Two-component jet model for multi-wavelength afterglow emission of the extremely energetic burst GRB 221009A

Recently gamma-ray bursts (GRBs) have been detected at very high-energy (VHE) gamma-rays by imaging atmospheric Cherenkov telescopes, and a two-component jet model has often been invoked to explain multi-wavelength data. In this work, multi-wavelength afterglow emission from an extremely bright gamma-ray burst, GRB 221009A, is examined. The isotropic-equivalent gamma-ray energy of this event is among the largest, which suggests that similarly to previous VHE GRBs, the jet opening angle is so small that the collimation-corrected gamma-ray energy is nominal. Afterglow emission from such a narrow jet decays too rapidly, especially if the jet propagates into uniform circumburst material. In the two-component jet model, another wide jet component with a smaller Lorentz factor dominates late-time afterglow emission, and we show that multi-wavelength data of GRB 221009A can be explained by narrow and wide jets with opening angles similar to those employed for other VHE GRBs. We also discuss how model degeneracies can be disentangled with observations.Comment: 5 pages + appendix, 3 figures, MNRAS Letters, in pres

High-energy emission as a test of the prior emission model for gamma-ray burst afterglows

We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts the high-energy gamma-ray emission when the prompt GRB photons from the main flow are up-scattered by relativistic electrons accelerated at the external shock due to the prior flow. The expected spectrum has the peak of 10-100 GeV at around the end time of the plateau phase for typical GRBs, and high-energy gamma rays from nearby and/or energetic GRBs can be detected by current and future Cherenkov telescopes such as MAGIC, VERITAS, CTA, and possibly Fermi. Multi-wavelength observations by ground-based optical telescopes as well as Fermi and/or Swift sattelites are important to constrain the model. Such external inverse-Compton emission may even lead to GeV-TeV gamma-ray signals with the delay time of 10-100 s, only if the plateau phase is short-lived.Comment: 5 pages, 4 figure

Inter-annual variation in CH4 efflux and the associated processes with reference to delta-13C-, delta-D-CH4 at the Lowland of Indigirka River in Northeastern Siberia

第6回極域科学シンポジウム分野横断セッション：[IA] 急変する北極気候システム及びその全球的な影響の総合的解明―GRENE北極気候変動研究事業研究成果報告2015―11月19日（木）　国立極地研究所１階交流アトリウ

The Atomic and Electronic structure of 0{\deg} and 60{\deg} grain boundaries in MoS2

We have investigated atomic and electronic structure of grain boundaries in monolayer MoS2, where relative angles between two different grains are 0 and 60 degree. The grain boundaries with specific relative angle have been formed with chemical vapor deposition growth on graphite and hexagonal boron nitride flakes; van der Waals interlayer interaction between MoS2 and the flakes restricts the relative angle. Through scanning tunneling microscopy and spectroscopy measurements, we have found that the perfectly stitched structure between two different grains of MoS2 was realized in the case of the 0 degree grain boundary. We also found that even with the perfectly stitched structure, valence band maximum and conduction band minimum shows significant blue shift, which probably arise from lattice strain at the boundary

Prospects for Detecting Gamma-Ray Bursts at Very High Energies with the Cherenkov Telescope Array

We discuss the prospects for the detection of gamma-ray bursts (GRBs) by the Cherenkov Telescope Array (CTA), the next generation, ground-based facility of imaging atmospheric Cherenkov telescopes (IACTs) operating above a few tens of GeV. By virtue of its fast slewing capabilities, the lower energy threshold compared to current IACTs, and the much larger effective area compared to satellite instruments, CTA can measure the spectra and variability of GRBs with excellent photon statistics at multi-GeV energies. Employing a model of the GRB population whose properties are broadly consistent with observations by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) onboard Fermi, we simulate follow-up observations of GRBs with the Large Size Telescopes (LSTs), the component of CTA with the fastest slew speed and the best sensitivity at energies below a few hundred GeV. For our fiducial assumptions, we foresee that the LSTs can detect ~0.1 GRBs per year during the prompt phase and ~0.5 per year in the afterglow phase, considering only one array site and both GBM and the Space-based multi-band astronomical Variable Object Monitor (SVOM) as the alert instruments. The detection rates can be enhanced by a factor of about 5 and 6 for the prompt emission and the afterglow, respectively, assuming two array sites with the same sensitivity and that the GBM localization error can be reduced to less than 1 deg. The expected distribution of redshift and photon counts are presented, showing that despite the modest event rate, hundreds or more multi-GeV photons can be anticipated from a single burst once they are detected. We also study how the detection rate depends on the intrinsic GRB properties and the delay time between the burst trigger and the follow-up observation.Comment: 15 pages, 9 figures, accepted for publication in MNRA

Methane Oxidation Potential of Arctic Wetland Soil of a Taiga-Tundra Ecotone in Northeastern Siberia

第6回極域科学シンポジウム分野横断セッション：[IA] 急変する北極気候システム及びその全球的な影響の総合的解明―GRENE北極気候変動研究事業研究成果報告2015―11月19日（木）　国立極地研究所１階交流アトリウ

Very low-frequency rTMS modulates SEPs over the contralateral hemisphere

In order to investigate the transcallosal effects of repetitive transcranial magnetic stimulation (rTMS), we studied median somatosensory evoked potentials (SEPs) before and after applying monophasic very low-frequency (0.2 Hz) subthreshold rTMS over the right motor cortex. For SEPs, median nerve was stimulated on each side. Sham rTMS served as the control. Twelve healthy subjects participated in this study. After rTMS over the right hemisphere, the amplitude of N34 component in right median SEPs recorded from the left parietal scalp (C3’) increased significantly. Other components of right or left median SEPs or those after sham stimulation showed no changes. Monophasic 0.2 Hz subthreshold rTMS over the motor cortex predominantly affected the contralateral SEPs, probably through the transcallosal pathway