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Published April 2012 | Published
Journal Article Open

A giant radio flare from Cygnus X-3 with associated γ-ray emission


With frequent flaring activity of its relativistic jets, Cygnus X-3 (Cyg X-3) is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high-energy γ-ray emission, thanks to detections by Fermi Large Area Telescope (Fermi/LAT) and AGILE. In 2011, Cyg X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy γ-ray emission. We present the results of a multiwavelength campaign covering a quenched state, when radio emission from Cyg X-3 is at its weakest and the X-ray spectrum is very soft. A giant (∼20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E≥ 100 MeV) reveal renewed γ-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the γ-ray emission is not exclusively related to the rare giant radio flares. A three-week period of γ-ray emission is also detected when Cyg X-3 was weakly flaring in radio, right before transition to the radio quenched state. No γ-rays are observed during the ∼1-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio-quenched) state trigger γ-ray emission, implying a connection to the accretion process, and also that the γ-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.

Additional Information

© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2012 January 9. Received 2012 January 9; in original form 2011 November 25. Article first published online: 20 Feb 2012. We thank the Fermi team for accepting and promptly conducting the LAT Target of Opportunity on Cyg X-3 in 2011 March. We acknowledge Elmar Koerding, Andrzej Zdziarski and the referee for their comments on the manuscript. The research by SC leading to these results has received funding from the European Community (EC) Seventh Framework Programme (FP7/2007-2013) under grant agreement number ITN 215212 Black Hole Universe. GD acknowledges support from the EC via contract ERC-StG-200911. JAT acknowledges partial support from NASA Fermi Guest Observer award NNX10AP83G and from NASA Astrophysics Data Analysis Programme award NNX11AF84G. The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged. This research has made use of the MAXI data provided by RIKEN, JAXA and the MAXI team. Swift/BAT transient monitor results provided by the Swift/BAT team. We also acknowledge the RXTE/ASM team for the X-ray monitoring ASM data. AMI is supported by STFC and the University of Cambridge. The OVRO 40-m monitoring programme was supported in part by NASA grants NNX08AW31G and NNG06GG1G and NSF grant AST-0808050. The RATAN-600 observations were carried out with the financial support of the Ministry of Education and Science of the Russian Federation.

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Published - Corbel2012p18068Mon_Not_R_Astron_Soc.pdf

Published - MNRAS-2012-Corbel-2947-55.pdf


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