4U 0115+63

L. Cominsky, F. Li, H. Bradt, G. W. Clark and S. Rappaport, Massachusetts Institute of Technology, report that the SAS-3 Group has measured the position of the hard, pulsing, transient x-ray source 4U 0115+63 (cf. IAUC 3161). The position determined from the rotation modulation collimators on SAS 3 is R.A. = 1h15m15s.7, Decl. = +63o28'45" (equinox 1950.0) with an error-circle radius of 30" (90-percent confidence). Attention is drawn to the star of mv ~ 16 that is the brightest one in the error circle; it is located about 11'.8 and 1'.0 east of SAO 011683 (mv = 8.2). M. Johnston, H. Bradt, R. Doxsey, H. Gursky, D. Schwartz and J. Schwarz, Massachusetts Institute of Technology and Center for Astrophysics, report an improved position for 4U 0115+63 obtained with the modulation collimator experiment on HEAO 1: R.A. = 1h15m13s.7, Decl. = +63o28'41" (equinox 1950.0). The error region (90-percent confidence) is approximated by a north-south band (p.a. 353o) of full width 20" and length 100". The mv ~ 16 star noted above lies within the error region, 3" +/- 4" west of the center. The two faint stars ~ 25" northwest of this star lie just (~ 5") outside the HEAO-1 and SAS-3 error regions. The 3s.6 period reported by the SAS-3 Group (IAUC 3161) is clearly evident in the HEAO data. The pulsed fraction (1-13 keV) is ~ 30 percent. On Jan. 16 the average intensity was ~ 0.30 that of the Crab.