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Multi-frequency radio observations of CTA 102 during enhanced activity state

ATel #9884; Simona Righini (INAF-IRA, Medicina), Marcello Giroletti, Filippo D'Ammando (INAF-IRA, Bologna), Claudia Raiteri, Massimo Villata (INAF-OATorino), Uwe Bach (MPIfR, Bonn)
on 20 Dec 2016; 15:54 UT
Credential Certification: Marcello Giroletti (giroletti@ira.inaf.it)

Subjects: Radio, AGN, Blazar, Quasar

Referred to by ATel #: 9901, 9911, 9924

We report on multi-frequency radio observations of CTA 102 (2230+114), obtained following the reports of intense gamma-ray emission by AGILE and Fermi (ATel #9863, #9869) and the record optical blazar state ever detected (ATel #9868). The observations were carried out in the context of our Medicina-Noto radio monitoring of gamma-ray loud blazars that is part of the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT).

We observed CTA 102 with the INAF Medicina 32 m radio telescope at 24, 8.4, and 5 GHz on 15 December 2016 21.25UT, 16 December 2016 10.21UT, and 17 December 2016 13.54UT, respectively. From our preliminary analysis, we measured a flux density of 3.75 +/- 0.10 Jy at 5 GHz, 4.00 +/- 0.10 Jy at 8.4 GHz, and 3.70 +/- 0.40 Jy at 24 GHz. The corresponding spectral index is -0.12 +/- 0.07 between 5 and 8.4 GHz and 0.07 +/- 0.11 between 8.4 and 24 GHz (defined by S(ν) ~ ν).

In comparison to reference flux densities reported for this source during a previous high activity phase (ATel #4449), the current measurements indicate an increase of the high frequency flux density and an overall flattening of the radio spectrum, consistent with the behaviour expected for an optically thick emitting region. We will continue to observe the source at these frequencies with the INAF Medicina radio telescope. Further monitoring with other facilities is encouraged.