Solar Bursts Research Articles

高压下LaBr3电子结构与光学性质的第一性原理

In some events, weak fast solar bursts (near the level of the quiet Sun) were observed in the background of numerous spikes in emission and absorption. In such a case, the background contains the noise signals of the receiver. In events on 2005 September 16 and 2002 April 14, the solar origin of fast bursts was confirmed by simultaneous recording of the bursts at several remote observatories. The noisy background pixels in emission and absorption can be excluded by subtracting a higher level of continuum when constructing the spectra. The wavelet spectrum, noisy profiles in different polarization channels and a spectrum with continuum level greater than zero demonstrates the noisy character of pixels with the lowest levels of emission and absorption. Thus, in each case, in order to judge the solar origin of all spikes, it is necessary to determine the level of continuum against the background of which the solar bursts are observed. Several models of microwave spikes are discussed. The electron cyclotron maser emission mechanism runs into serious problems with the interpretation of microwave millisecond spikes: the main obstacles are too high values of the magnetic field strength in the source (omega_(Pe) ≤ omega_(Be)). The probable mechanism is the interaction of plasma Langmuir waves with ion-sound waves (l + s t) in a source related to shock fronts in the reconnection region.

Concerning spikes in emission and absorption in the microwave range

In some events, weak fast solar bursts (near the level of the quiet Sun) were observed in the background of numerous spikes in emission and absorption. In such a case, the background contains the noise signals of the receiver. In events on 2005 September 16 and 2002 April 14, the solar origin of fast bursts was confirmed by simultaneous recording of the bursts at several remote observatories. The noisy background pixels in emission and absorption can be excluded by subtracting a higher level of continuum when constructing the spectra. The wavelet spectrum, noisy profiles in different polarization channels and a spectrum with continuum level greater than zero demonstrates the noisy character of pixels with the lowest levels of emission and absorption. Thus, in each case, in order to judge the solar origin of all spikes, it is necessary to determine the level of continuum against the background of which the solar bursts are observed. Several models of microwave spikes are discussed. The electron cyclotron maser emission mechanism runs into serious problems with the interpretation of microwave millisecond spikes: the main obstacles are too high values of the magnetic field strength in the source (ωPe ≤ ωBe). The probable mechanism is the interaction of plasma Langmuir waves with ion-sound waves (l + s → t) in a source related to shock fronts in the reconnection region.

Effective Temperature of the Sun Based on Log Periodic Dipole Antenna Performance In The Range From 45 MHz to 870 MHz

The Log Periodic Dipole Antenna (LPDA) performance of solar burst monitoring in the range of (45 -870) MHz is presented. This project is under the International Space Weather Initiative (ISWI) program in order to observe the solar activities within 12 hours per day. At the first stage, we make an effort by constructing LPDA that suitable with the criteria, specification and practical enough with 5.45 meter boom length size of the antenna. The rods then were perforated with nineteen (19) elements that were made of aluminum rods. Two (2) rod aluminums type with nineteenth (19) elements that signify different frequencies. The gain of this antenna is 6.67 which is required preamplifier to amplify the signal of the Sun. From the results, we found that the effective temperature of the antenna is 1.3 dB and the temperature of the Sun during that observation is 1578 K. Some suggestions on improving this design are also presented.

Combined Investigations of Solar Bursts Type III and V

This review intended to update the results of combination two burst, type III and V in one solar flare event. Magnetic reconnection of both burst will be explained theoretically. Both bursts are found on 19th September 2011 associated with Cclass flares on active region 1295. We concentrate on the mechanism of evolution the bursts which play a role in the event. It is found that type V burst appeared with five second after type III. There are a few sunspot regions on the solar disk but most are magnetically simple and have remained rather quiet. An interpretation of this new result depends critically on the number of sunspot and the role of active region 1295. Sunspot number is increases up to 144 with seven sunspots can be observed. During that event, the speed of solar wind exceeds 433.8 km/second with 2.0 g/cm3 density of proton in solar corona. Currently, radio flux is also high up to 150 sfu. Solar flare type C6 is continuously been observed in x-ray region for 24 hours since 1541 UT and a maximum C1 is detected on 1847 UT. Although the sources of both bursts are same, the direction and ejection explode differently. It is believed that the ejection of particles in type III burst is more compare type V. In summary, the behavior of type III should be critically understood in order to predict the formation of type V burst.

Application of Log Periodic Dipole Antenna (LPDA) in Monitoring Solar Burst at Low Region Frequencies Region

The Sun is considered as one of the strongest radio sources and observation in radio region can provide information on structures throughout the solar atmosphere. In radio wavelengths, we could possible to investigate high quality images within an arc second resolution at different layers of the solar atmosphere. Solar monitoring in this wavelength makes various demands on the used antennas. Therefore, Logarithmic Periodic dipole Antenna (LPDA) was constructed for monitoring Sun in the range of (45−870) MHz to precisely match the environmental requirements. Our work focuses on preparation and performance of the antenna. Observation results of the site will also be highlighted. From the analysis, we found that the signal to noise ratio is 3.9 dB. We also make an effort analyze a y-factor of a data by select a range of frequency from 220 MHz till 250 MHz due to this range consists burst. By constructing and understanding the principle of the log dipole periodic antenna and then connect it to the CALLISTO spectrometer as receiver, some solar activities observations such as solar flares and Coronal Mass Ejections (CMEs) can be done. In conclusion, the log-periodic dipole antenna (LPDA) is remains the simplest antenna with reliable bandwidth and gain estimates. solar activities

FIRST LIGHT FOR THE FIRST STATION OF THE LONG WAVELENGTH ARRAY

The first station of the Long Wavelength Array (LWA1) was completed in April 2011 and is currently performing observations resulting from its first call for proposals in addition to a continuing program of commissioning and characterization observations. The instrument consists of 258 dual-polarization dipoles, which are digitized and combined into beams. Four independently-steerable dual-polarization beams are available, each with two tunings of 16 MHz bandwidth that can be independently tuned to any frequency between 10 MHz and 88 MHz. The system equivalent flux density for zenith pointing is ~3 kJy and is approximately independent of frequency; this corresponds to a sensitivity of ~5 Jy/beam (5σ, 1 s); making it one of the most sensitive meter-wavelength radio telescopes. LWA1 also has two "transient buffer" modes which allow coherent recording from all dipoles simultaneously, providing instantaneous all-sky field of view. LWA1 provides versatile and unique new capabilities for Galactic science, pulsar science, solar and planetary science, space weather, cosmology, and searches for astrophysical transients. Results from LWA1 will detect or tightly constrain the presence of hot Jupiters within 50 parsecs of Earth. LWA1 will provide excellent resolution in frequency and in time to examine phenomena such as solar bursts, and pulsars over a 4:1 frequency range that includes the poorly understood turnover and steep-spectrum regimes. Observations to date have proven LWA1's potential for pulsar observing, and just a few seconds with the completed 256-dipole LWA1 provide the most sensitive images of the sky at 23 MHz obtained yet. We are operating LWA1 as an open skies radio observatory, offering ~2000 beam-hours per year to the general community. At the same time, we are operating a backend for all-sky imaging and total-power transient detection, approximately 6840 hours per year (~78% duty cycle).

The Multifrequency Siberian Radioheliograph

The ten-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the Local Area Network (LAN). The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West–East–South subarray of the SSRT. The radioheliograph will be fully constructed in the autumn of 2012. We plan to reach the brightness temperature sensitivity of about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and a polarization measurement accuracy about a few percent. First results with the ten-antenna prototype are presented of observations of solar microwave bursts. The prototype’s abilities to estimate source size and locations at different frequencies are discussed.

The Beginning Impulsive of Solar Burst Type IV Radio Emission Detection Associated with M Type Solar Flare

First light detection of solar burst type IV in Malaysia in the region of 260 MHz till 380 MHz has been successfully detected on 5 th March 2012. This significant solar burst variations is associated with solar flare type M level 2.0 occurred from 0412UT. Due to the effect, strong bursts that caused by extraordinary solar flares due to magnetic reconnection effect potentially induced in the near-Earth magneto tail. One possible reason behind the formation of this very complex long duration of this loop is the magnetic reconnection and disruption of the loops which is observed during flare maximum. Sunspot 1429 active region was a site of several intense in several days. In Malaysia, monitoring solar burst in radio region is just in beginning by involved the project under International Space Weather Initiative (ISWI) since 2011. We also analyzed multi wavelength observation from different sites as continuity of the phenomenon. Observations presented in this paper confirmed that Malaysia can be one of the potential countries to focus on solar monitoring solar radio emission at lowbroadband frequency (45-870) MHz using ground-based telescope due to 12 hours per day throughout a year.

Designing and Constructing Log Periodic Dipole Antennato Monitor Solar Radio Burst: e-Callisto Space Weather

A Log Periodic Dipole Antenna (LPDA) for solar burst monitor in the range of (45 -870) MHz applications is presented. In this paper, we make an effort in designing a portable LPDA that suitable with the criteria, specification and practical enough although is the boom length size of the antenna is 5.45 meter. We choose value of 0.14 spacing factor τ= 0.8 as a directivity of antenna. This LPDA is constructed by using two (2) rod aluminums type with nineteenth (19) elements of different sizes. Some of suggestions on improving this design are also presented.

Terahertz Photometer to Observe Solar Flares in Continuum

Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/s, smoothed for intervals larger than 4 s. For a 76 mm aperture, this corresponds to small solar burst intensities at THz frequencies. A system with 3 and 7 THz photometers is being built for solar flare observations on board of stratospheric balloon missions.

MICROWAVE ZEBRA PATTERN STRUCTURES IN THE X2.2 SOLAR FLARE ON 2011 FEBRUARY 15

Zebra pattern structure (ZP) is the most intriguing fine structure on the dynamic spectrograph of solar microwave burst. On 15 February 2011, there erupts an X2.2 flare event on the solar disk, it is the first X-class flare since the solar Schwabe cycle 24. It is interesting that there are several microwave ZPs observed by the Chinese Solar Broadband Radiospectrometer (SBRS/Huairou) at frequency of 6.40 ~ 7.00 GHz (ZP1), 2.60 ~ 2.75 GHz (ZP2), and the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at frequency of 1.04 ~ 1.13 GHz (ZP3). The most important phenomena is the unusual high-frequency ZP structure (ZP1, up to 7.00 GHz) occurred in the early rising phase of the flare, and there are two ZP structure (ZP2, ZP3) with relative low frequencies occurred in the decay phase of the flare. By scrutinizing the current prevalent theoretical models of ZP structure generations, and comparing their estimated magnetic field strengths in the corresponding source regions, we suggest that the double plasma resonance model should be the most possible one for explaining the formation of microwave ZPs, which may derive the magnetic field strengths as about 230 - 345 G, 126 - 147 G, and 23 - 26 G in the source regions of ZP1, ZP2, and ZP3, respectively.

South Korea's renewed focus on space weather

South Korea's renewed focus on space weather

Uncooled detectors of continuum terahertz radiation

THz continuum spectral photometry has new and unique applications in different civil and military areas presenting a number of distinctive advantages on the well known microwaves or mid- to near-infrared technologies. THz sensing is essential to investigate the emission mechanisms by high energy particle acceleration processes. Technical challenges appear to diagnose radiation produced by solar flare burst emissions measured from space as well as radiation produced by high energy electrons in laboratory accelerators. THz filters and detectors have been investigated for the construction of solar flare high cadence radiometers to operate outside the terrestrial atmosphere. Experimental setups have been assembled for testing THz continuum radiation response from distinct detectors: adapted commercial microbolometer array, pyroelectric module, and opto-acoustic (Golay cell). The results permitted the final design of a THz double radiometer using Golay cells to be flown in stratosphere balloon missions.

Electron distributions during the solar electron burst of 22 March 2002

[1] A compilation of various spacecraft measurements made over the last 30 years suggests that the pitch angle distribution (PAD) width of a solar electron burst may have a complex energy signature. To date, no study has considered the PAD width over a broad energy range during a single solar electron burst. Here we use Wind 3DP data to examine the energy dependence of the PAD width between 100 eV to 100 keV during the solar electron burst of 22 March 2002. We find that the PAD width during this event varied nonmonotonically with energy, with a minimum in the width-energy profiles often being observed between 10 and 20 keV. In addition, we find time periods during and after the burst when the PAD width-energy profile had a distinct maximum or protuberance below 10 keV. The times at which the protuberance appeared were coincident with Type III radio events. This suggests that the protuberance in the width-energy profiles may be a manifestation of electron scattering by the electron/electron instability, as previously predicted by simulations.

Fast Mid-IR Flashes Detected During Small Solar X-Ray Bursts

Solar observations in the mid-infrared 8-14 \mu\m band continuum were carried out with cadence of 5 frames per second, in December 2007. Rapid small heated sources, with typical duration of the order of seconds, were found on the bright plage-like areas around sunspots, in association with relatively weak GOES soft X-ray bursts. This work presents the analysis of fast mid-infrared flashes detected during a GOES B2.0-class event on 10 December 2007, beginning at about 10:40 UT. Rapid brightness temperature enhancements of 0.5 to 2.0 K were detected at the Earth by a microbolometer array, using a telescope with 10.5 cm diameter aperture producing a diffraction limited field-of-view of 25 arcsec. Minimum detectable temperature change was of 0.1 K. The corresponding fluxes are 30-130 solar flux units. At the solar surface the estimated rapid brightenings were of 50-150 K

Relation between the Spatial Distribution and Spectral Index of Superthermal Electron Distribution in Solar cm-Radio Sources

A series of solar cm-radio bursts are analyzed by a new inverse method estimating spatial changes of the superthermal electron distribution in solar cm-radio burst sources. It is found that the measure of the spatial change of superthermal electrons in the radio source νn is always greater than that for the magnetic field νB and it is linearly dependent on the spectral index of the electrons δ as νn≈0.5δ. This relation is explained in the simplified flare-loop model integrating the analytical solutions of the Fokker – Planck equation. The mean value of νB is found to be 0.36±0.04, which is very close to the value of νB=0.38±0.02 derived from the dependence of the magnetic field strength on the height in the active region measured by RATAN-600.

A Wideband Spectrometer with RFI Detection

ABSTRACTWe report on the design and construction of a wideband spectrometer of 500 MHz instantaneous bandwidth that includes automatic radio frequency interference (RFI) detection. The implementation is based on hardware developed at the Center for Astronomical Signal Processing and Electronics Research (CASPER). The unique aspect of the spectrometer is that it accumulates both power and power-squared, which are then used to develop a spectral kurtosis (SK) estimator. The SK estimator statistics are used for real-time detection and excision of certain types of RFI embedded in the received signal. We report on the use of this spectrometer in the Korean Solar Radio Burst Locator (KSRBL). This instrument utilizes four of these 500 MHz bandwidth SK spectrometers in parallel, to achieve a 2 GHz instantaneous bandwidth that is time multiplexed over the entire 0.24–18 GHz radio frequency range, to study solar bursts. The performance of the spectrometers for excising RFI over this range is presented. It is found that the algorithm is especially useful for excising highly intermittent RFI but is less successful for RFI due to digital signals. A method we call multiscale SK is presented that addresses the known blindness of Kurtosis-based estimators to 50% duty-cycle RFI. The SK algorithm can also be applied to spectral channels prior to correlation to remove unwanted RFI from interferometer data.

THE HARVARD RADIO ASTRONOMY STATION AT FORT DAVIS, TEXAS

The Harvard Radio Astronomy Station at Fort Davis, Texas, came into operation in 1956 as a radio extension of the U.S. Air Force Sacramento Peak Observatory. The location near Fort Davis was chosen for the low level of man-made radio signals. Initially the receiving equipment at the site included a 28-ft diameter antenna and covered the range 100-580 MHz. The receivers swept through this band approximately three times per second, recording the spectrum of solar radio activity. In subsequent years the frequency range was extended to cover all or parts of 10 MHz to 4 GHz. All recorded solar bursts were identified according to five principal spectral types, and lists including times, durations, and frequency ranges of all solar activity were published. Studies of the bursts included analyses of their relationships to flares and other optical solar phenomena, and also their relationships to geophysical phenomena, including magnetic storms and polar blackouts. An 85-ft diameter antenna was installed in 1963, which during 1970-1974 was used for solar observations in the range 580 MHz to 4 GHz. Otherwise this antenna was used for non-solar radio astronomy, including lunar occultations of radio sources, measurements of flux densities at 5 GHz, investigations of the Galactic Center, and similar projects. The solar program was closed in late 1982 after 26 years of continuous operation. After 1974 the 85-ft antenna was used mainly in a program of VLBI network observations conducted by astronomers from Caltech and NRAO. In 1991 it was replaced by an antenna of the VLBA program of the NRAO. This paper describes some details of the antennas and receivers, and results of the solar studies. It also includes a brief discussion of the non-solar observations other than the VLBI program.

On the correlation between spectra of solar microwave bursts and proton fluxes near the Earth

Studies of the extreme solar proton event of January 20, 2005 intensified the contest over of a long-standing problem: are solar cosmic rays arriving at the Earth accelerated by solar flares or by shocks preceding rapidly moving coronal mass ejections? Among the most important questions is the relationship between the energy spectra of the solar cosmic rays and the frequency spectra of flare microwave bursts. Some studies of previous solar-activity cycles have shown that such a relationship does exist, in particular, for protons with energies of tens of MeV. The present work analyzes this relation using data for 1987–2008. For flare events observed in the western half of the disk, there is a significant correlation between the index δ, which is equivalent to the power-law index of the integrated energy spectrum of 10–100 MeV protons detected near the Earth’s orbit, and radio burst parameters such as a ratio of peak fluxes S at two frequencies (for example, at 9 and 15 GHz) and a microwave peak frequency f m . Proton fluxes with hard (flat) energy spectra (δ ≤ 1.5) correspond to hard microwave frequency spectra (S 9/S 15 ≤ 1 and f m ≥ 15 GHz), while flares with soft radio spectra (S 9/S 15 ≥ 1.5 and f m ≤ 5 GHz) result in proton fluxes with soft (steep) energy spectra (δ ≥ 1.5–2). It is also shown that powerful high-frequency bursts with the hardest radio spectra (f m ≈ 30 GHz) can point at acceleration of significant proton fluxes in flares occurring in strong magnetic fields. These results argue that solar cosmic rays (or at least their initial impulses) are mainly accelerated in flares associated with impulsive and post-eruptive energy release, rather than in shocks driven by coronal mass ejections.

HIGHLIGHTING THE HISTORY OF FRENCH RADIO ASTRONOMY. 4: EARLY SOLAR RESEARCH AT THE ÉCOLE NORMALE SUPÉRIEURE, MARCOUSSIS AND NANÇAY

The first tentative steps in solar radio astronomy took place during the 1940s and early 1950s as physicists and engineers in a number of countries used recycled World War II equipment to investigate the flux levels and polarisation of solar bursts and emission from the quiet Sun, and sought to understand the connection between this emission and optical features in the solar photosphere and chromosphere. There was also an abiding interest in the terrestrial effects of this solar radio emission. Among these solar pioneers were French radio astronomers from the École Normale Supérieure in Paris. In this paper we review the early solar observations made by them from Paris, Marcoussis and Nançay prior to the construction of a number of innovative multi-element solar interferometers at the Nançay field station in the mid-1950s.