Brief X-Ray Transient

L. J. Kaluzienski, J. L. Robinson-Saba, E. A. Boldt, S. S. Holt, J. H. Swank, P. J. Serlemitsos and R. E. Rothschild, Goddard Space Flight Center, report the detection of a transient x-ray event in quick-look data from the A-2 experiment on HEAO-1. The source, located within an error box with corners at R.A. = 5h21m, Decl. = -53o.6; 5h22m, -54o.2; 4h39m, -57o3; 4h36m, -56o.8 (equinox 1950.0), is clearly present in the four high-energy (1-60 keV) detectors (soft x-ray detectors off) during a scan of this region on ~ Feb. 9d20h24m UT. The lower limit to the flux (2-20 keV) is S0 = 0.14 Crab, with no major variations (1s.28 integrations) evident over the 1-min scan duration. Concurrent observations of this region with the Ariel 5 all-sky monitor yield an upper limit of ~ 1.0 Crab (1.5-hr average) in the 3-6 keV band. The source is not visible (S <~ 0.05 S0) in A-2 scans occurring on ~ Feb. 9d01h24m and 11d02h12m UT. Preliminary wide-band spectral color ratios indicate a spectrum similar in hardness to that of the Crab Nebula with no significant low-energy (E <~ 3 keV) absorption. The present limit on the duration of the event (2 days >~ t >~ 1 min) is intermediate between that of the x-ray bursters and the 'weak, high-latitude' transients.