32 research outputs found
Dwarf Novae in the Shortest Orbital Period Regime: I. A New Short Period Dwarf Nova, OT J055717+683226
We report the observation of a new dwarf nova, OT J055717+683226, during its
first-ever recorded superoutburst in December 2006. Our observation shows that
this object is an SU UMa-type dwarf nova having a very short superhump period
of 76.67+/- 0.03 min (0.05324+/-0.00002 d). The next superoutburst was observed
in March 2008. The recurrence time of superoutbursts (supercycle) is, hence,
estimated to be ~480 d. The supercycle is much shorter than those of WZ
Sge-type dwarf novae having supercycles of >~ 10 yr, which are a major
population of dwarf novae in the shortest orbital period regime (<~85 min).
Using a hierarchical cluster analysis, we identified seven groups of dwarf
novae in the shortest orbital period regime. We identified a small group of
objects that have short supercycles, small outburst amplitudes, and large
superhump period excesses, compared with those of WZ Sge stars. OT
J055717+683226 probably belongs to this group.Comment: 14 pages, 11 figures, accepted for publication in PAS
X-ray Polarization Observations of BL Lacertae
Blazars are a class of jet-dominated active galactic nuclei with a typical
double-humped spectral energy distribution. It is of common consensus the
Synchrotron emission to be responsible for the low frequency peak, while the
origin of the high frequency hump is still debated. The analysis of X-rays and
their polarization can provide a valuable tool to understand the physical
mechanisms responsible for the origin of high-energy emission of blazars. We
report the first observations of BL Lacertae performed with the Imaging X-ray
Polarimetry Explorer ({IXPE}), from which an upper limit to the polarization
degree 12.6\% was found in the 2-8 keV band. We contemporaneously
measured the polarization in radio, infrared, and optical wavelengths. Our
multiwavelength polarization analysis disfavors a significant contribution of
proton synchrotron radiation to the X-ray emission at these epochs. Instead, it
supports a leptonic origin for the X-ray emission in BL Lac.Comment: 17 pages, 5 figures, accepted for publication in ApJ