DETECTION OF CLASS I METHANOL (CH<sub>3</sub>OH) MASER CANDIDATES IN SUPERNOVA REMNANTS

Pihlström, Y. M.; Sjouwerman, Loránt O.; Frail, D. A.; Claussen, M. J.; Mesler, Robert A.; McEwen, Bridget C.

doi:10.1088/0004-6256/147/4/73

Cited by 44 publications

(68 citation statements)

References 52 publications

(68 reference statements)

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“…Galactic class II masers are closely associated with young stellar objects (YSOs), which are often accompanied by OH and H 2 O masers, and are usually observed in one or two compact sites within a star formation region (e.g., Ellingsen 2006;Breen et al 2010;Caswell et al 2010). Class II masers are exclusively observed toward high-mass star formation regions (Breen et al 2013), while class I masers have been observed associated toward low-and high-mass star formation regions as well as supernova remnants (e.g., Kalenskii et al 2010;Pihlström et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

McCarthy

Ellingsen

Chen

et al. 2017

ApJ

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We have searched for emission from the 36.2 GHz (  -4 3 E 1 0 ) methanol transition toward NGC 4945, using the Australia Telescope Compact Array. 36.2 GHz methanol emission was detected offset southeast from the Galactic nucleus. The methanol emission is narrow, with a line width <10 km s −1 and a luminosity five orders of magnitude higher than Galactic class I masers from the same transition. These characteristics combined the with physical separation from the strong central thermal emission suggests that the methanol emission is a maser. This emission is a factor of ∼90 more luminous than the widespread emission detected from the Milky Way central molecular zone. This is the fourth detection of extragalactic class I emission and the third detection of extragalactic 36.2 GHz maser emission. These extragalactic class I methanol masers do not appear to be simply highly luminous variants of Galactic class I emission and instead appear to trace large-scale regions of low-velocity shocks in molecular gas, which may precede, or be associated with, the early stages of large-scale star formation.

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Section: Introductionmentioning

confidence: 99%

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

McCarthy

Ellingsen

Chen

et al. 2017

ApJ

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“…This means they are most likely formed in different regions in the shocked gas Pihlström et al 2014;McEwen et al 2014). The majority of the 44 GHz masers in the NE region have slightly lower velocity spread compared to the OH masers, which have an average of ∼ 57 km s −1 , and are located just to the SW of the group of 44 GHz CH 3 OH masers (in the rectangle region).…”

Section: Ne Regionmentioning

confidence: 98%

44 GHZ CLASS I METHANOL (CH₃OH) MASER SURVEY IN THE GALACTIC CENTER

McEwen

Sjouwerman

Pihlström

2016

ApJ

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We report on a large 44 GHz (7 0 − 6 1 A + ) methanol (CH 3 OH) maser survey of the Galactic Center (GC). The Karl G. Jansky Very Large Array was used to search for CH 3 OH maser emission covering a large fraction of the region around Sgr A. In 25 pointings, over 300 CH 3 OH maser sources (> 10σ) were detected. The majority of the maser sources have a single peak emission spectrum with line of sight velocities that range from about −13 km s −1 to 72 km s −1 . Most maser sources were found to have velocities around 35−55 km s −1 , closely following velocities of neighboring interacting molecular clouds. The full width half maximum of each individual spectral feature is very narrow (∼0.85 km s −1 on average). In the north, where Sgr A East is known to be interacting with the 50 km s −1 molecular cloud, more than 100 44 GHz CH 3 OH masers were detected. In addition, three other distinct concentrations of masers were found, which appear to be located closer to the interior of the interacting molecular clouds. Possibly a subset of masers are associated with star formation, although conclusive evidence is lacking.

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“…So-called 'class I' CH 3 OH masers are commonly associated with the molecular shocks of HII regions, but in the case of Region W, no such counterpart was identified, leaving the W28 shock as the most plausible trigger mechanism [25]. CH 3 OH masers might be a more-numerous, but less-intense, tracer of SNR shocks than 1720 MHz OH masers [39]. Furthermore, the existence of cospatial CH 3 Figure 2), and are associated with a dense molecular clump, hereafter referred to as the "Region Y clump", at a line of sight central velocity of ∼21 kms −1 , which is ∼8-12 kms −1 (see "Core 1" in [22]) faster than the central velocity of the gas component unambiguously shown to be associated with W28 and HESS J801−233.…”

Section: The Shocked Molecular Cloud Towards Hess J1801−233mentioning

confidence: 99%

Molecular shocks and the gamma-ray clouds of the W28 supernova remnant

Maxted¹,

Rowell²,

Wilt³

et al. 2017

AIP Conference Proceedings

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Abstract. Interstellar medium clouds in the W28 region are emitting gamma-rays and it is likely that the W28 supernova remnant is responsible, making W28 a prime candidate for the study of cosmic-ray acceleration and diffusion. Understanding the influence of both supernova remnant shocks and cosmic rays on local molecular clouds can help to identify multi-wavelength signatures of probable cosmic-ray sources. To this goal, transitions of OH, SiO, NH 3 , HCO + and CS have complemented CO in allowing a characterisation of the chemically rich environment surrounding W28. This remnant has been an ideal test-bed for techniques that will complement arcminute-scale studies of cosmic-ray source candidates with future GeV-PeV gamma-ray observations. The W28 RegionW28 is an old-age (>10 4 years, see [1,2,3]) supernova remnant (SNR), which exhibits non-thermal synchrotron emission seen in 90 cm radio continuum in Figure 1. The W28 SNR has been implicated as a cosmic ray (CR) accelerator due to a correspondence between TeV gamma-ray emission and molecular gas at a distance of 1.2-3.3 kpc [4,5,6,7]. This correspondence is true of both HESS J1801−233 -a TeV gamma-ray source immediately adjacent/overlapping the SNR, and HESS J1800−240 -a multi-component TeV gamma-ray source spatially separated by 0.25-0.75• in the plane of the sky. Such gamma-ray-gas overlap points to gamma-ray emission via the decay of neutral pions created by CR interactions with gas. It follows that the W28 SNR is a likely cosmic-ray accelerator [8,9,5]. Some uncertainty exists in the 3D geometry of the cloud complex surrounding W28 and the energy-dependent diffusion speed of CRs throughout that region. But, successive multi-wavelength campaigns have reinforced evidence for a SNR-cloud interaction and supported a hadronic scenario for gamma-ray emission. The Shocked Molecular Cloud towards HESS J1801−233As illustrated in Figure 2, CO-traced molecular gas [10,11,5] between kinematic velocities 0 and 20 kms −1 corresponds to the TeV gamma-ray emission of HESS J1801−233. A component of shock-heated molecular gas is seen in H 2 [12,13] and high-J CO transitions [10] along the radio-continuum-traced W28 shock, while 1720 MHz OH masers (indicated in Figure 2) are also encompassed within this velocity-range [14,15]. 1720 MHz OH maser lines are commonly associated with the wake of old ( 10 4 yr) supernova remnant shocks (e.g.[15]), and modelling suggests that very specific collisional conditions are required for their generation [16,17,18]. C-type shocks (∼25 kms −1 ) moving through dense (∼10 4 -10 5 cm −3 ), warm (50-125 K) molecular gas can sustain OH maser emission provided that a source of H 2 O-dissociation is present to maintain a large OH column density (∼10 16 cm −2 ), possibly a weak UV flux emitted by H 2 that has been indirectly excited by CRs and/or X-ray photons [19].

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DETECTION OF CLASS I METHANOL (CH₃OH) MASER CANDIDATES IN SUPERNOVA REMNANTS

Cited by 44 publications

References 52 publications

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

44 GHZ CLASS I METHANOL (CH₃OH) MASER SURVEY IN THE GALACTIC CENTER

Molecular shocks and the gamma-ray clouds of the W28 supernova remnant

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DETECTION OF CLASS I METHANOL (CH3OH) MASER CANDIDATES IN SUPERNOVA REMNANTS

Cited by 44 publications

References 52 publications

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

44 GHZ CLASS I METHANOL (CH3OH) MASER SURVEY IN THE GALACTIC CENTER

Molecular shocks and the gamma-ray clouds of the W28 supernova remnant

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DETECTION OF CLASS I METHANOL (CH₃OH) MASER CANDIDATES IN SUPERNOVA REMNANTS

44 GHZ CLASS I METHANOL (CH₃OH) MASER SURVEY IN THE GALACTIC CENTER