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IAUC 7870: 2002cb; XTE J1751-305

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                                                  Circular No. 7870
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2002cb IN MCG +8-24-34
     T. Boles, Coddenham, Suffolk, reports his discovery of an apparent
supernova (mag 17.0) on a 30-s unfiltered CCD image taken on Apr. 7.145 UT
(limiting mag 18.5) with a 0.35-m Schmidt-Cassegrain reflector, in the
course of the U.K. Nova/Supernova patrol.  The new object is confirmed at a
similar magnitude in a subsequent image taken by R. Arbour, South Wonston,
Hants., on Apr. 7.851 on a 45-s CCD image using a 0.30-m f/6.3
Schmidt-Cassegrain reflector.  It is also confirmed by M. Armstrong, Rolvenden,
Kent, on Apr. 7.862 (0.35-m Schmidt-Cassegrain + CCD).  The object is
located at R.A. = 13h04m23s.97, Decl. = +47d35'53".2, which is 9".5 east and
6".4 north of MCG +8-24-34.  Armstrong gives end figures 23s.92, 53".1.
The new object is not present on Palomar Sky Survey images taken on 1991.280
(red, limiting mag 20.5) and 1995.236 (blue, limiting mag 22.0).

     R. Chornock, W. D. Li and A. V. Filippenko, University of California,
Berkeley, report that inspection of CCD spectra (range 330-1000 nm) obtained on
Apr. 8 with the Shane 3-m reflector at Lick Observatory reveals that the
object is indeed a supernova, of type IIn.  The spectrum exhibits weak, narrow
emission lines of the hydrogen Balmer series superposed on a smooth, almost
featureless blue continuum.

XTE J1751-305
     C. B. Markwardt, University of Maryland and Goddard Space Flight
Center (GSFC); and J. H. Swank, GSFC, report that the orbital period of
the recently discovered pulsar XTE J1751-305 (IAUC 7867) is 2545.3(1)
s.  RXTE PCA observations taken intermittently during Apr. 4.64-7.54
UT show doppler modulation of the pulsed signal, with a projected
semimajor axis of 10.06(6) light-ms.  The barycentric mean spin frequency
of the pulsar is 435.31812(4) Hz, and the epoch of 90-deg mean
longitude is JD 2452369.1389(1).  The mass function of the pulsar is
1.26 x 10**-6 solar mass, which gives a minimum mass for the companion of
0.014 solar mass (approximately 15 Jupiter masses).  No x-ray eclipses or
absorption dips were observed, indicating that the source is not viewed
directly edge-on.  A power-law fit to the x-ray spectrum has a photon
index of 1.9.  The neutral-hydrogen-absorption column density for a
range of spectral models is 1 to 3 x 10**22 cm-2, indicating that the
optical counterpart will be heavily absorbed.  The x-ray flux is
variable at the 1-to-2-percent level (r.m.s.), primarily on the timescale
of several orbital periods.  The average x-ray flux has declined from
56 to 43 mCrab, corresponding to an exponential-decay constant of 10
days, thus justifying prompt follow-up observations.

                      (C) Copyright 2002 CBAT
2002 April 8                  (7870)              Brian G. Marsden

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