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We present a detailed study of the MASTER OT J030227.28+191754.5 outburst in 2021-2022, reaching an amplitude of 10.2 mag and a duration of 60 d. The detections of (1) the double-peaked optical emission lines, and (2) the early and ordinary superhumps, established that MASTER OT J030227.28+191754.5 is an extremely energetic WZ Sge-type dwarf nova (DN). Based on the superhump observations, we obtained its orbital period and mass ratio as 0.05986(1) d and 0.063(1), respectively. These are within a typical range of low-mass-ratio DNe. According to the binary parameters derived based on the thermal-tidal instability model, our analyses showed that (1) the standard disk model requires an accretion rate $\simeq$ 10$^{20}$ g s$^{-1}$ to explain its peak optical luminosity and (2) large mass was stored in the disk at the outburst onset. These cannot be explained solely by the impact of its massive ($\gtrsim$ 1.15 M$_\odot$) primary white dwarf implied by Kimura et al. (2023). Instead, we propose that the probable origin of this enormously energetic DN outburst is the even lower quiescence viscosity than other WZ Sge-type DNe. This discussion is qualitatively valid for most possible binary parameter spaces unless the inclination is low ($\lesssim 40^\circ$) enough for the disk to be bright explaining the outburst amplitude. Such low inclinations, however, would not allow detectable amplitude of early superhumps in the current thermal-tidal instability model. The optical spectra at outburst maximum showed the strong emission lines of Balmer, He I, and He II series whose core is narrower than $\sim 800$ km s$^{-1}$. Considering its binary parameters, a Keplerian disk cannot explain this narrow component, but the presumable origin is disk winds., Comment: 23 pages, 13 figures, 2 tables. Accepted by PASJ. Part of the online supplemental information is included

We present three-dimensional (3D) maps of Jupiter's atmospheric circulation at cloud-top level from Doppler-imaging data obtained in the visible domain with JIVE, the second node of the JOVIAL network, which is mounted on the Dunn Solar Telescope at Sunspot, New Mexico. We report on 12 nights of observations between May 4 and May 30, 2018, representing a total of about 80 hours. Firstly, the average zonal wind profile derived from our data is compatible with that derived from cloud-tracking measurements performed on Hubble Space Telescope images obtained in April 2018 from the Outer Planet Atmospheres Legacy (OPAL) program. Secondly, we present the first ever two-dimensional maps of Jupiter's atmospheric circulation from Doppler measurements. The zonal velocity map highlights well-known atmospheric features, such as the equatorial hot spots and the Great Red Spot (GRS). In addition to zonal winds, we derive meridional and vertical velocity fields from the Doppler data. The motions attributed to vertical flows are mainly located at the boundary between the equatorial belts and tropical zones, which could indicate active motion in theses regions. Qualitatively, these results compare well to recent Juno data that have unveiled the three-dimensional structure of Jupiter's wind field. To the contrary, the motions attributed to meridional circulation are very different from what is obtained by cloud tracking, except at the GRS. Because of limitations with data resolution and processing techniques, we acknowledge that our measurement of vertical or meridional flows of Jupiter are still to be confirmed.

This study provides the results of simultaneous multicolor observations for the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite, STARLINK-1113 in the $U$, $B$, $V$, $g'$, $r$, $i$, $R_{\rm C}$, $I_{\rm C}$, $z$, $J$, $H$, and $K_s$ bands to quantitatively investigate the extent to which Visorsat reduces its reflected light. Our results are as follows: (1) in most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on Visorsat, therefore, contributes to the reduction of the reflected sunlight; (2) the magnitude at 550 km altitude (normalized magnitude) of both satellites often reaches the naked-eye limiting magnitude ($<$ 6.0); (3) from a blackbody radiation model of the reflected flux, the peak of the reflected components of both satellites is around the $z$ band; and (4) the albedo of the near infrared range is larger than that of the optical range. Under the assumption that Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering factor, $C_{\rm f}$, of the sunshade on Visorsat, using the blackbody radiation model: the covering factor ranges from $0.18 \leq C_{\rm f} \leq 0.92$. From the multivariable analysis of the solar phase angle (Sun-target-observer), the normalized magnitude, and the covering factor, the phase angle versus covering factor distribution presents a moderate anti-correlation between them, suggesting that the magnitudes of Visorsat depend not only on the phase angle but also on the orientation of the sunshade along our line of sight. However, the impact on astronomical observations from Visorsat-designed satellites remains serious. Thus, new countermeasures are necessary for the Starlink satellites to further reduce reflected sunlight., Comment: 31 pages, 9 figures, published in PASJ

The surface of airless bodies like asteroids in the Solar System are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In December 2010, the T-type asteroid 596 Scheila underwent a collision with a few-tens-of-meters impactor. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10-year period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the Solar System. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203 Pompeja). New observations show that 203 Pompeja has a X-type-like surface, with some local surface areas exhibiting a very red spectrum., Comment: 16 pages, 9 figures, 2 tables, Accepted for publication in ApJ Letters

Context. Asteroids in comet-like orbits (ACOs) consist of asteroids and dormant comets. Due to their similar appearance, it is challenging to distinguish dormant comets from ACOs via general telescopic observations. Surveys for discriminating dormant comets from the ACO population have been conducted via spectroscopy or optical and mid-infrared photometry. However, they have not been conducted through polarimetry. Aims. We conducted the first polarimetric research of ACOs. Methods. We conducted a linear polarimetric pilot survey for three ACOs: (944) Hidalgo, (3552) Don Quixote, and (331471) 1984 QY1. These objects are unambiguously classified into ACOs in terms of their orbital elements (i.e., the Tisserand parameters with respect to Jupiter $T_\mathrm{J}$ significantly less than 3). Three ACOs were observed by the 1.6 m Pirka Telescope from UT 2016 May 25 to UT 2019 July 22 (13 nights). Results. We found that Don Quixote and Hidalgo have polarimetric properties similar to comet nuclei and D-type asteroids (optical analogs of comet nuclei). However, 1984 QY1 exhibited a polarimetric property consistent with S-type asteroids. We conducted a backward orbital integration to determine the origin of 1984 QY1, and found that this object was transported from the main belt into the current comet-like orbit via the 3:1 mean motion resonance with Jupiter. Conclusions. We conclude that the origins of ACOs can be more reliably identified by adding polarimetric data to the color and spectral information. This study would be valuable for investigating how the ice-bearing small bodies distribute in the inner Solar System., Comment: 12 pages, 6 figures, accepted for publication in Astronomy and Astrophysics (A&A)

We present the $g'$-, $R_{\rm c}$-, and $I_{\rm c}$-band magnitudes and associated colors of the Starlink's STARLINK-1113 (one of the standard Starlink satellites) and 1130 (Darksat) with a darkening treatment to its surface. By the 105 cm Murikabushi telescope/$\it{MITSuME}$, simultaneous multicolor observations for the above satellites were conducted four times: on April 10, 2020, May 18, 2020 (for Darksat), and June 11, 2020 (for Darksat and STARLINK-1113). We found that (1) $g'$-band apparent magnitudes of Darksat ($6.95~\pm~0.11-7.65~\pm~0.11$ mag) are comparable to or brighter than that of STARLINK-1113 ($7.69~\pm~0.16$ mag), (2) the shorter the observed wavelength is, the fainter the satellite magnitudes tend to become, (3) the reflected flux by STARLINK-1113 is extremely ($> 1.0$ mag) redder than that of Darksat, (4) there is no clear correlation between the solar phase angle and orbital-altitude-scaled magnitude, (5) by flux-model fitting of the satellite trails with the blackbody radiation, it is found that the albedo of Darksat is about a half of that of STARLINK-1113. Especially, the result (1) is inconsistent with the previous studies. However, considering both solar and observer phase angles and atmospheric extinction, the brightness of STARLINK-1113 can be drastically reduced in the $g'$ and $R_{\rm c}$ band. Simultaneous multicolor-multispot observations more than three colors would give us more detailed information regarding the impact by the low Earth orbit satellite constellations., Comment: accepted to ApJ. 18 pages, 10 figures

We investigate the correlation between rest-frame UV flux variability of broad absorption line (BAL) quasars and their variability in BAL equivalent widths (EWs) in a various timescale from $<10$~days to a few years in the quasar rest-frame. We use the data sets of BAL EWs taken by the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project and photometric data taken by the intermediate Palomar Transient Factory (iPTF) in $g$ and $R$-bands and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in $grizy$ bands. Our results are summarized as below; (1) the distributions of flux variability versus BAL variability show weak, moderate, or a strong positive correlation, (2) there is no significant difference in flux variability amplitudes between BAL quasar with significant short timescale EW variability (called class S1) and without (class S2), (3) in all time scales considered in this paper, the class S1 quasars show systematically larger BAL variability amplitudes than those of the class S2 quasars, and (4) there are possible correlations between BAL variability and physical parameters of the quasars such as black hole masses (moderate positive), Eddington ratios, and accretion disk temperature (strong negative) in the class S2 quasars. These results indicate that the BAL variability requires changing in the ionizing continuum and an ancillary mechanism such as variability in X-ray shielding gas located at the innermost region of an accretion disk., Comment: 22 pages

We present optical observations of type Ia supernova (SN) 2019ein, starting at 2 days after the estimated explosion date. The spectra and the light curves show that SN 2019ein belongs to the High-Velocity (HV) and Bload Line groups with relatively rapid decline in the light curves (Delta m15(B) = 1.36 +- 0.02 mag) and the short rise time (15.37 +- 0.55 days). The Si II 6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ~ 20,000 km s-1 at 12 days before the B-band maximum. The line velocity however decreased very rapidly and smoothly toward the maximum light, where it was ~ 13,000 km s-1 as relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated not only to the velocity at the maximum light, but also to the light curve decline rate like 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 the 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 Delta m15(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 Delta m15) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe., Comment: 15 pages, 12 figres, Accepted to ApJ

The third observing run by LVC has brought the discovery of many compact binary coalescences. Following the detection of the first binary neutron star merger in this run (LIGO/Virgo S190425z), we performed a dedicated follow-up campaign with the Zwicky Transient Facility (ZTF) and Palomar Gattini-IR telescopes. The initial skymap of this single-detector gravitational wave (GW) trigger spanned most of the sky observable from Palomar Observatory. Covering 8000 deg$^2$ of the initial skymap over the next two nights, corresponding to 46\% integrated probability, ZTF system achieved a depth of $\approx$\,21 $m_\textrm{AB}$ in $g$- and $r$-bands. Palomar Gattini-IR covered 2200 square degrees in $J$-band to a depth of 15.5\,mag, including 32\% integrated probability based on the initial sky map. The revised skymap issued the following day reduced these numbers to 21\% for the Zwicky Transient Facility and 19\% for Palomar Gattini-IR. We narrowed 338,646 ZTF transient "alerts" over the first two nights of observations to 15 candidate counterparts. Two candidates, ZTF19aarykkb and ZTF19aarzaod, were particularly compelling given that their location, distance, and age were consistent with the GW event, and their early optical lightcurves were photometrically consistent with that of kilonovae. These two candidates were spectroscopically classified as young core-collapse supernovae. The remaining candidates were ruled-out as supernovae. Palomar Gattini-IR did not identify any viable candidates with multiple detections only after merger time. We demonstrate that even with single-detector GW events localized to thousands of square degrees, systematic kilonova discovery is feasible.

We report X-ray, optical, and near-infrared monitoring of the new X-ray transient MAXI J1820$+$070 discovered with MAXI on 2018 March 11. Its X-ray intensity reached $\sim 2$ Crab in 2--20 keV at the end of March, and then gradually decreased until the middle of June. In this period, the X-ray spectrum was described by Comptonization of the disk emission, with a photon index of $\sim$1.5 and an electron temperature of $\sim$50 keV, which is consistent with a black hole X-ray binary in the low/hard state. The electron temperature and the photon index were slightly decreased and increased with increasing flux, respectively. The source showed significant X-ray flux variation on timescales of seconds. This short-term variation was found to be associated with changes in the spectral shape, and the photon index became slightly harder at higher fluxes. This suggests that the variation was produced by a change in the properties of the hot electron cloud responsible for the strong Comptonization. Modeling a multi-wavelength SED around the X-ray flux peak at the end of March, covering the near-infrared to X-ray bands, we found that the optical and near-infrared fluxes were likely contributed substantially by the jet emission. Before this outburst, the source was never detected in the X-ray band with MAXI (with a 3$\sigma$ upper limit of $\sim$0.2 mCrab in 4--10 keV, obtained from the 7-year data in 2009--2016), whereas weak optical and infrared activity was found at their flux levels $\sim$3 orders of magnitude lower than the peak fluxes in the outburst., Comment: 14 pages, 9 figures, accepted for publication in ApJ

Sample return from the near-Earth asteroid known as 25143 Itokawa was conducted as part of the Hayabusa mission, with a large number of scientific findings being derived from the returned samples. Following the Hayabusa mission, Hayabusa2 was planned, targeting sample return from a primitive asteroid. The primary target body of Hayabusa2 was asteroid 162173 Ryugu; however, it was also necessary to gather physical information for backup target selection. Therefore, we examined five asteroids spectroscopically, 43 asteroids spectrophotometrically, and 41 asteroids through periodic analysis. Hence, the physical properties of 74 near-Earth asteroids were obtained, which helped the Hayabusa2 backup target search and, also, furthered understanding of the physical properties of individual asteroids and their origins., Comment: 31 pages, 2 figures, and 4 tables, accepted for publication in PASJ

We present optical and near-infrared observations of a low-luminosity Type IIP supernova (SN) 2016bkv from the initial rising phase to the plateau phase. Our observations show that the end of the plateau is extended to $\gtrsim 140$ days since the explosion, indicating that this SN takes one of the longest time to finish the plateau phase. among Type IIP SNe (SNe IIP), including low-luminosity (LL) SNe IIP. The line velocities of various ions at the middle of the plateau phase are as low as 1,000--1,500 km s$^{-1}$, which is the lowest even among LL SNe IIP. These measurements imply that the ejecta mass in SN 2016bkv is larger than that of the well-studied LL IIP SN 2003Z. In the early phase, SN 2016bkv shows a strong bump in the light curve. In addition, the optical spectra in this bump phase exhibit a blue continuum accompanied with a narrow H$\alpha$ emission line. These features indicate an interaction between the SN ejecta and the circumstellar matter (CSM) as in SNe IIn. Assuming the ejecta-CSM interaction scenario, the mass loss rate is estimated to be $\sim 1.7 \times 10^{-2} M_{\odot}$ yr$^{-1}$ within a few years before the SN explosion. This is comparable to or even larger than the largest mass loss rate observed for the Galactic red supergiants ($\sim 10^{-3} M_{\odot}$ yr$^{-1}$ for VY CMa). We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion., Comment: 9 pages, 12 figures. Accepted for publication in ApJ

We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles $\alpha$= 57 deg--141deg around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are $P_\mathrm{max}$=7.32$\pm$0.25 % at phase angles of $\alpha_\mathrm{max}$=124$\pm$8 deg in the $V$-band and $P_\mathrm{max}$=7.04$\pm$0.21 % at $\alpha_\mathrm{max}$=124$\pm$6 deg in the $R_\mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of $p_\mathrm{V}$=0.25$\pm$0.02, which is in agreement with that of Q-type taxonomic asteroids. $\alpha_\mathrm{max}$ is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance $q$=0.187 au and a short rotational period of $T_\mathrm{rot}$=2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon., Comment: 32 pages, 6 figures, accepted for publication in AJ

We present monitoring campaign observations at optical and near-infrared (NIR) wavelengths for a radio-loud active galactic nucleus (AGN) at z=0.840, SDSS~J110006.07+442144.3 (hereafter, J1100+4421), which was identified during a flare phase in late February, 2014. The campaigns consist of three intensive observing runs from the discovery to March, 2015, mostly within the scheme of the OISTER collaboration. Optical-NIR light curves and simultaneous spectral energy distributions (SEDs) are obtained. Our measurements show the strongest brightening in March, 2015. We found that the optical-NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability. This constant SED shape is confirmed to extend to $\sim5~\mu$m in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of $\alpha_{\nu}\sim-1.4$, where $f_{\nu}\propto\nu^{\alpha_{\nu}}$, synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seems most plausible as an optical-NIR emission mechanism. The steep optical-NIR spectral shape and the large amplitude of variability are consistent with this object being a low $\nu_{\rm{peak}}$ jet-dominated AGN. In addition, sub-arcsec resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths. The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift and hence a merging hypothesis for this AGN-related activity is not supported by our observations., Comment: 22 pages, 7 figures, 2 tables. Accepted for publication in PASJ

We present the early-phase spectra and the light curves of the broad-lined supernova (SN) 2016coi from $t=7$ to $67$ days after the estimated explosion date. This SN was initially reported as a broad-lined Type SN Ic (SN Ic-BL). However, we found that spectra up to $t=12$ days exhibited the He~{\sc i} $\lambda$5876, $\lambda$6678, and $\lambda$7065 absorption lines. We show that the smoothed and blueshifted spectra of normal SNe Ib are remarkably similar to the observed spectrum of SN 2016coi. The line velocities of SN 2016coi were similar to those of SNe Ic-BL and significantly faster than those of SNe Ib. Analyses of the line velocity and light curve suggest that the kinetic energy and the total ejecta mass of SN 2016coi are similar to those of SNe Ic-BL. Together with broad-lined SNe 2009bb and 2012ap for which the detection of He~{\sc i} were also reported, these SNe could be transitional objects between SNe Ic-BL and SNe Ib, and be classified as broad-lined Type `Ib' SNe (SNe `Ib'-BL). Our work demonstrates the diversity of the outermost layer in broad-lined SNe, which should be related to the variety of the evolutionary paths., Comment: 9 pages, 10 figures. Accepted for publication in ApJ

Multiple outbursts of a Jupiter-family comet, 15P/Finlay, occurred from late 2014 to early 2015. We conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 January 15.6-15.7. The gas, consisting mostly of C2 and CN, and dust particles expanded at speeds of 1,110 +/- 180 m/s and 570 +/- 40 m/s at a heliocentric distance of 1.0 AU. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity beta_max = 1.6 +/- 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 10^8-10^9 kg of dust particles (assumed to be 0.3 micron - 1 mm) were ejected through each outburst. Although the total mass is three orders of magnitude smaller than that of the 17P/Holmes event observed in 2007, the kinetic energy per unit mass (104 J/kg) is equivalent to the estimated values of 17P/Holmes and 332P/2010 V1 (Ikeya-Murakami), suggesting that the outbursts were caused by a similar physical mechanism. From a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15P/Finlay-class outbursts occur >1.5 times annually and inject dust particles from Jupiter-family comets and Encke-type comets into interplanetary space at a rate of ~10 kg/s or more., Comment: 37 pages, 9 figures

We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from $-11$ to $+140$ days after the date of its $B$-band maximum in the optical and near-infrared (NIR) wavelengths conducted through the OISTER ToO program. The NIR light curves and color evolutions up to 35 days after the $B$-band maximum provided an excellent match with those of another SC SN 2009dc, providing a further support to the nature of SN 2012dn as a SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from $30$ days after the $B$-band maximum. The $H$ and $K_{s}$-band light curves exhibited much later maximum dates at $40$ and $70$ days after the $B$-band maximum, respectively, compared with those of normal SNe Ia. The $H$ and $K_{s}$-band light curves subtracted by those of SN 2009dc displayed plateaued evolutions, indicating a NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to be $4.8 - 6.4\times10^{-2}$ pc. No emission lines were found in its early phase spectrum, suggesting that the ejecta-CSM interaction could not occur. On the other hand, we found no signature that strongly supports the scenario of dust formation. The mass loss rate of the pre-explosion system is estimated to be $10^{-6}-10^{-5}$ M$_{\odot}$ yr$^{-1}$, assuming that the wind velocity of the system is $10-100$ km~s$^{-1}$, which suggests that the progenitor of SN 2012dn could be a recurrent nova system. We conclude that the progenitor of this SC SN could be explained by the single-degenerate scenario., Comment: 22 pages, 10 pages, 8 tables, accepted for publication in PASJ. Reference corrected

We performed a monitoring observation of a Jupiter-Family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using aperture photometry package and derived the Afrho parameter, a proxy for the dust production rate. We found that Afrho showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance r_h=2.6-3.1 AU to a maximal value of 185 cm at r_h = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at r_h = 3.2 AU during the outbound orbit. We applied a model for characterizing dust production rates as a function of r_h and found that the fractional active area of the cometary nucleus had dropped from 20%-40% in 2008-2011 (around the aphelion) to 0.1%-0.3% in 2014-2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the sun. Although a minor eruption was observed on UT 2015 January 26 at r_h = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust (<~ 10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity., Comment: 25 pages, 6 figures, 2 tables, ApJ accepted on December 29, 2015

This paper reports a new optical observation of 17P/Holmes one orbital period after the historical outburst event in 2007. We detected not only a common dust tail near the nucleus, but also a long narrow structure that extended along the position angle 274.6+/- 0.1 degree beyond the field of view of the Kiso Wide Field Camera, i.e., >0.2 degree eastward and >2.0 degree westward from the nuclear position. The width of the structure decreased westward with increasing distance from the nucleus. We obtained the total cross section of the long extended structure in the field of view, C= (2.3 +/- 0.5)x10^10 m^2. From the position angle, morphology and the mass, we concluded that the long narrow structure consists of materials ejected during the 2007 outburst. On the basis of the dynamical behavior of dust grains in the solar radiation field, we estimated that the long narrow structure would be composed of 1 mm-1 cm grains having an ejection velocity of >50 m/s. The velocity was more than one order of magnitude faster than that of millimeter - centimeter grains from typical comets around a heliocentric distance rh of 2.5 AU. We considered that sudden sublimation of a large amount of water ice (about 10^30 mol/s) would be responsible for the high ejection velocity. We finally estimated a total mass of M=(4-8)x10^11 kg and a total kinetic energy of E=(1-6)x10^15 J for the 2007 outburst ejecta, which are consistent with those of previous studies that conducted soon after the outburst., Comment: 23 pages, 8 figures. Astrophysical Journal, accepted on December 4, 2015

We conducted an optical and near-infrared polarimetric observation of the highly dormant Jupiter-Family Comet, 209P/LINEAR. Because of its low activity, we were able to determine the linear polarization degrees of the coma dust particles and nucleus independently, that is $P_n$=30.3$^{+1.3}_{-0.9}$% at $\alpha$=92.2$^\circ$ and $P_n$=31.0$^{+1.0}_{-0.7}$% at $\alpha$=99.5$^\circ$ for the nucleus, and $P_c$=28.8$^{+0.4}_{-0.4}$% at $\alpha$=92.2$^\circ$ and 29.6$^{+0.3}_{-0.3}$% at $\alpha$=99.5$^\circ$ for the coma. We detected no significant variation in $P$ at the phase angle coverage of 92.2$^\circ$-99.5$^\circ$, which may imply that the obtained polarization degrees are nearly at maximum in the phase-polarization curves. By fitting with an empirical function, we obtained the maximum values of linear polarization degrees $P_\mathrm{max}$=30.8% for the nucleus and $P_\mathrm{max}$=29.6% for the dust coma. The $P_\mathrm{max}$ of the dust coma is consistent with those of dust-rich comets. The low geometric albedo of $P_v$=0.05 was derived from the slope-albedo relationship and was associated with high $P_\mathrm{max}$. We examined $P_\mathrm{max}$-albedo relations between asteroids and 209P, and found that the so-called Umov law seems to be applicable on this cometary surface., Comment: 27 pages, 7 figures, accepted on 2015 October 14 for publication in the Astrophysical Journal

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until $\sim$ $260$ days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) Target-of-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes ($M_{J}\sim-18.1$ mag and $M_{H}\sim-18.3$ mag) and the rate of decline of the light curve ($\Delta$ $m_{15}$($B$)$=1.6 \pm 0.1$ mag) are very similar to those of SN 2005hk ($M_{J}\sim-17.7$ mag, $M_{H}\sim$$-18.0$ mag, and $\Delta$ $m_{15}$($B$)$\sim1.6$ mag), yet differ significantly from SNe 2008ha and 2010ae ($M_{J}\sim-14 - -15$ mag and $\Delta$ $m_{15}$($B$)$\sim2.4-2.7$ mag). The estimated rise time is $12.0 \pm 3.0$ days, which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the $^{56}$Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of 6--8. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a `failed deflagration' model, although the pulsational delayed detonations is not excluded., Comment: 42 pages, 13 figures, 8 tables, accepted for publication in ApJ

Multi-wavelength observations of the black-widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating up the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52$^{\circ}$ < i < 59$^{\circ}$, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10$^{11}$ cm from the pulsar, the pulsar wind is already in particle dominant-stage, with a magnetization parameter of $\sigma$ < 0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of orbital modulation. The observed phenomenon may be related to an unstable pulsar-wind activity or a weak mass accretion, both of which can result in the temporal extinction of radio-pulse., Comment: 13pages, 11 figures, Accepted(ApJ)

We report a new observation of the Jupiter-family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance rh = 1.6 au and showed weak activity at rh < 1.4 au. We found an active region of <0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index q=-3.25+-0.10. We derived a mass loss rate of 2-10 kg/s during the active phase and a total mass of ~5x10^7 kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4 m/s, which is comparable to the escape velocity from the nucleus (1.4 m/s). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage., Comment: 18 pages, 4 figures, accepted on 2014 December 11 for publication in the Astrophysical Journal Letters

We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the international Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions, the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range (alpha = 5-75 deg) and shows weak nonlinear opposition brightening at alpha< 5 deg, providing a more reliable absolute magnitude of Hv = 19.25 +- 0.03. The phase slope (0.039 +- 0.001 mag/deg) and opposition effect amplitude (parameterized by the ratio of intensity at alpha=0.3 deg to that at alpha=5 deg, I(0.3)/I(5)=1.31+-0.05) are consistent with those of typical C-type asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w=0.041, g=-0.38, B0=1.43, and h=0.050, assuming a surface roughness parameter theta=20 deg. By combining our photometric study with a thermal model of the asteroid (Mueller et al. in preparation), we obtained a geometric albedo of pv = 0.047 +- 0.003, phase integral q = 0.32 +- 0.03, and Bond albedo AB = 0.014 +- 0.002, which are commensurate with the values for common C-type asteroids., Comment: 27 pages, 4 figure, accepted for publication in the Astrophysical Journal

We present results of optical polarimetric and multi-band photometric observations for gamma-ray loud narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by 1.5 m Kanata telescope since 2012 September but following a gamma-ray flux enhancement detected by Fermi-LAT on MJD 56483 (2013 July 10) dense follow-up was performed by ten 0.5-2.0 m telescopes in Japan over one week. The 2-year R_C-band light curve showed clear brightening corresponding to the gamma-ray flux increase and then decayed gradually. The high state as a whole lasted for ~20 days, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0-1% in quiescence to ~3% at maximum and then declined to the quiescent level, with the duration of the enhancement of less than 10 days. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hour continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band., Comment: 7 pages, 4 figures, 1 table. Accepted by PASJ

Short-period comet P/2010 V1 (Ikeya-Murakami, hereafter V1) was discovered visually by two amateur astronomers. The appearance of the comet was peculiar, consisting of an envelope, a spherical coma near the nucleus and a tail extending in the anti-solar direction. We investigated the brightness and the morphological development of the comet by taking optical images with ground-based telescopes. Our observations show that V1 experienced a large-scale explosion between UT 2010 October 31 and November 3. The color of the comet was consistent with the Sun (g'-RC=0.61+-0.20, RC-IC=0.20+-0.20, and B-RC=0.93+-0.25), suggesting that dust particles were responsible for the brightening. We used a dynamical model to understand the peculiar morphology, and found that the envelope consisted of small grains (0.3-1 micron) expanding at a maximum speed of 500+-40 m/s, while the tail and coma were composed of a wider range of dust particle sizes (0.4-570 micron) and expansion speeds 7-390 m/s. The total mass of ejecta is ~5x10^8 kg and kinetic energy ~5x10^12 J. These values are much smaller than in the historic outburst of 17P/Holmes in 2007, but the energy per unit mass (1x10^4 J/kg) is comparable. The energy per unit mass is about 10% of the energy released during the crystallization of amorphous water ice suggesting that crystallization of buried amorphous ice can supply the mass and energy of the outburst ejecta., Comment: 32 pages, 10 figures, Accepted by ApJ

We report on optical photopolarimetric results of the radio-loud narrow line Seyfert 1 (RL-NLSy1) galaxy PMN J0948+0022 on 2012 December to 2013 February triggered by flux enhancements in near infrared and gamma-ray bands. Thanks to one-shot polarimetry of the HOWPol installed to the Kanata telescope, we have detected very rapid variability in the polarized-flux light curve on MJD 56281 (2012 December 20). The rise and decay times were about 140 sec and 180 sec, respectively. The polarization degree (PD) reached 36 +/- 3% at the peak of the short-duration pulse, while polarization angle (PA) remained almost constant. In addition, temporal profiles of the total flux and PD showed highly variable but well correlated behavior and discrete correlation function analysis revealed that no significant time lag of more than 10 min was present. The high PD and minute-scale variability in polarized flux provides a clear evidence of synchrotron radiation from a very compact emission region of 10^14 cm size with highly ordered magnetic field. Such micro variability of polarization are also observed in several blazar jets, but its complex relation between total flux and PD are explained by multi-zone model in several blazars. The implied single emission region in PMN J0948+0022 might be reflecting a difference of jets between RL-NLSy1s and blazars., Comment: 19 pages, 4 figures, Accepted for publication in the Astrophysical Journal Letters

We present visible spectroscopic observations of a near-earth object (NEO) 2012 DA14. The asteroid 2012 DA14 came close to the surface of the Earth on February 15, 2013 at a distance of 27,700 km. Its estimated diameter is around 45 m. The physical properties of such a small asteroid have not yet been well determined. The close encounter is a good opportunity to conduct a variety of observations. The purpose of this paper is to deduce the taxonomy of 2012 DA14 by visible spectroscopic observations using the 0.4 m f/10 telescope at the Fujii Kurosaki Observatory. We conclude that the taxonomy of 2012 DA14 is an L-type in the visible wavelength region. In addition, we refer to the availability of a small, accessible telescope for NEOs smaller than 100 m., Comment: 6 pages, 1 figures, accepted for publication in PASJ

An inner main-belt asteroid, P/2010 A2, was discovered on January 6th, 2010. Based on its orbital elements, it is considered that the asteroid belongs to the Flora collisional family, where S-type asteroids are common, whilst showing a comet-like dust tail. Although analysis of images taken by the Hubble Space Telescope and Rosetta spacecraft suggested that the dust tail resulted from a recent head-on collision between asteroids (Jewitt et al. 2010; Snodgrass et al. 2010), an alternative idea of ice sublimation was suggested based on the morphological fitting of ground-based images (Moreno et al. 2010). Here, we report a multiband observation of P/2010 A2 made on January 2010 with a 105 cm telescope at the Ishigakijima Astronomical Observatory. Three broadband filters, $g'$, $R_c$, and $I_c$, were employed for the observation. The unique multiband data reveals that the reflectance spectrum of the P/2010 A2 dust tail resembles that of an Sq-type asteroid or that of ordinary chondrites rather than that of an S-type asteroid. Due to the large error of the measurement, the reflectance spectrum also resembles the spectra of C-type asteroids, even though C-type asteroids are uncommon in the Flora family. The reflectances relative to the $g'$-band (470 nm) are 1.096$\pm$0.046 at the $R_c$-band (650 nm) and 1.131$\pm$0.061 at the $I_c$-band (800 nm). We hypothesize that the parent body of P/2010 A2 was originally S-type but was then shattered upon collision into scaterring fresh chondritic particles from the interior, thus forming the dust tail., Comment: 4 figures, 1 table, accepted for publication in ApJL

Strange-looking dust cloud around asteroid (596) Scheila was discovered on 2010 December 11.44-11.47. Unlike normal cometary tails, it consisted of three tails and faded within two months. We constructed a model to reproduce the morphology of the dust cloud based on the laboratory measurement of high velocity impacts and the dust dynamics. As the result, we succeeded in the reproduction of peculiar dust cloud by an impact-driven ejecta plume consisting of an impact cone and downrange plume. Assuming an impact angle of 45 deg, our model suggests that a decameter-sized asteroid collided with (596) Scheila from the direction of (alpha, delta) = (60deg, -40deg) in J2000 coordinates on 2010 December 3. The maximum ejection velocity of the dust particles exceeded 100 m/s. Our results suggest that the surface of (596) Scheila consists of materials with low tensile strength., Comment: 4 figures 1 table, accepted for publication in ApJL

Origin of the magnetic field ubiquitous in the Universe is studied based on the Biermann mechanism, which is expected to work in the non-barotropic region. We perform a series of two-dimensional MHD simulations of the first generation supernova remnant (SNR) expanding in the inhomogeneous interstellar matter (ISM) and study the Biermann mechanism working in the interior of the SNR. Especially, we pay attention to the relaxation process of electron and ion temperatures via the Coulomb interaction. In the early SNR in which the electron temperature is much lower than the ion temperature, the Biermann mechanism is ineffective, since the gradient of electron pressure is small. Magnetic fields begin to be generated just behind the shock front when the electron temperature is sufficiently relaxed. Assuming the explosion energy of 10^52 erg, the total magnetic energy generated reaches about 10^26 erg and does not depend strongly on the parameters of either SNR or ISM. Analytic expression to estimate the magnetic total energy is presented and it is shown this agrees well with our numerical results. Finally we evaluate the expected amplitude of magnetic fields in protogalaxies as ~10^-19 G, which is sufficient for seed fields of the observed galactic magnetic fields., Comment: 24 pages, 9 figures, submitted to PASJ

A generation of magnetic fields from cosmological density perturbations is investigated. In the primordial plasma before cosmological recombination, all of the materials except dark matter in the universe exist in the form of photons, electrons, and protons (and a small number of light elements). Due to the different scattering nature of photons off electrons and protons, electric currents and electric fields are inevitably induced, and thus magnetic fields are generated. We present a detailed formalism of the generation of cosmological magnetic fields based on the framework of the well-established cosmological perturbation theory following our previous works. We numerically obtain the power spectrum of magnetic fields for a wide range of scales, from $k\sim 10^{-5}$ Mpc$^{-1}$ up to $k\sim 2\times 10^{4}$ Mpc$^{-1}$ and provide its analytic interpretation. Implications of these cosmologically generated magnetic fields are discussed., Comment: 21 pages, 6 figures

Magnetic field plays a very important role in many astronomical phenomena at various scales of the universe. It is no exception in the early universe. Since the energy density, pressure, and tension of the primordial magnetic field affect gravitational collapses of plasma, the formation of seeds for large scale structures should be influenced by them. Here we numerically investigate the effects of stochastic primordial magnetic field on the seeds of large scale structures in the universe in detail. We found that the amplitude ratio between the density spectra with and without PMF ($|P(k)/P_0(k)|$ at $k>0.2$ Mpc$^{-1}$) lies between 75% and 130% at present for the range of PMF strengths 0.5 nG $< B_\lambda < 1.0$ nG, depending on the spectral index of PMF and the correlation between the matter density and the PMF distributions., Comment: 20 pages, 5 figures, submitted to PRD 23 Jan 2006, Revised 02 Oct 2006, accepted for publication in PRD

The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and electrons are considered, then cosmological density fluctuations, which explain the large scale structure of the universe, can also produce magnetic fields on cosmological scales before the epoch of recombination. By evaluating the power spectrum of these cosmological magnetic fields on a range of scales, we show here that magnetic fields of 10^{-18.1} gauss are generated at a 1 megaparsec scale and can be even stronger at smaller scales (10^{-14.1} gauss at 10 kiloparsecpc). These fields are large enough to seed magnetic fields in galaxies and may therefore have affected primordial star formation in the early universe., Comment: 11 pages, 3 figures, accepted draft for publication in Science. Edited version and supporting online material are available at: http://www.sciencemag.org/cgi/content/abstract/311/5762/827

We discuss generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton and photon) evaluating the collision term between elecrons and photons up to the second order. The collision term is shown to induce electric current, which then generate magnetic field. There are three contributions, two of which can be evaluated from the first-order quantities, while the other one is fluid vorticity which is purely second order. We compute numerically the magnitudes of the former contributions and shows that the amplitude of the produced magnetic field is about $\sim 10^{-19} {\rm G}$ at 10kpc comoving scale at present. Compared to astrophysical and inflationary mechanisms for seed-field generation, our study suffers from much less ambiguities concerning unknown physics and/or processes., Comment: 4pages, 2figures, to appear in the Proc. of the Int. Conference on "The Origin and Evolution of Cosmic Magnetism", Bologna, 29 August - 2 September 2005, eds. R. Beck, G. Brunetti, L. Feretti and B. Gaensler (Atronomische Nachrichten, Wiley, 2005)

We have studied the generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of the first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We have performed a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the produced magnetic fields. We find that magnetic fields with amplitude $10^{-14}-10^{-17}$ G are generated inside the bubble, though the amount of magnetic fields generated depend on specific values of initial conditions. This corresponds to magnetic fields of $10^{28}-10^{31}$ ergs per each supernova remnant, which is strong enough to be the seed magnetic field for a galactic and/or interstellar dynamo., Comment: 4pages, 2figures, to appear in the Proc. of the Int. Conference on "The Origin and Evolution of Cosmic Magnetism", Bologna, 29 August - 2 September 2005, eds. R. Beck, G. Brunetti, L. Feretti and B. Gaensler (Atronomische Nachrichten, Wiley, 2005)

The evolution of supernova remnants (SNRs) is studied, with particular attention to the effect of magnetic fields with axisymmetric two-dimensional magnetohydrodynamical simulations. The evolution of magnetic SNRs is the same as non-magnetic ones in the adiabatic Sedov stage. After a thin shell is formed, the shell is driven by the pressure of the hot interior gas (bubble). Evolution in the pressure-driven snow-plow phase is much affected by the magnetic field. The shell sweeping the magnetic field lines thickens owing to the magnetic pressure force. After $5\times 10^5{\rm yr}$ - $2\times 10^6{\rm yr}$, the inner boundary of the thick shell begins to contract. This compresses the hot bubble radially and maintains its thermal pressure. Thus, the bubble forms a prolate spheroidal shape and becomes thinner and thinner, since it expands in a direction parallel to the magnetic field for $B_0 \gtrsim 3\mu {\rm G}$. Finally, the bubble contracts. The porosity of the hot low-density gas in ISM is reduced, taking the effect of the magnetic field into account., Comment: 32pages and 39figures

In this letter, we discuss generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton and photon) evaluating the collision term between elecrons and photons up to the second order. The collision term is shown to induce electric current, which then generate magnetic field. There are three contributions, two of which can be evaluated from the first-order quantities, while the other one is fluid vorticity which is purely second order. We estimate the magnitudes of the former contributions and shows that the amplitude of the produced magnetic field is about $\sim 10^{-19} {\rm G}$ at 10Mpc comoving scale at the recombination. Compared to astrophysical and inflationary mechanisms for seed-field generation, our study suffers from much less ambiguities concerning unknown physics and/or processes., Comment: 4 pages, 1 figure, published version in Physical Reveiw Letters

We study generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We perform a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the produced magnetic fields. We find that magnetic fields with amplitude $10^{-14}-10^{-17}$ G are generated inside the bubble, though the amount of magnetic fields generated depend on specific values of initial conditions. This corresponds to magnetic fields of $10^{28}-10^{31}$ erg per each supernova remnant, which is strong enough to be the seed magnetic field for galactic and/or interstellar dynamo., Comment: 12 pages, 3 figures