@article{DentonOfmanShpritsetal.2019, author = {Denton, Richard E. and Ofman, L. and Shprits, Yuri and Bortnik, J. and Millan, R. M. and Rodger, C. J. and da Silva, C. L. and Rogers, B. N. and Hudson, M. K. and Liu, K. and Min, K. and Glocer, A. and Komar, C.}, title = {Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves}, series = {Journal of geophysical research : Space physics}, volume = {124}, journal = {Journal of geophysical research : Space physics}, number = {7}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9402}, doi = {10.1029/2018JA026384}, pages = {5610 -- 5626}, year = {2019}, abstract = {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.}, language = {en} } @misc{NishikawaZhangChoietal.2012, author = {Nishikawa, K.-I. and Zhang, B. and Choi, E. J. and Min, K. W. and Niemiec, J. and Medvedev, M. and Hardee, P. and Mizuno, Y. and Nordlund, A. and Frederiksen, J. and Sol, H. and Pohl, Martin and Hartmann, D. H. and Fishman, G.J.}, title = {Radiation from accelerated particles in shocks}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {600}, issn = {1866-8372}, doi = {10.25932/publishup-41312}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413128}, pages = {371 -- 372}, year = {2012}, abstract = {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.}, language = {en} } @misc{EllisBauerBacigalupoetal.2018, author = {Ellis, S. C. and Bauer, S. and Bacigalupo, C. and Bland-Hawthorn, J. and Bryant, J. J. and Case, S. and Content, R. and Fechner, T. and Giannone, D. and Haynes, R. and Hernandez, E. and Horton, A. J. and Klauser, U. and Lawrence, J. S. and Leon-Saval, S. G. and Lindley, E. and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Min, S. -S. and Pai, N. and Roth, M. and Shortridge, K. and Waller, L. and Xavier, Pascal and Zhelem, Ross}, title = {PRAXIS: an OH suppression optimised near infrared spectrograph}, series = {Ground-based and Airborne Instrumentation for Astronomy VII}, volume = {10702}, journal = {Ground-based and Airborne Instrumentation for Astronomy VII}, publisher = {SPIE-INT Soc Optical Engineering}, address = {Bellingham}, isbn = {978-1-5106-1958-6}, issn = {0277-786X}, doi = {10.1117/12.2311898}, pages = {16}, year = {2018}, abstract = {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.}, language = {en} } @article{NishikawaHardeeZhangetal.2013, author = {Nishikawa, Ken-Ichi and Hardee, P. and Zhang, B. and Dutan, I. and Medvedev, M. and Choi, E. J. and Min, K. W. and Niemiec, J. and Mizuno, Y. and Nordlund, Ake and Frederiksen, Jacob Trier and Sol, H. and Pohl, Martin and Hartmann, D. H.}, title = {Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability}, series = {Annales geophysicae}, volume = {31}, journal = {Annales geophysicae}, number = {9}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {0992-7689}, doi = {10.5194/angeo-31-1535-2013}, pages = {1535 -- 1541}, year = {2013}, abstract = {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).}, language = {en} }