[vsnet-alert 3577] Re: XTE J1859+226: BVR photometry urgently needed

[Rob I Hynes <R.I.Hynes@open.ac.uk>]

Dear colleagues,

Here are the coordinates and other information on XTE J1859+226 omitted 
from Carole Haswell's earlier e-mail.  If you can obtain any useful data 
please copy to:

Carole A Haswell <C.A.Haswell@open.ac.uk>
Rob Hynes <rih@astro.soton.ac.uk>
Sylvain Chaty <S.Chaty@open.ac.uk>

Regards,
        Rob Hynes

IAU 7276:

The exact position based on the
HST Guide Star Catalog is R.A. = 18h58m41s.58, Decl. = +22o39'29".4
(equinox 2000.0; estimated uncertainty 0".5).                         



XTE J1859+226
     P. M. Garnavich and K. Z. Stanek, Harvard-Smithsonian Center
for Astrophysics; and P. Berlind, Fred L. Whipple Observatory
(FLWO), report the detection of an optical counterpart to the new
x-ray transient XTE J1859+226.  CCD images taken on Oct. 12.07 UT
with the FLWO 1.2-m telescope show a bright stellar object not seen
on the second Palomar Sky Survey.  The exact position based on the
HST Guide Star Catalog is R.A. = 18h58m41s.58, Decl. = +22o39'29".4
(equinox 2000.0; estimated uncertainty 0".5).  This is just to the
east of the x-ray error circle given on IAUC 7274 and about 80"
north of a 10th-mag star.  The brightness of the optical transient
is estimated to be R = 15.1, and it appears blue compared to other
stars in the field.  Images taken over a 3.3-hr span show < 0.05
mag variation in brightness.  A faint object (mag about 21) is
visible on the Sky Survey within 1" of the position of the
transient.  The spectrum obtained with the FLWO 1.5-m telescope on
Oct. 12.22 displays a strong blue continuum with weak emission
lines.  H-alpha, with an equivalent width of 0.54 nm, and a
velocity width of 1200 km/s (FWHM), is seen.  He II 468.6-nm is 3
times stronger than H-beta and blended with permitted C III and N
III.  The spectrum is consistent with an x-ray nova in outburst.  A
finder chart may be found at
http://cfa-www.harvard.edu/~peterg/gosox/j1859.jpg.


*********************

IAU 7274

XTE J1859+226
     A. Wood and D. A. Smith, Massachusetts Institute of Technology
(MIT); and F. E. Marshall and J. Swank, Goddard Space Flight Center
(GSFC), on behalf of the RXTE All-Sky Monitor (ASM) team at MIT and
GSFC, report the emergence of a new x-ray transient:  "The source's
intensity was measured to rise slowly during approximately a 12-hr
interval to 160 +/- 15 mCrab (2-12 keV) on Oct 9.658 UT and 250
mCrab by Oct. 10.523, confirmed by a PCA observation (with source
position given by Markwardt et al., below).  The rise was
consistent with a linear increase at a rate of about 6 mCrab/hr.
Extrapolation indicates that the outburst began around Oct. 8.55 UT.
The ASM spectrum is roughly Crab-like and shows no indication of
evolution.  Neither the ASM catalogue nor SIMBAD lists any known
x-ray sources in or near the positional error box.  Observations at
other wavelengths would be timely."
     C. B. Markwardt, University of Maryland and GSFC; and F. E.
Marshall and J. H. Swank, GSFC, write:  "The RXTE PCA observed the
transient source XTE J1859+226 on Oct. 10.56-10.60 UT for about
2000 s.  The intensity of the source was 1.7 x 10**-8 erg s**-1
cm**-2 in the band 2-60 keV (= 250 mCrab in the band 2-10 keV),
with fractional r.m.s. variability of about 32 percent.  PCA scans
during the observation determined a source position of R.A. =
18h58m35s, Decl. = +22o39'.3 (equinox 2000.0), with a 95-percent
uncertainty radius of 1', which also accounts for the intrinsic
variability of the source.  A power spectrum shows a quasiperiodic
oscillation and two harmonics, the fundamental being centered at
0.45 Hz (FWHM 0.11 Hz), with a fractional r.m.s. amplitude of about
17 percent.  No high-frequency pulsations or variability were seen.
The energy spectrum can be modeled as a power law with photon index
1.7 and neutral hydrogen absorption of about 3 x 10**21 cm**-2.
These timing and spectral characteristics together are reminiscent
of a galactic blackhole candidate.  Additional PCA observations are
planned."


1999 October 11                (7274)            Daniel W. E. Green

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