A5066432088- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Solar Radiation and Photovoltaics
- Particle Detector Development and Performance
- Stellar, planetary, and galactic studies
- Spacecraft Design and Technology
- Astrophysical Phenomena and Observations
- CCD and CMOS Imaging Sensors
- Calibration and Measurement Techniques
- Spacecraft and Cryogenic Technologies
- Earthquake Detection and Analysis
- Radiation Therapy and Dosimetry
- Planetary Science and Exploration
- Radiation Detection and Scintillator Technologies
- Astronomy and Astrophysical Research
- Nuclear Physics and Applications
- Geomagnetism and Paleomagnetism Studies
- Adaptive optics and wavefront sensing
- Advanced Semiconductor Detectors and Materials
- Advanced X-ray Imaging Techniques
- History and Developments in Astronomy
- Medical Imaging Techniques and Applications
- Advanced X-ray and CT Imaging
Twin Cities Orthopedics
2015-2024
University of Minnesota
2015-2024
University of Minnesota System
2016-2024
University of California, Berkeley
2009-2023
Center for Astrophysics Harvard & Smithsonian
2023
Goddard Space Flight Center
2023
National Postdoctoral Association
2023
Urban College of Boston
2023
Laboratory for Atmospheric and Space Physics
2023
University of Glasgow
2023
The first self-consistent simulations of electron acceleration during magnetic reconnection in a macroscale system are presented. Consistent with solar flare observations the spectra energetic electrons take form power-laws that extend more than two decades energy. drive mechanism for these nonthermal is Fermi reflection growing and merging flux ropes. A strong guide field found to suppress production by weakening mechanism. For weak total energy content dominates hot thermal even though...
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray microwave emissions in partially disk-occulted solar flare of 2007 December 31. STEREO mission provides EUV images site at different viewing angles, establishing a two-ribbon geometry occultation heights RHESSI NoRH observations ∼16 Mm ∼25 Mm, respectively. Despite occultation, intense emission up ∼80 keV occurs during impulsive phase from...
We report new measurements of the parity-violating asymmetry ${A}_{\mathrm{PV}}$ in elastic scattering 3 GeV electrons off hydrogen and $^{4}\mathrm{He}$ targets with $⟨{\ensuremath{\theta}}_{\mathrm{lab}}⟩\ensuremath{\approx}6.0\ifmmode^\circ\else\textdegree\fi{}$. The result is ${A}_{\mathrm{PV}}=\mathbf{(}+6.40\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.12(\mathrm{syst})\mathbf{)}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$....
Solar flares--the most powerful explosions in the solar system--are also efficient particle accelerators, capable of energizing a large number charged particles to relativistic speeds. A termination shock is often invoked standard model flares as possible driver for acceleration, yet its existence and role have remained controversial. We present observations flare trace morphology dynamics using high-cadence radio imaging spectroscopy. show that disruption coincides with an abrupt reduction...
The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload flew for the first time on 2012 November 2, producing focused images of Sun above 5 keV. To enable hard (HXR) imaging spectroscopy via direct focusing, FOXSI makes use grazing-incidence replicated optics combined with fine-pitch solid-state detectors. On its flight, observed several targets that included active regions, quiet Sun, and a GOES-class B2.7 microflare. This Letter provides an introduction to instrument...
Abstract Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how released energy is transported, it converted to other forms remain unclear. Here we report recurring bidirectional outflows located within large-scale sheet observed extreme-ultraviolet emission scattered white light during post-impulsive gradual phase X8.2 flare on 2017 September 10. Each originates from...
This paper investigates the solar source region of supra-thermal (few keV up to MeV range) electron beams observed near Earth by combining in situ measurements three-dimensional Plasma and Energetic Particles experiment on WIND spacecraft with remote-sensing hard X-ray observations Reuven Ramaty High Energy Solar Spectroscopic Imager. The are used identify events, then searched for signatures electrons radiating bremsstrahlung emission atmosphere. Only prompt events detected above 50 a close...
We have measured the beam-normal single-spin asymmetry $A_n$ in elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for first time $^4$He, $^{12}$C, $^{208}$Pb. For $^1$H, $^4$He measurements are agreement with calculations that relate to imaginary part two-photon exchange amplitude including inelastic intermediate states. Surprisingly, $^{208}$Pb result is significantly smaller than corresponding prediction using same formalism. These results suggest a systematic...
ABSTRACT We present results from the first campaign of dedicated solar observations undertaken by Nuclear Spectroscopic Telescope ARray ( NuSTAR ) hard X-ray (HXR) telescope. Designed as an astrophysics mission, nonetheless has capability directly imaging Sun at HXR energies (>3 keV) with increase in sensitivity least two magnitude compared to current non-focusing telescopes. In this paper we describe scientific areas where will make major improvements on existing measurements. report...
ABSTRACT We present the first observations of quiescent active regions (ARs) using Nuclear Spectroscopic Telescope Array ( NuSTAR ), a focusing hard X-ray telescope capable studying faint solar emission from high-temperature and non-thermal sources. analyze directly imaged spectrally resolved X-rays above 2 keV non-flaring ARs, observed near west limb on 2014 November 1. The images match bright features seen in extreme ultraviolet soft X-rays. imaging spectroscopy is consistent with...
We present observations of a metric type II solar radio burst that occurred on the 3rd November 2010 in association with an erupting plasmoid. The eruption was well observed by Atmospheric Imaging Assembly (AIA) board Solar Dynamics Observatory and Reuven Ramaty High Energy Spectroscopic Imager, while frequency range Nançay Radioheliograph (NRH). Such events, where emission occurs NRH range, allowing us to image burst, are infrequent. Combining these data sets, we find is located ahead hot...
We report a NuSTAR observation of solar microflare, SOL2015-09-01T04. Although it was too faint to be observed by the GOES X-ray Sensor, we estimate event an A0.1 class flare in brightness. This with only 5 counts per second detector RHESSI, is fainter than any hard (HXR) existing literature. The microflare occurred during pointing highly sensitive astrophysical observatory, which used its direct focusing optics produce detailed HXR spectra and images. exhibits properties commonly larger...
Abstract The X8.2-class limb flare on 2017 September 10 is among the best studied solar events owing to its great similarity standard model and broad coverage by multiple spacecraft ground-based observations. These multiwavelength observations indicate that electron acceleration transport are efficient in reconnection looptop regions. However, there lacks a comprehensive for explaining interpreting multi-faceted In this work, we early impulsive phase of flare. We solve Parker equation...
We report the first hard X-ray observation of a solar jet on limb with flare footpoints occulted, so that faint emission from accelerated electrons in corona can be studied detail. In this event 2003 August 21, RHESSI observed double coronal source pre-impulsive phase at both thermal and nonthermal energies. impulsive phase, two bursts consists single thermal/nonthermal coinciding lower earlier sources, second burst shows an additional nonthermal, elongated source, spatially temporally...
The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload flew for the second time on 2014 December 11. To enable direct Hard X-Ray (HXR) imaging spectroscopy, FOXSI makes use of grazing-incidence replicated focusing optics combined with fine-pitch solid-state detectors. FOXSI's first flight provided HXR focused images Sun. For several updates were made to instrument including updating and detectors as well adding a new Aspect Alignment System (SAAS). This paper provides an...
The Focusing Optics X-ray Solar Imager (FOXSI) is, in its initial form, a sounding rocket experiment designed to apply the technique of focusing hard (HXR) optics study fundamental questions about high-energy Sun. HXRs arise via bremsstrahlung from energetic electrons and hot plasma produced solar flares thus are one most direct diagnostics are-accelerated impulsive heating corona. Previous missions have always been limited sensitivity dynamic range by use indirect (Fourier) imaging due lack...
Abstract NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of microflare with Hinode /XRT on 2015 April 29 at ∼11:29 UT. This shows heating material to million Kelvin, soft X-rays /XRT, was faintly visible extreme ultraviolet SDO /AIA. For three four observations region (pre-flare, decay, post-flare phases), spectrum well fitted by single thermal...
We investigate the spatial, temporal, and spectral properties of 10 microflares from AR12721 on 2018 September 9 observed in X-rays using Nuclear Spectroscopic Telescope ARray (NuSTAR) Solar Dynamic Observatory's Atmospheric Imaging Assembly Helioseismic Magnetic Imager (SDO/AIA HMI). find GOES sub-A class equivalent microflare energies 10$^{26}$-10$^{28}$ erg reaching temperatures up to MK with consistent quiescent or hot active region core plasma 3-4 MK. One (SOL2018-09-09T10:33), an A0.1,...
Solar flares accelerate particles up to high energies (MeV and GeV scales for electrons ions, respectively) through efficient acceleration processes that are not currently understood. Hard X-rays (HXRs) the most direct diagnostic of flare-accelerated electrons. However, past current solar HXR observers lack necessary sensitivity imaging dynamic range make detailed studies faint sources in corona (where particle is thought occur); these limitations mainly due indirect Fourier techniques used...
Flares close to the solar limb, where footpoints are occulted, can reveal spectrum and structure of coronal loop-top source in X-rays. We aim at studying properties corresponding energetic electrons near their acceleration site, without footpoint contamination. To this end, a statistical study partially occulted flares observed with RHESSI is presented here, covering large part cycles 23 24. perform detailed spectra, imaging light curve analysis for 116 include contextual observations from...
In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by FOXSI-2 sounding rocket experiment, on 2014 December 11. The second FOXSI (Focusing Optics X-ray Solar Imager) flight was coordinated with instruments Hinode/XRT and SDO/AIA, which provided observations soft (SXR) Extreme Ultraviolet (EUV). This unique dataset offers an unprecedented temperature coverage useful for characterizing plasma distribution microflares....
We present X-ray imaging spectroscopy of one the weakest active region (AR) microflares ever studied. The microflare occurred at $\sim$11:04 UT on 2018 September 9 and we studied it using Nuclear Spectroscopic Telescope ARray (NuSTAR) Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). is observed clearly in 2.5-7 keV with NuSTAR Fe XVIII emission derived from hotter component 94 $\unicode{x212B}$ SDO/AIA channel. estimate event to be three orders magnitude lower than a GOES...