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GCN Circular 69

Subject
BSAX Observations of GRB980425 field
Date
1998-05-12T13:58:01Z (26 years ago)
From
Elena Pian at ITESRE-CNR,Bologna <pian@tesre.bo.cnr.it>
GRB980425


E. Pian, F. Frontera, Istituto TESRE, CNR, Bologna, Italy, 
L.A. Antonelli, SAX-SDC, Rome, Italy, L. Piro, IAS, CNR, Rome, Italy, 
also on behalf of the BeppoSAX team

report:  "A second Target-of-Opportunity observation of the BeppoSAX Wide
Field Camera (WFC) error box of GRB980425 (IAUC 6884) was done with the
BeppoSAX Narrow Field Instruments (NFI) in May 2.604-3.646 UT. Preliminary
analysis of the MECS data shows that the source 1SAXJ1935.0-5248 reported in
GCN N. 61 has a count rate of (3.0 +- 0.5)x10E-3 cts/s in the 1.6-10 keV range
(1.9x10E-13 erg sE-1 cmE-2 in 2-10 keV), and therefore has decreased only with
marginal significance with respect to the TOO observation performed in April
26.31-28.16 UT.  A 3-sigma upper limit of 1.5x10E-3 cts/s in the 1.6-10 keV
range is found for 1SAXJ1935.3-5252.  If one assumes for the X-ray emission of
this source a power-law temporal decay f ~ (t - t0)^{-alpha}, the measured
upper limit is consistent with the alpha >0.4 fading observed between the
first and second part of the first TOO NFI pointing (GCN N. 61), as well as
with the alpha ~1.4 decrease between the 2-10 keV flux preliminarily estimated
from the WFC detection (~2.6x10E-08 erg sE-1 cmE-2, Pian et al. 1998, in
preparation) and that observed in the first 27.7 hours of the first NFI
pointing (GCN N. 61). This variability behavior is typical of X-ray afterglows
of GRBs so far detected.
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