Continuing flux density increase in OQ 334 revealed by Sardinia Radio Telescope dual-frequency observations
ATel #13582; Nicola Marchili, Simona Righini, Marcello Giroletti (INAF Istituto di Radioastronomia), Elise Egron (INAF Osservatorio Astronomico di Cagliari)
on 24 Mar 2020; 08:04 UT
Credential Certification: Marcello Giroletti (giroletti@ira.inaf.it)
Subjects: Radio, Gamma Ray, VHE, AGN, Blazar, Quasar
Following the reported flaring state in the gamma rays (ATel #13382, #13412, #13417) of the flat-spectrum radio quasar OQ 334 (a.k.a B2 1420+32, z=0.681889), we carried out two epochs of observations of the source at frequencies of 6.1 and 23.8 GHz with the 64m Sardinia Radio Telescope (SRT), operated by INAF.
OQ 334 was observed a first time starting on 2020 Feb 29.00 and a second one on 2020 Mar 20.93; in both epochs, the total observing time covered an interval of about 1.5 hours. For the first epoch (MJD 58908.02) we measured average flux densities of 0.775 +/- 0.010 Jy (6.1 GHz), and 1.64 +/- 0.03 Jy (23.8 GHz), leading to a spectral index, alpha, (defined according to the convention S = S_0 ^ -alpha), of -0.55+/-0.01 The flux densities measured in the second epoch (MJD 58927.95) are 0.847 +/- 0.010 Jy (6.1 GHz), and 1.71 +/- 0.03 Jy (23.8 GHz), indicating an unchanged spectral index of -0.55+/-0.01.
Our measurements indicate that the source's radio emission is still rising, which is compatible with the typical radio-gamma delays observed in blazars' flares. By using a spectral index of -0.55, we interpolated our measurements to estimate an approximate flux at 8.63 GHz, to allow a comparison with the early February 2020 observations reported by Kharinov (ATel #13479). These range between 0.76 to 0.91 Jy; our interpolated values, in order of time, are 0.94 and 1.09 Jy, which confirms the flux density increase of the source.
The continuing rise and strongly inverted spectral index indicates that the radio flare is still ongoing, and further observations at all wavelengths should continue.
