X-Ray Flare

L. J. Kaluzienski and S. S. Holt, Goddard Space Flight Center, report the detection with the Ariel 5 all-sky monitor of a flare from the region containing the bright, variable source 4U 1642-45 and the recurrent transient 4U 1630-47. The net flux (3-6 keV, ~ half-day averages, units of the Crab Nebula) was measured at 0.85 +/- 0.1, 1.0 +/- 0.1 and 1.4 +/- 0.15 on Nov. 15, 17 and 21, respectively. For comparison, an average flux of ~ 0.6 +/- 0.1 was measured in separate (fine-mode) observations during Nov. 8-13. While an increase from 4U 1642-45 cannot be ruled out, the flare may represent a late appearance (by ~ 70 days) of the 'absent' turn-on in the proposed 615-day flare cycle of 4U 1630-47 (cf. IAUC 3104). The region also contains the much weaker variable source 4U 1624-49.