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

¹ INAF/IASF–Bologna, via Gobetti 101, 40129 Bologna, Italy ;
e-mail: bulgarelli@iasfbo.inaf.it
² INAF/IASF–Roma, via del Fosso del Cavaliere 100, 00133 Roma, Italy
³ CIFS–Torino, viale Settimio Severo 3, 10133 Torino, Italy
⁴ INAF/IASF–Milano, via E. Bassini 15, 20133 Milano, Italy
⁵ Dip. di Fisica, Univ. “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁶ Dip. di Fisica and INFN Trieste, via Valerio 2, 34127 Trieste, Italy
⁷ ENEA–Bologna, via Biancafarina 2521, 40059 Medicica ( BO), Italy
⁸ INFN–Roma “La Sapienza”, Piazzale A. Moro 2, 00185 Roma, Italy
⁹ INFN–Pavia, via Bassi 6, 27100 Pavia, Italy
¹⁰ INFN–Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹¹ Dip. di Fisica, Univ. dell’Insubria, via Valleggio 11, 22100 Como, Italy
¹² ENEA–Frascati, via E. Fermi 45, 00044 Frascati ( Roma), Italy
¹³ AS-ASDC, via G. Galilei, 00044 Frascati ( Roma), Italy
¹⁴ Dipartimento di Fisica, Universitá La Sapienza, Piazza Aldo Moro 2, 00185 Roma, Italy
¹⁵ INAF Osservatorio Astronomico di Cagliari, Poggio dei Pini, 09012 Capoterra ( Cagliari), Italy
¹⁶ Astrophysics Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
¹⁷ Special Astrophysical Observatory RAS, Karachaevo-Cherkassian Republic, Nizhnij Arkhyz 36916, Russia
¹⁸ Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
¹⁹ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisä lä ntie 20, 21500 Piikkiö, Finland
²⁰ Aalto University Metsähovi Radio Observatory Metsähovintie 114, 02540 Kylmälä, Finland
²¹ INAF/IASF–Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy
²² Astronomy And Astrophysics Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²³ CISAS “G. Colombo”, Univ. di Padova, via Venezia 15, 35131 Padova, Italy
²⁴ Department of Physics and Space Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
²⁵ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
²⁶ School of Physics, University of the Witwatersrand, Johannesburg Wits 2050, South Africa

Received: 11 November 2010
Accepted: 26 October 2011

Abstract

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.

Aims. Our goal is to study extreme particle acceleration and γ-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.

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 γ-ray monitoring of Cyg X-3 as well as the results from extensive multiwavelength campaigns involving radio (RATAN-600, AMI-LA and Metsähovi Radio Observatories) and X-ray monitoring data (XTE and Swift).

Results. We detect a series of repeated γ-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 γ-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 γ-ray flares that occurred before or near the radio peaks.

Conclusions. Our results confirm the transient nature of the extreme particle acceleration from the microquasar Cyg X-3. A series of repeated γ-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.