Detection of solar radio burst intensity based on a mod ified multifactor SVM algorithm

To realize the automatic detection of solar radio burst(SRB)intensity,detection based on a modified multifactor support vector machine(SVM)algorithm is proposed.First,the influence of SRB on global navigation satellite system(GNSS)signals is analyzed.Feature vectors,which can reflect the SRB intensity of stations,are also extracted.SRB intensity is classified according to the solar radio flux,and different class labels correspond to different SRB intensity types.The training samples are composed of feature vectors and their corresponding class labels.Second,training samples are input into SVM classifiers to one-against-one training to obtain the optimal classification models.Finally,the optimal classification model is synthesized into a modified multifactor SVM classifier,which is used to automatically detect the SRB intensity of new data.Experimental results indicate that for historical SRB events,the average accuracy of SRB intensity detection is greater than 90%when the solar incident angle is higher than 20°.Compared with other methods,the proposed method considers many factors with higher accuracy and does not rely on radio telescopes,thereby saving cost.

Evidence for a Strong Correlation of Solar Proton Events with Solar Radio Bursts

A statistical analysis is made on the correlation between solar proton events with energies >10Mev and solar radio bursts during the four-year period from 1997 November to 2000 November. We examine 28 solar proton events and their corresponding solar radio bursts at 15400, 8800, 4995, 2695, 1415, 606, 410 and 245 MHz. The statistical result shows that there is a close association between solar proton events and ≥3 solar radio bursts occurring at several frequencies, one or two days before. In particular, it is noteworthy that proton events occurring in pairs within the same month are preceded 1-2 days by individual radio bursts and most of the radio bursts of solar flares occur at all eight frequencies. Those 245 MHz radio bursts associated with proton events have intense peak fluxes (up to 67000 sfu). Solar proton events are preceded 1 or 2 days by≥ 3 radio bursts at several frequencies and proton events occurring in pairs within the same month are preceded 1 or 2 days by some individual radio bursts. These correlations may be used for providing short-term or medium-term prediction of solar proton events.

AR5629:A GREAT SOLAR RADIO OUTBURST ON AUGUST 15,1989

The great solar radio outburst without millisecond radio spikes on 15 August, 1989 was analysed and some significant results were given.

A quark nova in the wake of a core-collapse supernova:a unifying model for long duration gamma-ray bursts and fast radio bursts

By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.In our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding medium.Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but phenomenological.FRB-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel instability.Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently.The resulting emission frequency,luminosity and duration in our model are consistent with FRB data.We find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB(SGRB) with fits to BAT/XRT light curves.

Periodicity in fast radio bursts due to forced precession by a fallback disk

Recently,a 16-day periodicity in a fast radio burst was reported.We propose that this 16-day periodicity may be due to forced precession of the neutron star by a fallback disk.When the rotation axis is misaligned with respect to the normal direction of the disk plane,the neutron star will precess.The eccentricity of the neutron star may be due to rotation or strong magnetic field,or similar reasons.We found that the 16-day period may be understood using typical masses of the fallback disk.Polarization observations and information about the neutron star rotation period may help to discriminate different models.The possible precession observations in pulsars,magnetars and fast radio bursts may be understood together considering forced precession by a fallback disk.

Statistical properties of fast radio bursts elucidate their origins:magnetars are favored over gamma-ray bursts

Fast radio bursts(FRBs) are extremely strong radio flares lasting several milliseconds,most of which come from unidentified objects at a cosmological distance.They can be apparently repeating or not.In this paper,we analyzed 18 repeaters and 12 non-repeating FRBs observed in the frequency bands of 400–800 MHz from Canadian Hydrogen Intensity Mapping Experiment(CHIME).We investigated the distributions of FRB isotropic-equivalent radio luminosity,considering the K correction.Statistically,the luminosity distribution can be better fitted by Gaussian form than by power-law.Based on the above results,together with the observed FRB event rate,pulse duration,and radio luminosity,FRB origin models are evaluated and constrained such that the gamma-ray bursts(GRBs) may be excluded for the non-repeaters while magnetars or neutron stars(NSs) emitting the supergiant pulses are preferred for the repeaters.We also found the necessity of a small FRB emission beaming solid angle(about 0.1 sr) from magnetars that should be considered,and/or the FRB association with soft gamma-ray repeaters(SGRs) may lie at a low probability of about 10%.Finally,we discussed the uncertainty of FRB luminosity caused by the estimation of the distance that is inferred by the simple relation between the redshift and dispersion measure(DM).

Atlas of dynamic spectra of fast radio burst FRB 20201124A

Fast radio bursts(FRBs) are highly dispersed millisecond-duration radio bursts,[1,2]of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

THE CHARACTERISTICS AND INTERPRETATION OF H_α LIMB FLARE AND RADIO BURST ON AUG. 16,1989 IN AR 5629

We observed completely a large burst event produced in AR 5629 at the west limb of the Sun using chromospheric and 3 cm radio telescopes. We used Kopp-Pneuman and Sturrock models to interpret the event.

HOMOLOGOUS RADIO BURSTS AND THEIR EXCITING FUNCTIONS

In this paper, the homology of four radio bursts occuring on August 28, 1989 are discussed in time domain, in frequency domain and in their exciting functions.From the discussions, it may be possible that if two radio bursts are homologus, then their ratios of the duration time for rising phases, decaying phases and total bursts are similar in time domain, so do their exciting functions. Therefore they resemble each other in their Fourier apectra.

The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.

LSTM neural network for solar radio spectrum classification

A solar radio spectrometer records solar radio radiation in the radio waveband. Such solar radio radiation spanning multiple frequency channels and over a short time period could provide a solar radio spectrum which is a two dimensional image. The vertical axis of a spectrum represents frequency channel and the horizontal axis signifies time. Intrinsically, time dependence exists between neighboring columns of a spectrum since solar radio radiation varies continuously over time. Thus, a spectrum can be treated as a time series consisting of all columns of a spectrum, while treating it as a general image would lose its time series property. A recurrent neural network(RNN) is designed for time series analysis. It can explore the correlation and interaction between neighboring inputs of a time series by augmenting a loop in a network.This paper makes the first attempt to utilize an RNN, specifically long short-term memory(LSTM), for solar radio spectrum classification. LSTM can mine well the context of a time series to acquire more information beyond a non-time series model. As such, as demonstrated by our experimental results, LSTM can learn a better representation of a spectrum, and thus contribute better classification.

OBSERVATION OF SOLAR RADIO EMISSION AT 3.2cm WAVELENGTH AT UAS

Ⅰ.INTRODUVTION This paper made preliminaily reduction of the data which we observed in March1989 at the active region AR5395. I list a part of microwave bursts and draw out a few oftime profiles at the end of the paper.

Possible bias of the constraints on the Hubble constant owing to the quasi-Gaussian distribution of DM_(IGM)in fast radio bursts

Fast radio bursts(FRBs)are useful cosmological probes with numerous applications in cosmology.The distribution of the dispersion measurement contribution from the intergalactic medium is a key issue.A quasi-Gaussian distribution has been used to replace the traditional Gaussian distribution,yielding promising results.However,this study suggests that there may be additional challenges in its application.We used 35 well-localized FRBs to constrain the Hubble constant H_(0)along with two FRB-related parameters,yielding H_(0)=■The best-fitting Hubble constant H_(0)is smaller than the value obtained from the Cosmic Microwave Background(CMB),which may be caused by the small sample size of current FRB data.Monte Carlo simulations indicate that a set of 100 simulated FRBs provides a more precise fitting result for the Hubble constant.However,the precision of the Hubble constant does not improve when further enlarging the FRB sample.Additional simulations reveal a systematic deviation in the fitting results of H_(0),attributed to the quasi-Gaussian distribution of the dispersion measure in the intergalactic medium.Despite this,the results remain reliable within 1σuncertainty,assuming that a sufficient number of FRB data points are available.

A solar radio moving type Ⅳ burst of expanding arches type involving multi-sources

A complex solar radio moving type IV burst was observed on 23 September 1998 with the broadband (1.0-2.0 GHz and 2.6-3.8 GHz) spectrometers with high temporal and spectral resolutions at National Astronomical Observatories of China (NAOC). Comparing to the high spatial resolution data of Siberian Solar Radio Telescope (SSRT), we find that this burst is a rare type of moving type IV burst which is caused by the expanding arches, and the spatial structure oscillations of the radio sources are related with the time structure pulsations of the radio emission. Furthermore, the burst is associated with the multiple quasi-periodic long-term pulsations, and this suggests the existence of multi-scale magnetic structures in a large expanding coronal arch. We think the moving type IV burst is due to the synchrotron emission of the energetic electrons trapped in the expanding arch, and the multiple quasi-periodic pulsations are due to the second harmonic plasma emission.

On theories of solar type Ⅲ radio bursts

In solar radiophysics,many theories for type Ⅲ bursts have been proposed during the past 60 years.Almost all these theories are based on the plasma hypothesis,which assumes that(i)the radiation is mainly generated by Langmuir waves via nonlinear processes and(ii)the radiation has frequencies close to the local plasma frequency and/or its second harmonic in the source region. We feel strongly that it is time to advocate an alternative approach without recourse to the plasma hypothesis.This brief discussion explains why.

The physics of fast radio bursts

In 2007, a very bright radio pulse was identified in the archival data of the Parkes Telescope in Australia, marking the beginning of a new research branch in astrophysics. In 2013, this kind of millisecond bursts with extremely high brightness temperature takes a unified name, fast radio burst(FRB). Over the first few years, FRBs seemed very mysterious because the sample of known events was limited. With the improvement of instruments over the last five years, hundreds of new FRBs have been discovered.The field is now undergoing a revolution and understanding of FRB has rapidly increased as new observational data increasingly accumulate. In this review, we will summarize the basic physics of FRBs and discuss the current research progress in this area.We have tried to cover a wide range of FRB topics, including the observational property, propagation effect, population study,radiation mechanism, source model, and application in cosmology. A framework based on the latest observational facts is now under construction. In the near future, this exciting field is expected to make significant breakthroughs.

Repeating fast radio bursts: Coherent circular polarization by bunches

Fast radio bursts(FRBs) are millisecond-duration signals that are highly dispersed at distant galaxies. However, the physical origin of FRBs is still unknown. Coherent curvature emission by bunches, e.g., powered by starquakes, has already been proposed for repeating FRBs. It has the nature of understanding narrowband radiation exhibiting time-frequency drifting. Recently, a highly active FRB source, i.e., FRB 20201124A, was reported to enter a newly active episode and emit at least some highly circular-polarized bursts. In this study, we revisit the polarized FRB emission, particularly investigating the production mechanisms of a highly circular polarization(CP) by deriving the intrinsic mechanism and propagative effect. The intrinsic mechanisms of invoking charged bunches are approached with radiative coherence. Consequently, a highly CP could naturally be explained by the coherent summation of outcome waves, generated or scattered by bunches, with different phases and electric vectors. Different kinds of evolutionary trajectories are found on the Poincaré sphere for the bunch-coherent polarization, and this behavior could be tested through future observations. Cyclotron resonance can result in the absorption of R-mode photons at a low altitude region of the magnetosphere, and an FRB should then be emitted from a high-altitude region if the waves have strong linear polarization. Circularly polarized components could be produced from Faraday conversion exhibiting a λ-oscillation, but the average CP fraction depends only on the income wave, indicating a possibility of a highly circular-polarized income wave. The analysis could be welcome if extremely high(e.g., almost 100%) CP from repeating FRBs is detected in the future. Finally, the production of a bulk of energetic bunches in the pulsar-like magnetosphere is discussed, which is relevant to the nature of the FRB central engine.

Possible radio precursors/signatures of the CMEs onset:radio type Ⅲ bursts and fine structures in the centimeter-metric wavelength region

Seventy-one occurrences of coronal mass ejections （CMEs） associated with radio bursts, seemingly associated with type III bursts/fine structures （FSs）, in the centimeter-metric frequency range during 2003-2005, were obtained with the spectrometers at the National Astronomical Observatories, Chinese Academy of Sciences （NAOC） and the Culgoora radio spectrometer and are presented. The statistical results of 68 out of 71 events associated with the radio type III bursts or FSs during the initiation or early stages of the CMEs indicate that most CMEs contain the emissions of radio type III bursts/FSs near the time of the CME＇s onset, in spite of their fast or slow speeds. Therefore, we propose that type III bursts and FSs are possible precursors of the onset of CMEs. We stress that the radio type III bursts/FSs in the centimetermetric wavelength region and the CME transients possibly occurred in conjunction with the origin of the coronal precursor structures. Thus, the statistical results support the suggestions that type III bursts/FSs are indicators of extra energy input into the corona at the CMEs＇ onset, and that the type III bursts/FSs are produced primarily due to a coronal instability which eventually triggers the CME process. This may signify that the centimeter-metric radio bursts corresponding to or near the CME＇s onset are caused by the disturbed corona （possibly including minor magnetic reconnections）.

Cosmology with fast radio bursts in the era of SKA

We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.

Inferring redshift and energy distributions of fast radio bursts from the first CHIME/FRB catalog

We reconstruct the extragalactic dispersion measure-redshift(DM_(E)-z)relation from well-localized fast radio bursts(FRBs)using Bayesian inference.Then,the DM_(E)-z relation is used to infer the redshift and energy of the first CHIME/FRB catalog.We find that the distributions of the extragalactic dispersion measure and inferred redshift of the non-repeating CHIME/FRBs follow a cut-off power law but with a significant excess at the low-redshift range.We apply a set of criteria to exclude events that are susceptible to the selection effect,but the excess at low redshifts still exists in the remaining FRBs(which we call the gold sample).The cumulative distributions of fluence and energy for both the full sample and the gold sample do not follow the simple power law,but they can be well fitted by the bent power law.The underlying physical implications require further investigation.