2011ApJ...743....4Z

We investigate the molecular environment of the Galactic supernova remnant (SNR) Kesteven 78 and perform an XMM-Newton X-ray spectroscopic study for the northeastern edge of the remnant. SNR Kes 78 is found to interact with the molecular clouds (MCs) at a systemic local standard of rest velocity of 81 km/s. At around this velocity, the SNR appears to contact a long molecular strip in the northeast and a large cloud in the east as revealed in the ¹³CO line, which may be responsible for the radio brightness peak and the OH maser, respectively. The ¹²CO-line bright region morphologically matches the eastern bright radio shell in general, and the SNR is consistent in extent with a CO cavity. Broadened ¹²CO-line profiles discerned in the eastern maser region and the western clumpy molecular arc and the elevated ¹²CO (J = 2-1)/(J = 1-0) ratios along the SNR boundary may be signatures of shock perturbation in the molecular gas. The SNR-MC association places the SNR at a kinematic distance of 4.8 kpc. The X-rays arising from the northeastern radio shell are emitted by underionized hot (∼1.5 keV), low-density (∼0.1/cm3) plasma with solar abundance, and the plasma may be of intercloud origin. The age of the remnant is inferred to be about 6 kyr. The size of the molecular cavity in Kes 78 implies an initial mass around 22 M_☉ for the progenitor.