The quiescent radio spectrum of SS 433

Abstract

Nearly simultaneous low- and high-radiofrequency observations of SS 433 on two epochs for which the source was relatively quiescent show that its nonthermal spectrum flattens and probably turns over near 0.3 GHz. Several physical mechanisms are examined as possible causes of the observed spectrum. The analysis makes it possible to rule out foreground absorption by the interstellar medium or an intervening H II region, but several other mechanisms intrinsic to the source are plausible. A map made at 160 MHz shows the source is essentially unresolved, indicating an angular diameter less than about 1 arcmin at that frequency.