyg X-3 as it may undergo a giant flaring episode in the coming days. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. For this source the Fermi LAT contact persons are Alan Loh (alan.loh@obspm.fr) and Stephane Corbel (stephane.corbel@cea.fr). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.