No abstract

Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

Masuda et al. found a hard X-ray source well above a soft X-ray loop in impul sive compact-loop flares near the limb. This indicates that main energy release is going on above the soft X-ray loop, and suggests magnetic reconnection occurring above the loop, similar to the classical model for two ribbon flares. If the reconnection hypothesis is correct, a hot plasma (or plasmoid) ejection is expected to be associated with these flares. Using the images taken by the soft X-ray telescope aboard Yohkoh, we searched for such plasma ejections in eight impulsive compact-loop flares near the limb, which are selected in an unbiased manner and include also the Masuda flare, 1992 January 13 flare. We found that all these flares were associated with X-ra y plasma ejections high above the sof t X-ra y loop and the velocity of ejections is within the range of 50-400 km s Ϫ1. This result gives further support for magnetic reconnection hypothesis of these impulsive compact-loop flares.

No abstract

Abstract. Using the Dst index, more than 1200 geomagnetic storms, from weak to intense, spanning over three solar cycles have been examined statistically. Interplanetary magnetic field (IMF) and solar wind data have also been used in the study. It is found that for more than 50% of intense magnetic storms, the main phase undergoes a two-step growth in the ring current. That is, before the ring current has decayed significantly to the prestorm level, anew major particle injection occurs, leadingto a further development of the ring current, and making Dst decrease a second time. Thus intense magnetic storms may often be the result of two closely spaced moderate storms. The corresponding signature in the interplanetary medium is the arrival of double-structured southward IMF at the magnetosphere.

No abstract

A neutrino with energy ∼290 TeV, IceCube-170922A, was detected in coincidence with the BL Lac object TXS0506+056 during enhanced gamma-ray activity, with chance coincidence being rejected at ∼3σ level. We monitored the object in the very-high-energy (VHE) band with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes for ∼41 hr from 1.3 to 40.4 days after the neutrino detection. Day-timescale variability is clearly resolved. We interpret the quasi-simultaneous neutrino and broadband electromagnetic observations with a novel one-zone lepto-hadronic model, based on interactions of electrons and protons coaccelerated in the jet with external photons originating from a slow-moving plasma sheath surrounding the faster jet spine. We can reproduce the multiwavelength spectra of TXS 0506+056 with neutrino rate and energy compatible with IceCube-170922A, and with plausible values for the jet power of 10 4 10 erg s 45 46 1 -´-. The steep spectrum observed by MAGIC is concordant with internal γγ absorption above ∼100 GeV entailed by photohadronic production of a ∼290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton upscattering of external photons by accelerated electrons. The X-ray and VHE bands provide crucial constraints on the emission from both accelerated electrons and protons. We infer that the maximum energy of protons in the jet comoving frame can be in the range ∼10 14 -10 18 eV.

The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subeollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)-24, 24-35, 35-57, and 57-100 keV, with an ultimate angular resolution as fine as ~ 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches ~ 70 cm 2, about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above ~ 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.