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IAUC 6238: GRO J2058+42; 1995ac; C/1995 Q1

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                                                  Circular No. 6238
Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)

GRO J2058+42
     C. A. Wilson,  S. N. Zhang, M. H. Finger, R. B. Wilson, and M.
Scott, Marshall Space Flight Center, NASA; and T. Koh, D.
Chakrabarty, B. Vaughan, and T. A. Prince, California Institute of
Technology, report for the Compton Observatory BATSE team:
"Pulsations from a previously-uncatalogued source in the Cygnus
region in the energy band 20-50 keV have been detected since Sept.
14 and continue to be detected through Sept. 25.  A preliminary
location (95-percent confidence) is bounded by a quadrilateral with
vertices (equinox 2000.0) at R.A. = 21h03m, Decl. = +40o.2; 20h56m,
+44o.0; 20h53m, +43o.2; 21h01m, +39o.4.  Positions estimated
independently from the pulsed and total flux are consistent.  An
rms pulsed flux of 130 +/- 40 mCrab in the energy band 20-50 keV
was observed on Sept. 23.  Observations between Sept. 20 and 23
show pulsations up to at least 70 keV and are consistent with a
barycentric pulse frequency of 5.05618(7) x 10E-3 Hz on Sept. 22.0
UT with a frequency derivative of 1.70(7) x 10E-11 Hz/s.  The total
flux, measured by Earth occultation, increased from < 100 mCrab on
Sept. 17 to 280 +/- 50 mCrab on Sept. 22 in the band 20-100 keV
and has remained approximately constant (within 15 percent) from
Sept. 22 to 24.  The energy spectrum of the total flux on Sept. 20-
24 was well fit by an optically-thin thermal bremsstrahlung model
with kT = 17 +/- 1 keV from 20 to 100 keV."

     C. Pollas, Observatoire de la Cote d'Azur, reports the
following precise position for SN 1995ac:  R.A. = 22h45m34s.14,
Decl. = -8o45'04".7 (equinox 2000.0), which is 2".1 west and 4".5
south of the galaxy's center.  A nearby star (V about 16.5) has
position end figures 38s.41, 44'27".3.

     Total visual magnitude estimates:  Aug. 26.37 UT, 5.2 (R. H.
McNaught, Coonabarabran, N.S.W., 10x50 binoculars); Sept. 23.52,
7.6 (C. S. Morris, southern CA, 0.26-m reflector); 25.18, 7.2 (J.
D. Shanklin, Cambridge, England, 14x100 binoculars); 26.45, 7.7 (G.
W. Kronk, Troy, IL, 0.33-m reflector); 27.16, 6.5 (G. A. Milani,
Mt. Grappa, Italy, 20x80 binoculars); 27.51, 7.7 (Morris, 20x80

1995 September 27              (6238)            Daniel W. E. Green

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