The capability of the ASM system to produce rapid positions of GRB is improving steadily. We have just initiated (Jan. 1999) automatic transmissions to the GCN when the ASM detects a new transient in two different collimators with sufficient signal strength to rule out noise signals with high confidence. These events can be either a GRB or a new transient, and they will have position precision of a few arcminutes in two dimensions. The trigger criteria would have picked up 6 of the 7 two-collimator burst detections recorded since 1996. In addition, it would also have picked up five new X-ray transients in the past year. For example, a preliminary version of this system detected the bright black hole transient XTE J1550-564 at an intensity of only 70 mCrab, very early in its rise from anonymity on 7 Sep. 1998 (Smith 1998a). The position notices are now automatically transmitted to the GCN within 5-60 minutes of the burst arrival time under normal operating conditions. We expect that about 1 to 2 GRB events per year will satisfy the trigger criteria.
The entire ASM team at M.I.T. has contributed to this work. We are grateful for the GRB groups of BATSE, Ulysses, and Konus for providing refined GRB positions for inclusion in Smith et al. (1999), some of which are reproduced herein in Fig. 1. Support for the ASM work was provided in part by NASA Contract NAS5-30612.
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