92 research outputs found
The 2006 November outburst of EG Aquarii: the SU UMa nature revealed
We report time-resolved CCD photometry of the cataclysmic variable EG Aquarii
during the 2006 November outburst During the outburst, superhumps were
unambiguously detected with a mean period of 0.078828(6) days, firstly
classifying the object as an SU UMa-type dwarf nova. It also turned out that
the outburst contained a precursor. At the end of the precursor, immature
profiles of humps were observed. By a phase analysis of these humps, we
interpreted the features as superhumps. This is the second example that the
superhumps were shown during a precursor. Near the maximum stage of the
outburst, we discovered an abrupt shift of the superhump period by
0.002 days. After the supermaximum, the superhump period decreased at the rate
of =, which is typical for SU UMa-type dwarf
novae. Although the outburst light curve was characteristic of SU UMa-type
dwarf novae, long-term monitoring of the variable shows no outbursts over the
past decade. We note on the basic properties of long period and inactive SU
UMa-type dwarf novae.Comment: 9 pages, 7 figures, accepted for PAS
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. II: The Second Year (2009-2010)
As an extension of the project in Kato et al. (2009, arXiv:0905.1757), we
collected times of superhump maxima for 61 SU UMa-type dwarf novae mainly
observed during the 2009-2010 season. The newly obtained data confirmed the
basic findings reported in Kato et al. (2009): the presence of stages A-C, as
well as the predominance of positive period derivatives during stage B in
systems with superhump periods shorter than 0.07 d. There was a systematic
difference in period derivatives for systems with superhump periods longer than
0.075 d between this study and Kato et al. (2009). We suggest that this
difference is possibly caused by the relative lack of frequently outbursting SU
UMa-type dwarf novae in this period regime in the present study. We recorded a
strong beat phenomenon during the 2009 superoutburst of IY UMa. The close
correlation between the beat period and superhump period suggests that the
changing angular velocity of the apsidal motion of the elliptical disk is
responsible for the variation of superhump periods. We also described three new
WZ Sge-type objects with established early superhumps and one with likely early
superhumps. We also suggest that two systems, VX For and EL UMa, are WZ
Sge-type dwarf novae with multiple rebrightenings. The O-C variation in OT
J213806.6+261957 suggests that the frequent absence of rebrightenings in very
short-Porb objects can be a result of sustained superoutburst plateau at the
epoch when usual SU UMa-type dwarf novae return to quiescence preceding a
rebrightening. We also present a formulation for a variety of Bayesian
extension to traditional period analyses.Comment: 63 pages, 77 figures, 1 appendix, Accepted for publication in PASJ,
data correctio
Structure in the early afterglow lightcurve of the gamma-ray burst of 29 March 2003
Gamma-ray bursts (GRBs) are energetic explosions that for 0.01--100 s are the
brightest gamma-ray sources in the sky. Observations of the early evolution of
afterglows we expected to provide clues about the nature of the bursts, but
their rapid fading has hampered such studies; some recent rapid localizations
of bursts have improved the situation. Here we report on an early detection of
the very bright afterglow of the burst of 29 March 2003 (GRB030329). Our data
show that, even early in the aferglow phase, the light curve shows unexpectedly
complicated structures superimposed on the fading background.Comment: 8 pages, 1 figure, To appear in Nature June 19 issue. For the access
to the data in the paper, see
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/GRB/grb030329/GRB030329_information
.htm
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
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