Detection of the SiO J=2-1 v=1 maser emission at 86.2 GHz in V838 Mon, an unusual nova-like variable

ATel #1996; S. Deguchi (NAOJ), N. Matsunaga (Kyoto U.), H. Fukushi (U. Tokyo), T. Kaminski (NCAC Torun)
on 31 Mar 2009; 01:30 UT
Credential Certification: Shuji Deguchi (deguchi@nro.nao.ac.jp)

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We report on a new detection of the SiO J=2-1 v=1 maser line at 86.243 GHz in V838 Mon. The observations were obtained on 2009 March 21--23 using the 45m telescope at Nobeyama with a newly built sensitive dual-polarization receiver. The maser line has a peak intensity of 0.39 Jy at V_lsr=53.7 km/s and exhibits a complex asymmetric pedestal with a stronger contribution at the lower velocity side; the total integrated intensity of the emission feature is of 2.8 Jy km/s. On 2009 March 21--23 we also observed the previously detected SiO J=1-0 v=1 and v=2 lines (Deguchi et al. 2005, PASJ 57, L25) at 43.122 and 42.821 GHz , respectively, and they were found to decrease to about a half of their strongest intensities as observed during late 2005 -- early 2006 (Deguchi et al. 2007, ASP Conf. Ser. 363, 81).

The ~5-year delay in emergence of the J=2-1 v=1 emission with respect to the J=1-0 maser implies a relatively slow expansion (~20 km/s) of the molecular envelope of V838 Mon in the region between the J=2-1 v=1 SiO maser emitting shell and the inner J=1-0 v=1 and v=2 shells.