A HIGH-RESOLUTION RADIO STUDY OF THE W50-SS-433 SYSTEM AND THE SURROUNDING MEDIUM

We present VLA images at 327.5 and 1465 MHz of the nebula W50 surround ing the stellar source of relativistic jets SS 433. At 1.4 GHz, we hav e produced an image of W50 with an angular resolution of 55 '' that co ntains all the spatial structures. The technique consists of a complex combination of 58 separate VLA pointings plus the addition of single- dish data into a single mosaic. For the first time, this high-quality radio image has revealed the puzzling structure of W50, which resemble s a seashell. The present data confirm the connection between the suba rcsecond relativistic jets from SS 433 and the extended nebula W50 ove r similar to 5 orders of magnitude in scale. The central component can be very accurately described by a circle 58' in diameter. The eastern wing exhibits a clear helical pattern that mirrors at larger scales t he precession of the jets from SS 433. The western wing, smaller and b righter than its eastern counterpart, has a bright bowed arch at the e dge, in the region where the structure appears to interact with a high er density medium. The spectral index of the radio continuum emission exhibits striking asymmetries: the central spherical component has a q uite normal spectrum for shell-type supernova remnants, alpha similar to 0.5 (S proportional to v(-alpha)), while it steepens toward the eas tern wing (alpha similar to 0.8) and flattens toward the western one ( alpha similar to 0.4). A ''chimney,'' apparently radiating away from W 50, is observed in the eastern wing. The atomic hydrogen emission was surveyed in an area of 4 degrees x 4 degrees around W50 using the NRAO Green Bank 140 foot (43 m) telescope. Based on these observations, un mistakable evidence of an interaction of W50 with the surrounding H I gas at the systemic radial velocity v = 42 km s(-1) is found. Clear tr aces of the interaction of the jets of SS 433 with the surrounding gas are shown. Based on these observations a kinematic distance of 3 kpc is determined for the W50-SS 433 system. An elliptical shell of simila r to 30,000 M-., expanding at about 76 km s(-1), can be associated wit h the radio nebula. The kinetic energy transferred into the ambient me dium is estimated (similar to 2 x 10(51) ergs), thus confirming that t he relativistic jets from SS 433 represent an important contribution t o the overall energy budget of W50.