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SUG08 - A Synchronized Variation of the 6.7GHz Methanol Maser in Cepheus A

Short title: Sugiyama et al. (2008)
Authors: Sugiyama, KoichiroFujisawa, KentaDoi, AkihiroHonma, MarekiIsono, YasukoKobayashi, HideyukiMochizuki, NanakoMurata, Yasuhiro
Journal: Publications of the Astronomical Society of Japan, Vol.60, No.5, pp.1001--1006
Bibcode:

Target type: Known_Class_II
Transitions: CH3OH_6(II)

Abstract
We present the results of monitoring observations of a 6.7GHz methanol maser in Cepheus A (Cep A) using the Yamaguchi 32m radio telescope and of imaging observations conducted with the JVN (Japanese VLBI Network). We identified five spectral features which are grouped into two groupes: redshifted (-1.9 and -2.7 km s^-1) and blueshifted (-3.8, -4.2, and -4.9 km s^-1). We detected rapid variabilities in these maser features within a monitoring period of 81d. The redshifted features decreased in flux density to 50% of the initial value, while the blueshifted ones rapidly increased within 30d. The time variation in these maser features had two remarkable properties: synchronization and negative correlation between the redshifted and the blueshifted. Based on the JVN observations, we found that the maser spots were associated with the CepAHW2 object and had an arched structure with a scale of 1400AU also, separations of the five maser features were found to be larger than 100AU. These properties of the masers, namely, the synchronization of the flux variation and the spectral and spatial isolations of the features, suggest that collisional excitation by a shock wave from a common exciting source is unlikely to happen. Instead, the synchronized time variation of the masers can be explained if all of the maser features are excited by infrared radiation from the dust that is heated by a common exciting source with a rapid variability.

Abstract

We present the results of monitoring observations of a 6.7GHz methanol maser in Cepheus A (Cep A) using the Yamaguchi 32m radio telescope and of imaging observations conducted with the JVN (Japanese VLBI Network). We identified five spectral features which are grouped into two groupes: redshifted (-1.9 and -2.7 km s^-1) and blueshifted (-3.8, -4.2, and -4.9 km s^-1). We detected rapid variabilities in these maser features within a monitoring period of 81d. The redshifted features decreased in flux density to 50% of the initial value, while the blueshifted ones rapidly increased within 30d. The time variation in these maser features had two remarkable properties: synchronization and negative correlation between the redshifted and the blueshifted. Based on the JVN observations, we found that the maser spots were associated with the CepAHW2 object and had an arched structure with a scale of 1400AU also, separations of the five maser features were found to be larger than 100AU. These properties of the masers, namely, the synchronization of the flux variation and the spectral and spatial isolations of the features, suggest that collisional excitation by a shock wave from a common exciting source is unlikely to happen. Instead, the synchronized time variation of the masers can be explained if all of the maser features are excited by infrared radiation from the dust that is heated by a common exciting source with a rapid variability.

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Detection table from Sugiyama et al. (2008)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Descr.	Line	V_peak	Telescope	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)					CH₃OH (class II)	(km/s)		(arcsec)	Yes/No		(kpc)
1	22 56 17.9	+62 01 49.6	109.8709	2.1144	G109.871+2.114	Cep A	Image	Descr	6.6 GHz (II);	-2.64	YAM	300	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		2007 August - October

DSS colored	2MASS colored	WISE colored
SDSS color	IRAC color I1,I2,I4	GLIMPSE 360
PACS color (70-160 um)	SPIRE color (250-500 um)	NVSS (1.4GHz)
ATLASGAL 870 um	ATLASGAL 870 um + Planck	Bolocam 1.1 mm
UKIDSS K Download UKIDSS K FITS	2MASS K Download 2MASS K FITS

select MAX(met2_data_all.ra_hms) as ra_hms,MAX(met2_data_all.dec_dms) as dec_dms,MAX(met2_data_all.source_name) as source_name,MAX(met2_data_all.ra) as ra,MAX(met2_data_all.dec) as dec,MAX(met2_data_all.l) as l,MAX(met2_data_all.b) as b,MAX(met2_data_all.grp) as grp,MAX(met2_data_all.other_name) as other_name,MAX(met2_data_all.other_desc) as other_desc,BOOL_OR(thermal) as thermal,MAX(met2_data_all.line) as line,MAX(met2_data_all.vrange) as vrange,MAX(met2_data_all.vpeak) as vpeak,MAX(met2_data_all.peak) as peak,MAX(met2_data_all.fwhm) as fwhm,MAX(met2_data_all.int) as int,MAX(met2_data_all.rms) as rms,MAX(met2_data_all.units) as units,MAX(met2_data_all.units_rms) as units_rms,MAX(met2_data_all.date_txt) as date_txt,MAX(met2_data_all.telescope_ref) as telescope_ref,MAX(met2_data_all.telescope_conf) as telescope_conf,MAX(met2_data_all.v_step) as v_step,MAX(met2_data_all.beam) as beam,MAX(met2_data_all.beam_maj) as beam_maj,MAX(met2_data_all.beam_min) as beam_min,MAX(met2_data_all.beam_pa) as beam_pa,MAX(met2_data_all.ref) as ref,MAX(met2_data_all.list_ref) as list_ref,MAX(met2_data_all.ascii) as ascii,MAX(met2_data_all.url) as url,MAX(met2_data_all.image) as image,MAX(met2_data_all.image2) as image2,MAX(met2_data_all.image3) as image3,MAX(met2_data_all.descr) as descr,MAX(met2_data_all.id) as id,BOOL_OR(mjy_flag) as mjy_flag,BOOL_OR(rms_mjy_flag) as rms_mjy_flag,MAX(met2_data_all.dist) as dist,1 as dist_parallax,MAX(met2_data_all.date_txt) as date_txt,MAX(line_det) as line_det,MAX(type) as type,MAX(simbad_types_cat) as simbad_types_cat FROM met2_data_all  LEFT JOIN all_objects_withmet ON met2_data_all.grp=all_objects_withmet.group_name LEFT JOIN object_categories ON all_objects_withmet.group_name = object_categories.group_name_cat AND object_categories.tbl_cat = 'all_objects_withmet' LEFT JOIN transitions ON met2_data_all.line=transitions."Line"  WHERE ref ilike 'SUG08' AND detected=true AND hide=false GROUP BY ref

select met2_data_all.ra_hms,met2_data_all.dec_dms,met2_data_all.source_name,met2_data_all.ra,met2_data_all.dec,met2_data_all.l,met2_data_all.b,met2_data_all.grp,met2_data_all.other_name,met2_data_all.other_desc,met2_data_all.thermal,met2_data_all.line,met2_data_all.vrange,met2_data_all.vpeak,met2_data_all.peak,met2_data_all.fwhm,met2_data_all.int,met2_data_all.rms,met2_data_all.units,met2_data_all.units_rms,met2_data_all.date_txt,met2_data_all.telescope_ref,met2_data_all.telescope_conf,met2_data_all.v_step,met2_data_all.beam,met2_data_all.beam_maj,met2_data_all.beam_min,met2_data_all.beam_pa,met2_data_all.ref,met2_data_all.list_ref,met2_data_all.ascii,met2_data_all.url,met2_data_all.image,met2_data_all.image2,met2_data_all.image3,met2_data_all.descr,met2_data_all.id,met2_data_all.mjy_flag,met2_data_all.rms_mjy_flag,met2_data_all.dist,met2_data_all.dist_parallax,met2_data_all.date_txt,line_det,type,simbad_types_cat FROM met2_data_all   LEFT JOIN all_objects_withmet ON met2_data_all.grp=all_objects_withmet.group_name LEFT JOIN object_categories ON all_objects_withmet.group_name = object_categories.group_name_cat AND object_categories.tbl_cat = 'all_objects_withmet' LEFT JOIN transitions ON met2_data_all.line=transitions."Line"  WHERE ref ilike 'SUG08' AND detected=true AND hide=false ORDER BY detected DESC,id

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SUG08 - A Synchronized Variation of the 6.7GHz Methanol Maser in Cepheus A

View as list of objects

Detection table from Sugiyama et al. (2008)