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Paper: Multifrequency Observation of Cygnus X–3 at the Time of Giant Flare in 2006 May-June
Volume: 407, The Low-Frequency Radio Universe
Page: 277
Authors: Pal, S.; Ishwara-Chandra, C.H.; Rao, A.P.
Abstract: We report multi-frequency radio observation of Galactic microquasar Cygnus X-3 during the giant flare of 2006 May-June, which was one of the largest flares in the recorded history of the source. We have used simultaneous observation at 244 and 614 MHz by Giant Metrewave Radio Telescope (GMRT) and archival observation data at 8.43, 22.5 and 43.3 GHz by Very Large Array (VLA). We study the evolution of radio spectrum of the source from our observations using GMRT and VLA and published results using RATAN. The radio spectrum shows turn-over and turn-over frequency shifts towards lower frequency region, as the flare evolves. We study variation of two point spectral index á, which is calculated from the simultaneous observations between 244 and 614 MHz. Two point spectral index show clear variation from positive (optically thick) to negative (optically thin) values, as the flare progresses. We show that this behavior is consistent with synchrotron self-absorption. We have proposed a possible model in terms of expanding plasma blob to explain the evolution of low frequency spectral index. We calculate the size of the emitting region, turn over frequency and corresponding peak flux density using the synchrotron self-absorption model. From the size of the radio emission region at different epochs of the flare, we estimate the velocity of expansion of the blob to be in the range 0.02 to 0.17c, assuming a magnetic field strength in the range 0.1 to 1 Gauss.
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