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Radio detection of V407 Cyg - the possible counterpart of the new Fermi LAT Gamma-ray Transient J2102+4542 with the Effelsberg 100-m, OVRO 40-m and IRAM 30-m telescopes

ATel #2506; I. Nestoras, L Fuhrmann, U. Bach, K. Sokolovsky (MPIFR), H. Ungerechts, D. Riquelme, A. Sievers (IRAM), J. L. Richards, W. Max-Moerbeck, T. J. Pearson, A. C. S. Readhead (OVRO, Caltech) , and the F-GAMMA team
on 24 Mar 2010; 20:06 UT
Credential Certification: Lars Fuhrmann (lfuhrmann@mpifr-bonn.mpg.de)

Subjects: Radio, Millimeter, Optical, X-ray, Gamma Ray, >GeV, Nova, Transient, Variables

Referred to by ATel #: 2511, 2514, 2529, 2536, 2546, 2741, 2905

Following the Fermi-LAT detection of transient gamma-ray emission near the Galactic Plane, J2102+4542, and its possible association with the symbiotic star and recent nova outburst of V407 Cyg (ATEL #2487, see also CBET #2199, ATEL #2498), we present the first radio detections and a quasi-simultaneous spectrum at the position of V407 Cyg (RA, Dec: 21 02 09.81, +45 46 33.0, J2000). The source was detected with the Effelsberg 100-m, OVRO 40-m and IRAM 30-m telescopes on March 22/23. We obtain flux densities of (8.5 ±0.8) mJy at 8.35 GHz, (11.6 ±0.9) mJy at 10.45 GHz, (14.6 ±1.2) mJy at 14.6 GHz (Effelsberg), (24.1 ±1.7) mJy at 15 GHz (OVRO) and (146 ±51) mJy at 142 GHz (IRAM 30-m). Tentative detections have been obtained at 32 and 86 GHz with flux densities of ~ 60 mJy and ~ 85 mJy, respectively. We are investigating the apparent discrepancy between the Effelsberg 14.6 GHz and OVRO 15 GHz flux densities, which could imply variability of the source.

Taking into account the previous non-detections of the source at radio bands (only upper limits, e.g. <0.06 mJy at 8.4GHz, Wendker, H. J. A&A, 1995, see also Ivison, R. J. et al. 1995, MNRAS, 273, 517), our measured flux densities indicate a high state of the source, in agreement with the observations at other spectral bands. The radio spectrum is highly inverted with a spectral index of 0.97 (S propto nu^alpha) possibly consistent with an optically thick expanding shell expected from such outburst.

We will continue to observe the source over the next few weeks and encourage other telescopes to observe this source at radio and other spectral bands.