摘要
We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new detections. The detection rate of H2O masers in our sample is 9% which is very low. The detection rate of H2O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H2O masers increase as the sources evolve. The detection rate of H2O masers toward BGPS sources without HCO＋ emission is low. The BGPS sources associated with both H2O and CH3OH masers seem to be more compact than those only associated with H2O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H2O maser source G133.715＋01.217, also well known as W3 IRS 5 which has a flux density of 2.9 × 103 Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H2O masers and their angular distance from the true source location, we get the influence radius r = 1/0.8 1og（F0/3rms）. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection.
We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new detections. The detection rate of H2O masers in our sample is 9% which is very low. The detection rate of H2O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H2O masers increase as the sources evolve. The detection rate of H2O masers toward BGPS sources without HCO＋ emission is low. The BGPS sources associated with both H2O and CH3OH masers seem to be more compact than those only associated with H2O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H2O maser source G133.715＋01.217, also well known as W3 IRS 5 which has a flux density of 2.9 × 103 Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H2O masers and their angular distance from the true source location, we get the influence radius r = 1/0.8 1og（F0/3rms）. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection.
基金
funded by the National Natural Science Foundation of China under grant 11373062
supported by the National Basic Research Program of China (973 program,2012CB821802)
the National Natural Science Foundation of China under grant Nos.11433008,11303081 and 10873025
the Program of the Light in China’s Western Region (LCRW) under grant Nos.RCPY201202 and XBBS-2014-24
