Falcke et al. 1999: Millimeter Outburst in IIIZw2

A major radio outburst in III Zw 2 with an extremely inverted, millimeter-peaked spectrum

Heino Falcke1, Geoffrey C. Bower1,2, Andrew R. Lobanov1, Thomas P. Krichbaum1, Alok R. Patnaik1, Margo F. Aller3, Hugh D. Aller3, Harri Teräasranta4, Melvyn C.H. Wright5, G\"oran Sandell6

1Max-Planck-Institut für Radioastronomie, Auf den Hügel 69, D-53121 Bonn, Germany (hfalcke@mpifr-bonn.mpg.de)
2Current address: NRAO, P.O. Box O, Socorro, NM 87801-0387
3Astronomy Department, University of Michigan, Ann Arbor, MI 48109-1090
4Metsähovi Radio Research Station, Metsahovintie, SF-02540 Kylm\"al\"a, Finland
5Radio Astronomy Laboratory, University of California, Berkeley, CA 94720
6National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944, U.S.A.

Astrophysical Journal Letters, Vol. 514, p. L17 (1999)


III Zw 2 is a spiral galaxy with an optical spectrum and faint extended radio structure typical of a Seyfert galaxy, but also with an extremely variable, blazar-like radio core. We have now discovered a new radio flare where the source has brightened more than twenty-fold within less than two years. A broad-band radio spectrum between 1.4 and 666 GHz shows a textbook-like synchrotron spectrum peaking at 43 GHz, with a self-absorbed synchrotron spectral index +2.5 at frequencies below 43 GHz and an optically thin spectral index -0.75 at frequencies above 43 GHz. The outburst spectrum can be well fitted by two homogenous, spherical components with equipartition sizes of 0.1 and 0.2 pc at 43 and 15 GHz, and with magnetic fields of 0.4 and 1 Gauss. VLBA observations at 43 GHz confirm this double structure and these sizes. Time scale arguments suggest that the emitting regions are shocks which are continuously accelerating particles. This could be explained by a frustrated jet scenario with very compact hotspots. Similar millimeter-peaked spectrum (MPS) sources could have escaped our attention because of their low flux density at typical survey frequencies and their stronger variability.

Paper: Available in PostScript and (AAS)LaTex. Please send an email request to hfalcke@mpifr-bonn.mpg.de for a preprint.

Other publications can be found here.

Questions: Heino Falcke, hfalcke@mpifr-bonn.mpg.de