ABSTRACT Blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. Polarized radiation from blazars is one key piece of evidence for ...synchrotron radiation at low energies, and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 July and 2014 December to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. BL Lacs) and consequently between different types of radio galaxies (FR I versus FR II).
ABSTRACT
We present the results based on photometric (Swift UVOT), broad-band polarimetric (V and Rbands) and optical spectroscopic observations of the Type IIn supernova (SN) 2017hcc. Our study is ...supplemented with spectropolarimetric data available in literature for this event. The post-peak light-curve evolution is slow (∼0.2 mag 100 d−1 in b band). The spectrum of ∼+27 d shows a blue continuum with narrow emission lines, typical of a Type IIn SN. Archival polarization data along with the Gaia DR2 distances have been utilized to evaluate the interstellar polarization (ISP) towards the SN direction which is found to be PISP = 0.17 ± 0.02 per cent and θISP = 140° ± 3°. To extract the intrinsic polarization of SN 2017hcc, both the observed and the literature polarization measurements were corrected for ISP. We noticed a significant decline of ∼3.5 per cent (V band) in the intrinsic level of polarization spanning a period of ∼2 months. In contrast, the intrinsic polarization angles remain nearly constant at all epochs. Our study indicates a substantial variation in the degree of asymmetry in either the ejecta and/or the surrounding medium of SN 2017hcc. We also estimate a mass-loss rate of $\dot{M}$ = 0.12 M⊙ yr−1 (for v$\mathrm{ w}$ = 20 km s−1) which suggests that the progenitor of SN 2017hcc is most likely a luminous blue variable.
ABSTRACT
We conducted optical polarimetry and near-infrared spectroscopy of Japan Aerospace Exploration Agency (JAXA)’s Hayabusa2# mission target, (98943) 2001 CC21, in early 2023. Our new ...observations indicate that this asteroid has a polarimetric inversion angle of ∼20°, absorption bands around 0.9 and 1.9 μm, and a geometric albedo of 0.23 ± 0.04. All these features are consistent with those of S types but inconsistent with L types. Based on this evidence, we conclude that JAXA’s Hayabusa2# spacecraft will explore an S-type asteroid (more specifically, an L or LL chondrite-like object) with albedo and size (0.44–0.53 km when we assume the absolute magnitude of 18.8) similar to (25143) Itokawa.
ABSTRACT
The investigation of asteroids near the Sun is important for understanding the final evolutionary stage of primitive Solar system objects. A near-Sun asteroid (NSA), (155140) 2005 UD, has ...orbital elements similar to those of (3200) Phaethon (the target asteroid for the JAXA’s DESTINY+ mission). We conducted photometric and polarimetric observations of 2005 UD and found that this asteroid exhibits a polarization phase curve similar to that of Phaethon over a wide range of observed solar phase angles (α = 20–105°) but different from those of (101955) Bennu and (162173) Ryugu (asteroids composed of hydrated carbonaceous materials). At a low phase angle (α ≲ 30°), the polarimetric properties of these NSAs (2005 UD and Phaethon) are consistent with anhydrous carbonaceous chondrites, while the properties of Bennu are consistent with hydrous carbonaceous chondrites. We derived the geometric albedo, pV ∼ 0.1 (in the range of 0.088–0.109); mean V-band absolute magnitude, HV = 17.54 ± 0.02; synodic rotational period, $T_\mathrm{rot} = 5.2388 \pm 0.0022 \, \mathrm{h}$ (the two-peaked solution is assumed); and effective mean diameter, $D_\mathrm{eff} = 1.32 \pm 0.06 \, \mathrm{km}$. At large phase angles (α ≳ 80°), the polarization phase curve are likely explained by the dominance of large grains and the paucity of small micron-sized grains. We conclude that the polarimetric similarity of these NSAs can be attributed to the intense solar heating of carbonaceous materials around their perihelia, where large anhydrous particles with small porosity could be produced by sintering.
We present optical observations of the Type Ia supernova (SN) 2019ein, starting two days after the estimated explosion date. The spectra and light curves show that SN 2019ein belongs to a ...high-velocity (HV) and broad-line group with a relatively rapid decline in the light curves (Δm15(B) = 1.36 0.02 mag) and a short rise time (15.37 0.55 days). The Si ii λ6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ∼20,000 km s−1 12 days before the B-band maximum. The line velocity, however, decreased very rapidly and smoothly toward maximum light, to ∼13,000 km s−1, which is relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated with not only the velocity at maximum light, but also the light-curve decline rate, as is the case for normal-velocity (NV) SNe Ia. Spectral synthesis modeling shows that the outermost layer at >17,000 km s−1 is well described by an O-Ne-C burning layer extending to at least 25,000 km s−1, and there is no unburnt carbon below 30,000 km s−1; these properties are largely consistent with the delayed detonation scenario and are shared with the prototypical HV SN 2002bo despite the large difference in Δm15(B). This structure is strikingly different from that derived for the well-studied NV SN 2011fe. We suggest that the relation between the mass of 56Ni (or Δm15) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.
Abstract We present an analysis of a stellar occultation event caused by a near-Earth asteroid (98943) 2001 CC21, an upcoming flyby target in the Hayabusa2 extended mission, on 2023 March 5. To ...determine the asteroid’s shape from diffraction-affected light curves accurately, we developed a novel data-reduction technique named the Diffracted Occultation’s United Simulator for Highly Informative Transient Explorations (DOUSHITE). Using DOUSHITE-generated synthetic models, we derived constraints on (98943) 2001 CC21’s shadow shape from the single-chord occultation data. Our results suggest a significant elongation of the shadow with an axis ratio of $b/a = 0.37\pm 0.09$. This shape could be crucial for planning Hayabusa2’s high-speed flyby to optimise the limited imaging opportunities.
ABSTRACT
We present the results of flux density, spectral index, and polarization intra-night monitoring studies of a sample of eight optically bright blazars, carried out by employing several small ...to moderate aperture (0.4 to 1.5 m diameter) telescopes fitted with CCDs and polarimeters located in Europe, India, and Japan. The duty cycle of flux variability for the targets is found to be ∼45 per cent, similar to that reported in earlier studies. The computed two-point spectral indices are found to be between 0.65 to 1.87 for our sample, comprised of low- and intermediate-frequency peaked blazars, with one exception: they are also found to be statistically variable for about half the instances where ‘confirmed’ variability is detected in flux density. In the analysis of the spectral evolution of the targets on hourly time-scale, a counterclockwise loop (soft-lagging) is noted in the flux–spectral index plane on two occasions, and in one case a clear spectral flattening with the decreasing flux is observed. In our data set, we also observe a variety of flux–polarization degree variability patterns, including instances with a relatively straightforward anticorrelation, correlation, or counterclockwise looping. These changes are typically reflected in the flux–polarization angle plane: the anticorrelation between the flux and polarization degree is accompanied by an anticorrelation between the polarization angle and flux, while the counterclockwise flux–PD looping behaviour is accompanied by a clockwise looping in the flux–polarization angle representation. We discuss our findings in the framework of the internal shock scenario for blazar sources.
A New Spectropolarimeter at the Dodaira Observatory Kawabata, Koji S.; Okazaki, Akira; Akitaya, Hiroshi ...
Publications of the Astronomical Society of the Pacific,
07/1999, Letnik:
111, Številka:
761
Journal Article
Recenzirano
Odprti dostop
We report a newly developed spectropolarimeter with a low‐dispersion resolution (
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} ...\usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackageOT2,OT1{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $R=40{\mbox{--}} 200$ \end{document}
) and a wide coverage in wavelength (400–900 nm). It is mainly used along with the 0.91 m telescope at the Dodaira Observatory of the National Astronomical Observatory, Japan. This instrument and the related reduction software are described briefly. The present polarimetric accuracy (rms) is estimated to be
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackageOT2,OT1{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $ ( P/ 50) ^{2}+( 0.05) ^{2} ^{1/2}$ \end{document}
%, wherePis the linear polarization degree in percent. The spectropolarimeter has the advantage of being most useful in the polarimetric studies of both the continuum and the strong emission and/or absorption lines. It is mainly used for the short‐ or long‐term monitoring of variable circumstellar polarization and of polarization in comets, and for studies on interstellar polarization.
Abstract
PTFO 8-8695 b (CVSO 30 b) is a young planet candidate whose host star is a $\sim\!\!{2.6}$-Myr-old T-Tauri star, and there have been continuous discussions about the nature of this system. ...To unveil the mystery of this system, we observed PTFO 8-8695 for around five years at optical and infrared bands simultaneously using the Kanata telescope at the Higashi-Hiroshima Observatory. Through our observations, we found that the reported fading event split into two: deeper but phase-shifted “dip-A” and shallower but equiphase “dip-B”. These dips disappeared at different epochs, and then, dip-B reappeared. Based on the observed wavelength dependence of dip depths, a dust clump and a precessing planet are likely origins of dip-A and B, respectively. Here we propose “a precessing planet associated with a dust cloud” scenario for this system. This scenario is consistent with the reported change in the depth of fading events, and even with the reported results, which were thought to be evidence against the planetary hypothesis.
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