TY  - JOUR
A1  - Denton, Richard E.
A1  - Ofman, L.
A1  - Shprits, Yuri
A1  - Bortnik, J.
A1  - Millan, R. M.
A1  - Rodger, C. J.
A1  - da Silva, C. L.
A1  - Rogers, B. N.
A1  - Hudson, M. K.
A1  - Liu, K.
A1  - Min, K.
A1  - Glocer, A.
A1  - Komar, C.
T1  - Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves
JF  - Journal of geophysical research : Space physics
N2  - Electromagnetic ion cyclotron (EMIC) waves have long been considered to be a significant loss mechanism for relativistic electrons. This has most often been attributed to resonant interactions with the highest amplitude waves. But recent observations have suggested that the dominant energy of electrons precipitated to the atmosphere may often be relatively low, less than 1 MeV, whereas the minimum resonant energy of the highest amplitude waves is often greater than 2 MeV. Here we use relativistic electron test particle simulations in the wavefields of a hybrid code simulation of EMIC waves in dipole geometry in order to show that significant pitch angle scattering can occur due to interaction with low-amplitude short-wavelength EMIC waves. In the case we examined, these waves are in the H band (at frequencies above the He+ gyrofrequency), even though the highest amplitude waves were in the He band frequency range (below the He+ gyrofrequency). We also present wave power distributions for 29 EMIC simulations in straight magnetic field line geometry that show that the high wave number portion of the spectrum is in every case mostly due to the H band waves. Though He band waves are often associated with relativistic electron precipitation, it is possible that the He band waves do not directly scatter the sub-megaelectron volts (sub-MeV) electrons, but that the presence of He band waves is associated with high plasma density which lowers the minimum resonant energy so that these electrons can more easily resonate with the H band waves.
KW  - electromagnetic ion cyclotron waves
KW  - EMIC
KW  - relativistic electron precipitation
KW  - pitch angle scattering
KW  - wave particle interaction
KW  - radiation belts
Y1  - 2019
U6  - https://doi.org/10.1029/2018JA026384
SN  - 2169-9402
VL  - 124
IS  - 7
SP  - 5610
EP  - 5626
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - GEN
A1  - Nishikawa, K.-I.
A1  - Zhang, B.
A1  - Choi, E. J.
A1  - Min, K. W.
A1  - Niemiec, J.
A1  - Medvedev, M.
A1  - Hardee, P.
A1  - Mizuno, Y.
A1  - Nordlund, A.
A1  - Frederiksen, J.
A1  - Sol, H.
A1  - Pohl, Martin
A1  - Hartmann, D. H.
A1  - Fishman, G.J.
T1  - Radiation from accelerated particles in shocks
T2  - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe
N2  - Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron’s transverse eflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has properties different from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We present synthetic spectra to compare with the spectra obtained from Fermi observations.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 600 
KW  - relativistic jets
KW  - Weibel instability
KW  - magnetic field generation
KW  - particle acceleration
KW  - radiation
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413128
SN  - 1866-8372
IS  - 600
SP  - 371
EP  - 372
ER  - 
TY  - GEN
A1  - Ellis, S. C.
A1  - Bauer, S.
A1  - Bacigalupo, C.
A1  - Bland-Hawthorn, J.
A1  - Bryant, J. J.
A1  - Case, S.
A1  - Content, R.
A1  - Fechner, T.
A1  - Giannone, D.
A1  - Haynes, R.
A1  - Hernandez, E.
A1  - Horton, A. J.
A1  - Klauser, U.
A1  - Lawrence, J. S.
A1  - Leon-Saval, S. G.
A1  - Lindley, E.
A1  - Löhmannsröben, Hans-Gerd
A1  - Min, S. -S.
A1  - Pai, N.
A1  - Roth, M.
A1  - Shortridge, K.
A1  - Waller, L.
A1  - Xavier, Pascal
A1  - Zhelem, Ross
T1  - PRAXIS: an OH suppression optimised near infrared spectrograph
T2  - Ground-based and Airborne Instrumentation for Astronomy VII
N2  - The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of similar to 1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of similar to 9 with the GNOSIS gratings and a factor of similar to 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests.
KW  - Near infrared
KW  - spectroscopy
KW  - OH suppression
KW  - astrophotonics
KW  - fibre Bragg gratings
Y1  - 2018
SN  - 978-1-5106-1958-6
U6  - https://doi.org/10.1117/12.2311898
SN  - 0277-786X
SN  - 1996-756X
VL  - 10702
PB  - SPIE-INT Soc Optical Engineering
CY  - Bellingham
ER  - 
TY  - JOUR
A1  - Nishikawa, Ken-Ichi
A1  - Hardee, P.
A1  - Zhang, B.
A1  - Dutan, I.
A1  - Medvedev, M.
A1  - Choi, E. J.
A1  - Min, K. W.
A1  - Niemiec, J.
A1  - Mizuno, Y.
A1  - Nordlund, Ake
A1  - Frederiksen, Jacob Trier
A1  - Sol, H.
A1  - Pohl, Martin
A1  - Hartmann, D. H.
T1  - Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability
JF  - Annales geophysicae
N2  - We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic jet and an unmagnetized sheath plasma. We have examined the strong magnetic fields generated by kinetic shear (Kelvin-Helmholtz) instabilities. Compared to the previous studies using counter-streaming performed by Alves et al. (2012), the structure of the kinetic Kelvin-Helmholtz instability (KKHI) of our jet-sheath configuration is slightly different, even for the global evolution of the strong transverse magnetic field. In our simulations the major components of growing modes are the electric field E-z, perpendicular to the flow boundary, and the magnetic field B-y, transverse to the flow direction. After the B-y component is excited, an induced electric field E-x, parallel to the flow direction, becomes significant. However, other field components remain small. We find that the structure and growth rate of KKHI with mass ratios m(i)/m(e) = 1836 and m(i)/m(e) = 20 are similar. In our simulations in the nonlinear stage is not as clear as in counter-streaming cases. The growth rate for a mildly-relativistic jet case (gamma(j) = 1.5) is larger than for a relativistic jet case (gamma(j) = 15).
KW  - Solar physics
KW  - astrophysics
KW  - astronomy (Energetic particles)
Y1  - 2013
U6  - https://doi.org/10.5194/angeo-31-1535-2013
SN  - 0992-7689
VL  - 31
IS  - 9
SP  - 1535
EP  - 1541
PB  - Copernicus
CY  - Göttingen
ER  -