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25 April 2024 |
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A Synchronized Variation of the 6.7 GHz Methanol Maser in Cepheus A | | Koichiro Sugiyama
; Kenta Fujisawa
; Akihiro Doi
; Mareki Honma
; Yasuko Isono
; Hideyuki Kobayashi
; Nanako Mochizuki
; Yasuhiro Murata
; | | Date: |
29 Apr 2008 | | Abstract: | We present the results of daily monitoring of 6.7 GHz methanol maser in
Cepheus A (Cep A) using Yamaguchi 32-m radio telescope as well as the results
of imaging observations conducted with the JVN (Japanese VLBI Network). We
indentified five spectral features, which are grouped into red-shifted (-1.9
and -2.7 km/s) and blue-shifted (-3.8, -4.2, and -4.9 km/s), and we detected
rapid variabilities of these maser features within a monitoring period of 81
days. The red-shifted features decreased in flux density to 50% of its initial
value, while the flux density of the blue-shifted features rapidly increased
within a 30 days. The time variation of these maser features showed two
remarkable properties; synchronization and anti-correlation between the
red-shifted and the blue-shifted. The spatial distribution of the maser spots
obtained by the JVN observation showed an arclike structure with a scale of
$sim$1400 AU, and separations of the five maser features were found to be
larger than 100 AU. The absolute position of the methanol maser was also
obtained based on the phase-referencing observations, and the arclike structure
were found to be associated with the Cep A-HW2 object, with the elongation of
the arclike structure nearly perpendicularly to the radio continuum jet from
the Cep A-HW2 object. These properties of the masers, namely, the
synchronization of flux variation, and the spectral and spatial isolation of
features, suggest that the collisional excitation by shock wave from a common
exciting source is unlikely. Instead, the synchronized time variation of the
masers can be explained if all the maser features are excited by infrared
radiation from dust which is heated by a common exciting source with a rapid
variability. | | Source: | arXiv, 0804.4623 | | Services: | Forum | Review | PDF | Favorites | |
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