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IAUC 7358: 2000G; SAX J1808.4-3658

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                                                  Circular No. 7358
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/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)

     T. Puckett, Mountain Town, GA, reports his discovery of an
apparent supernova (mag 17.2) on an unfiltered CCD frame (limiting
mag 20.1) taken with the Puckett Observatory 0.60-m automated
supernova patrol telescope on Feb. 5.04 UT.  SN 2000G is located at
R.A. = 2h18m15s.27, Decl. = +13o12'19".4 (equinox 2000.0), which is
0".13 east and 3".3 north of the center of UGC 1773.  The new
object was also present on an unfiltered CCD frame taken on Feb.
7.00, but it was not present on a frame taken on 1999 Sept. 7.34 --
nor does SN 2000G appear on a Palomar Sky Survey images taken on
1990 Oct. 14 (limiting mag about 21.2) or 1950 Aug. 14 (limiting
mag about 20.0).
     P. Garnavich, University of Notre Dame; and S. Jha, P. Challis,
and R. Kirshner, Harvard-Smithsonian Center for Astrophysics,
report that a spectrum of SN 2000G was obtained by K. Rines on Feb.
7.2 UT with the F. L. Whipple Observatory 1.5-m telescope, which
shows that it is a type-II supernova just past maximum light.  A
broad H-alpha emission feature is present, as well as H-beta
absorption, which indicates a photospheric velocity of 8300 km/s.
Narrow emission features from the host galaxy provide a recession
velocity of 3600 km/s.

SAX J1808.4-3658
     M. van der Klis, University of Amsterdam; D. Chakrabarty, J.
C. Lee, E. H. Morgan, and R. Wijnands, Massachusetts Institute of
Technology; C. B. Markwardt, University of Maryland and Goddard
Space Flight Center (GSFC); and J. H. Swank, GSFC, write:  "The
x-ray transient SAX J1808.4-3658, the only known accretion-powered
millisecond pulsar (IAUC 6876, 6877), has been detected at a low
x-ray-flux level of 3-12 mCrab (2-10 keV) since Jan. 21.1 UT with
the PCA instrument on the Rossi X-Ray Timing Explorer (RXTE).  The
start time of this outburst is not known because the source was
unobservable by RXTE from about 1999 Nov. 2 to 2000 Jan. 21, due to
its proximity to the sun.  On 1999 Nov. 2, the upper limit on the
source flux was < 0.5 mCrab (2-10 keV).  X-ray pulsations at the
401-Hz spin frequency were detected in several short observations
between Jan. 21.1 and Feb. 6.2.  Since Feb. 2, the source has
exhibited violent quasi-periodic x-ray flaring with an rms
amplitude varying between 40 and 100 percent of the average flux
and a repetition frequency varying between 0.9 and 1.5 Hz.  This is
unlike any phenomenon previously observed in a neutron-star
low-mass x-ray binary.   The source is still close to the sun, but
observations at other wavelengths (particularly radio and infrared)
are strongly encouraged."

                      (C) Copyright 2000 CBAT
2000 February 7                (7358)            Daniel W. E. Green

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