Investigating the mini and giant radio flare episodes of Cygnus X-3

Abstract

The microquasar Cygnus X-3 underwent a giant radio flare in April 2017, reaching a maximum flux of $\sim 16.5$ Jy at 8.5 GHz. We present results from a long monitoring campaign carried out with Medicina at 8.5, 18.6 and 24.1 GHz, in parallel to the Metsähovi radio telescope at 37 GHz, from 4 to 11 April 2017. We observe a spectral steepening from $\alpha =0.2$ to 0.5 (with $S_{\nu }\propto {\nu }^{-\alpha }$) within 6 h around the epoch of the peak maximum of the flare, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux density indicated the decay of the giant flare. We further study the radio orbital modulation of Cyg X-3 emission associated with the 2017 giant flare and with six mini-flares observed in 1983, 1985, 1994, 1995, 2002 and 2016. The enhanced emission episodes observed during the decline of the giant flare at 8.5 GHz coincide with the orbital phase $\varphi \sim 0.5$ (orbital inferior conjunction). On the other hand the light curves of the mini-flares observed at $15-22$ GHz peak at $\varphi \sim 0$, except for the 2016 light curve which is shifted of 0.5 w.r.t. the other ones. We attribute the apparent phase shift to the variable location of the emitting region along the bent jet. This might be explained by the different accretion states of the flaring episodes (the 2016 mini-flare occurred in the hypersoft X-ray state).

15 pages, 4 figures, accepted for publication in the Astrophysical Journal

References in corpus (12)

• Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection
• Spectral variability in Cygnus X-3
• The nature of the hard state of Cygnus X-3
• First e-VLBI observations of Cygnus X-3
• Cygnus X-3: Its Little Friend's Counterpart, the Distance to Cygnus X-3, and Outflows/Jets
• A classification of the X-ray and radio states of Cyg X-3 and their long-term correlations
• Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode
• Jet radio emission in Cygnus X-1 and its orbital modulation
• Opacity effects and shock-in-jet modelling of low-level activity in Cygnus X-3
• Synchrotron flaring behaviour of CygnusX-3 during the February-March 1994 and September 2001 outbursts
• A precise measurement of the orbital period parameters of Cygnus X-3
• Jets in the soft state in Cyg X-3 caused by advection of the donor magnetic field and unification with low-mass X-ray binaries

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• Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038
• A Flat-Spectrum Radio Transient at 122 Mpc consistent with an Emerging Pulsar Wind Nebula
• Black holes at cosmic dawn in the redshifted 21cm signal of HI
• Major and Minor Flares on Cygnus X-3 Revisited
• Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR