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We present a detection of a bright burst from FRB 20201124A, which is one of the most active repeating FRBs, based on S-band observations with the 64-m radio telescope at the Usuda Deep Space Center/JAXA. This is the first FRB observed by using a Japanese facility. Our detection at 2 GHz in February 2022 is the highest frequency for this FRB and the fluence of $>$ 189 Jy ms is one of the brightest bursts from this FRB source. We place an upper limit on the spectral index $\alpha$ = -2.14 from the detection of the S band and non-detection of the X band at the same time. We compare an event rate of the detected burst with ones of the previous research, and suggest that the power-law of the luminosity function might be broken at lower fluence, and the fluences of bright FRBs distribute up to over 2 GHz with the power-law against frequency. In addition, we show the energy density of the burst detected in this work was comparable to the bright population of one-off FRBs. We propose that repeating FRBs can be as bright as one-off FRBs, and only their brightest bursts could be detected so some of repeating FRBs intrinsically might have been classified as one-off FRBs., Comment: 8 pages, 5 figures, accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

Focusing on the electron and positron spectrum measured with CALET, which shows characteristic structures, we calculate flux contributions of cosmic rays escaped from supernova remnants, which were randomly born. We adopt a Monte Carlo method to take into account the stochastic property of births of nearby sources. We find that without a complicated energy dependence of the diffusion coefficient, simple power-law diffusion coefficients can produce spectra similar to the CALET spectrum even with a dispersion in the injection index. The positron component measured with AMS-02 is consistent with a bump-like structure around 300 GeV in the CALET spectrum. One to three nearby supernovae can contribute up to a few tens of percent of the CALET flux at 2--4 TeV, ten or more unknown and distant ($\gtrsim 500$ pc) supernovae account for the remaining several tens of percent of the flux. The CALET spectrum, showing a sharp drop at $\sim 1$ TeV, allows for a contribution of cosmic rays from an extraordinary event which occured $\sim 400$ kyr ago. This type of event releases electrons/positrons with a total energy more than 10 times the average energy for usual supernovae, and its occurrence rate is lower than $1/300$ of the usual supernova rate., Comment: 10 pages, 10 figures

We report on the multi-frequency multi-epoch radio observations of the magnetar, XTE J1810-197, which exhibited a radio outburst from December 2018 after its 10-year quiescent period. We performed quasi-simultaneous observations with VERA (22 GHz), Hitachi (6.9 GHz and 8.4 GHz), Kashima (2.3 GHz), and Iitate (0.3 GHz) radio telescopes located in Japan to trace the variability of the magnetar radio pulsations during the observing period from 13 December 2018 to 12 June 2019. The pulse width goes narrower as the observing frequency goes higher, analogous to the general profile narrowing behavior of ordinary pulsars. When assuming a simple power law in the range of 2.3 GHz and 8.7 GHz, the radio spectrum of the magnetar goes steeper with the average spectral index $ \langle \alpha \rangle \approx -0.85$ for the first four months. The wide-band radio spectra inferred from our observations and the literature suggest that XTE J1810-197 would have a double-peaked spectrum with a valley point in 22 - 150 GHz, where the first spectral peak infers a gigahertz-peaked spectrum (GPS) feature with a peak at a few GHz. The GPS and the high-frequency peak have been identified in the spectra of other radio-loud magnetars, thus they may be intrinsic features that can give a new insight to understand various emission mechanisms and surrounding environments of radio magnetars. Our study emphasizes the importance of simultaneous long-term broad-band observations toward radio-loud magnetars to capture the puzzling spectral features and establish a link to other types of neutron stars., Comment: 13 pages, 5 figures, accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8\pm0.7\%$ (a 5.4$\sigma$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts., Comment: 63 pages, 23 figures, 7 Tables. Published in Science

We have developed a sensor system based on an optical photon-counting imager with high timing resolution, aiming for highly time-variable astronomical phenomena. The detector is a monolithic Geiger-mode avalanche photodiode array customized in a Multi-Pixel Photon Counter with a response time on the order of nanoseconds. This paper evaluates the basic performance of the sensor and confirms the gain linearity, uniformity, and low dark count. We demonstrate the system's ability to detect the period of a flashing LED, using a data acquisition system developed to obtain the light curve with a time bin of 100 microseconds. The Crab pulsar was observed using a 35-cm telescope without cooling, and the equipment detected optical pulses with a period consistent with the data from the radio ephemeris. Although improvements to the system will be necessary for more reliability, the system has been proven to be a promising device for exploring the time-domain optical astronomy., Comment: 11 pages, 18 figures, accepted for publication in PASJ

There is growing evidence that a clear distinction between magnetars and radio pulsars may not exist, implying the population of neutron stars that exhibit both radio pulsations and bursting activities could be potentially large. In this situation, new insights into the burst mechanism could be gained by combining the temporal behavior of radio pulsations. We present a general model for radio suppression by relativistic $e^{\pm}$ plasma outflows at the onset of magnetar flares. A sudden ejection of magnetic energy into the magnetosphere would generate a fireball plasma, which is promptly driven to expand at relativistic speed. This would make the plasma cutoff frequency significantly higher than the rest frame radio frequency, resulting in the suppression of radio waves. We analytically show that any GHz radio emission arising from the magnetosphere is suppressed for $\sim100\ {\rm s}$, depending on the total fireball energy. On the other hand, thermal radiation is expected from the hot spot(s) on the stellar surface created by an inflow of dense plasma, which could be the origin of short bursts. Since our hypothesis predicts radio suppression in coincidence with short bursts, this could be an indirect method to constrain the occurrence rate of short bursts at the faint end that remain undetected by X-ray detectors. Furthermore, ultra-fast gamma-ray flashes from the fireball photosphere is also expected as a smoking gun, although the onboard detection is challenging due to its extremely short duration $\sim\mu$s. Finally, our model is applied to the radio pulsar with magnetar-like activities, PSR J1119-6127 in light of recent observations. Implications for fast radio bursts and the possibility of plasma lensing are also discussed., Comment: 13 pages, 5 figures, accepted for publication in MNRAS; v2

To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 -- 300 keV band and the Kashima NICT radio observatory in the 1.4 -- 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016, just before the loss of the Hitomi mission.The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1,000 and 100 GRPs were simultaneously observed at the main and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main or inter-pulse phases.All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main- or inter- pulse GRPs are 22\% or 80\% of the peak flux in a 0.20 phase width, respectively, in the 2 -- 300 keV band.The values become 25\% or 110\% for main or inter-pulse GRPs, respectively, when the phase width is restricted into the 0.03 phase.Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and the 70-300 keV are obtained for the first time, and those in other bands are consistent with previous reports.Numerically, the upper limits of main- and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) $\times 10^{-11}$ erg cm$^{-2}$, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere and the number of photon-emitting particles temporally increases.However, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a $>0.02$\% brightening of the pulse-peak flux under such conditions., Comment: 18 pages, 7 figure, 6 tables, accepted for publication in PASJ

The observed radial profiles of the X-ray emission from Pulsar Wind Nebulae (PWNe) have been claimed to conflict with the standard one-dimensional (1-D) steady model. However, the 1-D model has not been tested to reproduce both the volume-integrated spectrum and the radial profile of the surface brightness, simultaneously. We revisit the 1-D steady model and apply it to PWNe 3C 58 and G21.5-0.9. We find that the parameters of the pulsar wind, the radius of the termination shock $r_{\rm s}$ and magnetization $\sigma$, greatly affect both the photon spectrum and radial profile of the emission. We have shown that the parameters constrained by the entire spectrum lead to a smaller X-ray nebula than observed one. We have also tested the case that reproduces only the observations in X and gamma-rays, ignoring the radio and optical components. In this case, there are parameter sets that reproduce both the spectrum and emission profile, but the advection time to the edge of the nebula becomes much smaller than the age. Our detailed discussion clarifies that the standard 1-D steady model has severe difficulty to reproduce both the volume-integrated spectrum and the surface brightness simultaneously. This implies that the model should be improved by taking into account extra physical processes such as spatial diffusion of particles. Additionally, we calculate the surface brightness profile of the radio, optical and TeV gamma-rays. The future observations in these wavelengths are also important to probe the spatial distributions of the relativistic plasma and the magnetic field of PWNe., Comment: 15 pages, 10 figures, accepted for publication in ApJ

We present the results of the simultaneous observation of the giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70\% or more of the GRP spectra are consistent with single power laws and the spectral indices of them are distributed from $-4$ to $-1$. We also find that a significant number of GRPs have such a hard spectral index (approximately $-1$) that the fluence at 0.3 GHz is below the detection limit ("dim-hard" GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations., Comment: 19 pages, 25 figures, accepted for publication in ApJ

Recent $\gamma$-ray observations suggest that the particle acceleration occurs at the outer region of the pulsar magnetosphere. The magnetic field lines in the outer acceleration region (OAR) are connected to the neutron star surface (NSS). If copious electron--positron pairs are produced near the NSS, such pairs flow into the OAR and screen the electric field there. To activate the OAR, the electromagnetic cascade due to the electric field near the NSS should be suppressed. However, since a return current is expected along the field lines through the OAR, the outflow extracted from the NSS alone cannot screen the electric field just above the NSS. In this paper, we analytically and numerically study the electric-field screening at the NSS taking into account the effects of the back-flowing particles from the OAR. In certain limited cases, the electric field is screened without significant pair cascade if only ultrarelativistic particles ($\gamma\gg1$) flow back to the NSS. On the other hand, if electron--positron pairs with a significant number density and mildly relativistic temperature, expected to distribute in a wide region of the magnetosphere, flow back to the NSS, these particles adjust the current and charge densities, so that the electric field can be screened without pair cascade. We obtain the condition for the number density of particles to screen the electric field at the NSS. We also find that in ion-extracted case from the NSS, bunches of particles are ejected to the outer region quasi-periodically, which is a possible mechanism of observed radio emission., Comment: 15 pages, 13 figures, 1 table. Accepted for publication in Astrophysical Journal

The Square Kilometre Array will revolutionize pulsar studies with its wide field-of-view, wide-band observation and high sensitivity, increasing the number of observable pulsars by more than an order of magnitude. Pulsars are of interest not only for the study of neutron stars themselves but for their usage as tools for probing fundamental physics such as general relativity, gravitational waves and nuclear interaction. In this article, we summarize the activity and interests of SKA-Japan Pulsar Science Working Group, focusing on an investigation of modified gravity theory with the supermassive black hole in the Galactic Centre, gravitational-wave detection from cosmic strings and binary supermassive black holes, a study of the physical state of plasma close to pulsars using giant radio pulses and determination of magnetic field structure of Galaxy with pulsar pairs., Comment: 13 pages, 5 figures

We study stochastic acceleration models for the Fermi bubbles. Turbulence is excited just behind the shock front via Kelvin--Helmholtz, Rayleigh--Taylor, or Richtmyer--Meshkov instabilities, and plasma particles are continuously accelerated by the interaction with the turbulence. The turbulence gradually decays as it goes away from the shock fronts. Adopting a phenomenological model for the stochastic acceleration, we explicitly solve the temporal evolution of the particle energy distribution in the turbulence. Our results show that the spatial distribution of high-energy particles is different from those for a steady solution. We also show that the contribution of electrons that escaped from the acceleration regions significantly softens the photon spectrum. The photon spectrum and surface brightness profile are reproduced by our models. If the escape efficiency is very high, the radio flux from the escaped low-energy electrons can be comparable to that of the WMAP haze. We also demonstrate hadronic models with the stochastic acceleration, but they are unlikely in the viewpoint of the energy budget., Comment: 9 pages, 12 figures, accepted for publication in ApJ

The spectral shape of the prompt emissions of gamma-ray bursts (GRBs) is typically expressed by the Band function: smooth joining of two power-law functions for high-energy and low-energy regions. To reveal the origin of the Band function, we revisit the stochastic acceleration model, in which electrons are accelerated via scattering with turbulent waves in the GRB outflow. The balance between the acceleration and synchrotron cooling yields a narrow energy-distribution similar to the Maxwellian distribution. The synchrotron spectrum becomes consistent with the observed hard photon index for the low-energy region. On the other hand, the narrow electron energy distribution contradicts the power-law spectrum for the high-energy region. We consider an evolution of the electron energy distribution to solve this problem. The turbulence and magnetic field induced by a certain hydrodynamical instability gradually decay. According to this evolution, the typical synchrotron photon energy also decreases with time. The time-integrated spectrum forms the power-law shape for the high-energy region. We discuss the required evolutions of the turbulence and magnetic field to produce a typical Band function. Although the decay of the turbulence is highly uncertain, recent numerical simulations for decaying turbulence seem comparatively positive for the stochastic acceleration model. Another condition required to reconcile observations is a much shorter duration of the stochastic acceleration than the dynamical timescale., Comment: 11 pages, 4 figuers, accepted for MNRAS

Induced Compton scattering (ICS) is an interaction between intense electro-magnetic radiations and plasmas, where ICS transfers the energy from photons to plasmas. Although ICS is important for laser plasma interactions in laboratory experiments and for radio emission from pulsars propagating in pulsar wind plasmas, the detail of photon cooling process has not been understood. The problem is that, when ICS dominates, evolution of photon spectra is described as a nonlinear convection equation, which makes photon spectra to be multi-valued. Here, we propose a new approach to treat evolution of photon spectra affected by ICS. Starting from the higher-order Kompaneets equation, we find a new equation that resolves the unphysical behavior of photon spectra. In addition, we find the steady-state analytic solution, which is linearly stable. We also successfully simulate the evolution of photon spectra without artificial viscosity. We find that photons rapidly lose their energy by ICS with continuously forming solitary structures in frequency-space. The solitary structures have the logarithmically same width characterized by an electron temperature. The energy transfer from photons to plasma is more effective for broader spectrum of photons such as expected in astrophysical situations., Comment: Accepted for publication in PTEP, 15 pages, 3 figures

In this paper we propose a new mechanism describing the initial spike of giant flares in the framework of the starquake model. We investigate the evolution of a plasma on a closed magnetic flux tube in the magnetosphere of a magnetar in the case of a sudden energy release and discuss the relationship with observations of giant flares. We perform one-dimensional numerical simulations of the relativistic magnetohydrodynamics in Schwarzschild geometry. We assume energy is injected at the footpoints of the loop by a hot star surface containing random perturbations of the transverse velocity. Alfv\'en waves are generated and propagate upward, accompanying very hot plasma that is also continuously heated by nonlinearly generated compressive waves. We find that the front edges of the fireball regions collide at the top of the tube with their symmetrically launched counterparts. This collision results in an energy release which can describe the light curve of initial spikes of giant flares., Comment: 13 pages, 11 figures, accepted for publication in ApJ

We present the results of the search for a correlation between giant radio pulses (GRPs) at 1.4 GHz and hard X-rays at 15-75 keV from the Crab pulsar. We made simultaneous ground and satellite observations of the Crab pulsar over 12 hours in three occasions in April 2010, March and September 2011, and got a sample of 1.3*10^4 main-pulse phase GRPs. From these samples we have found statistically marginal enhancement (21.5%, 2.70 sigma) of hard X-ray flux within +/- 1.5 degree phase angle of the synchronous peak of main-pulse phase GRPs. This enhancement, if confirmed, implicates that GRPs may accompany plasma density increases in the pulsar magnetosphere., Comment: 4 pages, 1 figure, 2 tables, submitted to the proceedings of APPC12 - the 12th Asia Pacific Physics Conference

{\it Fermi} satellite has detected extra spectral components in GeV energy range in several GRBs. Those components have power-law shapes, which may contribute to also X-ray band. The limited photon statistics make it difficult to determine the origin of GeV photons, namely internal or external shocks. We try to explain the extra components with our numerical simulations based on internal dissipation picture. Our leptonic model may reproduce not only the GeV excess via SSC emission but also the low-energy excess via the late synchrotron emission from remnant electrons. The hadronic models also reproduce keV-GeV power-law components by synchrotron and SSC emissions from secondary electron-positron pairs. In most cases the hadronic models require a much larger energy of protons than gamma-rays. However, the keV-GeV flat spectra detected in GRB 090902B is well explained with a comparable energy in protons and gamma-rays Finally, we discuss both advantages and weaknesses for both the leptonic and hadronic models. To overcome difficulties in internal dissipation models, we propose introduction of continuous acceleration similar to the second-order Fermi acceleration., Comment: 2011 Fermi Symposium proceedings - eConf C110509

We study effects of particle re-acceleration (or heating) in the post-shock region via magnetohydrodynamic/plasma turbulence, in the context of a mixed hadronic-leptonic model for the prompt emission of gamma-ray bursts (GRBs), using both analytical and numerical methods. We show that stochastically accelerated (or heated) leptons, which are injected via pp and pg reactions and subsequent pair cascades, are plausibly able to reproduce the Band function spectra with alpha~1 and beta~2-3 in the ~MeV range. An additional hard component coming from the proton-induced cascade emission is simultaneously expected, which is compatible with observed extra power-law spectra far above the MeV range. We also discuss the specific implications of hadronic models for ongoing high-energy neutrino observations., Comment: 12 pages, 8 figures, accepted for publication in ApJ, discussions added, typos fixed. Results unchanged

H-alpha emission from supernova remnants (SNRs) implies the existence of neutral hydrogen in the circumstellar medium. Some of the neutral particles penetrating the shock are ionized by the charge exchange process and make a cold ion beam in the shock downstream region. We perform linear analyses of collisionless plasma instabilities between the cold beam and the hot downstream plasma. We find that, under typical SNR conditions, either the resonant instability or the Weibel instability is the most unstable. This mechanism may amplify the magnetic field to more than 100 micro G and changes the shock structure. As a result, the radio spectrum and the large magnetic field can be explained, apart from the widely discussed Bell's mechanism., Comment: 10 pages, 1 figures, accepted for publication in ApJL

We present a theoretical model describing magnetar giant flares on the basis of solar flare/coronal mass ejection theory. In our model, a preflare activity plays a crucial role in driving evaporating flows and supplying baryonic matters into the magnetosphere. The loaded baryonic matter, that is called "prominence", is then gradually uplifted via crustal cracking with maintaining a quasi-force-free equilibrium of the magnetosphere. Finally the prominence is erupted by the magnetic pressure force due to the loss of equilibrium triggered by the explosive magnetic reconnection. The giant flare should be induced as a final outcome of the prominence eruption accompanied by large-scale field reconfigurations. An essential difference between solar and magnetar flares is the control process of their evolutionary dynamics. The flaring activity on magnetars is mainly controlled by the radiative process unlike the solar flare governed by the electron conduction. It is highly suggestive that our model is accountable for the physical properties of the extraordinary giant flare observed on 2004 December 27 from SGR1806-20, including the source of baryonic matters loaded in the expanding ejecta observed after the giant burst., Comment: Accepted for Publications of the Astronomical Society of Japan (PASJ Vol.62 No.4), 21 pages, 4 figures

On December 27, 2004, plasma particle detectors on the GEOTAIL spacecraft detected an extremely strong signal of hard X-ray photons from the giant flare of SGR1806-20, a magnetar candidate. While practically all gamma-ray detectors on any satellites were saturated during the first ~500 ms interval after the onset, one of the particle detectors on GEOTAIL was not saturated and provided unique measurements of the hard X-ray intensity and the profile for the first 600 ms interval with 5.48 ms time resolution. After ~50 ms from the initial rapid onset, the peak photon flux (integrated above ~50 keV) reached the order of 10^7 photons sec^{-1} cm^{-2}. Assuming a blackbody spectrum with kT=175 keV, we estimate the peak energy flux to be 21 erg sec^{-1} cm^{-2} and the fluence (for 0-600 ms) to be 2.4 erg cm^{-2}. The implied energy release comparable to the magnetic energy stored in a magnetar (~10^{47} erg) suggests an extremely efficient energy release mechanism., Comment: 6 pages, 2 color figures, submitted to Nature

The outer shells of young supernova remnants (SNRs) are the most plausible acceleration sites of high-energy electrons with the diffusive shock acceleration (DSA) mechanism. We studied spatial and spectral properties close to the shock fronts in four historical SNRs (Cas A, Kepler's remnant, Tycho's remnant, and RCW 86) with excellent spatial resolution of {\it Chandra}. In all of the SNRs, hard X-ray emissions were found on the rims of the SNRs, which concentrate in very narrow regions (so-called "filaments"); apparent scale widths on the upstream side are below or in the order of the point spread function of {\it Chandra}, while 0.5--40 arcsec (0.01--0.4 pc) on the downstream side with most reliable distances. The spectra of these filaments can be fitted with both thermal and nonthermal (power-law and {\tt SRCUT}) models. The former requires unrealistic high temperature ($\ga$2 keV) and low abundances ($\la$1 solar) for emission from young SNRs and may be thus unlikely. The latter reproduces the spectra with best-fit photon indices of 2.1--3.8, or roll-off frequencies of (0.1--28)$\times 10^{17}$ Hz, which reminds us of the synchrotron emission from electrons accelerated via DSA. We consider various physical parameters as functions of the SNR age, including the previous results on SN 1006 \citep{bamba2003b}; the filament width on the downstream side increases with the SNR age, and the spectrum becomes softer keeping a nonthermal feature. It was also found that a function, that is the roll-off frequency divided by the square of the scale width on the downstream side, shows negative correlation with the age, which might provide us some information on the DSA theory., Comment: 23 pages, 23 figures, accepted by ApJ

Characteristic scale lengths of nonthermal X-rays from the SN1006 NE rim, which are observed by Chandra, are interpreted in the context of the diffusive shock acceleration on the assumption that the observed spatial profile of nonthermal X-rays corresponds to that of accelerated electrons with energies of a few tens of TeV. To explain the observed scale lengths, we construct two simple models with a test particle approximation, where the maximum energy of accelerated electrons is determined by the age of SN1006 (age-limited model) or the energy loss (energy loss-limited model), and constrain the magnetic field configuration and the diffusion coefficients of accelerated electrons. When the magnetic field is nearly parallel to the shock normal, the magnetic field should be in the range of 20-85 micro Gauss and highly turbulent both in upstream and downstream, which means that the mean free path of accelerated electrons is on the order of their gyro-radius (Bohm limit). This situation can be realized both in the age-limited and energy loss-limited model. On the other hand, when the magnetic field is nearly perpendicular to the shock normal, which can exist only in the age-limited case, the magnetic field is several micro Gauss in the upstream and 14-20 micro Gauss in the downstream, and the upstream magnetic field is less turbulent than the downstream., Comment: 9 pages, 4 figures, accepted for publication in A&A