A search for OH 6 GHz maser emission towards southern supernova remnants
aa r X i v : . [ a s t r o - ph ] A p r Astrophysical Masers and their Environments IAU SymposiumProceedings IAU Symposium No. 242, 2007J.M. Chapman & W.A. Baan, eds. c (cid:13) A search for OH 6 GHz maser emissiontowards southern supernova remnants
Korinne E. McDonnell, Alan E. Vaughanand Mark Wardle
Department of Physics, Macquarie University, Sydney, NSW 2109, Australiaemail: { korinnem, alanv, wardle } @physics.mq.edu.au Abstract.
OH masers at 1720 MHz have proven to be excellent indicators of interactions be-tween supernova remnants and molecular clouds. Recent calculations suggest that the 6049 MHzOH maser line is excited for higher column densities than for the 1720 MHz line. It is thereforea potentially valuable indicator of remnant-cloud interaction.We present preliminary results of a survey using the Parkes Methanol Multibeam receiver for6049 MHz and 6035/6030 MHz OH masers towards 36 supernova remnants and 4 fields in theLarge and Small Magellanic Clouds. While no 6049 MHz masers have been found, three newsites of 6035 and 6030 MHz OH maser emission have been discovered in star-forming regions.
Keywords. supernova remnants, masers, stars: formation, radio lines: ISM
OH masers at 1720 MHz have proven to be an almost unambiguous indicator of theinteraction between supernova remnants and molecular clouds (Frail et al. 1994). OHexcitation calculations (Pavlakis & Kylafis 2000; Wardle, these proceedings) suggest thatthe 6049 MHz satellite line may be present at higher OH column densities where the1720 MHz line is weak or absent.A survey using the Parkes Methanol Multibeam receiver at 6049 and 6035/6030 MHzwas conducted towards 36 supernova remnants and 4 fields in the Large and SmallMagellanic Clouds. An 8 MHz bandwidth with 2048 channels was used, allowing a channelwidth of 0.2 km s − . The beam size is approximately 3.3 arcminutes and both circularpolarisations were observed. Scans in right ascension and declination were conducted overthe supernova remnants, with a total observing time in one direction of ∼
100 minutesper square degree. The data was flux-calibrated, continuum subtracted and gridded usingthe programs Livedata and Gridzilla. The data cubes produced were searched for maseremission using the program Duchamp (Whiting 2007).While preliminary analysis has not discovered any 6049 MHz maser emission, 5 masersites at 6035 MHz have been identified (2 containing 6030 MHz emission as well). Masers6.86-0.09, 34.27-0.20 and 48.98-0.30 are new discoveries (see Fig. 1), while 336.941-0.156and 337.705-0.053 are already known (Caswell & Vaile 1995; Caswell 2001).As left and right-hand circular polarisations (LHCP and RHCP) were observed, Zee-man pairs can be recognised. A 1 mG magnetic field produces splittings equivalent to0.079 km s − and 0.056 km s − in the 6030 and 6035 MHz transitions respectively. Themagnetic fields calculated can be found in Table 1 and have an uncertainty of approxi-mately 2 mG.The 6035 MHz maser discovered at 48.98-0.30 is approximately coincident with twoH II regions and is likely to be associated with one of them. It is expected that the other6030 and 6035 MHz masers are associated with star forming regions.These results are preliminary and further analysis may yield weaker 6 GHz masers. In11920 McDonnell, Vaughan & Wardle Table 1.
Masers at the 6035- and 6030- MHz OH transitions. The velocity and flux of thepeaks are taken at the brightest peak, if multiple peaks are observed.6035 MHz 6035 MHz 6030 MHzOH maser RA (2000) Dec (2000) Velocity Peak Peak flux Magnetic Peak(l b) LHCP RHCP LHCP RHCP Field (L and/or R)( ◦ ◦ ) (h m s) ( ◦ ′ ′′ ) (km s − ) (Jy) (mG) (Jy)336.941-0.156 16 35 55.20 -47 38 45.4 -65.6 -65.1 3.35 1.86 +8.9 1.03 0.46337.705-0.053 16 38 29.67 -47 00 35.8 -53.6 -50.7 1.63 2.22 - -6.86-0.09 18 00 48 -22 58 14 -2.37 -1.98 4.23 1.03 +7.0 -34.27-0.20 18 54 36 +01 05 54 54.3 54.5 4.60 2.33 +3.6 1.76 (L)48.98-0.30 19 22 27 +14 06 53 67.5 67.7 1.55 4.27 +3.6 - −10 −5 0 5024 55 60 65 70 75 8002450 55 60024 Radial Velocity (km s −1 ) F l u x D en s i t y ( Jy )
50 55 60024 48.98−0.30 603534.27−0.20 6030 34.27−0.20 60356.86−0.09 6035
Figure 1.
Spectra of new OH masers at the 6030- and 6035-MHz transitions. LHCP and RHCPare displayed as dashed and solid lines, respectively. The channel resolution is 0.2 km s − andthe beamsize is approximately 3 arcminutes. addition, data from ATCA observations of seventeen supernova remnants remain to beanalysed. Acknowledgements
We would like to thank Catherine Braiding for helping with the observing, Stacy Maderfor observing assistance and help with data reduction, and James Caswell for assistancewith maser identification.
References
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