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IAUC 7451: XTE J1859+226; C/1998 L2, 1998 L3, 1998 L4, 1998 L5, 1998 L6

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                                                  Circular No. 7451
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)


XTE J1859+226
     J. Casares, P. Rodrigues, C. Zurita and T. Shahbaz, Instituto de
Astrofisica de Canarias (IAC); P. Charles and R. Hynes, Southampton University;
T. Abbott, Nordic Optical Telescope (NOT); and P. Hakala, Turku Observatory,
report on long-term optical photometric monitoring of the soft x-ray
transient XTE J1859+226 (IAUC 7274, 7279): "R-band photometry using the IAC-80
and OGS telescopes on Tenerife and the 2.5-m NOT on La Palma showed a smooth
decline of 0.017 mag/day until a large dip from R about 19 to 21.5 occurred
around May 30 (day 235 from the 1999 Oct. 9 outburst).  The brightness
recovered within five days to an extrapolation of the previous decline and then
dropped again around June 11 to a minimum of R = 21.7 on June 24.  Within a
week it began a rapid rise into a minioutburst, reaching R about 18 on July 4,
since when it has been flat (with superposed variations of about 0.2 mag).
This is remarkably similar behavior (timescale and amplitude) to that of RX
J0422+32 (Chevalier and Ilovaisky 1995, A.Ap. 297, 103).  We therefore urge
further coverage at all wavelengths both now and during the coming months."
     Charles, Abbott, Hakala, Casares, and also G. Israelian (IAC), report
that their time-resolved (less than about 1 min) B-band photometry with the
NOT on July 5 and 6 showed large variations in the lightcurve: "On July 5
(B = 19.2, V = 18.7) the source faded by about 0.3 mag for about 3 hr, during
which time it exhibited QPO flaring activity (up to about 20 percent
amplitude) on a 21.5-min period.  The flaring ceased when the source returned
to its predip level.  The QPO timescale is very close to that reported by
Hynes et al. on IAUC 7294.  On July 6 no such flaring activity was seen;
instead the source exhibited a smooth sinusoidal modulation (amplitude 0.1
mag) on a timescale of about 6 hr, comparable to the 6.7 hr reported on
IAUC 7303.  This could be the orbital, or perhaps superhump modulation
timescale.  Further x-ray monitoring of this flaring activity is urged
during the current and any future minioutbursts."


COMETS C/1998 L2, 1998 L3, 1998 L4, 1998 L5, 1998 L6
     Details on these SOHO Kreutz sungrazers are on MPEC 2000-N25.

     1998 UT           R.A. (2000) Decl.       Comet
     June  3.519       4 44.5      +20 36      C/1998 L2
           4.087       4 46.5      +20 40      C/1998 L3
           4.936       4 49.9      +20 44      C/1998 L4
           5.401       4 51.4      +20 48      C/1998 L5
           5.791       4 52.9      +20 51      C/1998 L6

                      (C) Copyright 2000 CBAT
2000 July 11                   (7451)              Brian G. Marsden

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