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IAUC 6598: C/1995 O1; GRB 970111 AND GRB 970228

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                                                  Circular No. 6598
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/cfa/ps/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)

     K. Birkle and U. Thiele, Max Planck Institute for Astronomy,
Heidelberg; and H. Boehnhardt, University Observatory, Munich, report:
"A pattern of at least 12 straight dust striae appears almost identically
on exposures with the Calar Alto Schmidt on Mar. 17.185
(see http://caserv.caha.es/CAHA/halebopp.html) and 18.172 UT
at a nuclear distance of 1.5 to 3 deg in the dust tail, the projected
drift velocity of the pattern being about 15 km/s.  The striae are 1 to 3
arcmin wide, and some of them extend over more than 1 deg across the tail.
The average position angle, about 335 deg, of the striae indicates that
the pattern does not follow the synchronic direction for direct emission
from the nucleus.  The striae may thus be considered as due to secondary
processes influencing the dust grains in the outer coma or in the dust-tail
region.  The overall appearance resembles the striae patterns seen in
comets C/1975 V1 (West) and probably also in comet C/1910 A1 (Great
January Comet).  We also notice an enhanced brightness level in the dust-tail
region northward of p.a. 315 deg, this indicating enhanced dust
activity in the nucleus after about Feb. 5."

GRB 970111 AND GRB 970228
      A. J. Castro-Tirado and J. Gorosabel, Laboratorio de Astrofisica
Espacial y Fisica Fundamental, Madrid, report, on behalf also of
J. Heidt, T. Seitz, E. Thommes, C. Wolf, N. Lund, H. Pedersen, E. Costa,
F. Frontera, J. Heise, J. in't Zand, C. Bartolini, A. Guarnieri,
A. Masetti, A. Piccioni and E. Palazzi: "Following the detection of
GRB 970111 (IAUC 6533), deep frames (25 min in B and 10 min in R) were
obtained on Jan. 12.2, Feb. 10.2 and 11.2 UT (only R on the last occasion)
with the Calar Alto 2.2-m telescope (+ CAFOS).  No fading object was
detected, within the entire IPN/SAX error box (IAUC 6578), between
the first set of images (taken 19 hr after the burst) and the later data.
Any fading was < 0.2 mag for objects with B < 21, R < 20.8 and < 0.5 mag
for those down to B = 23, R = 22.6.  Taking into account the fact that
GRB 970111 has a higher gamma-ray fluence than GRB 970228 does, and
unless the flux from x-ray to optical wavelengths was absorbed by
intervening matter close to the source, the nondetection of either an
x-ray counterpart (by the SAX narrow-field instruments) or a fading
optical counterpart in the GRB 970111 field indicates a significant
difference in the behavior of GRB 970111 in comparison to that of
GRB 970228, for which a presumably-related x-ray/optical counterpart
has been reported (IAUC 6576, 6584)."

                      (C) Copyright 1997 CBAT
1997 March 21                  (6598)              Brian G. Marsden

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