Circular No. 6569
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
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Phone 617-495-7244/7440/7444 (for emergency use only)
 

GRB 960720 AND GRB 970111
    J. in 't Zand, J. Heise, P. Hoyng, and R. Jager, Space Research
Organization of the Netherlands (SRON), Utrecht; L. Piro, E. Costa,
and M. Feroci, Istituto Astrofisica Spaziale, CNR, Frascati; F.
Frontera, D. Dal Fiume, M. Orlandini, G. Pizzichini, and L.
Nicastro, Istituto Tecnologie e Studio delle Radiazioni
Extraterrestri, CNR, Bologna; and J. Muller, BeppoSAX, Rome, and
SRON, Utrecht, write:  "The positions of the x-ray counterparts to
GRB 960720 and GRB 970111 as determined with the BeppoSAX Wide
Field Cameras (cf. IAUC 6467 and 6533, respectively) have been
refined through an improvement of the spatial calibration of the
instruments.  The calibration concerns small misalignments between
both cameras and between the cameras and the satellite coordinate
system, the image scales of both WFCs, and the modeling of the
point spread function.  The calibration was tested with 123
detections of catalogued x-ray sources with accurately known
positions, as found in 15 SAX WFC observations with a variety of
orientation angles.  These sources have a representative range of
intensities and off-axis angles.  None of the detections has a
difference between catalogue and measured source positions > 3'.9,
and 97 percent have a difference of < 3'.  In a subset of fourteen
sources having significance levels that are within a factor of 2 of
the levels of GRB 960720 and GRB 970111, one source shows a
difference of > 3' from the catalogue position.  For GRB 960720, we
find a 3'-radius error circle centered on R.A. = 17h30m37s, Decl. =
+49o05'.8 (equinox 2000.0).  This position is 10'.5 from the
previously reported position, for which a 10' error circle radius
was reported.  Neither the previously reported SAX NFI source (IAUC
6480) nor the optical source (IAUC 6526) lies within the error
circle.  The new error circle does include the radio-loud quasar 4C
49.29 (z = 1.038).  The error circle for GRB 970111 is centered on
R.A. = 15h28m15s, Decl. = +19o36'.3.  This center is 4'.2 from the
previously reported position, and the circle overlaps the IPN
annulus reported by Hurley et al. (IAUC 6545).  None of the
previously reported SAX NFI sources (Butler et al., IAUC 6539),
RASS sources (Voges et al., IAUC 6539), radio source (Frail et al.,
IAUC 6545), and ROSAT HRI source (IAUC 6567) lies within the 3'-
radius error circle."


COMET 29P/SCHWASSMANN-WACHMANN 1
     Visual m1 estimates:  Feb. 2.19 UT, 11.6 (K. Hornoch,
Lelekovice, Czech Republic, 0.35-m refl.); 8.15, 14.1: (J. D.
Shanklin, Cambridge, England, 0.3-m refractor); 16.18, 14.1 (J.
Carvajal, Teruel, Spain, 0.44-m refl.).

                      (C) Copyright 1997 CBAT                    
1997 March 1                   (6569)            Daniel W. E. Green