AGILE detection of Cygnus X-3 gamma-ray active states during the period mid-2009/mid-2010

Context. Cygnus X-3 (Cyg X-3) is a well-known microquasar producing variable emission at all wavelengths. Cyg X-3 is a prominent X-ray binary producing relativistic jets, and studying its high energy emission is crucial for the understanding of the fundamental acceleration processes in accreting compact objects. <BR /> Aims Our goal is to study extreme particle acceleration and gamma-ray production above 100 MeV during special spectral states of Cyg X-3 usually characterized by a low hard X-ray flux and enhanced soft X-ray states. <BR /> Methods We observed Cyg X-3 with the AGILE satellite in extended time intervals from 2009 Jun.-Jul., and 2009 Nov.-2010 Jul. We report here the results of the AGILE gamma-ray monitoring of Cyg X-3 as well as the results from extensive multiwavelength campaigns involving radio (RATAN-600, AMI-LA and Metshovi Radio Observatories) and X-ray monitoring data (XTE and Swift). <BR /> Results We detect a series of repeated gamma-ray flaring activity from Cyg X-3 that correlate with the soft X-ray states and episodes of decreasing or non-detectable hard X-ray emission. Furthermore, we detect gamma-ray enhanced emission that tends to be associated with radio flares greater than 1 Jy at 15 GHz, confirming a trend already detected in previous observations. The source remained active above 100 MeV for an extended period of time (almost 1.5 months in 2009 Jun.-Jul. and 1 month in 2010 May). We study in detail the short timescale gamma-ray flares that occurred before or near the radio peaks. <BR /> Conclusions Our results confirm the transient nature of the extreme particle acceleration from the microquasar Cyg X-3. A series of repeated gamma-ray flares shows correlations with radio and X-ray emission confirming a well established trend of emission. We compare our results with Fermi-LAT and MAGIC TeV observations of Cyg X-3.