arXiv subjects

H. Nakaya

Publications and source records attributed to H. Nakaya.

6 recordsLinked to original sources

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↗

arXiv2012

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.

astro-ph.HE↗

arXiv2009

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 $Δm_{15}(B)=0.65\pm 0.03$, which is one of the slowest among SNe Ia. The peak $V$-band absolute magnitude is $M_{V}=-19.90\pm 0.15$ mag even if the host extinction is $A_{V}=0$ mag. It reaches $M_{V}=-20.19\pm 0.19$ mag for the host extinction of $A_{V}=0.29$ mag as inferred from the observed Na {\sc i} D line absorption in the host. Our $JHK_{s}$-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 $^{56}$Ni mass of $1.2\pm 0.3$ $\Msun$ for no host extinction case (or 1.6$\pm$ 0.4 M$_{\odot}$ for the host extinction of $A_{V}=0.29$ mag). The C {\sc ii} $λ$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} $λ$6355 is about 8000 km s$^{-1}$ 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.

astro-ph.HE↗

arXiv2004

Deep Near Infrared Imaging toward Vela Molecular Ridge C - 1: A Remarkable Embedded Cluster in RCW 36 -

We present deep near-infrared (J, H, Ks) images toward an embedded cluster which lies in a C18O clump in the cloud C of the Vela Molecular Ridge. This cluster has at least ~ 350 members and a radius of ~ 0.5 pc. The stellar surface number density is approximately 3000 stars pc^-2 in the central 0.1 pc x 0.1 pc region of the cluster. This is much higher than most of the young clusters within 1 kpc of the Sun. From the comparison of the luminosity function and near-infrared excess fraction with those of other embedded clusters, we estimate that the age of this cluster is approximately 2-3 Myr. This cluster exhibits an excess of brighter stars in its central region, from which we conclude that the more massive stars are located near the cluster center.

astro-ph↗

arXiv2003

An Optical and Near Infrared Search for Brown Dwarfs in the Pleiades Cluster

We have carried out a brown dwarf search over an area of 14' x 23' near the central portion of the Pleiades open cluster in five optical and near infrared bands (i', Z, J, H, Ks) with 10 sigma detection limits of i' = 22.0, J = 20.0 and Ks = 18.5 mag. The surveyed area has large extinction in excess of Av = 3 in the Pleiades region. We detected four new brown dwarf candidates from the colour-colour (J-K, i'-J) and the colour-magnitude (J, i'-K) diagrams. We estimated their masses as 0.046 Msun down to 0.028 Msun. The least massive one is estimated to have a mass smaller than Roque 25 or int-pl-IZ-69, and maybe the lowest mass object found so far in the Pleiades cluster.

astro-ph↗

arXiv2002

Evolution of Elliptical Galaxies at z >~ 1 Revealed from a Large, Multicolor Sample of Extremely Red Objects

We study the evolution of elliptical galaxies at z >~ 1 on the basis of a sample of 247 Extremely Red Objects (EROs) with R-Ks >= 3.35 (AB) and Ks <= 22.1 (AB) constructed from BVRi'z'JHKs multicolor data of a 114 arcmin2 area in the Subaru/XMM Deep Survey Field. By fitting template spectra of old ellipticals (OEs) and young, dusty starbursts (DSs) to the multicolor data, we classify EROs into these two classes and estimate their redshifts. We find that 58% of the EROs in our sample belong to the OE class and that 24% of the OEs are fit by a spectrum having a disk component with the B-band bulge-to-total luminosity ratio of <= 0.9. We compare the observed surface density of OEs with predictions from passive evolution models. We then derive rest-frame B-band luminosity functions (LFs) of OEs in our sample at z=1-1.5 and 1.5-2.5. We find that the LF at z=1-1.5 roughly agrees with the LF of local ellipticals if a dimming of 1.3 mag from z=1.25 to the present epoch is assumed. On the other hand, the amplitude of the LF at z=1.5-2.5 is found to be lower than that of the local LF by a factor of ~ 3 over the whole range of magnitude observed. Taking account of a strong decrease in the number density of morphologically classified early-type galaxies at z >~ 1.5 found by several authors, we conclude that the majority of ellipticals seen at present have not established either a red color or a smooth 1/4-law profile before z ~ 1.5$. (abridged)

astro-ph↗