The flaring H2O megamaser and compact radio source in Markarian 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 similar to130 km s(-1) with respect to the systemic velocity, is very broad, with an FWHM of 130 km s(-1), and has no detectable high-velocity components within 1500 km s(-1) on either side of the strong line. Monitoring observations made with the Effelsberg 100 m telescope show that the maser varies significantly on timescales as short as 1 day and that the integrated line flux is loosely correlated with the continuum flux. Very Long Baseline Array (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''.