Abstract
We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing ...on O
i
λλ
6300, 6363. The line profile and width of O
i
are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the O
i
/Ca
ii
ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the O
i
profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the ∼1
σ
level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between O
i
width and O
i
/Ca
ii
is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when O
i
/Ca
ii
increases, the fraction of objects with Gaussian O
i
profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.
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 optical and near-infrared observations of the nearby Type Iax supernova (SN) 2014dt from 14 to 410 d after the maximum light. The velocities of the iron absorption lines in the ...early phase indicated that SN 2014dt showed slower expansion than the well-observed Type Iax SNe 2002cx, 2005hk, and 2012Z. In the late phase, the evolution of the light curve and that of the spectra were considerably slower. The spectral energy distribution kept roughly the same shape after ∼100 d, and the bolometric light curve flattened during the same period. These observations suggest the existence of an optically thick component that almost fully trapped the γ-ray energy from 56Co decay. These findings are consistent with the predictions of the weak deflagration model, leaving a bound white dwarf remnant after the explosion.
We present optical and near-infrared observations of a low-luminosity (LL) 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 140 days since the explosion, indicating that this SN takes one of the longest times to finish the plateau phase among Type IIP SNe (SNe IIP), including LL SNe IIP. The line velocities of various ions at the middle of the plateau phase are as low as 1000-1500 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 by a narrow H 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 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 ( yr−1 for VY CMa). We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion.
ABSTRACT
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric ...albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3°. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.
Abstract
Since 2018 July, the black hole X-ray binary GRS 1915+105 has been in an X-ray low luminous state (XLLS), which is the faintest period ever observed in a soft X-ray band. We present here the ...results of near-infrared (NIR) observations from 2019 April–December in the XLLS using HONIR attached to the Kanata telescope, together with radio data obtained by the Yamaguchi Interferometer and archival X-ray data. We found the historical NIR brightening in the XLLS. For several tens of days in the XLLS, NIR flux showed a positive correlation with radio flux and negative correlation with X-ray flux. This result suggests that at least a jet contributes to the NIR bands in the NIR-bright XLLS period. An accretion disk is not likely a candidate for the NIR emission because of the decrease of X-ray flux. In contrast to the NIR band, there was no historical radio brightening in the XLLS. This implies that the NIR emission in the NIR-bright period cannot be explained by the jet alone. The X-ray obscuration suggested by X-ray data is another possible candidate for the nonjet emission component in the NIR band.
We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from -15.8 days to +49.1 days after B-band maximum. The decline rate of the light curve is Delta m ...sub(15)(B) = 1.39 + or - 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the "transitional" Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at a very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B-band maximum is estimated to be 17.6 + or - 0.5 days and the time of the explosion is MJD 56277.98 + or - 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than to subluminous SNe Ia.
Abstract
BL Lacertae (BL Lac) was in an unprecedented bright state since 2020 August. We have conducted long-term photometric and polarimetric observations of BL Lac in optical and near-infrared ...(NIR) bands using the Kanata telescope in the Higashi-Hiroshima Observatory. BL Lac had simultaneously brightened in the NIR, optical, X-ray, and gamma-ray bands during the brightening period. There were two peaks of brightness in the optical and NIR bands. The degree of polarization and electric-vector position angle (EVPA) were also found to have fluctuated in the optical and NIR bands. A bluer-when-brighter trend was observed between the optical and NIR bands during the entire period of our observation. Furthermore, during the first bright period, the EVPA became parallel to the position angle of the jet. On the other hand, the polarization during the second brightening showed a different behavior from that during the first brightening. The brightenings can be explained by a combination of a shock acceleration in which a shock was generated with the perpendicular-direction shock front of the jet and a variation of the inclination angle.
Abstract
We have obtained simultaneous and continuous photo-polarization observations of the blazar BL Lacertae in optical and near-infrared (NIR) bands during an historical outburst from 2020 to ...2021. In total, 14 nights of observations were performed where 10 observations show microvariability on timescales of a few minutes to several hours. This suggests a compact emission region, and the timescales are difficult to explain by a one-zone shock-in-jet model. Moreover, we found significant differences in the polarization degree (PD) and angle between optical and NIR bands. Nine nights showed a PD in the optical band that is greater than or equal to that in the NIR band, which can be explained by either a shock-in-jet model or the Turbulent Extreme Multi-Zone (TEMZ) model. On the other hand, five nights showed higher PD in an NIR band than an optical band, which cannot be explained by simple shock-in-jet models nor the simple TEMZ model. The observed timescales and wavelength-dependency of the PD and polarization angle suggest the existence of complicated multiple emission regions such as an irregular TEMZ model.
We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared (NIR) wavelengths from immediately after the explosion until ~260 days after the maximum luminosity using ...the Optical and Infrared Synergetic Telescopes for Education and Research Target-of-Opportunity program and the Subaru Telescope. We found that the NIR light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes (M sub(J) ~ -18.1 mag and M sub(H) ~ -18.3 mag) and the rate of decline of the light curve ( Delta m sub(15)(B) = 1.6 + or - 0.1 mag) are very similar to those of SN 2005hk (M sub(J) ~ -17.7 mag, M sub(H) ~ -18.0 mag, and Delta m sub(15)(B) ~ 1.6 mag), yet differ significantly from SNe 2008ha and 2010ae (M sub(J) ~ -14 to -15 mag and Delta m sub(15)(B) ~ 2.4-2.7 mag). The estimated rise time is 12.0 + or - 3.0 days, which is significantly shorter than that of SN 2005hk or any other SNe Ia. The rapid rise indicates that the super(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 six to eight. 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.
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