Abstract
We present the results of Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations of the nearby type Ic supernova (SN) 2020oi. Under the standard assumptions on the ...SN-circumstellar medium (CSM) interaction and the synchrotron emission, the data indicate that the CSM structure deviates from a smooth distribution expected from the steady-state mass loss in the very vicinity of the SN (≲10
15
cm), which is then connected to the outer smooth distribution (≳10
16
cm). This structure is further confirmed through the light-curve modeling of the whole radio data set as combined with the previously reported data at lower frequency. Because this is an explosion of a bare carbon-oxygen (C+O) star with a fast wind, we can trace the mass-loss history of the progenitor of SN 2020oi in the final year. The inferred nonsmooth CSM distribution corresponds to fluctuations on the subyear timescale in the mass-loss history toward the SN explosion. Our finding suggests that the pre-SN activity is likely driven by the accelerated change in the nuclear burning stage in the last moments just before the massive star’s demise. The structure of the CSM derived in this study is beyond the applicability of the other methods at optical wavelengths, highlighting the importance and uniqueness of quick follow-up observations of SNe by ALMA and other radio facilities.
As potential candidates for neutron scintillators, divalent rare-earth-doped Li2CaSiO4 (Ln:LCS) phosphors were synthesized and their photoluminescence (PL) properties were evaluated. LCS is as light ...as LiCaAlF6 and has a low density of 2.86 g/cm3 and a small effective atomic number of 14. In this study, a ferrosilicon powder was used as a safe and convenient reductive medium for the reduction of Ln3+ to Ln2+. Sm, Eu, and, Yb were doped into LCS, where they occupied the Ca2+ sites. Among the phosphors synthesized by embedding in the ferrosilicon powder, Eu:LCS, Yb:LCS, and Eu,Yb:LCS exhibited luminescence arising from 5d–4f electronic transitions of the divalent emitter ion. All three divalent ion-doped phosphors had slower PL decay components with lifetimes of the order of tens of microseconds. Although Ln:LCS appears to be unsuitable for neutron detection under high doses owing to the slow decay of the doped Ln2+ emission, the phosphors, notably Eu2+ phosphors, have relatively high emission intensities and can potentially be applied as high-temperature neutron scintillators.
Abstract
Recently, a new class of quasars, called changing-look quasars (CLQs), has been reported. CLQs exhibit significant changes in optical and mid-infrared luminosity, accompanied by the ...appearance or disappearance of broad emission lines. We performed spectroscopic observations at the Nishi-Harima Astronomical Observatory in 2018 May to identify objects that show long-term (∼10 yr) continuous optical luminosity variations as candidates for CLQs. We discovered significant fluctuations in the Hβ emission line of 3C 332. This source has previously been reported to have a characteristic double-peaked Hα emission line. To explain the shape of the emission lines, a ring disk model has been proposed, and the possibility of a binary black hole has also been suggested. To further investigate the characteristics of 3C 332, we performed nine spectroscopic observations at Okayama Observatory (Kyoto University) from 2020 February to June. Based on the change in the velocity offset of the emission lines and the negative correlation between the line intensity and the velocity difference between the two peaks, we conclude that the double-peaked origin of this source is consistent with the ring disk model. In addition, the timescale of the changing look (of the optical and mid-infrared luminosities) is consistent with the thermal timescale or the propagation timescale of the heating/cooling front.
We present results from a deep 2′ × 3′ (comoving scale of 3.7 Mpc × 5.5 Mpc at z = 3) survey at 1.1 mm, taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We ...observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 Jy beam−1 at a spatial resolution of 0 7. We detect 18 robust ALMA sources at a signal-to-noise ratio (S/N) > 5. Comparison between the ALMA map and a 1.1 mm map, taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE), indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least 10 of our 18 ALMA SMGs have spectroscopic redshifts of z 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with S/N > 10 have a median intrinsic angular size of ( physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected, the source counts show a possible excess compared to the counts in the general fields at S1.1mm ≥ 1.0 mJy, due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies.
Abstract
Orientation-controlled 2D perovskites consisting of octahedral monolayers have been realized on 3D perovskites. By bar-coating a Dion–Jacobson (DJ) phase 2D perovskite precursor solution ...onto 3D perovskite thin films, the conversion of the top layer of 3D perovskite to 2D perovskite was promoted, and the optimal 2D/3D heterostructure could be fabricated. The orientation of the DJ 2D perovskite could be controlled horizontally or obliquely according to the 3D perovskite template thin films; the 2D perovskite was obliquely oriented on (200)/(112)-oriented CH
3
NH
3
PbI
3
, and horizontally oriented on (110)-oriented CH
3
NH
3
PbI
2.5
Cl
0.5
. This approach would boost the stability and power conversion efficiency of 2D/3D heterostructures.
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 ∼2 crab at 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 ∼1.5 and an electron temperature of ∼50 keV, which is consistent with a black hole X-ray binary in the low/hard state. The electron temperature was slightly decreased, and the photon index increased, with increasing flux. The source showed significant X-ray flux variation on a timescale 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 spectral energy distribution 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 upper limit of ∼0.2 mcrab at 4-10 keV, obtained from seven years of data from 2009 to 2016), whereas weak optical and infrared activity was found at flux levels ∼3 orders of magnitude lower than the peak fluxes in the outburst.
Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of small solar system bodies. Although numerous observational and theoretical studies ...have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC15 in 2022 December to investigate its surface properties. The rotation period of 2010 XC15 is possibly a few to several dozen hours and the color indices of 2010 XC15 are derived as g − r = 0.435 ± 0.008, r − i = 0.158 ± 0.017, and r − z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC15 are a few percent at the phase angle range of 58°–114°. We found that 2010 XC15 is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC15 and 1998 WT24 are of common origin (i.e., an asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC15 and 1998 WT24 was transported from the main belt through the ν6 resonance or Hungaria region.
Thin films of a typical organic–inorganic halide perovskite material, CH3NH3PbI3 (MAPbI3), were fabricated by a bar-coating method, which is one of the candidate techniques for large-scale ...production. The film thickness of MAPbI3 markedly changed depending on the sweep speed of the coating bar, that is, it decreased in evaporation regime under the low-speed condition, and increased in the Landau–Levich regime under the high-speed condition. The typical inverted-type p-i-n planar solar cells with the MAPbI3 thin films demonstrated the photoelectric conversion efficiency of 14.0%, and their photovoltaic properties depending on the sweep speed were discussed by taking the surface morphology and crystallinity into consideration.
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