Aquila X-1

A. Davidson and colleagues (Space Sciences Laboratory, University of California, Berkeley) and P. Sanford, P. Davison, and K. Mason (Mullard Space Science Laboratory, University College London) report the following pre-outburst and current optical and x-ray data on Aql X-1 (3U 1908+00) (cf. IAU 2788): observations in the 2.5-7.5 keV band from OAO Copernicus intermittently during the past 2 years show the source present at 1-2 percent of the Crab Nebula, significantly below the level reported in the 3U. Thirty blue and ultraviolet plates of the field obtained during the same period, some simultaneous with OAO Copernicus, reveal no variable stars of amplitude greater than 0.3 mag. to B = 18, and no stars with significant uv excess. The only ultraviolet object found in the vicinity is a B = 16.6, B5v star at R.A. = 19 08 39.3, Decl. = + 0 29 1 (1950), 4' from the edge of the 3U error box. Spectroscopic observations show no abnormalities. The extinction in the field appears modest out to 10 kpc. X-ray observations obtained between 7h and 9h UT on 1975 June 19 reveal the source at an intensity of 70 percent of the Crab Nebula, with a significantly softer spectrum than the Crab. A blue plate obtained during outburst at 1975 June 18.38 UT shows no change greater than 0.4 mag. in any of the stars in the field to B = 17.5, including the blue candidate mentioned above.