We report the detection of a new H _ { 2 } O megamaser in the Seyfert 2 galaxy Mrk 348 with the MPIfR 100 m telescope in Effelsberg .
With an apparent isotropic luminosity of L _ { H _ { 2 } O } \simeq 420 L _ { \odot } the maser is the third most luminous maser discovered so far .
The detected line is unusually broad ( \Delta v \simeq 130 km s ^ { -1 } ) , is redshifted by \sim 130 km s ^ { -1 } from the systemic velocity , and is asymmetric with a pronounced blue wing .
While evidence for obscuring material towards the nucleus of this galaxy was found earlier , this detection is the first direct observation of molecular material in the vicinity of the AGN .
We also searched for absorption from ammonia ( NH _ { 3 } ) and cyclopropenylidene ( C _ { 3 } H _ { 2 } ) against the bright radio nucleus .
The H _ { 2 } O line was only marginally detected in archival data indicating that the maser flared recently in conjunction with a huge radio continuum flare .
Continuum and line flux density increased by a factor of three , suggesting an unsaturated maser .
The radio continuum flare has made Mrk 348 the most radio luminous megamaser galaxy known .
It is pointed out that megamaser galaxies contain a rather large fraction of galaxies with prominent radio cores and it is speculated that the flare in the maser emission in Mrk 348 is related to the flare in the nuclear jet .