The Influence of the Sun and Moon on the Observation of Very High Energy Gamma-ray Sources Using EAS Arrays

With great advance of ground-based extensive air shower arrays,such as LHAASO and HAWC,many very high energy(VHE)gamma-ray sources have been discovered and are being monitored regardless of the day and the night.Hence,the Sun and Moon would have some impacts on the observation of gamma-ray sources,which have not been taken into account in previous analysis.In this paper,the influence of the Sun and Moon on the observation of very high energy gamma-ray sources when they are near the line of sight of the Sun or Moon is estimated.The tracks of all the known VHE sources are scanned and several VHE sources are found to be very close to the line of sight of the Sun or Moon during some period.The absorption of very high energy gamma rays by sunlight is estimated with detailed method and some useful conclusions are achieved.The main influence is the block of the Sun and Moon on gamma rays and the shadow on the cosmic ray background.The influence is investigated considering the detector angular resolution and some strategies on data analysis are proposed to avoid the underestimation of the gamma-ray emission.

New Insight to the Surface Temperature of the Sun

Information is given on thermal radiation from the Sun, considered in practical engineering calculations of heat exchange. It was found that although the surface temperature of the Sun is assumed to be about 5800 K, the solar spectrum data measured by Kondratyev lead to a value of at least 7134 K. Such a higher value can be obtained by interpreting the Planck formula for the black radiation spectrum for the Kondratyev data. In addition, using the Stefan-Boltzmann law, the energetic emissivity of the Sun’s surface was determined to be 0.431. Furthermore, based on Petela’s formulae for exergy of thermal radiation, the exergetic emissivity of the Sun’s surface was also calculated at the level of 0.426.

Ground-based Observations of Ultraviolet and Total Solar Radiation in Shenyang,Northeast China

Objective This work explores the diurnal variation of Solar ultraviolet radiation （UVR） and total solar radiation （TSR） in northeast China,using daily observations of UVR and TSR in Shenyang.Methods UVR and TSR measurements were carried out from March 1st,2006 to December 31st,2009 in Shenyang,Liaoning province,China （41°51＇ N,123°27＇ E）.Results Both TSR and UVR showed seasonal variation,reaching the highest levels in summer and the lowest in winter.They showed the greatest fluctuation in summer and autumn.The irradiance of TSR and UVR on clear days around the equinoxes and solstices increased substantially compared with the mean seasonal irradiance,especially in autumn.The whole day accumulated dose of UVR in winter was far less than that during the middle part of a summer day （i.e.between 10：00 and 14：00）.It was also less than the accumulated summer dose of morning and afternoon （i.e.between 8：00 and 10：00 and 14：00 and 16：00）.Conclusion The instant irradiance and daily accumulated amount of UVR are low in Shenyang,especially in autumn and winter.Thus concern about the health effects arising because shortage of UVR in northeast China is warranted.

The Emission Heights of Transition Region Lines in an Equatorial Coronal Hole and the Surrounding Quiet Sun

Using the correlation between the radiance or Doppler velocity and the extrapolated magnetic field, we determined the emission heights of a set of solar transition region lines in an equatorial coronal hole and in the surrounding quiet Sun region. We found that for all of the six lower-transition-region lines, the emission height is about 4-5 Mm in the equatorial coronal hole, and around 2 Mm in the quiet Sun region. This result confirms the previous findings that plasma with different temperature can coexist at the same layer of transition region. In the quiet Sun region, the emission height of the upper-transition-region line Ne VIII is almost the same that of the lower-transition-region line, but in the coronal hole, it is twice as high. This difference reveals that the outflow of Ne VIII is a signature of solar wind in the coronal hole and is just a mass supply to the large loops in the quiet Sun.

Signature of high-order azimuthal MHD body modes in sunspot's low atmosphere

The five-minute oscillations inside sunspots appear to be the absorption of the solar p-mode. It is a potential tool to probe a sunspot＇s sub-structure. We studied the collective properties of five-minute oscillations in the power and phase distribution at the sunspot＇s umbra-penumbra boundary. The azimuthal distributions of the power and phase of five-minute oscillations enclosing a sunspot＇s umbra were obtained with images taken with the Solar Dynamics Observatory/Atmospheric Imaging Assembly （SDO/AIA）. The azimuthal modes were quantified with periodogram analysis and justified with significance tests. The azimuthal nodal structures in an approximately ax- ially symmetric sunspot AR 11131 （2010 Dec 08） were investigated. Mode numbers ra = 2, 3, 4, 7, 10 were obtained in both 1700 A and 1600A bandpasses. The 1600A channel also revealed an extra mode at m = 9. In the upper atmosphere （304 A）, fewer modes were detected at m = 3, 4, 7. The azimuthal modes in the sunspot＇s low atmo- sphere could be interpreted as high-order azimuthal MHD body modes. They were detected in the power and phase of the five-minute oscillations in sunspot AR 11131 with SDO/AIA data. Fewer modes were detected in the sunspot＇s upper atmosphere.

DSC based Dual-Resunet for radio frequency interference identification

Radio frequency interference(RFI)will pollute the weak astronomical signals received by radio telescopes,which in return will seriously affect the time-domain astronomical observation and research.In this paper,we use a deep learning method to identify RFI in frequency spectrum data,and propose a neural network based on Unet that combines the principles of depthwise separable convolution and residual,named DSC Based Dual-Resunet.Compared with the existing Unet network,DSC Based Dual-Resunet performs better in terms of accuracy,F1 score,and MIoU,and is also better in terms of computation cost where the model size and parameter amount are 12.5%of Unet and the amount of computation is 38%of Unet.The experimental results show that the proposed network is a high-performance and lightweight network,and it is hopeful to be applied to RFI identification of radio telescopes on a large scale.

Harmonic Structures of Gyrosynchrotron Radiation and Cyclotron Maser Instability

The harmonic structures of the gyrosynchrotron radiation are studied and compared with the results of the electron cyclotron maser instability. The structures only appear at lower harmonics (s < 10), and their peaks deviate by a small amount from integer harmonic numbers. The amplitudes of harmonic structures of the extraordinary modes are usually larger than that of the ordinary modes. The numbers and amplitudes of harmonic structures increase with increasing electron energy spectral index δand propagation angle θ.All the properties of harmonic structures are consistent with the predictions of the electron cyclotron maser instability in an extremely magnetized plasma on the basis of Maxwell and Vlasov equations. The physical relations between gyrosynchrotron radiation and cyclotron maser instability and a possible application of the properties of the harmonic structures are discussed.

An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4 × 1011 cm-3 at the chromosphere base.

The Gyrosynchrotron Radiation Spectrum in a Nonuniform Source

Effects of the energy spectral index δ, low energy cutoff E0 and number density N of energetic electrons on gyrosynchrotron spectrum are investigated for a model source with a nonuniform magnetic field. It is found that the flux density SVT of the x-mode and o-mode systematically increase with increasing E0, N and with decreasing δ. The peak frequency of the spectrum, vp, also systematically increases as increasing E0 and N, but it may not depend on δ. The gyrosynchrotron radiation in the nonuniform case is polarized predominately in the x-mode at v ≥ 3 GHz. A sense reversal of circular polarization also occurs but at much lower frequencies （v ≤ 3 GHz）. The reversal frequency also increases with increasing E0 and N, but it perhaps is independent of δ.

The Solar Upper Transition Region Imager(SUTRI)Onboard the SATech-01 Satellite

The Solar Upper Transition Region Imager(SUTRI)onboard the Space Advanced Technology demonstration satellite(SATech-01),which was launched to a Sun-synchronous orbit at a height of~500 km in 2022 July,aims to test the on-orbit performance of our newly developed Sc/Si multi-layer reflecting mirror and the 2k×2k EUV CMOS imaging camera and to take full-disk solar images at the Ne VII 46.5 nm spectral line with a filter width of~3 nm.SUTRI employs a Ritchey-Chrétien optical system with an aperture of 18 cm.The on-orbit observations show that SUTRI images have a field of view of~416×416 and a moderate spatial resolution of~8″without an image stabilization system.The normal cadence of SUTRI images is 30 s and the solar observation time is about16 hr each day because the earth eclipse time accounts for about 1/3 of SATech-01's orbit period.Approximately15 GB data is acquired each day and made available online after processing.SUTRI images are valuable as the Ne VII 46.5 nm line is formed at a temperature regime of~0.5 MK in the solar atmosphere,which has rarely been sampled by existing solar imagers.SUTRI observations will establish connections between structures in the lower solar atmosphere and corona,and advance our understanding of various types of solar activity such as flares,filament eruptions,coronal jets and coronal mass ejections.

Narrowband EUV Sc/Si Multilayer for the Solar Upper Transition Region Imager at 46.5 nm

The transition region is the key region between the lower solar atmosphere and the corona, which has been limitedly understood by human beings. Therefore, the Solar Upper Transition Region Imager(SUTRI) was proposed by Chinese scientists and launched in 2022 July. Right now, the first imaging observation of the upper transition region around 46.5 nm has been carried out by SUTRI. To ensure the spectral and temporal resolution of the SUTRI telescope, we have developed a narrowband Sc/Si multilayer. Based on the extreme ultraviolet(EUV)reflectivity measurements, the multilayer structure has been modified for ensuring the peak position of reflectivity was at 46.5 nm. Finally, the narrowband Sc/Si multilayer was successfully deposited on the hyperboloid primary mirror and secondary mirrors. The deviation of multilayer thickness uniformity was below than 1%, and the average EUV reflectivity at 46.1 nm was 27.8% with a near-normal incident angle of 5°. The calculated bandwidth of the reflectivity curve after primary and secondary mirrors was 2.82 nm, which could ensure the requirements of spectral resolution and reflectivity of SUTRI telescope to achieve its scientific goals.

LyαEmission Enhancement Associated with Soft X-Ray Microflares

Lyα(Lyα,1216 A)is the strongest emission line in the solar ultraviolet spectrum.In the present work,we obtained a Lyαenhancement catalog covering flares larger than B1 class from the GOES/EUVS data during 2010-2016.We focused on the 242 B-class events which are less investigated,however,show non-negligible Lyαemission enhancement.We found that on average the Lyαpeak of B-class flares is 0.85%stronger than the background.For the flare energetics,it is found that the weaker the soft X-ray(SXR)flare,the larger the ratio of the radiated energy in Lyαto SXR.Using the RHESSI data and multi-wavelength observations taken by SDO-AIA,we diagnose the thermal and non-thermal properties of several flares.Three case studies show that the coincidence of the Lyαpeak with the SXR time-derivative peak is not a sufficient condition of the nonthermal property of a Lyαmicroflare.The Lyαenhancement in the microflares may be caused by the nonthermal electron beams or/and thermal conduction.However for typeⅢevents,we found that the delay of the Lyαpeak with respect to the SXR peak can be attributed to either the Lyαemission from a filament erupted or the cooling of the thermal plasma in flare loops.Furthermore,interestingly the Lyαemission from filaments can not only occur in the decay phase of the flare,but also in the preflare phase.In this case,the Lyαemission was originated from an erupted filament which probably initiated the flare.

A review of solar type Ⅲ radio bursts

Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.

A New Catalogue of Fine Structures Superimposed on Solar Microwave Bursts

The 2.6-3.8 GHz, 4.5-7.5 GHz, 5.2-7.6 GHz and 0.7-1.5 GHz componentspectrometers of Solar Broadband Radio Spectrometer (SBRS) started routine observations,respectively, in late August 1996, August 1999, August 1999, and June 2000. They just managed tocatch the coming 23rd solar active maximum. Consequently, a large amount of microwave burst datawith high temporal and high spectral resolution and high sensitivity were obtained. A variety offine structures (FS) superimposed on microwave bursts have been found. Some of them are known, suchas microwave type Ⅲ bursts, microwave spike emission, but these were observed with more detail;some are new. Reported for the first time here are microwave type U bursts with similar spectralmorphology to those in decimetric and metric wavelengths, and with outstanding characteristics suchas very short durations (tens to hundreds ms), narrow bandwidths, higher frequency drift rates andhigher degrees of polarization. Type N and type M bursts were also observed. Detailed zebra patternand fiber bursts at the high frequency were found. Drifting pulsation structure (DPS) phenomenaclosely associated with CME are considered to manifest the initial phase of the CME, andquasi-periodic pulsation with periods of tens ms have been recorded. Microwave 'patches', unlikethose reported previously, were observed with very short durations (about 300 ms), very high fluxdensities (up to 1000 sfu), very high polarization (about 100% RCP), extremely narrow bandwidths(about 5%), and very high spectral indexes. These cannot be interpreted with the gyrosynchrotronprocess. A superfine structure in the form of microwave FS (ZPS, type U), consisting of microwavemillisecond spike emission (MMS), was also found.

Statistical study of EUV and X-ray transient brightenings

Using the visual inspection and base difference method and data from the X-ray Telescope （XRT） onboard Hinode and TRACE with improved spatial and temporal resolution, we selected 48 X-ray transient brightenings （XTBs） and 237 EUV transient brightenings （ETBs） to study the connection between these two types of transient brightenings （TBs）. These ETBs and XTBs have smaller areas （8.42 Mm^2 and 36.3 Mm^2, respectively, on average） and shorter durations （9.0 min and 6.9 min, respectively, on average） than previous studies. These XTBs show three types of morphological structure： point-like, single-loop and multiple-loop. We find only 20% of the ETBs have corresponding XTBs while the other 80% have no X-ray signatures at all. This is presumably due to the small amount of released energy, which is not enough to heat the plasma to coronal temperatures which produce X-ray emission rather than being due to the limitation of spatial resolution and temperature sensitivity of the X-ray instrument. These small ETBs may significantly contribute to the coronal heating.

BoxCox multi-output linear regression for 10.7 cm solar radio flux prediction

We consider the problem of predicting the mid-term daily 10.7 cm solar radio flux(F10.7),a widely-used solar activity index.A novel approach is proposed for this task,in which BoxCox transformation with a proper parameter is first applied to make the data satisfy the property of homoscedasticity that is a basic assumption of regression models,and then a multi-output linear regression model is used to predict future F10.7 values.The experiment shows that the BoxCox transformation significantly improves the predictive performance and our new approach works substantially better than the prediction from the US Airforce and other alternative methods like Auto-regressive Model,Multi-layer Perceptron,and Support Vector Regression.

Diagnosing physical conditions near the flare energy-release sites from observations of solar microwave typeⅢbursts

In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy- release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type III burst is believed to be a sensitive signature of primary energy release and electron accelerations in solar flares. This work takes into account the effect of the magnetic field on the plasma density and develops a set of formulas which can be used to estimate the plasma density, temperature, magnetic field near the magnetic reconnection site and particle acceleration region, and the velocity and energy of electron beams. We apply these formulas to three groups of microwave type III pairs in an X-class flare, and obtained some reasonable and interesting results. This method can be applied to other microwave type III bursts to diagnose the physical conditions of source regions, and provide some basic information to understand the intrinsic nature and fundamental processes occurring near the flare energy-release sites.

Observations of EUV and soft X-ray recurring jets in an active region

We present simultaneous observations of three recurring jets in EUV and soft X-ray （SXR）, which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic characteristics in these two different wavelengths, we found that EUV and SXR jets had similar locations, directions, sizes and velocities. We also analyzed their spectral properties by using six spectral lines from the EUV Imaging Spectrometer （EIS） onboard Hinode and found that these jets had temperatures from 0.05 to 2.0MK and maximum electron densities from 6.6× 10^9 to 3.4× 10^10cm^-3. For each jet, an elongated blue-shifted component and a red- shifted component at the jet base were simultaneously observed in the Fe XII A195 and the He II A256 lines. The three jets had maximum Doppler velocities from 25 to 121 km s-1 in the FexII A195 line and from 115 to 232 km s -1 in the HeII A256 line. They had maximum non-thermal velocities from 98 to 181 km s-1 in the Fe xII A195 line and from 196 to 399 km s-1 in the He II A256 line. We also examined the relationship between averaged Doppler velocities and maximum ionization temperatures of these three jets and found that averaged Doppler velocities decreased with the increase of maximum ionization temperatures. In the photosphere, magnetic flux emergences and cancelations continuously took place at the jet base. These observa- tional results were consistent with the magnetic reconnection jet model, implying that magnetic reconnection between emerging magnetic flux and ambient magnetic field occurred in the lower atmosphere.

Historical Dataset Reconstruction and a Prediction Method of Solar 10.7cm Radio Flux

We reconstruct the developing history of solar 10.7 cm radio flux （F10.7） since 1848, based on the yearly sunspot number and the variations. A relationship between the maximum and the linear regression slope of the first 3 years starting from minimum of the solar cycle is considered. We put forward a method of predicting the maximum of F10.7 by means of the slope-maximum relationship. Running tests for cycles 19 to 23 indicate that the method can properly predict the peak of F10.7.

Wavelet Cleaning of Solar Dynamic Radio Spectrograms

By applying the state-of-the-art mathematical apparatus, the wavelet transformation, we explore the possibility of a dynamic cleaning of raw data ob- tained with the Chinese solar radio spectrographs over a wide wavelength range (from 0.7 to 7.6 GHz). We consider the problem of eliminating the interference caused by combination rates of data sampling (10-20 ins), and the low-frequency interference (4-30 s) caused by the receiving equipment changing its characteristics with time. It is shown that the best choice to reconstruct a signal suffering from amplitude, frequency and phase instabilities, is by means of wavelet transformation at both high and low frequencies. We analysed observational data which contained interferences of nonsolar origin such as instrumental effects and other man-made signals. A subsequent comparison of the reference data obtained with the acousto- optical receiver of the Siberian Solar Radio Telescope (SSRT) with the 'cleaned' spectra confirms the correctness of this approach.