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Title:
Investigating Molecular Shocks in Supernova Remnants
Authors:
Hewitt, John W.
Affiliation:
AA(Northwestern Univ.)
Publication:
American Astronomical Society, AAS Meeting #213, #359.05; Bulletin of the American Astronomical Society, Vol. 41, p.502
Publication Date:
01/2009
Origin:
AAS
Bibliographic Code:
2009AAS...21335905H

Abstract

Maser emission from the 1720-MHz transition of hydroxyl(OH) has identified shock interactions in 10% of all supernova remnants(SNRs). Such maser-emitting SNRs are also bright in molecular line emission. Though somewhat rare, SNRs interacting with dense molecular clouds are an important class in which to study cosmic ray acceleration, SNR evolution, and effects on the energetics and chemistry of the interstellar medium. We have investigate such molecular shocks in the following ways:

(i) With the GBT we observe widespread OH(1720 MHz) emission and absorption in other OH lines across the interaction site. Observations of all four ground-state transitions at 1720, 1667/5 and 1612 MHz allows us to model OH excitation, yielding the temperature, density and OH abundance in the post-shock gas. Maser emission is found to be significantly brighter with the GBT than with high-resolution VLA observations for 10 of 15 observed remnants.

(ii) Sensitive VLA observations of select SNRs (W44, IC443, Kes69, 3C391, G357.7+0.3) reveal the nature of enhanced 1720 MHz emission. Numerous weak compact masers as well as diffuse extended emission are detected tracing the shock-front. Zeeman splitting of masers located across the shock interaction permits mapping of the post-shock magnetic field.

(iii) Rotational lines of molecular hydrogen are detected at the position of several masers with Spitzer IRS spectroscopy between 5 and 35 microns. We find excitation of the S(0)-S(7) lines requires the passage of a C-type shock through dense molecular gas, in good agreement with the physical conditions derived from OH excitation.

(iv) A new survey for SNR-masers has identified four new interacting SNRs within 10 degrees of the Galactic Center. We find Maser-emitting SNRs are preferentially distributed in the inner Galaxy. Two of the new SNRs are coincident with TeV gamma-ray sources. Nine maser-emitting SNRs are now identified with a gamma-ray association indicating possible cosmic-ray acceleration.

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