Discovery of water maser emission in five AGNs and a possible correlation between water maser and nuclear 2-10 keV luminosities

We report the discovery of water maser emission in five active galactic nuclei (AGNs) with the 100 m Green Bank Telescope (GBT). The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 sigma(0.''3 radio and 1.''3 optical) and most likely mark the locations of the embedded central engines. The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618 NED02, display the characteristic spectral signature of emission from an edge-on accretion disk with maximum orbital velocity of similar to 700, similar to 800, and similar to 1300 km s(-1), respectively. We also present a GBT spectrum of a previously known source, Mrk 0034, and interpret the narrow Doppler components reported here as indirect evidence that the emission originates in an edge-on accretion disk with orbital velocity of similar to 500 km s(-1). We obtained a detection rate of 12%(5 out of 41) among Seyfert 2 and LINER systems with 10,000 km s(-1) < v(sys) < 15,000 km s(-1). For the 30 nuclear water masers with available hard X-ray data, we report a possible relationship between unabsorbed X- ray luminosity (2-10 keV) and total isotropic water maser luminosity, L2-10 proportional to L-H2O(0.5 +/- 0.1), consistent with the model proposed by Neufeld and Maloney, in which X-ray irradiation and heating of molecular accretion disk gas by the central engine excites the maser emission.