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IAUC 7466: XTE J1859+226; 2000cr

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                                                  Circular No. 7466
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1859+226
     J. E. McClintock, Harvard-Smithsonian Center for Astrophysics
(CfA); R. A. Remillard, Massachusetts Institute of Technology; and
W. A. Heindl and J. A. Tomsick, University of California at San
Diego, report:  "We obtained 25 hr of photometry for this x-ray
nova on July 3-7 UT, using the 1.2-m telescope at the Fred L.
Whipple Observatory.  During 6 hr of continuous monitoring on July
3, the source was constant in intensity and relatively faint (V =
19.2).  On the following four nights, the source was brighter by
about 0.6 mag and varied nightly by up to 0.2 mag.  We searched
these four nights of data for a periodic modulation, using the
technique of Stellingwerf (1978, Ap.J. 224, 953).  The deepest
minimum in the variance statistic occurs at 18.72 +/- 0.48 hr,
which we identify as the orbital period.  We find no evidence for
the reported 6.73-hr period (IAUC 7303).  However, the reported
9.15-hr period (IAUC 7388) may be a subharmonic of the 18.7-hr
period reported herein.  The light curve folded on the 18.7-hr
period resembles that of GRO J1655-40 as it approached quiescence
(Bailyn et al. 1995, Nature 378, 157).  There is a primary minimum
with a depth of about 0.2 mag that is probably due to the partial
eclipse of the accretion disk by the secondary star.  There is also
a shallow secondary minimum that is displaced by about 0.5 in phase
from the primary minimum; this feature is probably due to the
eclipse of the secondary star by the disk.  The time of the primary
minimum is HJD 2451732.81 +/- 0.03.  There is a second deep mimimum
in the periodogram at twice 18.7 hr; however, the complexity of
features in the folded light curve argues that this is not the
orbital period."
     M. Garcia and J. McClintock, CfA; P. Callanan, University
College, Cork; and A. V. Filippenko, University of California at
Berkeley, report, following IAUC 7463, that they observed the
optical counterpart to this soft x-ray transient (cf. IAUC 7451,
7456) with the Cerro Tololo 0.9-m telescope on July 23.1, 24.1, and
25.1 UT, yielding the following R magnitudes, respectively:  20.8
+/- 0.3, 20.2 +/- 0.1, and 19.8 +/- 0.1.  Seeing was 2".7, 1".5,
and 1".4 on the respective nights, with thin clouds on the first
and clear skies on the next two.  Thus this object appears to be
undergoing yet another optical brightening.  Observations on the
Keck-II telescope also show a brightening in the K band between
July 22 and 24.

SUPERNOVA 2000cr IN NGC 5395
     CCD R magnitudes by K. Hornoch, Lelekovice, Czech Republic
(0.35-m reflector):  July 6.943 UT, 16.5; 12.910, 16.4.

                      (C) Copyright 2000 CBAT
2000 July 26                   (7466)            Daniel W. E. Green

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