DISCOVERY of BROAD MOLECULAR LINES and 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 (>4.′5 × 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 μm 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 3σ 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.