TITLE: GCN GRB OBSERVATION REPORT NUMBER: 290 SUBJECT: IPN localization for GRB990506 DATE: 99/05/06 20:28:10 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, on behalf of the Ulysses GRB team, and Scott Barthelmy, on behalf of the GCN team, report: We have obtained a preliminary IPN annulus for GRB990506 (BATSE #7549) using coarse time resolution BATSE/GCN and Ulysses data. This annulus is refined with respect to that in the GCN/IPN Notice sent out at 19:14:36 UT. The annulus is centered at RA(2000)= 144.960 degrees, Decl(2000)=-7.324 degrees, and has a radius of 37.424 +/- 0.035 degrees (3 sigma). It intersects both the BATSE Locburst location for this burst as well as the RXTE PCA source location sent out today at 17:27:37 UT. The latter intersection defines an ~4' wide by 1 degree long error box whose corners are: RA(2000) DEC(2000) 11 h 54 m 23.69 s -26 o 57 ' 59 " 11 h 56 m 15.28 s -26 o 03 ' 34 " 11 h 54 m 06.48 s -26 o 56 ' 11 " 11 h 55 m 58.07 s -26 o 01 ' 50 " Thus if the RXTE PCA source is found to be fading, it is quite likely to be the X-ray afterglow of the GRB. An image may be found at http://ssl.berkeley/edu/ipn3/990506. The IPN annulus can be refined considerably.