2 research outputs found
Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR
We present Low-Frequency Array (LOFAR) 143.5-MHz radio observations of
flaring activity during 2019 May from the X-ray binary Cygnus X-3. Similar to
radio observations of previous outbursts from Cygnus X-3, we find that this
source was significantly variable at low frequencies, reaching a maximum flux
density of about 5.8 Jy. We compare our LOFAR light curve with contemporaneous
observations taken at 1.25 and 2.3 GHz with the RATAN-600 telescope, and at 15
GHz with the Arcminute Microkelvin Imager (AMI) Large Array. The initial
143.5-MHz flux density level, 2 Jy, is suggested to be the delayed and
possibly blended emission from at least some of the flaring activity that had
been detected at higher frequencies before our LOFAR observations had begun.
There is also evidence of a delay of more than four days between a bright flare
that initially peaked on May 6 at 2.3 and 15 GHz, and the corresponding peak
( 5.8 Jy) at 143.5 MHz. From the multi-frequency light curves, we
estimate the minimum energy and magnetic field required to produce this flare
to be roughly 10 erg and 40 mG, respectively, corresponding to a minimum
mean power of 10 erg s. Additionally, we show that the
broadband radio spectrum evolved over the course of our observing campaign; in
particular, the two-point spectral index between 143.5 MHz and 1.25 GHz
transitioned from being optically thick to optically thin as the flare
simultaneously brightened at 143.5 MHz and faded at GHz frequencies
Multiwavelength behaviour of the blazar 3C 279: decade-long study from gamma-ray to radio
We report the results of decade-long (2008-2018) gamma-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and gamma-ray light curves correlate well, with no delay greater than or similar to 3 h, implying general cospatiality of the emission regions. The gamma-ray optical flux flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz Very Long Baseline Array images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain gamma-ray variability on very short time-scales, The Mg II emission line flux in the 'blue' and 'red' wings correlates with the optical synchrotron conlinuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. in the radio bands, we find progressive delays of the most prominent light-curve maxima with decreasing frequency, as expected from the frequency dependence of the tau = 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light. curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at similar to 5 GHz, These tendencies suggest. different Doppler boosting of stratified radio-emitting zones in the jet