IAUC 7369: SAX J1808.4-3658; XTE J1543-568; Corrs

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                                                  Circular No. 7369
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)


SAX J1808.4-3658
     R. Wijnands, D. Chakrabarty, and E. Morgan, Massachusetts
Institute of Technology; and M. van der Klis, University of
Amsterdam, report:  "Since the recent report of resumed activity
from the transient millisecond x-ray pulsar SAX J1808.4-3658 (IAUC
7358), intermittent monitoring with the PCA instrument on the Rossi
X-ray Timing Explorer has shown erratic variability of the source
intensity on time scales shorter than a day.  Between Feb. 8 and
25, the 2-10-keV x-ray intensity was sometimes as high as 12 mCrab
but at other times undetected (< 1 mCrab).  Detected emission
during this interval clearly showed pulsations at the 401-Hz spin
frequency but did not show the violent quasi-periodic x-ray
flaring that was observed during Feb. 2-6 (IAUC 7358).  The source
was completely undetected during Feb. 20-25, but it has been
intermittently detected since then at an intensity of roughly 10
mCrab.  All of these latest detections show the 401-Hz pulsation,
and some of them also again show violent x-ray flaring.  Given the
highly erratic behavior of the x-ray source, we strongly encourage
monitoring observations at all wavelengths."


XTE J1543-568
     T. Takeshima, Goddard Space Flight Center (GSFC) and
Universities Space Research Association (USRA); F. E. Marshall,
GSFC; R.~H.~D. Corbet, GSFC and USRA; and J. in 't Zand, Space
Research Organization Netherlands, report an improved position for
the 27.12-s pulsar XTE J1543-568 (IAUC 7363) from an RXTE/PCA
observation on Feb. 14.04 UT:  "The best-fit position is R.A. =
15h44m13s, Decl. = -56o44'.5 (equinox 2000.0; 90-percent confidence
error radius 4').  The source flux and the pulsed fraction remain
at about 6 mCrab and 60 percent (2-10 keV), respectively.
Observations at other wavelengths are encouraged."


CORRIGENDA
     On IAUC 7158, 'Supernovae 1999ac, 1999ad, 1999an, 1999be',
line 7, for  SN 1999ad  read  SN 1999ac
     On IAUC 7314, 'Supernova 1999fz in UGC 8164', lines 5-6, for
2".0 west  read  5".9 west
     On IAUC 7358, 'Supernova 2000G in UGC 1773', line 5, for
0".13 east  read  1".9 east

                      (C) Copyright 2000 CBAT
2000 February 28               (7369)            Daniel W. E. Green

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