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IAUC 6757: GRB 970828; XTE J1739-302; C/1997 T1

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                                                 Circular No. 6757
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970828
     J. Greiner and R. Schwarz, Astrophysical Institute, Potsdam;
J. Englhauser, Max-Planck-Institut fur Extraterrestrische Physik,
Garching; and P. J. Groot and T. J. Galama, Astronomical Institute,
Amsterdam, report:  "A 61 000-s ROSAT observation centered on GRB
970828 (IAUC 6728) during Sept. 3-5 reveals fifteen x-ray sources
within the HRI field-of-view above the 4-sigma level.  One of
these, located at R.A. = 18h08m31s.7, Decl. = +59o18'50" (equinox
2000.0; uncertainty +/- 10"; RX J1808.5+5918), is within the
RXTE/IPN error box and coincides with the x-ray source detected
with ASCA (IAUC 6732).  Using a power-law model with photon index 2
and the galactic column N_H = 3.7 x 10E20 cmE-2, the observed
countrate of (4 +/- 1) x 10E-4 counts/s corresponds to an
unabsorbed ROSAT flux (band 0.1-2.4 keV) of 2.5 x 10E-14 erg cmE-2
sE-1, consistent with a power-law decay.  Though the probability of
finding an x-ray source of that intensity within an 8-arcmin**2
error box is rather high (0.002), the coincidence in position and
expected fading flux suggests that we detected the x-ray afterglow
of GRB 970828.  In R-band images obtained with the 4.2-m William
Herschel Telescope between 3.5 hr and 8 days after the GRB event,
we detect seven objects in the ROSAT error box, with R magnitudes
in the range 24.1-25.0.  None of these is variable by more than 0.3
mag.  The object of mag K' = 19 reported on IAUC 6756 is located
within the 10" x-ray error circle and coincides with an optical
object for which R = 24.9 +/- 0.3 (obtained from point-spread-
function fitting).  The x-ray image, as well as an error box
overlay on R- and K-band images, is posted at

XTE J1739-302
     D. M. Smith, Space Sciences Laboratory, University of
California at Berkeley, communicates:  "The position originally
reported for XTE J1739-302 on IAUC 6748 was incorrect.  The correct
position is 7' away, at R.A. = 17h38m53s, Decl. = -30o15'.6
(equinox 2000.0).  An error radius of 3' at 99-percent confidence
is still appropriate, excluding the original field."

     Visual m_1 estimates:  Oct. 14.13 UT, 10.4 (G. W. Kronk, Troy,
IL, 0.33-m reflector); 18.76, 9.9 (R. J. Bouma, Groningen, The
Netherlands, 0.25-m reflector); 20.15, 9.4 (C. E. Spratt, Victoria,
BC, 0.20-m reflector).

                      (C) Copyright 1997 CBAT
1997 October 20                (6757)            Daniel W. E. Green

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