The Flaring H 2 O Megamaser and Compact Radio Source in Mrk 348

We report on single-dish monitoring and extremely high angular resolution observations of the flaring H2O megamaser in the Seyfert 2 galaxy Mrk 348. The H2O line is redshifted by ∼130 km s with respect to the systemic velocity, is very broad, with a FWHM of 130 km s, and has no detectable high velocity components within 1500 km s on either side of the strong line. Monitoring observations made with the Effelsberg 100m telescope show that the maser varies significantly on timescales as short as one day and that the integrated line flux is loosely correlated with the continuum flux. VLBA observations indicate that the maser emission arises entirely from a region less than 0.25 pc in extent, located toward a continuum component thought to be associated with the receding jet. We also report on integrated flux monitoring with the VLA between 1.4 and 43 GHz, and VLBA continuum observations of the milliarcsecond scale jets at 1.7, 8, 15, and 22 GHz. These observations have allowed us to tentatively pinpoint the location of the core, and also show the ejection of a new jet component during the current radio “flare.” Subject headings: masers – galaxies:active – galaxies:jets – radio lines:galaxies – galaxies:Seyferts – galaxies:individual (Mrk 348,NGC 262) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany current: Harvard-Smithsonian Center for Astrophysics, SAO/SMA Project, P.O. Box 824, Hilo, HI 96721, USA, [email protected] National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 Dept. of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 Dept. of Physics, Bucknell University, Lewisburg, PA 17837