INTERFEROMETRIC MONITORING OF GAMMA-RAY BRIGHT AGNs. I. THE RESULTS OF SINGLE-EPOCH MULTIFREQUENCY OBSERVATIONS

Abstract

We present results of single-epoch very long baseline interferometry (VLBI) observations of gamma-ray bright active galactic nuclei (AGNs) using the Korean VLBI Network (KVN) at the 22, 43, 86, and 129 GHz bands, which are part of a KVN key science program, Interferometric Monitoring of Gamma-Ray Bright AGNs. We selected a total of 34 radio-loud AGNs of which 30 sources are gamma-ray bright AGNs with flux densities of >6×10 −10 ph cm −2 s −1 . Single-epoch multifrequency VLBI observations of the target sources were conducted during a 24 hr session on 2013 November 19 and 20. All observed sources were detected and imaged at all frequency bands, with or without a frequency phase transfer technique, which enabled the imaging of 12 faint sources at 129 GHz, except for one source. Many of the target sources are resolved on milliarcsecond scales, yielding a core-jet structure, with the VLBI core dominating the synchrotron emission on a milliarcsecond scale. CLEAN flux densities of the target sources are 0.43-28 Jy, 0.32-21 Jy, 0.18-11 Jy, and 0.35-8.0 Jy in the 22, 43, 86, and 129 GHz bands, respectively. Spectra of the target sources become steeper at higher frequency, with spectral index means of −0.40, −0.62, and −1.00 in the 22-43 GHz, 43-86 GHz and 86-129 GHz bands, respectively, implying that the target sources become optically thin at higher frequencies (e.g., 86-129 GHz).

Exploring the Variability of the Flat Spectrum Radio Source 1633+382. I. Phenomenology of the Light Curves

“…For further details on the iMO-GABA calibration process see e.g. Algaba et al (2015); Hodgson et al (2016); Lee et al (2016).…”

“…Being one of the bright γ−ray blazars, 1633+382 is a typical target of several other monitoring programs, such as the Steward Observatory blazar monitoring program (Smith et al 2009), the VLBA-BU-BLAZAR program (Jorstad & Marscher 2016), the OVRO 15 GHz 40m monitoring program (Richards et al 2011), the Interferometric Monitoring of Gamma-ray Bright AGN (iMO-GABA) (Lee et al 2013;Algaba et al 2015;Lee et al 2016), and Swift X-Ray Telescope (XRT) (Stroh & Falcone 2013), to cite some. These programs aim to answer two questions: where are the γ−ray flares located and what are the emission mechanisms responsible for their origin.…”

The Power of Simultaneous Multi-frequency Observations for mm-VLBI: Beyond Frequency Phase Transfer

“…The brightest component we see at 86 GHz and lower frequencies does not correspond to the same feature due to free-free absorption (Walker et al 2000); See also Lee et al (2016).…”

“…We chose the 16th epoch of the KVN interferometric monitoring of gamma-ray bright AGN (iMOGABA) program, which is ideal for our test due to the fact that it observed up to 30 all-sky gamma-ray bright radio-loud AGNs with fluxes ranging from iMOGABA observations see e.g. Lee et al (2016) and Algaba et al (2015).…”

“…As most sources become optically-thin (e.g. Lee et al 2016), it is much easier to study their central regions at these frequencies. Such observations can probe upstream of the jets and into the vicinities of the AGN central engines, thus revealing key information about their source of energy, jet footpoint conditions, acceleration and collimation (e.g.…”