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VERA Observation of the W49NH2O Maser Outburst in 2003 October

Authors :: Seisuke Kuji
Riiko Nagayoshi
Akiharu Nakagawa
Sei-ichiro Sakakibara
Takaaki Jike
N. Kawaguchi
Hideyuki Kobayashi
T. Bushimata
Hiroshi Suda
Tomoharu Kurayama
José K. Ishitsuka
Tetsuo Sasao
Tomoya Hirota
K. Sato
T. Miyaji
Maria Rioja
R. Shimizu
Y. K. Choi
Hiroshi Imai
Yukitoshi Kan-ya
T. Fujii
Ryuichi Kamohara
Tomoaki Oyama
Seiji Manabe
K. Yamashita
Katsunori M. Shibata
Kouichirou Nakashima
Yoichi Tamura
Kasumi Sora
Noritomo Inomata
Mareki Honma
Kenzaburo Iwadate
K. Horiai
Toshihiro Omodaka
Osamu Kameya
Satoshi Sakai
Source :: Publications of the Astronomical Society of Japan. 56:L15-L18
Publication Year :: 2004
Publisher :: Oxford University Press (OUP), 2004.
Abstract: We report on a strong outburst of the W49N H2O maser observed with VERA. Single-dish monitoring with VERA 20 m telescopes detected a strong outburst of the maser feature at V_LSR = -30.7 km/s in 2003 October. The outburst had a duration of ~100 days and a peak intensity of 7.9 x 10^4 Jy, being one of the strongest outbursts in W49N observed so far. VLBI observations with the VERA array were also carried out near to the maximum phase of the outburst, and the outburst spot was identified in the VLBI map. While the map was in good agreement with previous studies, showing three major concentrations of maser spots, we found a newly formed arc-like structure in the central maser concentration, which may be a shock front powered by a forming star or a star cluster. The outburst spot was found to be located on the arc-like structure, indicating a possible connection of the present outburst to a shock phenomenon.<br />Comment: 4 pages, 2 figures included, to appear in PASJ letter (Vol.56, #3, 2004 June)