59132262
Quantifying solar superactive regions with vector magnetic field observations
Context. The vector magnetic field characteristics of superactive regions (SARs) hold the key for understanding why SARs are extremely active and provide the guidance in space weather prediction. Aims. We aim to quantify the characteristics of SARs using the vector magnetograms taken by the Solar Magnetic Field Telescope at Huairou Solar Observatory Station. Methods. The vector magnetic field characteristics of 14 SARs in solar cycles 22 and 23 were analyzed using the following four parameters: 1) the magnetic flux imbalance between opposite polarities; 2) the total photospheric free magnetic energy; 3) the length of the magnetic neutral line with its steep horizontal magnetic gradient; and 4) the area with strong magnetic shear. Furthermore, we selected another eight large and inactive active regions (ARs), which are called fallow ARs (FARs), to compare them with the SARs. Results. We found that most of the SARs have a net magnetic flux higher than 7.0×10 21 Mx, a total photospheric free magnetic energy higher than 1.0 ×10 24 ergcm −1 , a magnetic neutral line with a steep horizontal magnetic gradient (≥300 GMm −1 ) longer than 30 Mm, and an area with strong magnetic shear (shear angle ≥80 ◦ ) greater than 100 Mm 2 . In contrast, the values of these parameters for the FARs are mostly very low. The Pearson χ 2 test was used to examine the significance of the difference between the SARs and FARs, and the results indicate that these two types of ARs can be fairly distinguished by each of these parameters. The significance levels are 99.55%, 99.98%, 99.98%, and 99.96%, respectively. However, no single parameter can distinguish them perfectly. Therefore we propose a composite index based on these parameters, and find that the distinction between the two types of ARs is also significant with a significance level of 99.96%. These results are useful for a better physical understanding of the SAR and FAR.
17200560
Ionized ultraviolet and soft X-ray absorption in the low-redshift active galactic nucleus PG 1126−041
We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray-weak, far-infrared-loud AGN, PG 1126−041 (Mrk 1298). The first UV spectra taken in 1992 June, simultaneously with ROSAT, show strong absorption lines of N v, C iv and Si iv, extending over a velocity range from −1000 to −5000 km s−1 with respect to the corresponding line centre. Our analysis shows that the broad emission-line region (BELR) is, at least partially, covered by the material causing these absorption lines. In the IUE spectrum taken in 1995 January, the continuum was a factor of 2 brighter and the UV absorption lines are found to be considerably weaker than in 1992, but little variation in the emission-line fluxes is found. With UV spectral indices of αUV≃1.82 and 1.46 for the 1992 and 1995 data, the far-UV spectrum is steep. Based on the emission-line ratios and the broad-band spectral energy distribution, we argue that the steepness of the UV spectrum is unlikely to be caused by reddening. 
 
 
 
The soft X-ray emission in the ROSAT band is weak. A simple power-law model yields a very poor fit with a UV-to-X-ray spectral index αUVX=2.3. Highly ionized (warm) absorption is suggested by the ROSAT data. After correcting for a warm absorber, the optical to X-ray spectral slope is close to the average of αUVX≃1.67 for radio-quiet quasars. 
 
 
 
From photoionization calculations we find the following results. (1) A single-zone absorption model cannot explain simultaneously the UV absorption lines and the ionized X-ray absorption if metal abundances are solar. Furthermore, in order to be consistent with the equivalent width of the observed Lyα absorption line, the turbulent velocity of the warm absorber must be less than 190 km s−1, which imposes serious constraints on a disc wind model. (2) The UV absorption lines and their variability cannot be explained by a single-zone model with solar abundances and the large variability in the absorption lines suggests that C iv and N v absorption lines are not severely saturated. (3) The absorption of the ionizing continuum by warm material strongly affects the emission-line spectrum.
17167816
Two-Current-Sheet Reconnection Model of Interdependent Flare and Coronal Mass Ejection
Time-dependent resistive magnetohydrodynamic simulations are carried out to study a flux rope eruption caused by magnetic reconnection with implication in coexistent flare-CME (coronal mass ejection) events. An early result obtained in a recent analysis of double catastrophe of a flux rope system is used as the initial condition, in which an isolated flux rope coexists with two current sheets: a vertical one below and a transverse one above the flux rope. The flux rope erupts when reconnection takes place in the current sheets, and the flux rope dynamics depends on the reconnection sequence in the two current sheets. Three cases are discussed: reconnection occurs (1) simultaneously in the two current sheets, (2) first in the transverse one and then in the vertical one, and (3) in an order opposite that of case 2. Such a two-current-sheet reconnection exhibits characteristics of both magnetic breakout for CME initiation and the standard flare model. We argue that both breakout-like and tether-cutting reconnections could be important for CME eruptions and associated surface activities.
12993780
Measurement of CC interactions produced by ${}^8$B solar neutrinos at SNO
16824048
How Saturated Are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442?
Recently, convincing evidence was found for extremely large X-ray absorption by column densities greater than 1023 cm-2 in broad absorption line quasars. One consequence of this is that any soft X-ray emission from these QSOs would be the scattered light or leaked light from partially covering absorbing material. A detection of the unabsorbed soft X-ray and absorbed hard X-ray component will allow us to determine the total column density as well as the effective covering factor of the absorbing material, which are difficult to obtain from the UV absorption lines. Brinkmann et al. recently showed that both the unabsorbed and absorbed components are detected in the nearby very bright broad absorption line quasar PG 1411+442. In this Letter, we make a further analysis of the broadband X-ray spectrum and the UV spectrum from the Hubble Space Telescope and demonstrate that broad absorption lines are completely saturated at the bottom of absorption troughs.
1458695
The X-Ray Absorber in Broad Absorption Line Quasars
Recent observations of Broad Absorption Line (BAL) quasars demonstrated that the soft X-ray emission of these objects is extremely weak, and convincing evidence for very strong absorption by a high column density (~1023.5 cm-2) was obtained for PG 1411+442, even though it is one of the few BAL QSOs strongly detected in soft X-rays. This paper examines the ionization status and geometry of the X-ray absorber by combining the properties of the UV lines with the X-ray continuum absorption. We show that the gas has to have large column densities in ions of major UV absorption lines, such as C IV, N V, O VI, and Ne VIII, in order to have sufficient opacity around 0.2-0.35 keV. The UV absorption lines have to be saturated if the X-ray absorber intersects the line of sight to the UV continuum emission region. A uniformly covering UV and X-ray absorption model can be constructed for PG 1411+442, but in some other soft X-ray-detected BAL QSOs, such as PG 1001+054, the observed line optical depth is much lower than expected from the X-ray-absorbing material. We propose a scheme in which a substantial fraction of the line of sight to the continuum source may be covered by either an optically thick flow or clouds in a narrow velocity range, but in which the total covering factor of either the whole flow or all clouds is close to unity. The absorber can contribute significantly to the extremely highly ionized emission lines, such as O VI λλ1032/1037 and Ne VIII λλ770/780, if it covers a substantial fraction of solid angle and if the density is higher than 108 cm-3. However, it has very little impact on the medium- and low-ionization UV lines such as N V and C IV. The profiles of Ne VIII and O VI lines may be indicators for the kinematics of the X-ray absorber in QSOs. The observed Ne VIII line profiles in QSOs suggest that the velocity of the gas projected onto our line of sight is similar to that seen in the outflows of the UV BALs.
204179592
Cabibbo suppressed decays of D+ ---> pi+ pi0, K+ anti-K0, K+ pi0
207931813
Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies
Measurements of two-particle angular correlations between an identified strange hadron (K0S or Lambda/anti-Lambda) and a charged particle, emitted in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 35 inverse nanobarns, were collected at a nucleon-nucleon center-of-mass energy (sqrt(s[NN])) of 5.02 TeV with the CMS detector at the LHC. The results are compared to semi-peripheral PbPb collision data at sqrt(s[NN]) = 2.76 TeV, covering similar charged- particle multiplicities in the events. The observed azimuthal correlations at large relative pseudorapidity are used to extract the second-order (v[2]) and third-order (v[3]) anisotropy harmonics of K0S and Lambda/anti-Lambda particles. These quantities are studied as a function of the charged-particle multiplicity in the event and the transverse momentum of the particles. For high-multiplicity pPb events, a clear particle species dependence of v[2] and v[3] is observed. For pt < 2 GeV, the v[2] and v[3] values of K0S particles are larger than those of Lambda/anti-Lambda particles at the same pt. This splitting effect between two particle species is found to be stronger in pPb than in PbPb collisions in the same multiplicity range. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, both v[2] and v[3] for K0S particles are observed to be consistent with those for Lambda/anti-Lambda particles at the 10% level in pPb collisions. This consistency extends over a wide range of particle transverse kinetic energy and event multiplicities.
119241598
Central gas entropy excess as direct evidence for AGN feedback in galaxy groups and clusters
By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central ( R ≤10 h -1 71 kpc) gas entropy excess (∆ K 0 ), which corresponds to ≃ 0.1 - 0.5 keV per gas particle, beyond the power-law model that best fits the radial entropy profile of the outer regions. We also find a distinct correlation between the central entropy excess ∆ K 0 and K-band luminosity LK of the central dominating galaxies (CDGs), which is scaled as ∆ K 0 ∝ L 1.6±0.4 K , where L K is tightly associated with the mass of the supermassive black hole hosted in the CDG. In fact, if an effective mass-to-energy conversion- efficiency of 0.02 is assumed for the accretion process, the cumulative AGN feedback E AGN feedback ≃ ηM BH c 2 yields an extra heating of ≃0.5 - 17.0 keV per particle, which is sufficient to explain the central entropy excess. In most cases, the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius ( ≃0.002 - 2.2 keV per particle), and apparently exceeds the energy required to cause the scaling relations to deviate from the self-similar predictions ( ≃0.2 - 1.0 keV per particle). In contrast to the AGN feedback, the extra heating provided by supernova explosions accounts for ≃0.01 - 0.08 keV per particle in groups and is almost negligible in clusters. Therefore, the observed correlation between ∆ K 0 and L K can be considered as direct evidence for AGN feedback in galaxy groups and clusters.
16400877
VECTOR MAGNETIC FIELDS OF SOLAR GRANULATION
Observations of the quiet Sun from the Solar Optical Telescope/Spectro-Polarimeter aboard the Hinode spacecraft reveal the magnetic characteristics of the solar photosphere. By making use of the deep-mode observations of three quiet regions, we have statistically studied the vector magnetic fields of solar granulation. More than 2000 normal granules are manually selected to form a sample. It is recognized that some granules are even darker than the mean photosphere in intensity, and there is a linear correlation between intensity and Doppler velocity in the granules. The distributions of longitudinal and transverse apparent magnetic flux densities, Doppler velocity, and continuum intensity of granules are obtained, and their unsigned magnetic flux measured. Two approaches are used in this study. First, we obtained the magnetic properties of granulation by averaging the measurements for all the sampling granules. Second, we reconstructed an average granular cell based on a subsample, and obtained the detailed distribution of apparent magnetic flux density within the model granular cell. All the results have been compared with those for intergranular lanes and a few typical abnormal granules. Our statistical analysis reveals the following results. (1) The unsigned magnetic flux of individual granules spans the range from 1.1 × 1015 Mx to 3.3 × 1018 Mx with a peak distribution at 1.6 × 1016 Mx. (2) The unsigned longitudinal apparent flux density of granules ranges from almost 0 to 212 Mx cm–2 with a mean longitudinal apparent flux density of 12 Mx cm–2, while the transverse apparent flux density of granules ranges from 4 to 218 Mx cm–2 with a mean transverse apparent flux density of 79 Mx cm–2. The longitudinal and transverse apparent magnetic flux densities of granules are positively correlated, and the longitudinal apparent flux density of granules is weaker than the corresponding transverse apparent flux density. (3) The magnetic inclination of granules with respect to the surface that is perpendicular to the line of sight falls in the range of 4.8-76.7 degrees with a peak distribution at 25 degrees. On average, the magnetic vectors in granules are more vertical than those in the intergranular lanes. (4) There is a strong preference that both the vertical and horizontal fields on the quiet Sun reside in the intergranular lanes. (5) The detailed distributions of apparent flux density, Doppler velocity, and continuum intensity within an average granular cell are presented. These distributions can be empirically formulated well.
119129472
Magnetic Evolution and Temperature Variation in a Coronal Hole
We have explored the magnetic flux evolution and temperature variation in a coronal hole region, using Big Bear Solar Observatory deep magnetograms and SOHO EIT images observed from 2005 October 10 to 14. For comparison, we also investigated a neighboring quiet region of the Sun. The coronal hole evolved from its mature stage to its disappearance during the observing period. We have obtained the following results: (1) When the coronal hole was well developed on October 10, about 60% of the magnetic flux was positive. The EUV brightness was 420 counts pixel-1, and the coronal temperature, estimated from the line ratio of the EIT 195 and 171 A images, was 1.07 MK. (2) On October 14, when the coronal hole had almost disappeared, 51% of the magnetic flux was positive, the EUV radiance was 530 counts pixel-1, and the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an irregular variation, with a mean value of 870 counts pixel-1. The temperature was almost constant at 1.11 MK during the 5 day observation. Our results demonstrate that in a coronal hole less imbalance of the magnetic flux in opposite polarities leads to stronger EUV brightness and higher coronal temperatures.