Search Publications
A Comparative Study of Ground-level Enhancement Events of Solar Energetic Particles
Vainio, Rami; Riihonen, Esa; Kocharov, Leon +2 more
Major solar eruptions can accelerate protons up to relativistic energies. Solar relativistic ions arriving at 1 au may cause a solar particle event detectable by the worldwide network of neutron monitors (NMs), a ground-level enhancement (GLE) event. Using the newly computed NM yield function, we have fitted the 15 historic GLEs. Moments of the fi…
Modeling the Chromosphere and Transition Region of Planet-hosting Star GJ 436
Peacock, Sarah; Barman, Travis; Hatzes, Artie P. +12 more
Ahead of upcoming space missions intending to conduct observations of low-mass stars in the ultraviolet (UV) spectral region it becomes imperative to simultaneously conduct atmospheric modeling from the UV to the visible (VIS) and near-infrared (NIR). Investigations on extended spectral regions will help to improve the overall understanding of the…
Massive Hypervelocity Runaway Stars in the Large Magellanic Cloud
Xu, Ye; Liu, Dejian; Hao, Chaojie +3 more
Since the hypervelocity stars were discovered in the Milky Way, various mechanisms have been proposed to explain these runaway stars. Up to now, however, the dominant ejected mechanism of hypervelocity stars is still unclear. As the largest and closest face-on satellite galaxy of the Milky Way, the Large Magellanic Cloud (LMC) serves as a good tar…
NuSTAR Hard X-Ray Monitoring of Gravitationally Lensed Quasar RX J1131-1231
Zoghbi, Abderahmen; Dai, Xinyu; Morgan, Christopher W. +2 more
The X-ray emission from active galactic nuclei is believed to come from a combination of inverse Compton scattering of photons from the accretion disk and reprocessing of the direct X-ray emission by reflection. We present hard (10-80 keV) and soft (0.5-8 keV) X-ray monitoring of a gravitationally lensed quasar RX J1131-1231 (hereafter RXJ1131) wi…
A Dynamically Distinct Stellar Population in the Leading Arm of the Sagittarius Stream
Beers, Timothy C.; Lee, Young Sun; Kang, Gwibong +1 more
We present a chemical and dynamical analysis of the leading arm (LA) and trailing arm (TA) of the Sagittarius (Sgr) stream, as well as for the Sgr dwarf galaxy core (SC), using red giant branch, main-sequence, and RR Lyrae stars from large spectroscopic survey data. The different chemical properties among the LA, TA, and SC generally agree with re…
Evolution of Magnetic Fields and Energy Release Processes during Homologous Eruptive Flares
Joshi, Bhuwan; Cho, Kyung-Suk; Sahu, Suraj +1 more
We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 Marc…
A NICER Viewing Angle on the Accretion Stream of Vela X-1
Behar, Ehud; Rahin, Roi
Vela X-1 is the archetypal eclipsing high-mass X-ray binary, composed of a neutron star (NS) accreting the B-star wind. It was observed by nearly all X-ray observatories, often multiple times, featuring a rich spectrum of variable emission lines. However, the precise origin of these lines in the binary system remains uncertain. We perform a system…
Jitter Radiation as an Alternative Mechanism for the Nonthermal X-Ray Emission of Cassiopeia A
Greco, Emanuele; Vink, Jacco; Ferrigno, Carlo +1 more
Synchrotron radiation from relativistic electrons is usually invoked as responsible for the nonthermal emission observed in supernova remnants. Diffusive shock acceleration is the most popular mechanism to explain the process of particles acceleration and within its framework a crucial role is played by the turbulent magnetic field. However, the s…
Exploring the Origin of Solar Energetic Electrons. I. Constraining the Properties of the Acceleration Region Plasma Environment
Jeffrey, Natasha L. S.; Pallister, Ross
Solar flare electron acceleration is an efficient process, but its properties (mechanism, location) are not well constrained. Via hard X-ray (HXR) emission, we routinely observe energetic electrons at the Sun, and sometimes we detect energetic electrons in interplanetary space. We examine if the plasma properties of an acceleration region (size, t…
NGC 6302: The Tempestuous Life of a Butterfly
Frank, Adam; Balick, Bruce; Kastner, Joel H. +4 more
NGC 6302 (The Butterfly Nebula) is an extremely energetic and rapidly expanding bipolar planetary nebula (PN). If the central source is a single star, then its apparent location in an H-R diagram places it among the most massive, hottest, and presumably rapidly evolving of all central stars of PNe. Our proper motion study of NGC 6302, based on Hub…