Collisional excitation of OH(6049 MHz) masers in supernova remnant — molecular cloud interactions

摘要

OH (1720 MHz) masers serve as indicators of SNR – molecular cloud interaction sites. These masers are collisionally excited in warm (50-100 K) shocked gas with densities of order 10~5cm~(-3) when the OH column density is in the range 10~(16)-10~(17)cm~(-2). Here I present excitation calculations which show that when the OH column density exceeds 10~(17)cm~(-2) at similar densities and temperatures, the inversion of the 1720 MHz line switches off and instead the 6049 MHz transition in the first excited rotational state of OH becomes inverted. This line may serve as a complementary signal of warm, shocked gas when the OH column density is large.