515 research outputs found

    Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic particles

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    Approximate analytic expressions are presented for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution. From these, an expression for the degree of polarization is derived. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles

    Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic paricles

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    Approximate analytic expressions for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution are given. From these, an expression for the degree of polarization is derived. To accomplish this, previously developed methods of integration are used. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles

    Looptop Hard X-Ray Emission in Solar Flares: Images and Statistics

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    The discovery of hard X-ray sources near the top of a flaring loop by the HXT instrument on board the YOHKOH satellite represents a significant progress towards the understanding of the basic processes driving solar flares. In this paper we extend the previous study of limb flares by Masuda (1994) by including all YOHKOH observations up through August 1998. We report that from October 1991 to August 1998, YOHKOH observed 20 X-ray bright limb flares (where we use the same selection criteria as Masuda), of which we have sufficient data to analyze 18 events, including 8 previously unanalyzed flares. Of these 18 events, 15 show detectable impulsive looptop emission. Considering that the finite dynamic range (about a decade) of the detection introduces a strong bias against observing comparatively weak looptop sources, we conclude that looptop emission is a common feature of all flares. We summarize the observations of the footpoint to looptop flux ratio and the spectral indices. We present light curves and images of all the important newly analyzed limb flares. Whenever possible we present results for individual pulses in multipeak flares and for different loops for multiloop flares. We then discuss the statistics of the fluxes and spectral indices of the looptop and footpoint sources taking into account observational selection biases. The importance of these observations (and those expected from the scheduled HESSI satellite with its superior angular spectral and temporal resolution) in constraining acceleration models and parameters is discussed briefly.Comment: 27 pages (13 embedded figures). Accepted for publication in Ap

    Stereoscopic observations of hard x ray sources in solar flares made with GRO and other spacecraft

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    Since the launch of the Gamma Ray Observatory (GRO) in Apr. 1991, the Burst and Transient Source Experiment (BATSE) instrument on GRO has recorded a large number of solar flares. Some of these flares have also been observed by the Gamma-Ray Burst Detector on the Pioneer Venus Orbiter (PVO) and/or by the Solar X-Ray/Cosmic Gamma-Ray Burst Experiment on the Ulysses spacecraft. A preliminary list of common flares observed during the period May-Jun. 1991 is presented and the possible joint studies are indicated

    Global Energetics of Solar Flares: III. Non thermal Energies

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    This study entails the third part of a global flare energetics project, in which Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data of 191 M and X-class flare events from the first 3.5 yrs of the Solar Dynamics Observatory (SDO) mission are analyzed. We fit a thermal and a nonthermal component to RHESSI spectra, yielding the temperature of the differential emission measure (DEM) tail, the nonthermal power law slope and flux, and the thermal/nonthermal cross-over energy ecoe_{\mathrm{co}}. From these parameters we calculate the total nonthermal energy EntE_{\mathrm{nt}} in electrons with two different methods: (i) using the observed cross-over energy ecoe_{\mathrm{co}} as low-energy cutoff, and (ii) using the low-energy cutoff ewte_{\mathrm{wt}} predicted by the warm thick-target bremsstrahlung model of Kontar et al. {\bf Based on a mean temperature of Te=8.6T_e=8.6 MK in active regions we find low-energy cutoff energies of ewt=6.2±1.6e_{\mathrm{wt}} =6.2\pm 1.6 keV for the warm-target model, which is significantly lower than the cross-over energies eco=21±6e_{\mathrm{co}}=21 \pm 6 keV. Comparing with the statistics of magnetically dissipated energies EmagE_{\mathrm{mag}} and thermal energies EthE_{\mathrm{th}} from the two previous studies, we find the following mean (logarithmic) energy ratios with the warm-target model: Ent=0.41 EmagE_{\mathrm{nt}} = 0.41 \ E_{\mathrm{mag}}, Eth=0.08 EmagE_{\mathrm{th}} = 0.08 \ E_{\mathrm{mag}}, and $E_{\mathrm{th}} = 0.15 \ E_{\mathrm{nt}}$. The total dissipated magnetic energy exceeds the thermal energy in 95% and the nonthermal energy in 71% of the flare events, which confirms that magnetic reconnection processes are sufficient to explain flare energies. The nonthermal energy exceeds the thermal energy in 85\% of the events, which largely confirms the warm thick-target model.Comment: 34p, 9 Figs., 1 Tabl

    The space physics environment data analysis system (SPEDAS)

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    With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.Published versio

    Reconciliation of Waiting Time Statistics of Solar Flares Observed in Hard X-Rays

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    We study the waiting time distributions of solar flares observed in hard X-rays with ISEE-3/ICE, HXRBS/SMM, WATCH/GRANAT, BATSE/CGRO, and RHESSI. Although discordant results and interpretations have been published earlier, based on relatively small ranges (<2< 2 decades) of waiting times, we find that all observed distributions, spanning over 6 decades of waiting times (Δt103103\Delta t \approx 10^{-3}- 10^3 hrs), can be reconciled with a single distribution function, N(Δt)λ0(1+λ0Δt)2N(\Delta t) \propto \lambda_0 (1 + \lambda_0 \Delta t)^{-2}, which has a powerlaw slope of p2.0p \approx 2.0 at large waiting times (Δt11000\Delta t \approx 1-1000 hrs) and flattens out at short waiting times \Delta t \lapprox \Delta t_0 = 1/\lambda_0. We find a consistent breakpoint at Δt0=1/λ0=0.80±0.14\Delta t_0 = 1/\lambda_0 = 0.80\pm0.14 hours from the WATCH, HXRBS, BATSE, and RHESSI data. The distribution of waiting times is invariant for sampling with different flux thresholds, while the mean waiting time scales reciprocically with the number of detected events, Δt01/ndet\Delta t_0 \propto 1/n_{det}. This waiting time distribution can be modeled with a nonstationary Poisson process with a flare rate λ=1/Δt\lambda=1/\Delta t that varies as f(λ)λ1exp(λ/λ0)f(\lambda) \propto \lambda^{-1} \exp{-(\lambda/\lambda_0)}. This flare rate distribution represents a highly intermittent flaring productivity in short clusters with high flare rates, separated by quiescent intervals with very low flare rates.Comment: Preprint also available at http://www.lmsal.com/~aschwand/eprints/2010_wait.pd