489 research outputs found
Multiwavelength observation from radio through very-high-energy Gamma-ray of OJ 287 during the 12-year cycle flare in 2007
We performed simultaneous multiwavelength observations of OJ 287 with the
Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope
for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very
high energy (VHE) gamma-ray in 2007. The observations were conducted for a
quiescent state in April and in a flaring state in November-December. We
clearly observed increase of fluxes from radio to X-ray bands during the
flaring state while MAGIC could not detect significant VHE gamma-ray emission
from the source. We could derive an upper limit (95% confidence level) of 1.7%
of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC
observation. A simple SSC model suggests that the observed flaring activity
could be caused by evolutions in the distribution of the electron population
rather than changes of the magnetic field strength or Doppler beaming factor in
the jet.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Infrared/optical - X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506
We investigate the origin of short X-ray flares which are occasionally
observed in early stages of afterglows of gamma-ray bursts (GRBs). We observed
two events, GRB 071112C and GRB 080506, before the start of X-ray flares in the
optical and near-infrared (NIR) bands with the 1.5-m Kanata telescope. In
conjunction with published X-ray and optical data, we analyzed densely sampled
light curves of the early afterglows and spectral energy distributions (SEDs)
in the NIR-X-ray ranges. We found that the SEDs had a break between the optical
and X-ray bands in the normal decay phases of both GRBs regardless of the model
for the correction of the interstellar extinction in host galaxies of GRBs. In
the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB
071112C and 080506, respectively, and the X-ray spectra became harder than
those in the normal decay phases. No significant variation in the optical-NIR
range was detected together with the X-ray flares. These results suggest that
the X-ray flares were associated with either late internal shocks or external
shocks from two-component jets.Comment: 10 pages, 5 figures, accepted to Astronomy and Astrophysic
Early phase observations of extremely luminous Type Ia Supernova 2009dc
We present early phase observations in optical and near-infrared wavelengths
for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate
of the light curve is , which is one of the
slowest among SNe Ia. The peak -band absolute magnitude is mag even if the host extinction is mag. It reaches
mag for the host extinction of mag as
inferred from the observed Na {\sc i} D line absorption in the host. Our
-band photometry shows that the SN is one of the most luminous SNe Ia
also in near-infrared wavelengths. These results indicate that SN 2009dc
belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We
estimate the ejected Ni mass of \Msun for no host
extinction case (or 1.6 0.4 M for the host extinction of
mag). The C {\sc ii} 6580 absorption line keeps visible
until a week after maximum, which diminished in SN 2006gz before its maximum
brightness. The line velocity of Si {\sc ii} 6355 is about 8000 km
s around the maximum, being considerably slower than that of SN 2006gz,
while comparable to that of SN 2003fg. The velocity of the C {\sc ii} line is
almost comparable to that of the Si {\sc ii}. The presence of the carbon line
suggests that thick unburned C+O layers remain after the explosion. SN 2009dc
is a plausible candidate of the super-Chandrasekhar mass SNe Ia
Symmetries between Untwisted and Twisted Strings on Asymmetric Orbifolds
We study symmetries between untwisted and twisted strings on asymmetric
orbifolds. We present a list of asymmetric orbifold models to possess
intertwining currents which convert untwisted string states to twisted ones,
and vice versa. We also present a list of heterotic strings on asymmetric
orbifolds with supersymmetry between untwisted and twisted string states. Some
of properties inherent in asymmetric orbifolds, which are not shared by
symmetric orbifolds, are pointed out.Comment: Plain Tex, 35 pages, NBI-HE-92-34, KOBE-92-0
Optical and Near-Infrared Photometric Observation during the Superoutburst of the WZ Sge-Type Dwarf Nova, V455 Andromedae
We report on optical and infrared photometric observations of a WZ Sge-type
dwarf nova, V455 And during a superoutburst in 2007. These observations were
performed with the KANATA (V, J, and K_s bands) and MITSuME (g', Rc, and Ic
bands) telescopes. Our 6-band simultaneous observations allowed us to
investigate the temporal variation of the temperature and the size of the
emitting region associated with the superoutburst and short-term modulations,
such as early and ordinary superhumps. A hot (>11000 K) accretion disk suddenly
disappeared when the superoutburst finished, while blackbody emission, probably
from the disk, still remained dominant in the optical region with a moderately
high temperature (~8000 K). This indicates that a substantial amount of gas was
stored in the disk even after the outburst. This remnant matter may be a sign
of an expected mass-reservoir which can trigger echo outbursts observed in
several WZ Sge stars. The color variation associated with superhumps indicates
that viscous heating in a superhump source stopped on the way to the superhump
maximum, and a subsequent expansion of a low-temperature region made the
maximum. The color variation of early superhumps was totally different from
that of superhumps: the object was bluest at the early superhump minimum. The
temperature of the early superhump light source was lower than that of an
underlying component, indicating that the early superhump light source was a
vertically expanded low-temperature region at the outermost part of the disk.Comment: 14 pages, 12 figures, PASJ accepte
GRB 091208B: First Detection of the Optical Polarization in Early Forward Shock Emission of a Gamma-Ray Burst Afterglow
We report that the optical polarization in the afterglow of GRB 091208B is
measured at t = 149 - 706 s after the burst trigger, and the polarization
degree is P = 10.4% +/- 2.5%. The optical light curve at this time shows a
power-law decay with index -0.75 +/- 0.02, which is interpreted as the forward
shock synchrotron emission, and thus this is the first detection of the
early-time optical polarization in the forward shock (rather than that in the
reverse shock reported by Steele et al. (2009). This detection disfavors the
afterglow model in which the magnetic fields in the emission region are random
on the plasma skin depth scales, such as amplified by the plasma instabilities,
e.g., Weibel instability. We suggest that the fields are amplified by the
magnetohydrodynamic instabilities, which would be tested by future observations
of the temporal changes of the polarization degrees and angles for other
bursts.Comment: 12 pages, 4 figures, accepted for publication in ApJ Letter
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