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The composition of giant planets' atmospheres is an important tracer of their formation history. While many theoretical studies investigate the heavy-element accretion within a gaseous protoplanetary disk, the possibility of solid accretion after disk dissipation has not been explored. Here, we focus on the case of a gas giant planet excited to an eccentric orbit and assess the likelihood of solid accretion after disk dissipation. We perform N-body simulations of planetesimals and embryos around an eccentric giant planet. We consider various sizes and orbits for the eccentric planet and determine the fate of planetesimals and embryos. We find that the orbital evolution of solids, such as planetesimals and embryos, is regulated by weak encounters with the eccentric planet rather than strong close encounters. Even in the region where the Safronov number is smaller than unity, most solid materials fall onto the central star or are ejected from the planetary system. We also develop an analytical model of the solid accretion along the orbital evolution of a giant planet, where the accretion probability is obtained as a function of the planetary mass, radius, semi-major axis, eccentricity, inclination, and solid disk thickness. Our model predicts that $\sim$0.01-0.1 $M_\oplus$ of solids is accreted onto an eccentric planet orbiting in the outer disk ($\sim10$ au). The accreted heavy-element mass increases (decreases) with the eccentricity (inclination) of the planet. We also discuss the possibility of collisions of terrestrial planets and find that $\sim10\%$ of the hot Jupiters formed via high-eccentric migration collide with a planet of $10M_\oplus$. However, we find that solid accretion and collisions with terrestrial planets are minor events for planets in the inner orbit, and a different accretion process is required to enrich eccentric giant planets with heavy elements., Comment: 15 pages, 16 Figures, accepted to Astronomy and Astrophysics

GRAPES-3 is a mid-altitude (2200 m) and near equatorial ($11.4^{\circ}$ North) air shower array, overlapping in its field of view for cosmic ray observations with experiments that are located in Northern and Southern hemispheres. We analyze a sample of $3.7\times10^9$ cosmic ray events collected by the GRAPES-3 experiment between 1 January 2013 and 31 December 2016 with a median energy of $\sim16$ TeV for study of small-scale ($<60^{\circ}$) angular scale anisotropies. We observed two structures labeled as A and B, deviate from the expected isotropic distribution of cosmic rays in a statistically significant manner. Structure `A' spans $50^{\circ}$ to $80^{\circ}$ in the right ascension and $-15^{\circ}$ to $30^{\circ}$ in the declination coordinate. The relative excess observed in the structure A is at the level of $(6.5\pm1.3)\times10^{-4}$ with a statistical significance of 6.8 standard deviations. Structure `B' is observed in the right ascension range of $110^{\circ}$ to $140^{\circ}$. The relative excess observed in this region is at the level of $(4.9\pm1.4)\times10^{-4}$ with a statistical significance of 4.7 standard deviations. These structures are consistent with those reported by Milagro, ARGO-YBJ, and HAWC. These observations could provide a better understanding of the cosmic ray sources, propagation and the magnetic structures in our Galaxy.

We report a detailed study of the magnetic-field structure of the Crab pulsar wind nebula, using the X-ray polarization data in 2--8~keV obtained with the Imaging X-ray Polarimetry Explorer. Contamination of the pulsar emission to the data of the nebula region was removed through application of a stringent pulsation phase-cut, extracting a phase range of 0.7--1.0 only. We found that the electric field vector polarization angle (PA) was about $130^{\circ}$ from north to east with the polarization degree (PD) of about 25\% at the pulsar position, indicating that the direction of the toroidal magnetic field is perpendicular to the pulsar spin axis in the region close to the termination shock. The PA gradually deviated from the angle as an increasing function of the distance from the pulsar. There was a region of a low PD to the west of the X-ray torus. Although such a region is expected to be located at the torus edge, where geometrical depolarization due to a steep spatial variation of the PA is expected, the observed low-PD region positionally deviated from the edge. We found that the region of low PD positionally coincided with a dense filament seen in the optical band, and conjecture that the low-PD region may be produced through deflection of the pulsar wind. By comparing the values of the PD at the pulsar position between the data and a model, in which toroidal and turbulent magnetic fields were considered, we estimated the fractional energy of the turbulent magnetic field to be about $2/3$ of the total. We also evaluated a potential polarization of the northern jet in the nebula and derived the PD and PA to be about $30\%$ and $120^{\circ}$, respectively., Comment: This is a pre-copyedited, author-produced version of an article accepted for publication in PASJ following peer review

In association with a large solar flare on November 7, 2004, the solar neutron detectors located at Mt. Chacaltaya (5,250m) in Bolivia and Mt. Sierra Negra (4,600m) in Mexico recorded very interesting events. In order to explain these events, we have performed a calculation solving the equation of motion of anti-protons inside the magnetosphere. Based on these results, the Mt. Chacaltaya event may be explained by the detection of solar neutrons, while the Mt. Sierra Negra event may be explained by the first detection of very high energy solar neutron decay protons (SNDPs) around 6 GeV., Comment: Paper presented in the 21st International Symposium on Very High Energy Cosmic Ray Intercations (ISVHE-CRI 2022) by online

Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an international experiment that applies southern very-high-energy (VHE) gamma-ray astronomy to determine the origin of cosmic rays around the knee energy region ($10^{15}\, {\rm eV} - 10^{16}\, {\rm eV}$). The experiment consists of an air shower (AS) array with a surface of $83, 000\, {\rm m}^2$ and an underground water Cherenkov muon detector (MD) array covering $5, 400\, {\rm m}^2$. The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of $4, 740\, {\rm m}$ corresponding to $572\, {\rm g}/{\rm cm}^2$ atmospheric thickness. As the prototype experiment of ALPACA, the ALPAQUITA experiment aims to begin data acquisition in late 2021. The ALPAQUITA array consists of a smaller AS array ($18, 450\, {\rm m}^2$) and underground MD ($900\, {\rm m}^2$), which are now under construction. ALPAQUITA's sensitivity to gamma-ray sources is evaluated with Monte Carlo simulations. The simulation finds that five gamma-ray sources observed by H.E.S.S. and HAWC experiments will be detected by ALPAQUITA beyond 10 TeV and one out of these five - HESS J1702-420A - above 300 TeV in one calendar year observation. The latter finding means that scientific discussions can be made on the emission mechanism of gamma rays beyond 100 TeV from southern sources on the basis of the observational results of this prototype experiment., Comment: This is the manuscript accepted by Experimental Astronomy. For the published article, see https://doi.org/10.1007/s10686-021-09796-8

Low energy ground-based cosmic ray air shower experiments generally have energy threshold in the range of a few tens to a few hundreds of TeV. The shower observables are measured indirectly with an array of detectors. The atmospheric absorption of low energy secondaries limits their detection frequencies at the Earth's surface. However, due to selection effects, a tiny fraction of low energy showers, which are produced in the lower atmosphere can reach the observational level. But, due to less information of shower observables, the reconstruction of these showers are arduous. Hence, it is believed that direct measurements by experiments aboard on satellites and balloon flights are more reliable at low energies. Despite having very small efficiency ($\sim$0.1%) at low energies, the large acceptance ($\sim$5 m$^2$sr) of GRAPES-3 experiment allows observing primary cosmic rays down below to $\sim$1 TeV and opens up the possibility to measure primary energy spectrum spanning from a few TeV to beyond cosmic ray knee (up to 10$^{16}$ eV), covering five orders of magnitude. The GRAPES-3 energy threshold for primary protons through Monte Carlo simulations are calculated, which gives reasonably good agreement with data. Furthermore, the total efficiencies and acceptance are also calculated for protons primaries. The ability of GRAPES-3 experiment to cover such a broader energy range may provide a unique handle to bridge the energy spectrum between direct measurements at low energies and indirect measurements at ultra-high energies., Comment: 15 pages, 6 figures

The angular resolution of an extensive air shower (EAS) array plays a critical role in determining its sensitivity for the detection of point $\gamma$-ray sources in the multi-TeV energy range. The GRAPES-3 an EAS array located at Ooty in India (11.4$^{\circ}$N, 76.7$^{\circ}$E, 2200 m altitude) is designed to study $\gamma$-rays in the TeV-PeV energy range. It comprises of a dense array of 400 plastic scintillators deployed over an area of 25000 m$^2$ and a large area (560 m$^2$) muon telescope. A new statistical method allowed real time determination of the propagation delay of each detector in the GRAPES-3 array. The shape of shower front is known to be curved and here the details of a new method developed for accurate measurement of the shower front curvature is presented. These two developments have led to a sizable improvement in the angular resolution of GRAPES-3 array. It is shown that the curvature depends on the size and age of an EAS. By employing two different techniques, namely, the odd-even and the left-right methods, independent estimates of the angular resolution are obtained. The odd-even method estimates the best achievable resolution of the array. For obtaining the angular resolution, the left-right method is used after implementing the size and age dependent curvature corrections. A comparison of the angular resolution as a function of EAS energy by these two methods shows them be virtually indistinguishable. The angular resolution of GRAPES-3 array is 47$^{\prime}$ for energies E$>$5 TeV and improves to 17$^{\prime}$ at E$>$100 TeV and finally approaching 10$^{\prime}$ at E$>$500 TeV.

The SEDA-FIB is a detector designed to measure solar neutrons. This solar neutron detector was operated onboard the ISS on July 16, 2009 and March 31, 2018. Eighteen large solar flares were later observed by the GOES satellite in solar active region 12673 that appeared on September 4 and lasted until September 10, 2017, with intensity higher than > M2. In nine of those solar flares, the SEDA-FIB detected clear signals of solar neutrons, along with five minor excesses. Among these events, we focus on two associated with the flares of X2.2 (SOL2017-09-06) and X8.2 (SOL2017-09-10) that share a common feature: a process of accelerating electrons into high energies as clearly recorded by the FERMI-GBM detector. These events may provide us with useful information to elucidate the ion acceleration process. The X8.2 event was a limb flare that proved adequate for fixing the parameters needed to explain the process of particle acceleration into high energies. According to our analysis, the electron acceleration process may possibly be explained by the shock acceleration model. However, we found that it would be difficult to explain the simultaneous acceleration of ions with electrons, unless the ions were preheated prior to their rapid acceleration., Comment: submitted to International Conference on Cosmic Ras and Astroparticle Physics, held in Madison, 2019

The GRAPES-3 muon telescope located in Ooty, India records rapid ($\sim$10 min) variations in the muon intensity during major thunderstorms. Out of a total of 184 thunderstorms recorded during the interval April 2011-December 2014, the one on 1 December 2014 produced a massive potential of 1.3 GV. The electric field measured by four well-separated (up to 6 km) monitors on the ground was used to help estimate some of the properties of this thundercloud including its altitude and area that were found to be 11.4 km above mean sea level (amsl) and $\geq$380 km$^2$, respectively. A charging time of 6 min to reach 1.3 GV implied the delivery of a power of $\geq$2 GW by this thundercloud that was moving at a speed of $\sim$60 km h$^{-1}$. This work possibly provides the first direct evidence for the generation of GV potentials in thunderclouds that could also possibly explain the production of highest energy (100 MeV) $\gamma$-rays in the terrestrial $\gamma$-ray flashes., Comment: Received 6 January 2019, Revised 21 January 2019, Published 15 March 2019

The GRAPES-3 muon telescope in Ooty, India had claimed detection of a 2 hour (h) high-energy ($\sim$20 GeV) burst of galactic cosmic-rays (GCRs) through a $>$50$\sigma$ surge in GeV muons, was caused by reconnection of the interplanetary magnetic field (IMF) in the magnetosphere that led to transient weakening of Earth's magnetic shield. This burst had occurred during a G4-class geomagnetic storm (storm) with a delay of $\frac{1}{2}$h relative to the coronal mass ejection (CME) of 22 June 2015 (Mohanty et al., 2016). However, recently a group interpreted the occurrence of the same burst in a subset of 31 neutron monitors (NMs) to have been the result of an anisotropy in interplanetary space (Evenson et al., 2017) in contrast to the claim in (Mohanty et al., 2016). A new analysis of the GRAPES-3 data with a fine 10.6$^{\circ}$ angular segmentation shows the speculation of interplanetary anisotropy to be incorrect, and offers a possible explanation of the NM observations. The observed 28 minutes (min) delay of the burst relative to the CME can be explained by the movement of the reconnection front from the bow shock to the surface of Earth at an average speed of 35 km/s, much lower than the CME speed of 700 km/s. This measurement may provide a more accurate estimate of the start of the storm., Comment: Accepted for Publication in Physical Review D

At the 33rd ICRC, we reported the possible detection of solar gamma rays by a ground level detector and later re-examined this event. On March 7, 2011, the solar neutron telescope (SNT) located at Mt. Sierra Negra, Mexico (4,600 m) observed enhancements of the counting rate from 19:49 to 20:02 UT and from 20:50 to 21:01 UT. The statistical significance was 9.7sigma and 8.5sigma, respectively. This paper discusses the possibility of using this mountain detector to detect solar gamma rays. In association with this event, the solar neutron detector SEDA-FIB onboard the International Space Station has also detected solar neutrons with a statistical significance of 7.5sigma. The FERMI-LAT detector also observed high-energy gamma rays from this flare with a statistical significance of 6.7sigma. We thus attempted to make a unified model to explain this data. In this paper, we report on another candidate for solar gamma rays detected on September 25th, 2011 by the SNT located in Tibet (4,300 m) from 04:37 to 04:47 UT with a statistical significance of 8.0sigma (by the Li-Ma method)., Comment: 15 pages

We reported a photon detection at the arrival time of the gravitational wave on December 26th, 2015. According to the LIGO-Virgo collaboration, the gravitational wave was produced by the merging process of the two black holes. The merged time was determined at 03:38:53.6 UT on December 26th. At 03:38:54.05 GPS time, one of the detectors of SEDA-FIB on board the International Space Station (ISS) detected a photon, arriving from the direction of Corona Australis near the Galactic Bulge (GB). The energy of the photon was about (35+-7) MeV. A 3.0 sigma level detection of the photon is discussed., Comment: 9 pages, 5 figures, presented talk at JSPS in September 016, Miyazaki University

Previous works have suggested a correlation between the X-ray luminosity Lx and the rotational luminosity Lrot of the radio pulsars.However, none of the obtained regression lines are statistically acceptable due to large scatters. We construct a statistical model which has an intrinsic Lx-Lrot relation and reproduces the observed Lx distribution about it by using a Monte Carlo simulator, which takes into account the effects obscuring the intrinsic relation,i.e., the anisotropy of radiation, additional heating, uncertainty in distance and detection limit of the instruments. From the ATNF pulsar catalog we collect 57 `ordinary radio pulsars' with significant detection and 42 with upper limits.The sample does not include the high-magnetic field pulsars (>10^{13} G), which are separately analyzed. We obtain a statistically acceptable relation Lx (0.5 - 10 keV)= 10^{31.69} (Lrot / L_0)^{c_1} with c_1 = 1.03 \pm 0.27 and L_0 =10^{35.38}. The distribution about the obtained Lx-Lrot relation is reproduced well by the simulator. Pulsars with abnormally high Lx fall into two types: one is the soft gamma-ray pulsars, and the other is thermally bright pulsars in comparison with the standard cooling curve. On the other hand, pulsars showing low Lx are found to have dim pulsar wind nebulae. We argue that there is an unknown mechanism that governs both the magnetospheric emission and the pulsar wind nebulae, and it might involve the production rate of electron-positron pairs. The high-field pulsars form a distinctive population other than the ordinary pulsars due to their excess luminosities., Comment: 17 pages, 11 figures, to be published in ApJ

The solar neutron detector SEDA-FIB onboard the International Space Station (ISS) has detected several events from the solar direction associated with three large solar flares observed on March 5th (X1.1), 7th (X5.4), and 9th (M6.3) of 2012. In this study, we present the time profiles of those neutrons and discuss the physics that may be related to a possible acceleration scenario for ions over the solar surface. We compare our data with the dynamical pictures of the flares obtained by the ultra-violet telescope of the space-based Solar Dynamics Observatory., Comment: 8 pages, 8 figures, and 1 table Proceeding of the 34th International Cosmic Ray Conference in Hague in August, 2015

An M6.5-class flare was observed at N12E56 of the solar surface at 16:06 UT on July 8, 2014. In association with this flare, solar neutron detectors located on two high mountains, Mt. Sierra Negra and Chacaltaya and at the space station observed enhancements in the neutral channel. The authors analysed these data and a possible scenario of enhancements produced by high-energy protons and neutrons is proposed, using the data from continuous observation of a solar surface by the ultraviolet telescope onboard the Solar Dynamical Observatory (SDO)., Comment: 8 pages, 7 figures, and 2 Tables. Proceeding of the 34th International Cosmic Ray Conference in Hague in August, 2015

We analyzed a highly impulsive solar flare observed on June 3, 2012. In association with this flare, emissions of hard X-rays, high-energy gamma rays, and neutrons were detected by the detectors onboard the FERMI, RHESSI satellites and the International Space Station. We compared those results with the pictures taken by the UV telescope onboard the Solar Dynamics Observatory satellite and found the crossing structure of two magnetic ropes at two positions on the solar surface almost at the same time. High-energy gamma rays were detected by the Fermi Large Area Telescope satellite, implying that the impulsive flare was one of a major source of proton acceleration processes on the solar surface. At the beginning of research, impulsive solar flares were considered to be the main source of particle acceleration processes; our current observations have confirmed this hypothesis., Comment: 8 pages, 9 figures, Proceeding of the 34th International Cosmic Ray Conference in Hague in August,2015