The effective technique of the charged particles background discrimination in the atmospheric Cherenkov light detectors

It is shown that parameters of flashes, detected by multichannel image cameras of Cherenkov detectors with closed lids are close to those of Cherenkov flashes initiated by VHE gamma-quanta in the Earth atmosphere. Even after application of criteria for gamma-like events selection a considerable part of those flashes may be misclassified and accepted as gammas. Since the flashes of this kind are detected also during normal measurements with the opened lids of image cameras it just increases the background and, as a consequence, decreases the detector sensitivity even when one uses an anticoincidence scintillator shield around the camera (its efficiency is about 75 %). The use of detectors consisting of two (or more) sections no less than 20–30 m apart permits us to avoid the detection of both muon and local charged particles flashes in the course of observations.     

Fermi耀变体的gamma射线多波段辐射与射电辐射的关系

从Fermi 3期源表(3FGL)中选择了一个含935个耀变体(blazar)的样本, 包括415个平谱射电源(Flat Spectrum Radio Quasar, FSRQ), 520个蝎虎天体(BL Lac object, BL Lac), 其中高同步峰BL Lac (HBL) 233个, 中同步峰BL Lac (IBL) 144个, 低同步峰BL Lac (LBL) 143个. 研究了总样本、FSRQ、BL Lac及其子类HBL、LBL的射电1.4GHz 与gamma射线在0.1、0.3、1、3、10GeV处辐射流量密度的关系. 结果显示: 所有样本的射电1.4GHz与5个波段gamma射线的辐射流量都有强相关, 相关系数在0.48--0.81之间, 机会概率均小于$10^{-4; 对于不同的样本相关系数随着gamma射线辐射频率的变化有不同的变化趋势, 所有样本在5个波段的相关系数平均值随gamma射线频率的增加而减小. 该结果暗示, 随着频率的升高, blazar的gamma射线辐射主导机制在发生变化, 在相同频率处, 不同类型天体的辐射主导机制存在差异; HBL的gamma射线辐射主要由同步自康普顿主导, 而LBL的其他成份比HBL的更复杂; FSRQ的gamma射线起源较BL Lac的复杂.     

Long-Term Modulation of Cosmic-Ray Intensity and Correlation Analysis Using Solar and Heliospheric Parameters

Based on the monthly sunspot numbers (SSNs), the solar-flare index (SFI), grouped solar flares (GSFs), the tilt angle of heliospheric current sheet (HCS), and cosmic-ray intensity (CRI) for Solar Cycles 21?–?24, a detailed correlation study has been performed using the cycle-wise average correlation (with and without time lag) method as well as by the “running cross-correlation” method. It is found that the slope of regression lines between SSN and SFI, as well as between SSN and GSF, is continuously decreasing from Solar Cycle 21 to 24. The length of regression lines has significantly decreased during Cycles 23 and 24 in comparison to Cycles 21 and 22. The cross-correlation coefficient (without time lag) between SSN–CRI, SFI–CRI, and GSF–CRI has been found to be almost the same during Cycles 21 and 22, while during Cycles 23 and 24 it is significantly higher between SSN–CRI and HCS–CRI than for SFI–CRI and GSF–CRI. Considering time lags of 1 to 20 months, the maximum correlation coefficient (negative) amongst all of the sets of solar parameters is observed with almost the same time lags during Cycles 21?–?23, whereas exceptional behaviour of the time lag has been observed during Cycle 24, as the correlation coefficient attains its maximum value with two time lags (four and ten months) in the case of the SSN–CRI relationship. A remarkably large time lag (22 months) between HCS and CRI has been observed during the odd-numbered Cycle 21, whereas during another odd cycle, Cycle 23, the lag is small (nine months) in comparison to that for other solar/flare parameters (13?–?15 months). On the other hand, the time lag between SSN–CRI and HCS–CRI has been found to be almost the same during even-numbered Solar Cycles 22 and 24. A similar analysis has been performed between SFI and CRI, and it is found that the correlation coefficient is maximum at zero time lag during the present solar cycle. The GSFs have shown better maximum correlation with CRI as compared to SFI during Cycles 21 to 23, indicating that GSF could also be used as a significant solar parameter to study the cosmic-ray modulation. Furthermore, the running cross-correlation coefficient between SSN–CRI and HCS–CRI, as well as between solar-flare activity parameters (SFI and GSF) and CRI is observed to be strong during the ascending and descending phases of solar cycles. The level of cosmic-ray modulation during the period of investigation shows the appropriateness of different parameters in different cycles, and even during the different phases of a particular solar cycle. We have also studied the galactic cosmic-ray modulation in relation to combined solar and heliospheric parameters using the empirical model suggested by Paouris et al. (Solar Phys.280, 255, 2012). The proposed model for the calculation of the modulated cosmic-ray intensity obtained from the combination of solar and heliospheric parameter gives a very satisfactory value of standard deviation as well as \(R^{2}\) (the coefficient of determination) for Solar Cycles 21?–?24.     

Correlations Between CME Parameters and Sunspot Activity

Smoothed monthly mean coronal mass ejection (CME) parameters (speed, acceleration, central position angle, angular width, mass, and kinetic energy) for Cycle 23 are cross-analyzed, showing that there is a high correlation between most of them. The CME acceleration (a) is highly correlated with the reciprocal of its mass (M), with a correlation coefficient r=0.899. The force (Ma) to drive a CME is found to be well anti-correlated with the sunspot number (R _z), r=?0.750. The relationships between CME parameters and R _z can be well described by an integral response model with a decay time scale of about 11 months. The correlation coefficients of CME parameters with the reconstructed series based on this model (\(\overline{r}_{\mathrm{f1}}=0.886\)) are higher than the linear correlation coefficients of the parameters with R _z (\(\overline{r}_{\mathrm{0}}=0.830\)). If a double decay integral response model is used (with two decay time scales of about 6 and 60 months), the correlations between CME parameters and R _z improve (\(\overline{r}_{\mathrm{f2}}=0.906\)). The time delays between CME parameters with respect to R _z are also well predicted by this model (19/22=86%); the average time delays are 19 months for the reconstructed and 22 months for the original time series. The model implies that CMEs are related to the accumulation of solar magnetic energy. These relationships can help in understanding the mechanisms at work during the solar cycle.     

Cooling curves and initial models for low-mass white dwarfs (<0.25 M⊙) with helium cores

We present a detailed calculation of the evolution of low-mass (<0.25 M_⊙) helium white dwarfs. These white dwarfs (the optical companions to binary millisecond pulsars) are formed via long-term, low-mass binary evolution. After detachment from the Roche lobe, the hot helium cores have a rather thick hydrogen layer with mass between 0.01 and 0.06 M_⊙. As a result of mixing between the core and outer envelope, the surface hydrogen content ( X _surf) is 0.5–0.35 , depending on the initial value of the heavy element Z and the initial secondary mass. We found that the majority of our computed models experience one or two hydrogen shell flashes. We found that the mass of the helium dwarf in which the hydrogen shell flash occurs depends on the chemical composition. The minimum helium white dwarf mass in which a hydrogen flash takes place is 0.213 M_⊙ ( Z =0.003), 0.198 M_⊙ ( Z =0.01), 0.192 M_⊙ ( Z =0.02) or 0.183 M_⊙ ( Z =0.03). The duration of the flashes (independent of chemical composition) is between a few ×10⁶ and a few ×10⁷ yr. In several flashes the white dwarf radius will increase so much that it forces the model to fill its Roche lobe again. Our calculations show that the cooling history of the helium white dwarf depends dramatically on the thickness of the hydrogen layer. We show that the transition from a cooling white dwarf with a temporarily stable hydrogen-burning shell to a cooling white dwarf in which almost all residual hydrogen is lost in a few thermal flashes (via Roche lobe overflow) occurs between 0.183 and 0.213 M_⊙ (depending on the heavy element value).     

Infrared variability properties of the blazar 3C 279

The long-term (about 27 years) near-infrared K light curve is constructed from the published literature for the blazar 3C 279. The Jurkevich method is adopted to analyse the periodicity, and a strong 7.1±0.44 yr period is found, suggesting that the next near-infrared outburst will occur in 2002/03. The correlation between colour index (spectral index) and magnitude is discussed, and a significant correlation between ( J − H ) and K is found with a correlation coefficient r =0.72 ( p =2.0×10⁻¹⁰), which is consistent with Brown et al.'s proposal.     

Helicity Measurements from Two Magnetographs

We use 270 pairs of vector magnetograms observed by Haleakala Stokes Polarimeter (HSP) and Solar Magnetic Field Telescope (SMFT) of Huairou Solar Observing Station from 1997 to 2000 to compare current helicity derived by these two instruments. We apply the same approach to both data sets to resolve 180^∘ azimuth ambiguity and compute α coefficient of linear force-free field. After careful consideration of various aspects of both data sets, we find that in ≈80% of cases SMFT and HSP data result in the same sign of α, and the Pearson linear correlation coefficient between two data sets is r_p = 0.64. Operated by the Association of Universities for Research in Astronomy (AURA, Inc) under cooperative agreement with the National Science Foundation (NSF).     

A measurement of the flux of cosmic ray iron at 5×10 eV

We present results from the initial flight of our Balloon Air CHerenkov (BACH) payload. BACH detects air Cherenkov radiation from cosmic ray nuclei as coincident flashes in two optical modules. The flight (dubbed PDQ–BACH) took place on April 22, 1998 from Ft. Sumner, New Mexico. During an exposure of 2.75 h, with a typical threshold energy for iron nuclei of 2.2×10¹³ eV, we observed several events cleanly identifiable as iron group nuclei. Analysis of the data yields a new flux measurement that is fully consistent with that reported by other investigations.     

Cosmic gamma-ray bursts detected in the RELEC experiment onboard the Vernov satellite

The RELEC scientific instrumentation onboard the Vernov spacecraft launched on July 8, 2014, included the DRGE gamma-ray and electron spectrometer. This instrument incorporates a set of scintillation phoswich detectors, including four identical X-ray and gamma-ray detectors in the energy range from 10 keV to 3 MeV with a total area of ~500 cm² directed toward the nadir, and an electron spectrometer containing three mutually orthogonal detector units with a geometry factor of ~2 cm² sr, which is also sensitive to X-rays and gamma-rays. The goal of the space experiment with the DRGE instrument was to investigate phenomena with fast temporal variability, in particular, terrestrial gammaray flashes (TGFs) and magnetospheric electron precipitations. However, the detectors of the DRGE instrument could record cosmic gamma-ray bursts (GRBs) and allowed one not only to perform a detailed analysis of the gamma-ray variability but also to compare the time profiles with the measurements made by other instruments of the RELEC scientific instrumentation (the detectors of optical and ultraviolet flashes, the radio-frequency and low-frequency analyzers of electromagnetic field parameters). We present the results of our observations of cosmicGRB 141011A and GRB 141104A, compare the parameters obtained in the GBM/Fermi and KONUS–Wind experiments, and estimate the redshifts and E _iso for the sources of these GRBs. The detectability of GRBs and good agreement between the independent estimates of their parameters obtained in various experiments are important factors of the successful operation of similar detectors onboard the Lomonosov spacecraft.     

Infrared and radio features of galaxies with UV excess

This is a statistical study of galaxies with a UV excess. A sample of 702 Kazarian galaxies (KG) is used. The KGs are identified with objects from the MAPS, IRAS FSC, IRAS PSC, and NVSS catalogs. The O and E magnitudes are known for more than 92% of the KGs. It is shown that the KG sample is complete up to 16m.0 in the blue and to 16m.5 in the red. More than 36% of the KGs are identified with infrared (IR) sources at wavelengths of 12, 25, 60, and 100 m. Calculations of the far IR (FIR) luminosities show that 4% of the KGs are strong FIR emitters (L_FIR ≥ 10¹¹ L_⊙). More than 32% of the KGs have been identified as radio sources at a frequency of 1.4 GHz. A determination of the radio luminosities shows that the sample of KGs with known radial velocities include one powerful, L_R ≥ 10²⁵ W/Hz, radio object (Kaz 273) which is a BL Lac object. A close correlation (r=0.93) is bound between the FIR and radio luminosities for galaxies with a UV excess. An examination of the relationship between the FIR and radio luminosities for galaxies in different spectral classes shows that the correlation coefficient is higher (r=0.99) and the slope of the fit curve is larger (a=1.18) for Seyfert galaxies. Calculations of the logarithm of the ratio of the FIR and radio fluxes indicate that the sample includes 4 KGs with a radio excess, while there are none with an IR excess. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 369–379 (August 2007).     

Nonlinear density fluctuation field theory for large scale structure

We develop an effective field theory of density fluctuations for a Newtonian self-gravitating N-body system in quasi-equilibrium and apply it to a homogeneous uni-verse with small density fluctuations. Keeping the density fluctuations up to second or-der, we obtain the nonlinear field equation of 2-pt correlation ξ(r), which contains 3-pt correlation and formal ultra-violet divergences. By the Groth-Peebles hierarchical ansatz and mass renormalization, the equation becomes closed with two new terms beyond the Gaussian approximation, and their coefficients are taken as parameters. The analytic solu-tion is obtained in terms of the hypergeometric functions, which is checked numerically.With one single set of two fixed parameters, the correlation ξ(r) and the corresponding power spectrum P(k) simultaneously match the results from all the major surveys, such as APM, SDSS, 2dfGRS, and REFLEX. The model gives a unifying understanding of several seemingly unrelated features of large scale structure from a field-theoretical per-spective. The theory is worth extending to study the evolution effects in an expanding universe.     

Confidence intervals for the correlation between the gamma-ray burst peak energy and the associated supernova peak brightness

A strong correlation between the gamma-ray burster peak energy and the peak luminosity of the associated supernova was discovered by Li for four GRBs. Despite the fact that the formal significance level of the correlation is 0.3 per cent, the smallness of the data set requires careful further evaluation of the result. Subject to the assumption that the data are bivariate Gaussian, a 95 per cent confidence interval of  (−0.9972, 0.02)  for the correlation is derived. Using data from the literature, it is shown that the distribution of known peak GRB energies is not Gaussian if X-ray flashes are included in the sample. This leads to a proposed alternative to the bivariate Gaussian model, which entails describing the dependence between the two variables by a Gaussian copula. The copula is still characterized by a correlation coefficient. The Bayesian posterior distribution of the correlation coefficient is evaluated using a Markov chain Monte Carlo method. The mean values of the posterior distributions range from −0.33 to about zero, depending on the specifics of the supernova (SN) peak brightness distribution. The implication is that the existing data favour a modest correlation between the GRB peak energy and the SN peak brightness; confidence intervals are very wide and include zero.     

Possible patterns in the distribution of planetary formation regions

Eris, an object larger than Pluto, is known to reside in the transneptunian region further away than Pluto. One can wonder whether its semimajor orbital axis fits in a generalized Titius–Bode law, in the same way as Pluto does. We performed a new least-squares fit to a generalized Titius–Bode law including Eris and found that not only does Eris fit in the trend, but also the correlation coefficient improves. In addition, there is a remarkable symmetry of the location of the planetary formation regions with respect to Jupiter when the natural logarithm of the heliocentric distance is used as the metric. The issue of whether the observed patterns have some physical meaning or are due to mere chance is addressed using a Monte Carlo approach identical to that of Lynch. Although the probability of chance occurrence is highly dependent on the way in which the random configurations of synthetic planetary systems are selected, we find that in all reasonable scenarios of random planetary systems the probability of chance occurrence of the observed patterns is small (below 1 per cent in most cases). If the trend were used as a prediction tool, one might expect another planet or dwarf planet or a swarm of bodies with semimajor orbital axis of 120 ± 20 au. Simple calculations show that the protoplanetary nebula most likely had enough mass to allow the accretion of at least a dwarf planet at that distance. We also found that if the surface density of the nebula decayed with heliocentric distance ( r ) as a power of −2, the regular spacing in ln  r in the Solar system could be a natural consequence of the existence of a threshold mass for planetary formation.     

The study of umbral flashes in the umbrae of two sunspots

The results of observations of the umbral flashes in two sunspots are reported. The sunspots differ in their morphological properties (evolution rates and activity levels) and in observation conditions (heliocentric distances). The oscillation parameters of the two sunspots do not coincide. The most significant differences are pronounced in the phase relations and amplitudes of observed oscillations.     

On the proposed associations of solar neutrino flux with solar particles,cosmic rays,and the solar activity cycle

It has been proposed that the observed solar neutrino flux exhibits important correlations with solar particles, galactic cosmic rays, and the sunspot cycle, with the latter correlation being opposite in phase and lagging behind the sunspot cycle by about one year. Re-examination of the data-available interval 1971–1981, employing various tests of statistical significance, however, suggests that such a claim is, at present, unwarrantable. For example, on the associations of solar neutrino flux and cosmic-ray flux with the Ap geomagnetic index, neither were found to be statistically significant (at the 95% level of confidence), regardless of the choice of lag (-1, 0, or +1 yr). Presuming linear fits, all correlations with Ap had coefficients of determination (r ², where r is the linear correlation coefficient) less than 16%, meaning that 16% of the variation in the selected test parameters could be explained by the variation in Ap. Similarly, on the associations of solar neutrino flux and cosmic ray flux with sunspot number, only the latter association proved to be of statistical importance. Using the best linear fits, the correlation between yearly averages of solar neutrino flux and sunspot number had r ² 19%, the correlation between weighted moving averages (of order 5) of solar neutrino flux and sunspot number had r ² 45%, and the correlation between cosmic-ray flux and sunspot number had r ² 76%, all correlations being inverse associations. Solar neutrino flux was found not to correlate strongly with cosmic-ray flux, and the Ap geomagnetic index was found not to correlate strongly with sunspot number.     

The relationship between the IMF magnitude and the frequency of Pc 3, 4 pulsations on the ground: Simultaneous events

Several attempts have been made to predict the strength of the interplanetary magnetic field (IMF) from the frequency of Pc 3, 4 pulsations measured on the ground. The predictive capability of the ground pulsations depends on the relationship which exists between their frequency and the IMF magnitude. It has been suggested that the relationship improves considerably when coincident frequencies between two stations are used.In this paper we show the correlation between the IMF magnitude and the frequency of coincident pulsation events in a network of five stations in the IGS magnetometer array. We do find that the frequency-field strength relationship is very good for the coincident events at the stations with large longitudinal separation ( > 3 h). We also confirm that the frequency taken from a network of ground stations is a better predictor of IMF magnitude than that from a single station.     

Some Viscous Fluid Cosmological Models in General Relativity

The motivation of this paper is to investigate two viscous fluid cosmological models in General Relativity in which the expansion is only in two directions i.e. one of the Hubble parameters is zero. In the first model, coefficient of shear viscosity is assumed to be constant while in the second model, the coefficient of shear viscosity is proportional to the rate of expansion in the model. Here no additional condition is assumed except for coefficient of shear viscosity. These models are new and different from those models obtained by Bali and Jain (1987, 1988) in which free gravitational field was assumed to be Petrov Type D and non-degenerate for Marder (1958) metric and coefficient of shear viscosity is proportional to the rate of expansion in the model. The various physical and geometrical aspects of the models are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stereoscopic measurements of flares from PHOBOS and GOES

A unique approach to observing the Sun stereoscopically in soft X-rays was afforded by the PHOBOS mission to Mars during 1989. Concurrent measurements of two flares from two widely separated spacecraft allowed us to obtain estimates of each flare's height above the solar surface. The requirement was that the flare had to be over the limb as observed by one spacecraft and on the visible disk as viewed by the other. The first flare occurred on March 4, when the active region was beyond the east limb as observed by GOES (at Earth), but on the disk as viewed by PHOBOS (at Mars). The second flare, on March 15, was on the disk for GOES, but beyond the west limb for PHOBOS. We believe that the same extraordinary active region, 5395, was responsible for both events. Soft X-ray photometers on each spacecraft contained two broad-band channels. The two-channel data were used to computeflare (assumed isothermal) plasma temperatures. The sharply peaked flare on March 4 indicated essentially identical maximum electron temperatures ( 13 Mk) at both spacecraft, confirming that the hottest plasma was indeed concentrated at the highest (unocculted) part of the loop. However, in the case of the long-duration March 15 flare, whose loop was in apparent upwards motion, the partially occulted flare indicated substantially cooler temperatures. This finding suggests that the hot core of this flare may have been below the limb, or that the partially occulted flux originated not from post-flare loops but from an independent, higher X-ray arch. The PHOBOS and GOES X-ray photometers were intercompared in July 1988, soon after the PHOBOS launch, to establish relative calibration parameters.     

A model of slingshot prominences in rapidly rotating stars

We analyse the spatial clustering properties of the ROSAT All-Sky Survey (RASS) 1 Bright Sample, an X-ray flux-limited catalogue of galaxy clusters selected from the southern part of the survey. The two-point correlation function ( r ) of the whole sample is well fitted (in an Einsteinde Sitter model) by the power law =( r r ₀) , with and (95.4 per cent confidence level with one fitting parameter). We use the RASS 1 Bright Sample as a first application of a theoretical model that aims to predict the clustering properties of X-ray clusters in flux-limited surveys for different cosmological scenarios. The model uses the theoretical and empirical relations between mass, temperature and X-ray cluster luminosity, and fully accounts for the redshift evolution of the underlying dark matter clustering and cluster bias factor. The comparison between observational results and theoretical predictions shows that the Einsteinde Sitter models display too low a correlation length, while models with a matter density parameter _0m=0.3 (with or without a cosmological constant) are successful in reproducing the observed clustering. The dependence of the correlation length r ₀ on the X-ray limiting flux and luminosity of the sample is generally consistent with the predictions of all our models. Quantitative agreement is however only reached for _0m=0.3 models. The model presented here can be reliably applied to future deeper X-ray cluster surveys: the study of the clustering properties will provide a useful complementary tool to the traditional cluster abundance analyses used to constrain the cosmological parameters.     

Study of Geomagnetic Storms and Solar and Interplanetary Parameters for Solar Cycles 22 and 24

The aim of this paper is to investigate the association of geomagnetic storms with the component of the interplanetary magnetic field (IMF) perpendicular to the ecliptic (\(Bz\)), the solar wind speed (\(V\)), the product of solar wind speed and \(Bz\) (VBz), the Kp index, and the sunspot number (SSN) for two consecutive even solar cycles, Solar Cycles 22 (1986?–?1995) and 24 (2009?–?2017). A comparative study has been done using the superposed epoch method (Chree analysis). The results of the present analysis show that \(Bz\) is a geoeffective parameter. The correlation coefficient between Dst and \(Bz\) is found to be 0.8 for both Solar Cycles 22 and 24, which indicates that these two parameters are highly correlated. Statistical relationships between Dst and Kp are established and it is shown that for the two consecutive even solar cycles, Solar Cycles 22 and 24, the patterns are strikingly similar. The correlation coefficient between Dst and Kp is found to be the same for the two solar cycles (?0.8), which clearly indicates that these parameters are well anti-correlated. For the same studied period we found that the SSN does not show any relationship with Dst and Kp, while there exists an inverse relation between Dst and the solar wind speed, with some time lag. We have also found that VBz is a more relevant parameter for the production of geomagnetic storms, as compared to \(V\) and \(Bz\) separately. In addition, we have found that in Solar Cycles 22 and 24 this combined parameter is more relevant during the descending phase as compared to the ascending phase.