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IAUC 6487: GRB 960720; C/1996 N1

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                                                  Circular No. 6487
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)


GRB 960720
     J. Greiner, Max-Planck-Institut (MPI) fur Extraterrestrische
Physik, Garching; H.-J. Hagen, Hamburg Observatory; and A. Heines,
MPI group at Jena University, report:  "A 6300-s ROSAT HRI
observation on Aug. 31 reveals the existence of eight x-ray sources
above the 3-sigma level within the 10'-radius error box of GRB
960720 (IAUC 6467).  All eight x-ray sources have intensities below
the ROSAT all-sky-survey sensitivity threshold and their brightness
history thus remains unknown.  Further optical and x-ray
observations are necessary to search for variability patterns that
might suggest a relationship of one of these sources to GRB 960720.
Three of these eight x-ray sources are located within the 1'-radius
error box of the x-ray source detected with BeppoSAX (IAUC 6480)
and ASCA (IAUC 6481), 2'.9 off the GRB-error-box center.  Each of
these three x-ray-source error boxes (+/- 10") contains only one
optical object down to the POSS limit (a finding chart can be found
at http://www.rosat.mpe-garching.mpg.de/~jcg/grb.html).  Optical
spectra in the range 350-900 nm, obtained on Oct. 3 and 4 with the
MPI fur Astronomie 2.2-m telescope at Calar Alto, show strong and
broad emission lines at 373.8 and 546.1 nm in RX J1729.5+4904 and
at 356.4 and 525.5 nm in RX J1729.3+4904.  These two lines in each
object are interpreted as C III] at 190.9 nm and Mg II at 279.8 nm,
resulting in redshifts of 0.96 and 0.87 for these objects.  The
optical intensities (magnitudes B = 20.8 and 20.0) and redshifts
suggest a Seyfert-galaxy nature for both objects.  The optical
object seen on the POSS O plate within the error circle of the
third x-ray source (RX J1729.4+4905) is currently fainter than B =
22.  Assuming a power-law model for the x-ray spectrum with photon
index -1.9 and only galactic absorption (2.5 x 10E20 cmE-2), the
HRI countrate of 0.0017 count/s for RX J1729.5+4904 transforms into
an unabsorbed x-ray flux of 9.4 x 10E-14 erg cmE-2 sE-1 in the
range 0.1-2.4 keV.  The flux of the single source seen with
BeppoSAX and ASCA is consistent with the sum of all three HRI x-ray
sources (0.0011 count/s for RX J1729.3+4904 and 0.0008 count/s for
RX J1729.4+4905)."


COMET C/1996 N1 (BREWINGTON)
      Visual m1 estimates by K. Hornoch, Lelekovice, Czech Republic
(B = 10x80 binoculars; L = 0.35-m reflector):  Sept. 2.81 UT, 8.4
(B); 11.85, 9.0 (B); 19.83, 9.3 (B); Oct. 3.83, 10.1 (L); 7.77,
11.0 (L).

                      (C) Copyright 1996 CBAT
1996 October 9                 (6487)            Daniel W. E. Green

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