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IAUC 6688: C/1996 D1; GRB 970616

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                                                  Circular No. 6688
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)
URL http://cfa-www.harvard.edu/cfa/ps/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)


COMET C/1996 D1 (SOHO)
     C. St. Cyr, Naval Research Laboratory, reports, for the SOHO-LASCO
Consortium (see IAUC 6685), the discovery of another faint comet,
evidently a Kreutz sungrazer, in SOHO-LASCO C3 coronagraph images by
B. McCarty, University of Birmingham, using the automated search
software developed by D. Biesecker.  Some of the images may have shown
a small tail.  The comet appeared close to the pylon holding the occulter,
so there is some uncertainty in the vignetting.  Measurements by St. Cyr
and D. Lewis have been reduced by G. V. Williams and are given on MPEC
1997-M10 in detail, the approximate discovery position being as follows:

     1996 UT           R.A. (2000) Decl.        m1
     Feb. 18.150      22 30.8      -13 41        5

The comet was observed approaching the sun in p.a. 124 deg (from the
solar north pole) until Feb. 18.59 UT (i.e., over a range of only 24.7
to 17.3 solar radii).  Orbital computations by the undersigned, also
given in detail on MPEC 1997-M10, indicate perihelion passage on Feb. 19.41.


GRB 970616
     A. J. Castro-Tirado and J. Gorosabel, Laboratorio de Astrofisica
Espacial y Fisica Fundamental, Madrid; D. Thompson and
K. Birkle, Max Planck Institut fur Astronomie, Heidelberg; and
J. Greiner, Astrophysikalisches Institut, Potsdam, report, on
behalf of a large international collaboration: "Following the detection
of GRB 970616 by BATSE and RXTE (IAUC 6683), images in the K'-band
(2.1 microns) were obtained with the 3.5-m CAHA telescope (+ OMEGA)
at the German-Spanish Calar Alto Observatory on June 21.18, 25.17
and 26.18 UT.  A comparison between the first and third frames reveals
no variations larger than 0.5 mag for sources with K' < 17, either within
the fading ASCA x-ray source error circle (IAUC 6687), or in the rest
of the RXTE/IPN annulus (IAUC 6687) in a 5' x 4' region southeastward
from this source.  The optical variable reported by Galama et al. is
present on all three images but does not show any obvious variation:
preliminary K' magnitude estimates are 17.5 +/- 0.4, 17.5 +/- 0.3
and 17.4 +/- 0.4, respectively.  This suggests a different origin for
the observed optical fading.  With the estimated R about 24 on
June 24.61 (IAUC 6687), the R-K' color on that date was about 6.5,
placing it on the red side of the distribution of all objects at
K' about 18."

                      (C) Copyright 1997 CBAT
1997 June 27                   (6688)              Brian G. Marsden

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