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AGILE detection of enhanced gamma-ray emission from Cygnus X-3

ATel #3141; A. Bulgarelli (INAF/IASF Bologna, Italy), G. Piano, M. Tavani (INAF/IASF Roma), F. Gianotti, M. Trifoglio (INAF/IASF Bologna), G. Pooley (Cavendish Lab., Cambridge, UK), M. McCollough (Smithsonian Astrophys. Observatory, USA), Sergei A. Trushkin (Special Astrophysical Observatory, Russia), E. Striani (Univ. Tor Vergata), C. Pittori, F. Verrecchia, F. Lucarelli (ASDC), A. Argan, A. Trois, G. De Paris, V. Vittorini, E. Costa, I. Donnarumma, M. Feroci, L. Pacciani, E. Del Monte, F. Lazzarotto, P. Soffitta, Y. Evangelista, I. Lapshov, S. Sabatini (INAF-IASF-Rm), A. Chen, A. Giuliani(INAF-IASF-Milano), M. Marisaldi, G. Di Cocco, C. Labanti, F. Fuschino, M. Galli (INAF/IASF Bologna), P. Caraveo, S. Mereghetti, F. Perotti (INAF/IASF Milano), G. Pucella, M. Rapisarda (ENEA-Roma), F. D'Ammando, S. Vercellone (IASF-Pa), A. Pellizzoni, M. Pilia (INAF/OA-Cagliari), G. Barbiellini, F. Longo (INFN Trieste), P. Picozza, A. Morselli (INFN and Univ. Tor Vergata), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), P. W. Cattaneo, A. Rappoldi (INFN Pavia), P. Giommi, P. Santolamazza, (ASDC), L. Salotti, G. Valentini (ASI)
on 1 Feb 2011; 21:31 UT
Credential Certification: Marco Tavani (tavani@iasf-roma.inaf.it)

Subjects: Radio, X-ray, >GeV, Binary, Transient

Referred to by ATel #: 3151, 8591

AGILE is detecting an enhanced gamma-ray emission from a source positionally consistent with the microquasar Cygnus X-3.

Integrating during the period 2011-01-27 20:00 UT to 2011-02-01 11:00 UT (MJD= 55588.83-55593.45) the AGILE-GRID multi-source likelihood analysis finds enhanced gamma-ray emission above 100 MeV from a source at Galactic coordinates (l,b) = (79.50,1.05) +/- 0.7 (stat.) +/- 0.1 (syst.) deg, (R.A.,Dec.) = (307.46, 40.89) deg, with flux F = (200 +/- 60) e-8 ph/cm2/sec above 100 MeV (about 4 sigma significance for the 1-day integration period between MJD 55592.375 and 55593.375).

The AGILE exposure of Cygnus X-3 reported above covers the millimeter-wave radio flare period reported in the ATel #3130, and the radio observation of ATel #3135.

We also report radio data obtained by the RATAN-600 telescope and AMI Large Array. RATAN-600 has been monitoring Cygnus X-3 daily from Jan. 8th until Jan. 31st, 2011, at 4.8, 7.7 and 11.2 GHz (typical flux errors near 5-10 per cent). The radio light curve of Cygnus X-3 shows inverted spectra with a typical spectral index near +1. The power-law fit spectrum of 28 Jan. 2011, when extrapolated to higher frequencies gives a flux near 2 Jy at 98 GHz. This value is consistent with the NRO data (ATel #3130). This activity is also consistent with an optical thick flare of flux fainter than 1 Jy at cm wavelengths. An AMI-LA measurement obtained on Feb. 1, 2011, gives a flux of about 350 mJy at 15 GHz.

The hard X-ray flux of Cygnus X-3 from Swift/BAT shows over the last few months a downward trend towards a possible quenched state in the hard X-rays. There have been a few brief (~0.5 day) periods of very low hard X-ray flux during this period. The enhanced gamma-ray emission from Cygnus X-3 along with the recent spectral transition reported in the ATel 3139 appears to be following the trend that was identified in previous episodes of low hard X-ray emission (Tavani et al. 2009, Nature 462, 620; Abdo et al. 2009, Science 326, 1512; ATel #2609; ATel #2645).

We strongly encourage multifrequency observations of Cygnus X-3.