The microwave radiation of the corona above a large single sunspot in right- and left-circular polarization

Results of a study of the corona above a large sunspot in the active region NOAA 10105 with a penumbra size of ～70″ observed in September 2002 are reported. Maps of the active region and emission spectra were constructed using observational data from the NoRH, SSRT, and RATAN-600 telescopes. The sizes and brightness temperatures of the microwave emission above the sunspot are determined. SOHO/MDI and Kitt Peak magnetograms, as well as CaII K line images obtained at the Meudon Observatory, are compared. The derived characteristics are interpreted as cyclotron emission of thermal plasma, assuming a dipole structure for themagnetic field. A stable darkening at the sunspot center observed at short wavelengths and only in the ordinary emission mode was detected. A jump-like change was observed in the structure of the sunspot source in the ordinary emission mode, due to an increase in the size and spectral flux density. These results demand a fundamental correction of model concepts about cyclotron emission sources above sunspots, since they are at variance with the initial assumptions. It is suggested that, at the top of the transition region, the cyclotron emission source may be represented only by the third gyrolevel, but is observed in the extraordinary and ordinary emission modes (in contrast to the generally accepted model, which has a combination of the second and third gyrolevels). Taking into account the new observational data may allow us to refine model distributions of the main parameters of the coronal plasma above sunspots (the electron temperature and density) and information about the character of the magnetic field.     

Coronal mass ejection of April 27, 2003, and evolution of the active region NOAA 10338 in the radio

The results of a study of the coronal mass ejection (CME) of April 27, 2003, which was intrinsically associated with the active region NOAA 10338, are reported. Particular attention is paid to the initial stage of the event, which was accompanied by X-ray bursts of class C9.3 and C6.7, with the aim of determining the origin of CMEs. The energy source of the ejection was in the active region NOAA 10338. This region had a complicated and dynamic magnetic-field topology, and produced a series of CME-type events. The basis for the study was observations at wavelengths of 1.92–17 cm with high spatial resolution, 17″–20″, obtained on the Siberian Solar Radio Telescope (SSRT) and RATAN-600, together with simultaneous data from the Nobeyama Radio Heliograph (NoRH, wavelength 1.76 cm) and 195 Å ultraviolet data from the TRACE spacecraft. The development of the event was followed over three hours, first through observations against the disk at heights of 10,000–100,000 km from the photosphere, then in the post-limb stage to distances of the order of 10⁶ km from the solar center, i.e., in the zone inaccessible to the LASCO coronographs. According to the radio observations, ～10 min before the beginning of the event, the radio structure of the active region NOAA 10338 had an S-shaped (sigmoid) configuration. A rising, gradually expanding dark loop originated at the points where this structure was observed; according to the TRACE data, this loop initiated the event. Subsequently, the structure of the radio image drastically changed, suggesting that coronal plasma was heated and cooled at different sites of the emission region (or was shielded by the cooler material of the ejection). Profiles of the burst that accompanied the ejection are presented for four points in the region. The post-limb part of the event first had a compact (～50″) structure receding from the Sun and visible to distances ～10⁶ km. An asymmetric loop was then formed, with its material falling back onto the Sun at the end of the event. The brightness temperature of the loop was ～15 × 10³ K, and its emission was weakly polarized (P ≈16%). The mean speed of the material was 160 km/s. It is concluded that the observations of the event of April 27, 2003 are most consistent with the model of Amari et al., in which the formation of an eruptive twisted magnetic rope, taken to be responsible for CME-type events, is explained by the emergence of new magnetic flux within an old field of opposite polarity.     

Short-period variations in the proper motions of sunspots from SOHO (MDI) observations

Short-period (1–60 min) variations in the coordinates of the centers of gravity of isolated sunspots are analyzed. The sunspot coordinated were determined using two sets of observational data—magnetograms and intensities—obtained by SOHO (MDI) on December 6, 1998, from 01:00 to 21:57 UT with temporal resolution 60 s and spatial resolution 0.6″/pixel. A slow drift in the sunspot coordinates was removed using a low-frequency filter with a 61-min integration window. The guiding errors (RMS～0.014″) were determined by analyzing correlated motions in pairs of sunspots, and were removed from the time series before determining the sunspot proper motions. Based on the calculated power spectra for the sunspot proper motions, two period intervals containing appreciable power were identified. One coincides with the well-known 5-min acoustic solar oscillations. The concentration of power in this interval is greater for the coordinate variations derived the magnetograms than those derived from the intensities; the harmonic amplitude for some peaks reaches ～±30 km. The other spectral interval corresponds to periods exceeding 30 min. Overall, the rms short-period variations in the sunspot proper motions are 9.9±2.2 and 16.7±7.6 km (0.014″±0.003″ and 0.024″±0.010″) for the magnetogram and intensity data, respectively.     

The fast variable maser source IRAS 05338-0624

A new OH maser was detected in January 2008 toward the infrared source IRAS 05338-0624 in the dark cloud L1641N. The observations were carried out on the Nan cay Radio Telescope (France) in the 1667 and 1665 MHz OH lines. In the spectra of both lines, thermal OH emission from the surrounding molecular cloud is present at radial velocities V _LSR = 6–9 km/s. In addition, a narrow maser feature is present in both lines at V _LSR = 2 km/s in the profiles obtained on January 7, 2008; the peak flux densities at 1667 and 1665 MHz are 1.5 and 0.4 Jy, respectively. No OH maser emission was detected in February–July 2008. Then, a maser feature was again observed in the 1665 MHz line on August 20, 2008, at the same velocity as in January, V _LSR = 2 km/s, with a peak flux density of 0.4 Jy. No 1667 MHz counterpart was observed with an upper limit of ～0.1 Jy. Emission in both OH lines was again absent on September 18. The source was also observed in the H₂O line at λ = 1.35 cm on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) on February 7 and 13, 2008. In both cases, a maser feature was detected at V _LSR = 9 km/s, with peak flux densities of 35 and 15 Jy, respectively. After the its apparent absence in April, H₂O maser emission reappeared on May 14, 2008, at V _LSR = 7 km/s with a flux density of about 15 Jy. The history of previous observations of the object in the OH and H₂O lines is traced. The maser displays strong and rapid flux variability in the lines of both molecules, as is typical of young low-luminosity stellar objects at early stages of their evolution.     

Long-term monitoring and interpretation of flares in the H<Subscript>2</Subscript>O maser emission of IRAS 16293–2422

The results of a study of the H₂O and OH maser emission from the cool IR source IRAS 16293?2422 are presented. The observations analyzed were obtained in H₂O lines with the 22-m telescope of the Pushchino Radio Astronomy Observatory during 1999–2015 and in OH lines with the Nanc¸ ay radio telescope (France). A large number of very strong flares of the H₂O maser were detected, reaching fluxes of tens of thousands of Jansky. Individual features can form organized structures resembling chains ～2 AU in length with a radial-velocity gradient along them. The observed drift of the H₂O emission (2003–2004) in space and velocity (from 4.3 to 5.3 km/s) is not due solely to proper motion of the features. The other origin of the drift is a drift of the emission maximum during a flare as the shock consecutively excites spatially separated features in the structure in the form of a chain. The OH-line observations at 18 cm show that the emission remains unpolarized and thermal, with a line width of 0.7 km/s, which corresponds to a cloud temperature of ～30 K.     

The Hydrogen and Helium Lines of the Symbiotic Binary Z And during Its Brightening at the End of 2002

High resolution observations in the region of the Hα, HeII λ 4686, and Hγ lines in the spectrum of the symbiotic binary Z And were performed during a small-amplitude flare at the end of 2002. The profiles of the hydrogen lines were double-peaked, and suggest that the lines may be emitted mainly by an optically thin accretion disk. Since the Hα line is strongly contaminated by emission from the envelope, the Hγ line is used to investigate the properties of the accretion disk. The Hα line has broad wings, believed to be determined mostly by radiation damping, although the high-velocity stellar wind from the compact object in the system may also contribute. The Hγ line has a broad emission component, assumed to be emitted mainly from the inner part of the accretion disk. The HeIIλ 4686 line also has a broad emission component, but is believed to arise in a region of high-velocity stellar wind. The outer radius of the accretion disk can be calculated from the shift between the peaks. Assuming that the orbital inclination can range from 47° to 76°, we estimate the outer radius to be 20–50 R_⨀. The behavior of the observed lines can be interpreted in the model proposed for the line spectrum during the first large 2000–2002 flare of this binary.     

Search for H<Subscript>2</Subscript>O Maser Flares in Regions of Formation of Massive Stars

Results of systematic observations of a sample of bright H₂O maser sources with fluxes, on average, exceeding 200 Jy in their main spectral feature during April–September 2017 (G25.65+1.05, G25.825?0.178, G27.184?0.082, G34.403+0.233, G35.20?0.74, G43.8?0.13, G107.30+5.64) are presented. These observations were carried out in preparation for Very Long Baseline Interferometry observations with an array including the Crimean Astrophysical Observatory 22-m radio telescope. All these sources display fairly strong variability during the time interval considered, encompassing fluxes from ～40 to ～2300 Jy. A flare reaching ～17 000 Jy was detected at a velocity of 42.8 km/s in G25.65+1.05 on September 7, 2017, which subsequently grew to 60 000 Jy at the end of September 2017. This suggests the presence of compact maser structures. The velocities covered by various spectral components range from 5 to 20 km/s. In three sources (G25.65+1.05,G25.825?0.178,G35.20?0.74), a general growth in the fluxes of all the spectral features is observed, which may indicate variations in the conditions for pumping by an external source, for example, variations in the infrared flux from a central source or the passage of a shock. Possible evidence for the presence of bipolar outflows or disk structures in G25.65+1.05 is discussed.     

Detection of a cyclotron line in the radio spectrum of a solar active region and its interpretation

Observations of the active region AR 7962 obtained at 2–32 cm on the RATAN-600 radio telescope on May 10–12, 1996, are presented. The high-resolution measurements detected a narrow feature near 8.5 cm against the background of the smooth spectrum of the local source associated with sunspots. This narrow-band emission is identified with a bright, pointlike, high-frequency source at 1.7 cm recorded on maps made using the Nobeyama radio telescope. The characteristics of the observed line (lifetime 3 days, brightness temperature of the order of several million Kelvin, relative width of about 10%) suggest that it can be explained as thermal cyclotron radiation at the third harmonic of the electron gyrofrequency from a compact source containing a dense, hot plasma; the corresponding higher frequency emission could be due to thermal Bremsstrahlung. Analysis of the RATAN-600 and Nobeyama data can be used to probe the magnetic field, kinetic temperature, and electron density in the radiation source in the corona.     

The three-dimensional structure of the corona above active region NOAA 9591 from microwave observations

We study the active region NOAA 9591 using observations at 1.92–10.17 cm obtained on two large Russian radio instruments: the RATAN-600 radio telescope and the Siberian Solar Radio Telescope. The active region was associated with an isolated spot at the photospheric level, whose magnetic field had a well-defined Delta configuration. The radio observations show that the structure of the coronal source located above the spot cannot be described in a simple (unipolar) cyclotron model. A comparison with X-ray observations indicates that the three-dimensional structure of the corona above the spot can be represented as a strongly elongated loop whose apex resembles a cusp brightening (a qualitative model for the structure is presented). Unexpectedly, radiation with a high degree of polarization (～25%) was detected far (～100 000 km) from the photosphere. The need for a quantitative model for coronal sources above the strong Delta-configuration magnetic fields, which are known to play an important role in active solar processes (flares, phenomena such as coronal-mass ejections) is outlined. Thanks to its simple morphology, which enabled the identification of a pure Delta configuration, the active region NOAA 9591 provides high-quality observational material for the creation of such a model.     

Regions of primary energy release of solar flares associated with singularities in the magnetic field

The locations of sites of primary energy release of solar flares are studied. Magnetic singularities revealed earlier—self-intersections (reconnections) of F = 0 surfaces, where F is a differential factor determining the structural singularity in a potential magnetic field—are considered as possible sites of energy release. Six flare events demonstrating paired sources of non-thermal hard X-rays emission observed on March 17, 2002, July 17, 2002, April 6, 2004, November 4, 2004, November 6, 2004, and December 1, 2004 are analyzed for probable singularities. In each event analyzed, each source of non-thermal hard X-rays emission can be associated with an individual magnetic singularity; in other words, there is a magnetic-field line passing near the singularity and ending near (i.e. within about 10″) the source located on the photosphere (in the chromosphere). For the homologous flares observed on November 4 and 6, 2004, the same magnetic singularity is responsible for the source of non-thermal hard X-rays emission observed in the eastern sector of the flare region on November 4 and the source observed in the western part on November 6. A proposed interpretation associates these observations with a reversal of the electric field generated in the magnetic singularity on November 6, compared with the electric field generated on November 4, attributed to corresponding changes occurring in the photospheric magnetic field.     

When and where are solar cosmic rays accelerated most efficiently?

The acceleration of particles by solar flares with extremely large proton fluxes whose energies exceed 100 MeV is considered. Most importantly, the location of the source of such acceleration in the flare of July 14, 2000, is determined assuming that the acceleration time coincides with the observed burst of hard line and continuous gamma-ray emission. The onset of this event corresponds to 10:19 UT, when data taken by the TRACE space observatory show that one of the flare ribbons reached a large sunspot in a group. The time interval for the development of the flare, 10:20–10:28 UT, is associated with the beginning of an increasing proton flux at the Earth. The region of efficient acceleration is estimated to be approximately two to three times higher than the height where the hard X-ray pulse usually originates (about 7000 km). The results are generalized for 28 powerful flares with extremely efficient acceleration of relativistic particles—in particular, for the well-studied events of June 15, 1991, and May 24, 1990—and are compared with the results of a statistical analysis of over 1100 increasing-proton-flux events. Efficient particle acceleration seems to be associated with the powerful impulsive episodes of the large flares analyzed. The results suggest that, along with sources of local (as in impulsive flares) and post-eruptive acceleration, there is an additional, very efficient, moderate-scale “accelerator” in tenuous regions with fairly strong magnetic fields and magnetic-field gradients.     

Long-term oscillations in solar active regions based on magnetic fields and radio emission

A comparative analysis of sunspot oscillations and related radio sources in the active regions AR 8949, AR 8951, and AR 8953 is carried out using SOHO MDI data and simultaneous observations with the Nobeyama Radioheliograph, with a one-minute time resolution on scales of tens to hundreds of minutes. The radio sources in the selected active regions are ～40 000–60 000 km away from the corresponding spots, with the periods of long-term oscillations of the radio sources being ～12% longer.     

表层岩溶系统中土-气-水界面碳流通的短尺度效应——以贵州茂兰国家喀斯特森林公园的秋季日动态监测为例

在2001年秋季对贵州省荔波县茂兰国家喀斯特森林公园林地、草地植被下土壤CO₂呼吸释放及岩溶表层泉水HCO₃及其^δ13C值的变化进行了日动态的野外监测,表明岩溶系统中土-气-水界面间存在着碳交换的日动态变化以及所伴随的同位素交换的变化,这种变化与土温的日动态有密切的关系。林地植被显示了平抑这种日动态幅度的效应,而草地植被则显示响应于温度变化的较灵敏的动态变化。这种短尺度的变化构成了表层岩溶系统对外界条件的灵敏响应,进一步揭示了在生物作用下岩溶地质作用在碳循环过程及其同位素交换上的灵敏性和动态性。其不同植被系统下的日动态差异在解释岩溶沉积记录和讨论岩溶作用与碳循环时值得充分注意     

Superflares of H<Subscript>2</Subscript>O Maser Emission Toward the Protostellar Object G25.65+1.05 (IRAS 18316−0602)

The results of a study of the maser source IRAS 18316?0602 in the H₂O line at λ = 1.35 cm are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from June 2002 until March 2017. Three superflares were detected, in 2002, 2010, and 2016, with peak flux densities of >3400, 19 000, and 46 000 Jy, respectively. An analysis of these superflares is presented. The flares took place during periods of high maser activity in a narrow interval of radial velocities (40.5–42.5 km/s), and could be associated with the passage of a strong shock. The emission of three groups of features at radial velocities of about 41, 42, and 43 km/s dominated during themonitoring. The flare in 2016 was accompanied by a considerable increase in the flux densities of several features with velocities of 35–56 km/s.     

Solar cyclicity during the Maunder minimum

A multifaceted statistical study of all available data on solar activity during the Maunder minimum (1645–1715) is presented. The data include European telescope observations, Asian sunspot observations using the unaided eye, concentrations of cosmogeneous isotopes, and catalogues of polar aurorae. Joint analyses of data on the cosmogeneous isotopes ¹⁰Be and ¹⁴C are a promising source of information on solar activity in the past. The dates of relative sunspot maxima during the Maunder minimum are consistent with the idea that there were chaotic bursts of solar activity randomly distributed in time during this interval. The available evidence that the 11-year cyclicity was preserved in 1645–1715 are worthy of attention but require additional deep study and verification. No convincing evidence for a 22-year periodicity of the occurrence of sunspots during the Maunder minimum has been found.     

Magnetic-field variations and solar flare activity

Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H?? line are used to study variations in filaments, in particular, in arch filament systems (AFSs). These are considered as an indicator of emerging new magnetic flux, providing information about the spatial locations of magnetic-field elements. Magnetic-field maps for the active region NOAA 10030 are analyzed as an example. A method developed earlier for detecting elements of emerging flux using SOHO/MDI magnetograms indicates a close link between the increase in flare activity in theNOAA 10030 group during July 14?C18, 2002 and variations in the topological disconnectedness of the magnetograms. Moreover, variations in the flare activity one day before a flare event are correlated with variations in the topological complexity of the field (the Euler characteristic) in regions with high field strengths (more than 700 G). Analysis of multi-wavelength polarization observations on the RATAN-600 radio telescope during July 13?C17, 2002 indicate dominance of the radio emission above the central spot associated with the increase in flare activity. In addition to the flare site near the large spot in the group, numerous weak flares developed along an extended local neutral line, far from the central line of the large-scale field. The statistical characteristics of the magnetic-field maps analyzed were determined, and show flare activity of both types, i.e., localized in spot penumbras and above the neutral line of the field.     

Observational manifestations of gaseous baryon dark matter

The paper considers possible observational implications of the presence of dark matter in the Galaxy in the form of dense gas clouds—clumpuscules with masses M _c ～10^?3 M _⊙ and radii R _c～3×10¹³ cm. The existence of such clouds is implied by modern interpretations of extreme scattering events—variations in quasar radio fluxes due to refraction in dense plasma condensations in the Galactic halo. The rate of collisions between these clouds is shown to be rather high: from 1 to 10M _⊙ per year is ejected into the interstellar medium as a result of such collisions. The optical continuum and 21-cm emission from hot post-collision gas could be observable. Gas clouds composed of dark matter could be formed around O stars in an H II region with radius R～30 pc and emission measure EM?20 cm^?6 pc. They could also be observable in the H_α line. The evaporation of clumpuscules by external ionizing radiation could be a substantial source of matter for the interstellar medium. Assuming that the total mass of matter entering the interstellar medium over the Hubble time does not exceed the mass of luminous matter in the Galaxy, upper limits are found for the cloud radii (R _c<3.5×10¹² cm) and the contribution of clouds to the surface density of the Galaxy (<50M _⊙pc^?2). Dissipation of the kinetic energy of matter lost by clumpuscules could provide an efficient mechanism for heating gas in the Galactic halo.     

Map of the 6.7 GHz class II methanol maser emission of the protoplanetary disk G23.01-0.41

We present images of the star-forming regionG23.01–0.41 at 6.7GHz in the Class II methanol maser transition 5₁–6₀ A ⁺, produced from archival observations on the European VLBI Network. Our map of the source and its maser spots contains 24 maser components. The data for each spot—absolute coordinates, coordinates relative to the calibration feature, peak flux and flux integrated over the spot, size, position angle, velocity along the line of sight, and line full width at half-maximum—are collected in tabular form. The spatial region occupied by the maser spots is approximated by a 200×130 milliarcsec ellipse in position angle PA = −0.40°, centered on the absolute coordinates α ₀ = 18^h34^m40.282^s, δ ₀ = −09°00′38.27″ (J2000). If the source is a protoplanetary disk, then, for the distance estimate derived from trigonometric parallax, its diameter is 1800 AU, and the mass of the central protostar is 23.5M _⊙.     

An Unusually Powerful Water-Maser Flare in the Galactic Source W49N

The most powerful flare ever registered in the Galactic water-maser source W49N has been detected in long-term monitoring data in the 6₁₆–5₂₃ transition with line frequency f = 22.235 GHz carried out on the 22-m Simeiz, 32-m Toruń, 100-m Effelsberg, and 32-m Medicina radio telescopes, beginning in September 2017 and continuing in 2018. Some stages of the flare were monitored daily. Detailed variations of the source spectral flux density with time have been obtained. At the flare maximum, the flux exceeded P ≈ 8 × 10⁴ Jy, and this was record highest flux registered over the entire history of observations of this source. Important conclusions related to details of the mechanism for the H₂O line emission have been drawn. An exponential increase in the flare flux density was detected during both the rise and decline of the flare. The data obtained indicate that the maser is unsaturated, and remained in this state up to the maximum observed flux densities. Additional support for the idea that the maser is unsaturated is the shape of the dependence of the line width on the flux. The characteristics of the variations of the spectral flux density are probably associated with a sharp increase in the density of the medium and the photon flux that led to an increase in the temperature from an initial level of 10–40 K to hundreds of Kelvins. Interferometric maps of the object during the increase in the spectral flux density of the flare have been obtained. A possible mechanism for the primary energy release in W49N is considered.

     

A RATAN-600 Zenith-Field sky survey. Catalog of radio sources

A catalog of radio sources detected in a deep RATAN-600 survey is presented. The catalog was obtained in the region 0^h ≤ RA_2000.0 ≤ 24^h, Dec_2000.0 = 41°30′42″ ± 2′, at the declination of the bright radio source 3C 84. There were nine sessions of multi-wavelength observations at wavelengths λ = 1–55 cm, and more than 300 daily scans were accumulated at each wavelength. This is the first stage in the reduction of an extensive database accumulated by the Cosmological Gene Project. The RATAN-600 Zenith Field (RZF) catalog was obtained at the central wavelength of 7.6 cm, and contains 437 radio sources, virtually all of which have been identified with NVSS objects. Most of the flux densities for the catalog sources are above the 5σ level. Noise from faint (mainly new) background sources at a level of about 0.8 mJy has been detected. The minimum flux density of the catalog, 2.5 mJy, is comparable to the flux-density linit of the NVSS catalog. The catalog is more than 80% complete for sources with flux densities >3 mJy.