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Register a new userRadio, Hard X-Ray, and Gamma-Ray Emissions Associated with a Far-Side Solar Event
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The SOL2014-09-01 far-side solar eruptive event produced hard electromagnetic and radio emissions observed with detectors at near-Earth vantage points. Especially challenging was a long-duration >100 MeV $gamma$-ray burst probably produced by accelerated protons exceeding 300 MeV. This observation raised a question of how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a CME-driven shock high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the Nanc{c}ay Radioheliograph and hard X-ray data from the High Energy Neutron Detector (HEND) of the Gamma-Ray Spectrometer onboard the Mars Odyssey space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earths direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. Their reacceleration is possible in these loops by a shock wave, which was excited by the eruption, being initially not CME-driven. The results highlight the ways to address remaining questions.
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High energy emissions from supernovae (SNe), originated from newly formed radioactive species, provide direct evidence of nucleosynthesis at SN explosions. However, observational difficulties in the MeV range have so far allowed the signal detected only from the extremely nearby core-collapse SN 1987A. No solid detection has been reported for thermonuclear SNe Ia, despite the importance of the direct confirmation of the formation of 56Ni, which is believed to be a key ingredient in their nature as distance indicators. In this paper, we show that the new generation hard X-ray and soft gamma-ray instruments, on board Astro-H and NuStar, are capable of detecting the signal, at least at a pace of once in a few years, opening up this new window for studying SN explosion and nucleosynthesis.
The detection of photons above 10 keV through MeV and GeV energies is challenging due to the penetrating nature of the radiation, which can require large detector volumes, resulting in correspondingly high background. In this energy range, most detectors in space are either scintillators or solid-state detectors. The choice of detector technology depends on the energy range of interest, expected levels of signal and background, required energy and spatial resolution, particle environment on orbit, and other factors. This section covers the materials and configurations commonly used from 10 keV to > 1 GeV.
Around the peaks of substantial flares, bright artifact nearly horizontal saturation streaks (B-streaks) corresponding to the brightest parts of the flare sources appear in the STEREO/EUVI 195 A images. We show that the length of such B-streaks can be used for the solution of an actual problem of evaluating the soft X-ray flux and class of far-side flares registered with double STEREO spacecraft but invisible from Earth. For this purpose from data on about 350 flares observed from January 2007 to July 2014 (mainly exceeding the GOES M1.0 level) both with GOES and STEREO, an empirical relation is established correlating the GOES 1-8 A peak flux and the B-streak length. This allowed us for the same years to estimate the soft X-ray classes for approximately 65 strong far-side flares observed by STEREO. The results of this simple and prompt method are consistent with the estimations of Nitta et al. (Solar Phys., 288, 241, 2013) based on the calculations of the EUVI full-disk digital number output. In addition, we studied some features of the B-streaks in impulsive and long-duration flares and demonstrated that B-streaks in several consecutive EUVI images can be used to reconstruct a probable time history of strong far-side flares.
Coronal mass ejections (CMEs) are large-scale eruptions of magnetized plasma that may cause severe geomagnetic storms if Earth-directed. Here we report a rare instance with comprehensive in situ and remote sensing observa- tions of a CME combining white-light, radio, and plasma measurements from four different vantage points. For the first time, we have successfully applied a radio direction-finding technique to an interplanetary type II burst detected by two identical widely separated radio receivers. The derived locations of the type II and type III bursts are in general agreement with the white light CME recon- struction. We find that the radio emission arises from the flanks of the CME, and are most likely associated with the CME-driven shock. Our work demon- strates the complementarity between radio triangulation and 3D reconstruction techniques for space weather applications.
With frequent flaring activity of its relativistic jets, Cygnus X-3 is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy Gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cygnus X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy Gamma-ray emission. We present the results of a multi-wavelength campaign covering a quenched state, when radio emission from Cygnus X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~ 20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E >100 MeV) reveal renewed Gamma-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the Gamma-ray emission is not exclusively related to the rare giant radio flares. A 3-week period of Gamma-ray emission is also detected when Cygnus X-3 was weakly flaring in radio, right before transition to the radio quenched state. No Gamma rays are observed during the ~ one-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio quenched) state trigger Gamma-ray emission, implying a connection to the accretion process, and also that the Gamma-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.
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