arXiv subjects

K. Kawaguchi

Publications and source records attributed to K. Kawaguchi.

23 records · Page 2Linked to original sources

arXiv2015

Study of the X-ray emission mechanism of radio-loud narrow-line Seyfert 1 galaxy

1H0323+342 is one of narrow-line radio-loud Seyfert 1 galaxies (RL-NLS1), which is a new class of gamma-ray emitting AGNs. Narrow-line Seyfert 1 galaxies (NLS1) have a small-mass black hole, but its mass accretion rate is almost as high as Eddington limit. Therefore, by observing NLS1s, we can know the evolution of supermassive black holes at the center of galaxies. Some of NLS1s are radio-loud and we call them RL-NLS1. From past observations, multi-wavelength spectrum of RL-NLS1s is similar to that of typical blazars; the synchrotron emission in the lower energy band up to the optical band, and inverse Compton scattering of low energy photons from disk, torus, and broad line region. X-ray band is a transittion region between the synchrotron and inverse Compton, and also there is a possible disk/corona emission. Therefore, we studied the energy-dependence of time variability of the X-ray emission of 1H0323+342, which have been observed by Suzaku in 2009 and 2013, in order to constrain the emission mechanism. We found that the lower energy below 1 keV and the higher energy above 7 keV show a different variability from the middle energy band, indicating at least two emission components in the X-ray band. X-ray spectrum is not a simple power-law, but requires an additional features; a broken power-law plus flat hard component, or a power-law plus a relativistic reflection component. Each spectral component seems to vary independently.

astro-ph.HE↗

arXiv2014

Optical and Near-Infrared Polarimetry of Highly Reddened Type Ia Supernova 2014J: Peculiar Properties of Dust in M82

We presented optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia SN~2014J appeared in M82. SN~2014J exhibits large polarization at shorter wavelengths, e.g., $4.8$\% in $B$ band, and the polarization decreases rapidly at longer wavelengths, with the position angle of the polarization remaining at approximately $40^{\circ}$ over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely to be caused predominantly by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by Serkowski law for Galactic interstellar polarization. These suggests that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of $<0.1\ μ$m.

astro-ph.SR↗

arXiv2003

First Fringe Detection with VERA's Dual-Beam System and its Phase Referencing Capability

We present the results of first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry). The first dual-beam observations of a pair of H2O maser sources W49N and OH43.8-0.1 have been carried out on 2002 May 29 and July 23, and fringes of H2O maser lines at 22 GHz have been successfully detected. While the residual fringe phases of both sources show rapid variations over 360 degree due to the atmospheric fluctuation, the differential phase between the two sources remains constant for 1 hour with r.m.s. of 8 degree, demonstrating that the atmospheric phase fluctuation is removed effectively by the dual-beam phase referencing. The analysis based on Allan standard deviation reveals that the differential phase is mostly dominated by white phase noise, and the coherence function calculated from the differential phase shows that after phase referencing the fringe visibility can be integrated for arbitrarily long time. These results demonstrate VERA's high capability of phase referencing, indicating that VERA is a promising tool for phase referencing VLBI astrometry at 10 microarcsec level accuracy.

astro-ph↗

arXiv2001

Observations of H3+ in the Diffuse Interstellar Medium

Surprisingly large column densities of H3+ have been detected using infrared absorption spectroscopy in seven diffuse cloud sightlines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H3+ column densities imply unreasonably long path lengths (~1 kpc) and low densities (~3 cm^-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H3+ must be increased by one to two orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller value of the H3+ dissociative recombination rate constant than implied by laboratory experiments.

astro-ph↗

arXiv1999

Identification of SH $Δv=1$ ro-vibrational lines in R And

We report the identification of SH $Δv=1$ ro-vibrational lines in the published high-resolution infrared spectrum of the S-type star, R And. This is the first astronomical detection of this molecule. The lines show inverse P-Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shell model with a constant infall velocity is adopted to determine the condition of the layer. It is found that a single excitation temperature of 2200 K reproduces the observed line intensities satisfactory. SH is located in a layer from 1.0 to ~1.1 stellar radii, which is moving inward with a velocity of 9 km s-1. These results are consistent with the previous measurements of CO $Δv=3$ transitions. The estimated molecular abundance SH/H is 1x10^-7, consistent with a thermal equilibrium calculation.

astro-ph↗