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IAUC 5649: GEMINGA; 1992t

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                                                  Circular No. 5649
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)


GEMINGA
    The Compton Observatory EGRET Team (H. A. Mayer-Hasselwander,
K. Brazier, G. Kanbach, and C. von Montigny, Max-Planck-Institut
fur Extraterrestrische Physik; D. L. Bertsch, B. L. Dingus, C. E.
Fichtel, R. C. Hartman, S. D. Hunter, P. W. Kwok, J. R. Mattox, P.
Sreekumar, and D. J. Thompson, Goddard Space Flight Center, NASA;
D. A. Kniffen, Hampden-Sydney College; J. Chiang, J. Fierro, Y. C.
Lin, P. F. Michelson, and P. L. Nolan, Stanford University; and E.
Schneid, Grumman Aerospace Corporation) communicates:  "Since
deriving the previous EGRET ephemeris (IAUC 5583), we have obtained 4
more weeks of low-sensitivity exposure to Geminga (30 deg off-
axis).  This allows an accurate ephemeris to be derived from EGRET
data alone:  T0 = 1991 May 24.0 Barycentric Dynamical Time (TDB),
f0 = 4.217 674 997 9 Hz, f1 = -1.9526(7) x 10E-13 Hz/s.  The phase
of peak 1 is 0.64(1) at T0 at the barycenter and 0.21(1) on 1991
May 24.0 UT at the geocenter.  This ephemeris is expected to be
correct to within 0.1 of a revolution for the interval 1990.3-
1993.7.  The EGRET data indicate that the second frequency derivative
is < 2 x 10E-23 Hz sE-2.  The frequency derivative f1 is
inconsistent with the value given in the previous EGRET ephemeris,
which was obtained by an extrapolation of the COS-B ephemeris (IAUC
5541).  Thus, the phase of the previous EGRET ephemeris is correct
to within 0.1 of a revolution for a shorter interval (1990.6-1992.9)
than previously specified.  The epoch of the previous EGRET ephemeris
was specified as UT.  However, it was actually TDB.  We apologize
for the confusion this has caused.  The position of Geminga is
R.A. = 6h33m54s.02, Decl. = +17 46'11".5 (equinox J2000.0)"


PERIODIC COMET SWIFT-TUTTLE (1992t)
     Further total visual magnitude estimates (cf. IAUC 5645): Oct.
30.06 UT, 6.2 (B. H. Granslo, Fjellhamar, Norway, 0.06-m refractor);
31.83, 5.9 (S. Garro, Merlette, France, naked eye); Nov. 1.99, 6.0
(B. G. Marsden, Lexington, MA, 7x50 binoculars); 3.40, 5.8 (M.
Ohkuma, Mt. Fuji, Japan, 10x70 binoculars; 1 deg tail in p.a. 40
deg); 5.09, 5.4 (W. G. Dillon, Missouri City, TX, 7x50 binoculars);
5.78, 5.5 (M. Tombelli, Montelupo, Italy, 11x80 binoculars).


1992 November 6                (5649)            Daniel W. E. Green

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