Discovery of Broad Molecular Lines of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, SPITZER, and SOFIA Observations

We report a discovery of shocked gas from the supernova remnant (SNR) G357.7+0.3. Our millimeter and submillimeter observations reveal broad molecular lines of CO(2-1), CO(3-2), CO(4-3), 13CO (2-1), and 13CO (3-2), HCO+, and HCN using the Heinrich Hertz Submillimeter Telescope, the Arizona 12 m Telescope, APEX, and the MOPRA Telescope. The widths of the broad lines are 15–30 km s−1, and the detection of such broad lines is unambiguous, dynamic evidence showing that the SNR G357.7+0.3 is interacting with molecular clouds. The broad lines appear in extended regions (>45 × 5'). We also present the detection of shocked H2 emission in the mid-infrared but lacking ionic lines using Spitzer /IRS observations to map a few-arcminute area. The H2 excitation diagram shows a best fit with a two-temperature local thermal equilibrium model with the temperatures of ∼200 and 660 K. We observed [C ii] at 158 μ m and high- J CO(11-10) with the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on the Stratospheric Observatory for Infrared Astronomy. The GREAT spectrum of [C ii], a 3 σ detection, shows a broad line profile with a width of 15.7 km−1 that is similar to those of broad CO molecular lines. The line width of [C ii] implies that ionic lines can come from a low-velocity C-shock. Comparison of H2 emission with shock models shows that a combination of two C-shock models is favored over a combination of C- and J-shocks or a single shock. We estimate the CO density, column density, and temperature using a RADEX model. The best-fit model with n (H2) = 1.7 × 104 cm−3, N(CO) = 5.6 × 1016 cm−2, and T = 75 K can reproduce the observed millimeter CO brightnesses.