DISCOVERY OF WATER MASER EMISSION IN FIVE AGNs AND A POSSIBLE CORRELATION BETWEEN WATER MASER AND NUCLEAR 2-10 keV LUMINOSITIES

摘要

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 σ (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 ～700, ～800, and ～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 ～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, L_(2-10) ∝ L_(H_2O)~(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.