A synchrotron self-Compton scenario for the very high energy γ-ray emission of the intermediate BL Lacertae object W Comae

W Comae has significant variability in multi-wavelengthes, from radio to gamma-ray bands. A bright outburst in optical and X-ray bands was observed in 1998, and most recently, a strong TeV flare was detected by VERITAS in 2008. It is the first TeV intermediate-frequency-peaked BL Lacertae source. I find that both the broadband spectral energy distributions （SEDs） which were quasi-simultaneously obtained during the TeV flare and during the optical/X-ray outburst are well fit by using a single-zone synchrotron ＋ synchrotron-self-Compton model. The satisfactory fitting requires a large beaming factor, i.e., δ- 25 and δ- 20 for the TeV flare and the optical/X-ray outburst, respectively, suggesting that both the optical/X-ray outburst and the TeV flare are from a relativistic jet. The size of the emission region of the TeV flare is three times larger than that of the optical/X-ray outburst, and the strength of the magnetic field for the TeV flare is - 14 times smaller than that of the X-ray/optical outburst, likely indicating that the region of the TeV flare is more distant from the core than that of the X-ray/optical outburst. The inverse Compton component of the TeV flare peaks around 1.3 GeV, but it is around 20 MeV for the X-ray/optical outburst, lower than that for the TeV flare by two orders of magnitude. The model predicts that the optical/X-ray outburst might be accompanied by a strong MeV/GeV emission, but the TeV flare may be not associated with the X-ray/optical outburst. The GeV emission is critical for characterizing the SEDs of the optical/X-ray outburst and the TeV flare. The predicted GeV flux is above the sensitivity of Fermi/LAT, and it could be verified with the observations by Fermi/LAT in the near future.     

High energy properties of the flat spectrum radio quasar 4C 50.11

We investigate theγ-ray and X-ray properties of the flat spectrum radio quasar(FSRQ)4C 50.11 at redshift z=1.517.The Fermi-LAT data indicate that this source was in an active state since July 2013.During this active period,the source’s emission appeared harder inγ-rays,with the flux having increased by more than a factor of three.We analyze two distinct flares seen in the active state and find that the variability is as short as several hours.The Swift-XRT data show that the source was variable at X-ray energies,but no evidence is found for flux or spectral changes related to theγ-ray activity.The broad-band X-ray spectrum obtained with Swift-XRT and Nu STAR is described well by a broken power law model,with an extremely flat spectrum(Γ_1~0.1)below the break energy,E_(break)~2.1 keV,and Γ_2~1.5 above the break energy.The spectral flattening below~3 keV is likely due to the low energy cut-off in the energy distribution of the photon-emitting electron population.We fit the broad-band spectral energy distribution of the source during both the active and quiescent states.The X-ray andγ-ray emission from the jet is mainly due to the inverse-Compton scattering process,with seed photons provided from the broad line region,and the jet is estimated to be larger than the accretion power if the jet is mainly composed of electron-proton pairs.     

Highly variable γ-ray emission of CTD 135 and implications for its compact symmetric structure

The γ-ray emission properties of CTD 135,a typical compact symmetric object(CSO),are investigated with ～11-year Fermi/LAT observations.We show that it has bright and significantly variable GeV emission,with the γ-ray luminosity of L_γ～ 10~(47) erg s~(-1) and a variation index of TS_(var)=1002.A quasi-periodic oscillation(QPO) with a periodicity of ～460 days is detected in the global 95% false-alarm level.These γ-ray emission features are similar to that of blazars.Its broadband spectral energy distribution(SED) can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region.The SED modeling shows that the γ-rays are from the core region,which has a Doppler boosting factor of δ～10.8 and relativistically moves with a small viewing angle,being similar to blazar jets.On the base of the analysis results,we propose that the episodic activity of the central engine in CTD135 results in a blazar-like jet and the bubble-like lobes as the Fermi bubbles in the Galaxy.The strong 7-ray emission with obvious variability is from the jet radiations and the symmetric radio structure is attributed to the bubbles.The jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio sources,indicating that its jet radiation may also be driven by the Eddington ratio.     

Fermi/LAT observations of lobe-dominant radio galaxy 3C 207 and possible radiation region of γ-rays

3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data acquired during the past 9 years. Different from the radio and optical emission from the core, it is found that theγ-ray emission is steady without detection of flux variation at over a 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical and X-ray data of knot-A,the closest knot from the core at 1.4′′, and compile its spectral energy distribution(SED). Although the single-zone synchrotron+SSC+IC/CMB model that assumes knot-A is at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates from the equipartition condition by 3 orders of magnitude. Assuming that knot-A is moving relativistically, its SED from radio to γ-ray bands would be represented well with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition. These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with radio data.     

Study of temporal and spectral characteristics of the X-ray emission from solar flares

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer(SOXS) during 2003–2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride(CZT)detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation(R ≈0.2) between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated(R = 0.61) with the rise time of the flares while positively correlated(R = 0.28) with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25–30 keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure(DEM) evolution is delayed by 60–360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.     

BL Lacertae： Hard Optical Spectrum and GeV γ-ray Emission

The spectral energy distribution (SED) of the γ-ray flare observed in July 1997 in BL Lacertae is re-considered. It is pointed out that the optical observations made by Webb et al. showed the associated optical flare has a hard spectrum (the average spectral index αopt～0.48, Fν∝ν^-α), and the ASCA observations made by Tanihata et al. showed very steep spectra in the soft X-ray band (0.7-1.5 keV) (αx～3-4). We find that the flux densities and spectral indices in both the optical and soft X-ray bands are closely consistent with a ‘canonical‘ synchrotron spectrum emitted by relativistic electrons of a power-law energy distribution with a high energy cutoff, and thus the peak of the SED of the synchrotron radiation (in representation of νFν) is located in the EUV - soft X-ray bands. Therefore, the GeV γ-ray emission observed in the July 1997 outburst may be mainly due to the synchrotron self-Compton (SSC) process, contrasting with the current explanations in terms of external radiation Compton (ERC) process, in which the seed photons are mostly taken to be the UV emission from the clouds of the broad emission line region. We argue that the hard optical spectra observed during the γ-ray outburst may be an important signature for the acceleration of high energy electrons (γe-10^4) in the γ-ray emitting region.     

On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk.The first major flare(of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 around 01:50 UT.We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager(HMI) instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare.The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5 spatial scale at a cadence of 45 s along with imaging spectroscopy.We have identified five locations of velocity transients in the active region during the flare.These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12–25 keV from RHESSI.The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations.Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength,Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.     

Analysis of sudden variations in photospheric magnetic fields during a large flare and their influences in the solar atmosphere

The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A? acquired by the Helioseismic and Magnetic Imager(HMI) onboard the Solar Dynamics Observatory(SDO) spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Hα 6562.8 A? by the Global Oscillation Network Group(GONG) to study the evolution of flareribbons and intensity oscillations in this active region. The Hα intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.     

Flux and spectral variation characteristics of 3C 454.3 at the GeV band

We analyze the long-term lightcurve of 3C 454.3 observed with Fermi/LAT and investigate its relation to flux in the radio,optical and X-ray bands.By fitting the 1-day binned Ge V lightcurve with multiple Gaussian functions(MGF),we propose that the typical variability timescale in the Ge V band is 1–10 d.The Ge V flux variation is accompanied by the spectral variation characterized as fluxtracking,i.e.,"harder when brighter."The Ge V flux is correlated with the optical and X-ray fluxes,and a weak correlation betweenγ-ray flux and radio flux is also observed.Theγ-ray flux is not correlated with the optical linear polarization degree for the global lightcurves,but they show a correlation for the lightcurves before MJD 56000.The power density spectrum of the global lightcurve shows an obvious turnover at~7.7 d,which may indicate a typical variability timescale of 3C 454.3 in theγ-ray band.This is also consistent with the derived timescales by fitting the global lightcurve with MGF.The spectral evolution and an increase in the optical linear polarization degree along with the increase inγ-ray flux may indicate that the radiation particles are accelerated and the magnetic field is ordered by the shock processes during the outbursts.In addition,the nature of 3C 454.3 may be consistent with a self-organized criticality system,similar to Sagittariusand thus the outbursts could be from plasmoid ejections driven by magnetic reconnection.This may further support the idea that the jet radiation regions are magnetized.     

Jet-dominated quiescent state in black hole X-ray binaries: the cases of A0620–00 and XTE J1118+480

The radiative mechanism of black hole X-ray transients(BHXTs) in their quiescent states(defined as the 2–10 ke V X-ray luminosity 10~(34) erg s~(-1)) remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum(including radio, infrared, optical, ultraviolet and X-ray)of two BHXTs, A0620–00 and XTE J1118+480. We find that these two sources can be well described by a coupled accretion – jet model. More specifically, most of the emission(radio up to infrared, and the X-ray waveband) comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared(the synchrotron peak). Emission from the outer cold disk is only evident in the UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg and confirm that the quiescent state is jet-dominated.     

Comparison between the eruptive X2.2 flare on 2011 February15 and confined X3.1 flare on 2014 October 24

We compare two contrasting X-class flares in terms of magnetic free energy, relative magnetic helicity and decay index of the active regions(ARs) in which they occurred. The events in question are the eruptive X2.2 flare from AR 11158 accompanied by a halo coronal mass ejection(CME) and the confined X3.1 flare from AR 12192 with no associated CME. These two flares exhibit similar behavior of free magnetic energy and helicity buildup for a few days preceding them. A major difference between the two flares is found to lie in the time-dependent change of magnetic helicity of the ARs that hosted them. AR 11158 shows a significant decrease in magnetic helicity starting ～4 hours prior to the flare, but no apparent decrease in helicity is observed in AR 12192. By examining the magnetic helicity injection rates in terms of sign, we confirmed that the drastic decrease in magnetic helicity before the eruptive X2.2 flare was not caused by the injection of reversed helicity through the photosphere but rather the CME-related change in the coronal magnetic field. Another major difference we find is that AR 11158 had a significantly larger decay index and therefore weaker overlying field than AR 12192. These results suggest that the coronal magnetic helicity and the decay index of the overlying field can provide a clue about the occurrence of CMEs.     

Flare-induced signals in polarization measurements during the X2.6 flare on 2005 January 15

Flare-induced signals in polarization measurements which were manifested as apparent polarity reversal in magnetograms have been reported since 1981. We are motivated to further quantify the phenomenon by asking two questions： can we distinguish the flare-induced signals from real magnetic changes during flares, and what we can learn about flare energy release from the flare-induced signals？ We select the X2.6 flare that occurred on 2005 January 15, for further study. The flare took place in NOAA active region （AR） 10720 at approximately the central meridian, which makes the interpretation of the vector magnetograms less ambiguous. We have identified that flare-induced signals during this flare appeared in six zones. The zones are located within an average distance of 5 Mm from their weight center to the main magnetic neutral line, have an average size of （0.6±0.4） ×10^17 cm^2, duration of 13±4 min, and flux density change of 181±125 G in the area of reversed polarity. The following new facts have been revealed by this study： （1） the flare-induced signal is also seen in the transverse magnetograms but with smaller magnitude, e.g., about 50 G; （2） the flare-induced signal mainly manifests itself as apparent polarity reversal, but the signal starts and ends as a weakening of flux density; （3） The flare-induced signals appear in phase with the peaks of hard X-ray emission as observed by the Ramaty High Energy Solar Spectroscopic Imager （RHESSI）, and mostly trace the position of RHESSI hard X-ray footpoint sources. （4） in four zones, it takes place cotemporally with real magnetic changes which persist after the flare. Only for the other two zones does the flux density recover to the pre-flare level immediately after the flare. The physical implications of the flare-induced signal are discussed in view of its relevance to the non-thermal electron precipitation and primary energy release in the flare.     

An Annular Gap Acceleration Model for γ-ray Emission of Pulsars

If the binding energy of the pulsar's surface is not so high (the case of a neutron star), both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for γ-ray emission of pulsars is suggested. It is emphasized that: (1) Two kinds of acceleration regions (annular and core) need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. (2) If the potential drop in the annular region of a pulsar is high enough (normally the case for young pulsars), charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. (3) The potential drop grows more rapidly in the annular region than in the core region. The annular acceleration process is a key process for producing the observed wide emission beams. (4) The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the γ-ray emission from the annular flow are analogous to that pre-sented in a previous work by Qiao et al., which match the observations well. (5) Since charges with different signs leave the pulsar through the annular and the core regions respectively, the current closure problem can be partially solved.     

The GeV emission of PSR B1259–63 during its last three periastron passages observed by Fermi-LAT

PSR B1259–63 is a γ-ray emitting high mass X-ray binary system, in which the compact object is a millisecond pulsar.The system has an orbital period of 1236.7 d and shows peculiar γ-ray flares when the neutron star moves out of the stellar disk of the companion star.The γ-ray flare events were firstly discovered by using Fermi-LAT around the 2010 periastron passage, which was repeated for the 2014 and 2017 periastron passages.We analyze the Fermi-LAT data for all the three periastron passages and found that in each flare the energy spectrum can be represented well by a simple power law.The γ-ray light curves show that in 2010 and 2014 after each periastron there are two main flares,but in 2017 there are four flares including one precursor about 10 d after the periastron passage.The first main flares in 2010 and 2014 are located at around 35 d after the periastron passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to that in 2010.In the 2017 flare, the source shows a precursor about 10 d after the periastron passage, but the following two flares become weaker and lag behind those in 2010 by roughly 5 d.The strongest flares in 2017 occurred 58 d and 70 d after the periastron passage.These results challenge the previous models.     

Observational Characteristics of Radio Emission Related to Multi-polar Magnetic Configuration

We present a, large complex radio burst and its associated fast tune structures observed on 2001 April 10 in the frequency range of 0.65-7.6 GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar (a 'bipolar + remote unipolar'), and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a 'Y-type' re-connection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type III bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a 'three-legged' structure, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the 'inverted Y-type' (bipolar) and the 'three-legged' structures (tripolar or quadrupolar).     

New CCD photometric investigation of the early-type overcontact binary BH Cen in the young star-forming Galactic cluster IC 2944

BH Cen is a short-period early-type binary with a period of 0.792 din the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A_3 = 0.024 d and a period of P_3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M_2 = 2.8×10~(-6) M_⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M_⊙at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.     

A magnetic confinement nuclear fusion mechanism for solar flares

We propose a magnetic confinement nuclear fusion mechanism for the evolution of a solar flare in the solar atmosphere.The mechanism agrees with two observed characteristics of explosive flares and coronal mass ejections(CMEs) that have proved to be very difficult to explain with previous mechanisms:the huge enrichments of3 He and the high energy gamma ray radiation.The twisted magnetic flux rope is a typical structure during the solar flares,which is closely related to the solar active region that magnetic fields have almost complete control over the plasma.Consequently,the plasma inside the flux rope is heated to more than 1.0×107 K by an adiabatic compression process,and then the thermonuclear fusion can take place in the flux rope accompanied with high energy gamma rays.We utilize the time-dependent ideal 2.5-dimensional magnetohydrodynamic(MHD) simulation to demonstrate the physical mechanism for producing flares,which reveals three stages of flare development with the process of magnetic energy conversion and intense release during the solar flares and CMEs in the solar atmosphere.Furthermore,we discuss the relationship between magnetic reconnection and solar eruptions.     

Superpenumbral chromospheric flare

We observed a C-class flare at the outer boundary of the superpenumbra of a sunspot. The flare was triggered by an emerging magnetic bipolar region that was obliquely oriented with respect to the superpenumbral fibrils. The flare started due to the low height magnetic reconnection of emerging magnetic flux with a superpenumbral field resulting in hot multi-temperature plasma flows in the inverse Evershed flow channel and its overlying atmosphere. Inverse Evershed flows in the chromosphere start from the superpenumbra towards the sunspot that end at the outer boundary of the penumbra. The hot plasma flow towards the sunspot in the inverse Evershed channels show about 10 km s~(-1) higher velocity in Hα wavelengths compared to the plasma emissions at various temperatures as seen in different AIA filters. Even though these velocities are about seven times higher than the typical inverse Evershed flow speeds, the flow is diminished at the outer boundary of the sunspot's penumbra. This suggests that the superpenumbral field lines that carry inverse Evershed flows are discontinued at the boundary where the penumbral field lines dive into the sun and these two sets of field lines are completely distinct. The discontinuity in the typical magnetic field and plasma properties at the adjoining of these two sets of field lines further leads to discontinuity in the characteristic magnetoacoustic and Alfv′en speeds, thereby stopping the plasma flows further on. The multi-temperature plasma in the inverse Evershed channels exhibits possible longitudinal oscillations initially during the onset of the flare, and later flows towards the sunspot. In the multi-temperature view, the different layers above the flare region have a mixture of supersonic as well as subsonic flows.     

Solar flares： radio and X-ray signatures of magnetic reconnection processes

This review summarizes new trends in studies of magnetic reconnection in solar flares. It is shown that plasmoids play a very important role in this primary flare process. Using the results of magnetohydrodynamic and particle-in-cell simulations, we describe how the plasmoids are formed, how they move and interact, and how a flare current sheet is fragmented into a cascade of plasmoids. Furthermore, it is shown that during the interactions of these plasmoids electrons are not only very efficiently accelerated and heated, but electromagnetic（radio） emission is also produced.We also describe possible mechanisms for the triggering of magnetic reconnection.The relevant X-ray and radio signatures of these processes（such as radio drifting pulsation structures, narrowband dm-spikes, and the loop-top and above-the-loop-top X-ray sources） are then described. It is shown that plasmoids can also be formed in kinked magnetic ropes. A mapping of X-points of the magnetic reconnection on the chromosphere（as e.g. a splitting of flare ribbons） is mentioned. Supporting EUV and white-light observations of plasmoids are added. The significance of all these processes for the fast magnetic reconnection and electron acceleration is outlined. Their role in fusion experiments is briefly mentioned.     

Flare evolution and polarization changes in fine structures of solar radio emission in the 2013 April 11 event

The measurement of positions and sizes of radio sources in observations is important for understanding of the flare evolution. For the first time, solar radio spectral fine structures in an M6.5 flare that occurred on 2013 April 11 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometer at Huairou(SBRS/Huairou), Ondˇrejov Radio Spectrograph in the Czech Republic(ORSC/Ondˇrejov), Badary Broadband Microwave Spectropolarimeter(BMS/Irkutsk), and spectrograph/IZMIRAN(Moscow, Troitsk). The fine structures included microwave zebra patterns(ZPs), fast pulsations and fiber bursts. They were observed during the flare brightening located at the tops of a loop arcade as shown in images taken by the extreme ultraviolet(EUV) telescope onboard NASA's satellite Solar Dynamics Observatory(SDO). The flare occurred at 06:58–07:26 UT in solar active region NOAA 11719 located close to the solar disk center. ZPs appeared near high frequency boundaries of the pulsations, and their spectra observed in Huairou and Ondˇrejov agreed with each other in terms of details. At the beginning of the flare's impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed in almost unpolarized emission. After 07:00 UT a ZP appeared with a moderate right-handed polarization.In the flare decay phase(at about 07:25 UT), ZPs and fiber bursts become strongly right-hand polarized.BMS/Irkutsk spectral observations indicated that the background emission showed a left-handed circular polarization(similar to SBRS/Huairou spectra around 3 GHz). However, the fine structure appeared in the right-handed polarization. The dynamics of the polarization was associated with the motion of the flare exciter, which was observed in EUV images at 171 ?A and 131 ?A by the SDO Atmospheric Imaging Assembly(AIA). Combining magnetograms observed by the SDO Helioseismic and Magnetic Imager(HMI) with the homologous assumption of EUV flare brightenings and ZP bursts, we deduced that the observed ZPs correspond to the ordinary radio emission mode. However, future analysis needs to verify the assumption that zebra radio sources are really related to a closed magnetic loop, and are located at lower heights in the solar atmosphere than the source of pulsations.