VLBA Observations of AGN Activity in NGC 2617
ATel #5347; J. Jencson (Ohio State), Kara Kundert (National Radio Astronomy Observatory), Amy Mioduszewski (National Radio Astronomy Observatory), Adrian Lucy (University of Oklahoma), Jennifer Kadowaki (University of California, Los Angeles), Samuel N. Mellon (Westminster College)
on 30 Aug 2013; 18:20 UT
Credential Certification: Michael P. Rupen (mrupen@nrao.edu)
NGC 2617 is an active galaxy at z=0.0142 (~60 Mpc, 1 mas = 0.3 pc). A strong outburst was discovered by the All Sky Automated Survey for SuperNovae (ASAS-SN) in NGC 2617 at 2013 UT Apr. 10.27. A follow-up optical spectrum indicated a dramatic spectral type change from a Type 1.8 Seyfert to a Type 1 Seyfert within the last decade (Shappee et al. 2013, ATel #5010). Additional follow-up observations by Swift/BAT (Shappee et al. 2013, ATel #5059) and INTEGRAL (Tsygankov et al. 2013, ATel #5103) showed increasing X-ray activity. European VLBI Network observations were carried out on 2013 June 7 and detected compact radio emission with a flux density of 1.5 ± 0.3 mJy at 1.6 GHz positionally coincident with the nucleus of NGC 2617. These data constrained the source size to less than 4 milliarcseconds and implied a lower limit on the brightness temperature of 8.7 × 107 K (Yang et al. 2013, ATel #5125).
We conducted VLBA observations of the nucleus of NGC 2617 at 5 and 1.7 GHz on 2013 June 29. Radio emission was detected with flux densities of 1.5 ± 0.1 mJy at 5 GHz and 1.6 ± 0.3 mJy at 1.7 GHz, indicating little to no variability since the e-EVN observations in June. See our naturally weighted detection images here. From our measurements we find a spectral index of -0.1 ± 0.7, which is consistent with a flat spectrum. We believe the source is barely resolved at 5 GHz, with a major and minor axis of 2.6 ± .6 mas and 1.5 ± .2 mas, respectively. Adopting the redshift of the host galaxy, this corresponds to a physical size of ~ 0.8 by 0.5 pc. However, because the size and position angle of the source is very near to that of the beam, higher resolution observations are required to verify this result. Utilizing data on our calibration source (J0834-0437) and a well-known check source (J0847-0520), we solved for a position for the nucleus of NGC 2617 of 08:35:38.7845 right ascension and -04:05:17.802 declination (J2000). Further observations at higher frequencies to achieve better resolution and improved measurements of the spectral index are encouraged.
We would like to thank Vivek Dhawan for his invaluable contributions and guidance along the course of this observing project. We also thank NRAO for granting us the time for the this observation, and the observatory crew. This research was supported by the National Science Foundation under Grant No. ATM-1062154.
