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Session 74 - Supernova Remnants.
Display session, Thursday, June 13
Great Hall,

[74.08] 1720 MHz OH Maser Emission from SNR G359.1-0.5

B. Robinson, F. Yusef-Zadeh (Northwestern U.), D. Roberts (U. Illinois, Urbana-Champaign)

G359.1-0.5, a supernova remnant surrounded completely by a ring of CO gas, was recently reported to be associated with several compact 1720 MHz OH masers, as well as an extended region of 1720 MHz OH emission (Yusef-Zadeh, Uchida, and Roberts, 1995, Science, 270, 801.). Higher spatial and spectral resolution (4.5'' and 0.27 km\(s^-1\)) observations were carried out in the BnC configuration of the VLA, at frequencies of 1665, 1667, and 1720 MHz, confirming the presence of the six compact 1720 MHz masers, as well as finding an additional 1720 MHz maser located at the interface between the CO cloud and the non-thermal shell of the remnant. All velocities were approximately --5 km\(s^-1\). The extended 1720 MHz feature was not detected. The 1665 and 1667 MHz OH emission lines were also undetected above 80 mJy, lending support to the model of collisional pumping as the source of the 1720 MHz masers. In this model, the expansion of the SNR drives a shock into the molecular cloud. Zeeman fitting of the V spectra of three masers estimates line of sight magnetic field strength values between 0.4 and 0.56 milliGauss.

A puzzling aspect of this region is the discrepancy between the velocity of the OH masers, and the velocity of the molecular cloud surrounding SNR G359.1-0.5. The velocities of the masers range between --4.7 and --6.6 km\(s^-1\), while the dominant component of the velocity of the associated molecular cloud ranges between --60 and --190 km\(s^-1\). The possible causes of this discrepancy will be discussed.

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