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IAUC 6064: RX J0045.4+4154; PSR 0833-45

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                                                  Circular No. 6064
Central Bureau for Astronomical Telegrams
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

RX J0045.4+4154
     N. E. White, Laboratory for High Energy Astrophysics, Goddard
Space Flight Center (GSFC); P. Giommi, European Space Information
System, European Space Agency; L. Angelini, GSFC; and S. Fantasia,
University of Maryland, report the discovery of a recurrent supersoft
x-ray transient in ROSAT archival data on M31:  "The first outburst
began on 1992 Feb. 2 and lasted at least four days (the end of that
particular ROSAT observation sequence).  The source had 'turned off'
by the time of the next ROSAT observation of this region, which
began on 1992 Aug. 10.  A second outburst began on 1993 Jan. 7; the
peak of the outburst was reached in about 4 days, after which a
decline started.  When the ROSAT observation ended 2.5 days after
the peak, the source had not yet reached the minimum.  Fitting of
the source spectra on both occasions yields a blackbody temperature
of 0.095 keV, consistent with the definition of a supersoft source.
The hydrogen column density is 1.2 x 10E21 cmE-2 and the unabsorbed
source luminosity in the band 0.1-4.0 keV is 3.4 x 10E38 erg/s
(assuming the source is located in M31).  The source position is
R.A. = 0h45m28s.6, Decl. = +41o54'11".3 (equinox 2000.0; 90-percent
confidence radius 13").  In the ROSAT archive there are four time
periods in which this part of the sky was observed, each separated
by six months (1991 July, 1992 Jan.-Feb. and Aug., 1993 Jan.).  On
two occasions each the source was in outburst (1992 Jan.-Feb. and
1993 Jan.) and in quiescence.  If this source is not a foreground
object, then it is the first recurrent x-ray transient to be found
in M31.  Further outbursts might be expected.  If they are periodic,
the next will occur in 1994 Nov.  Further observations are suggested."

PSR 0833-45
     C. Flanagan, Hartebeesthoek Radio Astronomy Observatory,
Johannesburg, writes:  "PSR 0833-45 (the Vela pulsar) has undergone
a further spin-up, the eleventh observed to date, 32 days after the
previous such event (IAUC 6038).  The most recent event occurred on
Aug. 27.158, and involved a relative change in spin-period dP/P of
-1.99(2) x 10E-7, 23 percent the size of the glitch of July 26.
Unlike the July 26 event, for which the observed relative change in
period derivative < 0.005, the Aug. 27 event was accompanied by an
increase in period derivative dP'/P' of +0.12(2)."

1994 August 29                 (6064)            Daniel W. E. Green

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