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GCN Circular 700

Subject
GRB000528: follow-up X-ray measurements and update of IPN annulus
Date
2000-06-13T18:52:48Z (24 years ago)
From
Jean int Zand at SRON <jeanz@sron.nl>
GRB000528: follow-up X-ray measurements and update of IPN annulus 

E. Kuulkers, L. Kuiper, J.J.M. in 't Zand, J. Heise (Space Research
Organization Netherlands), L.A. Antonelli (Osservatorio Astronomico di Roma),
K. Hurley (University of California, Berkeley), L. Salotti (ASI, Rome),
M. Stornelli, G. Celidonio (Telespazio, Rome), E. Costa, M. Feroci, 
G. Gandolfi (IAS-CNR, Rome), F. Frontera (ITESRE-CNR, Bologna, and University
of Ferrara) L. Nicastro (IFCAI-CNR, Palermo), T. Cline (NASA Goddard Space
Flight Center), E Mazets (Ioffe Physici-Technical Institute, St. Petersburg), 
C. Guidorzi, and E. Montanari (University of Ferrara) report:

The BeppoSAX narrow-field instruments observed the region of GRB000528 twice:
from May 28.71 to May 29.57 UT (TOO1, 8.3-28.9 hours after the burst) and
from May 31.65 to June 1.49 (TOO2). The total exposure time obtained with
the Medium-Energy Concentrator Spectrometers (MECS) is 58 ksec. Two X-ray
sources close to one another were detected in the field, one at
R.A. = 10h 45h 28m, Dec. = -33d 58' 14" (J2000.0), which we designate as
1SAX J1045.5-3358 (object 1 in GCN 683), and the other at R.A. = 10h 45m 08s,
Dec. = -33d 59' 26", which we designate as 1SAX J1045.1-3359 (object 2 in GCN
683). Both sources have a conservative positional error of 1.5'. Object 2 is
inside the WFC error region (GCN 677) while the centroid of object 1 is 2.5
arcmin outside that region. We note that a bright and archival radio source
has been reported coincident with object 1 (GCN 686). A refined IPN analysis
using Ulysses, BeppoSAX, and Konus data indicates that object 1 is far less
consistent with the IPN annuli than object 2. The countrates for object 1
in MECS units 2 and 3 combined are (2.10+/-0.44)E-3 and (1.21+/-0.36)E-3 c/s
for TOO1 and TOO2 respectively and for object 2 (2.40+/-0.46)E-3 and
(0.65+/-0.32)E-3 c/s. Object 2 shows the strongest fading. Based on all
pieces of information, we identify object 2 (1SAX J1045.1-3359) as the
likely X-ray afterglow of GRB 000528.

For maps of the error regions, see URL http://wfc.sron.nl/GRB000528/

Neither the WFC nor the GRBM observed the delayed emission 600 s after
the burst (GCN 681); the source was unocculted at this time, and this
emission would have been detected with high significance if it had
originated from this source.  We conclude that this emission was either
solar in origin, or possibly from a different GRB.

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