Optical Afterglow of the Hard X-ray Flare in the Symbiotic Star CH Cygni
ATel #2192; A. Skopal, S. Shugarov, D. Chochol (Astronomical Institute, Slovak Academy of Sciences, Tatranska Lomnica), T. Pribulla (Astrophysikalisches Institut und Universitaets-Sternwarte, Jena), M. Wolf (Astronomical Institute, Charles University, Prague)
on 9 Sep 2009; 08:41 UT
Credential Certification: Augustin Skopal (email@example.com)
Subjects: Optical, X-ray, Binary, Variables
We report on the recent optical photometric and spectroscopic
signatures of the hard X-ray recovery of the symbiotic system
CH Cyg (see ATEL #2046). Our UBVR_C photometry taken at the observatories
of the Astronomical Institute of the Slovak Academy of Sciences
showed that CH Cyg started a gradual brightening in the U photometric
passband from 2008 October (U ~ 11.9) to the present. During our
last observation from 2009 September 7 it was seen at U = 10.82.
On 2009 July 25, Mukai et al. (ATEL #2046) detected a very bright
hard X-ray (2-10 keV) flare, whereas our simultaneous observations
showed only a small brightening from U = 11.29 on July 24.817
to U = 11.05 on July 25.925.
The optical afterglow of the hard X-ray flare was detected later
on July 28.099 UT, when CH Cyg peaked at U = 10.13. The ~ 2 days
delay of the optical afterglow suggests particle density of a few
times 10^7 cm^-3 in the emitting region ionized by the X-ray
photons. The UBVR_C light curves are available at http://www.ta3.sk/~astrskop/symbphot/ch_cyg/chcyg_flare.png .
On 2008 March 17.415 and on 2009 August 27.852 UT, we obtained
high-resolution spectra of CH Cyg, in the range of 6400-6700A,
at the David Dunlap Observatory, University of Toronto, and
the Ondrejov Observatory, Academy of Sciences of the Czech
Republic, respectively. Spectra showed pronounced signatures of
the red giant continuum. The hydrogen H-alpha emission was cut
with a strong absorption shifted to about of -30 km/s relative
to the systemic velocity, with the red peak width of only 0.8
and 1.4A at the half of its maximum that was as high as double
of the local continuum. Nebular emissions of [NII] 6548 and 6584A
were well pronounced on the 2008 spectrum with a maximum of the
half continuum level for the 6584A line, while on the 2009 spectrum
they were seen as faint features. On both spectra, their profiles
were broad and flat at their tops with the width of about 3A.
This evolution suggests an increase of particle density of their
emitting region. The recent photometric and spectroscopic
observations of CH Cyg thus indicate its transition to a new
active phase. Therefore, further multifrequency observations from
the ground-based and space observatories are required to understand
better this intriguing symbiotic system.