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MCE16B - NH3(3,3) and CH3OH near Supernova Remnants: GBT and VLA Observations

Interferometry data

Short title: McEwen et al. (2016b)
Authors: McEwen, Bridget C. Pihlström, Ylva M. Sjouwerman, Loránt O.
Journal: The Astrophysical Journal, Volume 826, Issue 2, article id. 189, 11 pp. (2016).
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Target type: SNR
Transitions: SiO_1-0v0,CH3OH_25-30_GHz(I),CH3OH_36(I),CH3OH_44(I),CH3OH_84(I),CH3OH_95(I),CH3OH_6(II),CH3OH_37(II),CH3OH_38(II)

Abstract
We report on Green Bank Telescope 23.87 GHz NH₃(3,3) emission observations in five supernova remnants (SNRs) interacting with molecular clouds (G1.4-0.1, IC 443, W44, W51C, and G5.7-0.0). The observations show a clumpy gas density distribution, and in most cases the narrow line widths of &tilde3-4 km s^-1 are suggestive of maser emission. Very Large Array observations reveal 36 and/or 44 GHz CH₃OH maser emission in a majority (72%) of the NH₃ peak positions toward three of these SNRs. This good positional correlation is in agreement with the high densities required for the excitation of each line. Through these observations we have shown that CH₃OH and NH₃ maser emission can be used as indicators of high-density clumps of gas shocked by SNRs, and provide density estimates thereof. Modeling of the optical depth of the NH₃(3,3) emission is compared to that of CH₃OH, constraining the densities of the clumps to a typical density of the order of 10⁵ cm^-3 for cospatial masers. Regions of gas with this density are found to exist in the post-shocked gas quite close to the SNR shock front, and may be associated with sites where cosmic rays produce gamma-ray emission via neutral pion decay. eprintid: arXiv:1606.01263

Abstract

We report on Green Bank Telescope 23.87 GHz NH₃(3,3) emission observations in five supernova remnants (SNRs) interacting with molecular clouds (G1.4-0.1, IC 443, W44, W51C, and G5.7-0.0). The observations show a clumpy gas density distribution, and in most cases the narrow line widths of &tilde3-4 km s^-1 are suggestive of maser emission. Very Large Array observations reveal 36 and/or 44 GHz CH₃OH maser emission in a majority (72%) of the NH₃ peak positions toward three of these SNRs. This good positional correlation is in agreement with the high densities required for the excitation of each line. Through these observations we have shown that CH₃OH and NH₃ maser emission can be used as indicators of high-density clumps of gas shocked by SNRs, and provide density estimates thereof. Modeling of the optical depth of the NH₃(3,3) emission is compared to that of CH₃OH, constraining the densities of the clumps to a typical density of the order of 10⁵ cm^-3 for cospatial masers. Regions of gas with this density are found to exist in the post-shocked gas quite close to the SNR shock front, and may be associated with sites where cosmic rays produce gamma-ray emission via neutral pion decay. eprintid:

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Detection table from McEwen et al. (2016b)

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ID	Obs. RA	Obs. Dec	RA offset	Dec offset	l	b	Group id	#	Maser spot	Source name	Other name	Image	Line	V_peak	F_peak	∫F dv	Telescope	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(mas)	(mas)	(deg.)	(deg.)					Other Name		CH₃OH (class I)	(km/s)	(Jy/beam)	(Jy/beam*km/s)		(arcsec)	Yes/No		(kpc)
1	+19 23 50	+14 06 00			49.140452	-0.602805	G48.990-0.299			W51C	G049.2-0.7	Image	36 GHz (I);	57.6 .. 76.2	0.13 .. 0.54	..	GBT	2.65 x 1.9	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		2014 September 4
	+19 22 42.69	+14 09 55.5	-1.00965e+06 mas	235500 mas	49.069663	-0.332183		1	B36-1	W51C				57.6	0.25
	+19 22 42.21	+14 09 51.5	-1.01685e+06 mas	231500 mas	49.067769	-0.330998		2	B36-2	W51C				59.6	0.14
	+19 22 42.76	+14 10 02	-1.0086e+06 mas	242000 mas	49.071389	-0.331581		3	B36-3	W51C				57.6	0.13
	+19 22 41.42	+14 09 3.5	-1.0287e+06 mas	183500 mas	49.054506	-0.334473		4	B36-4	W51C				74.1	0.24
	+19 22 25.7	+14 06 35	-1.2645e+06 mas	35000 mas	48.988175	-0.297916		5	F36-1	W51C				65.9	0.43
	+19 22 26.01	+14 06 36	-1.25985e+06 mas	36000 mas	48.989011	-0.298890		6	F36-2	W51C				65.9	0.54
	+19 22 26.11	+14 06 37	-1.25835e+06 mas	37000 mas	48.989446	-0.299115		7	F36-3	W51C				63.8	0.5
	+19 22 12.08	+14 02 49.5	-1.4688e+06 mas	-190500 mas	48.906984	-0.278896		8	L36-1	W51C				67.9	0.43
	+19 22 7.34	+14 02 18.5	-1.5399e+06 mas	-221500 mas	48.890360	-0.266055		9	L36-2	W51C				76.2	0.19
2	+17 59 02	-24 04 1.14255e-10			5.718211	-0.100383	G5.618-0.082			G5.7-0.0	-	Image	36 GHz (I);	-26.4	0.21 .. 0.38	..	GBT	2.65 x 1.9	+H₂O +CH₃OH I +CH₃OH II	SFR		2016 September 4
	+17 58 44.99	-24 08 38	-255149 mas	-277999 mas	5.619011	-0.082833		1	A36-1	G5.7-0.0				-26.4	0.38
	+17 58 45.17	-24 08 39.5	-252449 mas	-279499 mas	5.618991	-0.083634		2	A36-2	G5.7-0.0				-26.4	0.26
	+17 58 44.85	-24 08 36.5	-257249 mas	-276499 mas	5.619106	-0.082164		3	A36-3	G5.7-0.0				-26.4	0.21
3	+17 59 02	-24 04 1.14255e-10			5.718211	-0.100383	G5.618-0.082			G5.7-0.0	-		44 GHz (I);	-24.4	0.35 .. 1.31	..	GBT	2.11 x 1.84	+H₂O +CH₃OH I +CH₃OH II	SFR		2017 September 4
	+17 58 44.48	-24 08 37	-262799 mas	-276999 mas	5.618284	-0.081014		1	A44-1	G5.7-0.0				-24.4	1.31
	+17 58 44.88	-24 08 37	-256799 mas	-276999 mas	5.619043	-0.082332		2	A44-2	G5.7-0.0				-24.4	0.35
4	+18 56 00	+01 22 00			34.668302	-0.391577	G34.731-0.633			W44	G034.7-0.4	Image	36 GHz (I);	40.9 .. 47.1	0.09 .. 0.3	..	GBT	2.65 x 1.9	+H₂O +CH₃OH I	SFR		2018 September 4
	+18 56 43.96	+01 23 54.2	659400 mas	114199 mas	34.780092	-0.540037		1	A36-1	W44				40.9	0.25
	+18 56 48.39	+01 18 45.7	725850 mas	-194301 mas	34.712260	-0.595565		2	F36-1	W44				42.9	0.09
	+18 56 50.82	+01 18 17.3	762300 mas	-222701 mas	34.709860	-0.608172		3	G36-1	W44				42.9	0.14
	+18 56 50.86	+01 18 21.8	762900 mas	-218201 mas	34.711049	-0.607750		4	G36-2	W44				40.9	0.11
	+18 56 52.49	+01 18 12.3	787350 mas	-227701 mas	34.711799	-0.614996		5	G36-3	W44				47.1	0.12
	+18 56 58.46	+01 18 41.7	876900 mas	-198301 mas	34.730416	-0.633396		6	K36-1	W44				45	0.3
5	+18 56 00	+01 22 00			34.668302	-0.391577	G34.712-0.595			W44	G034.7-0.4		44 GHz (I);	6.7 .. 56.9	0.21 .. 0.31	..	GBT	2.11 x 1.84	-H₂O +CH₃OH I +CH₃OH II -SiO	SFR		2019 September 4
	+18 56 49.86	+01 18 43.2	747900 mas	-196801 mas	34.714437	-0.601331		1	K44-1	W44				56.9	0.21
	+18 56 48.36	+01 18 46.2	725400 mas	-193801 mas	34.712327	-0.595391		2	L44-1	W44				45	0.31
	+18 56 57.86	+01 17 27.7	867900 mas	-272301 mas	34.710985	-0.640554		3	P44-1	W44				35.6	0.26
	+18 56 59.69	+01 19 17.2	895350 mas	-162801 mas	34.741530	-0.633455		4	Q44-1	W44				6.7	0.24

Non-detection table from McEwen et al. (2016b)