Polarization in cyclotron radiation in strong magnetic fields

We revisit the problem of radiative transitions of electrons in the presence of a strong magnetic field. We derive fully relativistic cyclotron transition rates for an arbitrary magnetic field, for any orientation of electron spin and for any polarization of the emitted radiation. Also, we obtain the transition rates for any value of the initial electron＇s parallel momentum. For very strong magnetic fields, transitions to the ground state predominate. Transition rates summed over the electron＇s spin orientation and for unpolarized radiation are also obtained, which confirm previous results by Latal. Transition widths are calculated for different electron spin orientations and different polarizations of radiation. We obtain general expressions for transition rates that reduce to the results for the non-relativistic case and for unpolarized radiation. Additionally we get, for the non-relativistic approximation, the transition rates for any polarization of radiation. As an application, the first five emission lines are evaluated and compared to the X-ray emitting neutron star V0332＋53, which has multiple observable cyclotron lines, taking into account gravitational redshift. The most probable polarization is ε（2）.

Are Seyfert 2 Galaxies without Polarized Broad Emission Lines More Obscured?

New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5 - 10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines （PBLs） are absorbed by NH 〈 1024 cm^-2, while two of three Seyfert 2 galaxies without PBLs show evidence of Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs, Adding the measured obscuration indicators （NH, T ratio, and Fe Kα line EW） of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for NH, 99.1% to 99.4% for T ratio, and 95.3% to 97.4% for Fe Kα line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angles of the line of sight to the putative dusty toms, which leads to the obscuration of the broad-line scattering screen, as expected in the unification model.

Excitation of Annual Polar Motion by the Pacific,Atlantic and Indian Oceans

The global oceans play important roles in exciting the annual polar motion besides the atmosphere. However, it is still unclear about how large the regional oceans contribute to the annual polar motion. We investigate systemically the contributions of the Pacific, Atlantic and Indian Oceans to the excitation of the annual polar motion, based on the output data of ocean current velocity field and ocean bottom pressure field from ＂Estimating the Circulation and Climate of the Ocean （ECCO）＂ ocean circulation model over the period 1993-2005. The result shows that due to its particular location and shape, the Atlantic Ocean makes a less significant contribution to the x-component of the annual polar motion excitation than the Pacific and Indian Oceans, while all these three oceans contribute to the y-component of the annual polar motion excitation to some extent.

Studies of grand minima in sunspot cycles by using a flux transport solar dynamo model

We propose that grand minima in solar activity are caused by simultane- ous fluctuations in the meridional circulation and the Babcock-Leighton mechanism for the poloidal field generation in the flux transport dynamo model. We present the following results： （a） fluctuations in the meridional circulation are more effective in producing grand minima; （b） both sudden and gradual initiations of grand minima are possible; （c） distributions of durations and waiting times between grand minima seem to be exponential; （d） the coherence time of the meridional circulation has an effect on the number and the average duration of grand minima, with a coherence time of about 30 yr being consistent with observational data. We also study the occurrence of grand maxima and find that the distributions of durations and waiting times between grand maxima are also exponential, like the grand minima. Finally we address the question of whether the Babcock-Leighton mechanism can be operative during grand minima when there are no sunspots. We show that an a-effect restricted to the upper portions of the convection zone can pull the dynamo out of the grand minima and can match various observational requirements if the amplitude of this a-effect is suitably fine-tuned.

Solar sail time-optimal interplanetary transfer trajectory design

The fuel consumption associated with some interplanetary transfer trajectories using chemical propulsion is not affordable. A solar sail is a method of propulsion that does not consume fuel. Transfer time is one of the most pressing problems of solar sail transfer trajectory design. This paper investigates the time-optimal interplanetary transfer trajectories to a circular orbit of given inclination and radius. The optimal control law is derived from the principle of maximization. An indirect method is used to solve the optimal control problem by selecting values for the initial adjoint vari- ables, which are normalized within a unit sphere. The conditions for the existence of the time-optimal transfer are dependent on the lightness number of the sail and the inclination and radius of the target orbit. A numerical method is used to obtain the boundary values for the time-optimal transfer trajectories. For the cases where no time-optimal transfer trajectories exist, first-order necessary conditions of the optimal control are proposed to obtain feasible solutions. The results show that the transfer time decreases as the minimum distance from the Sun decreases during the transfer duration. For a solar sail with a small lightness number, the transfer time may be evaluated analytically for a three-phase transfer trajectory. The analytical results are compared with previous results and the associated numerical results. The transfer time of the numerical result here is smaller than the transfer time from previous results and is larger than the analytical result.

Temporal variations and spectral properties of the Be/X-ray pulsar GRO J1008–57 studied by INTEGRAL

The spin period variations and hard X-ray spectral properties of the Be/Xray pulsar GRO J1008-57 are studied with INTEGRAL observations during two out- bursts in 2004 June and 2009 March. The pulsation periods of -93.66 s in 2004 and - 93.73 s in 2009 are determined. Pulse profiles of GRO J1008-57 during out- bursts are strongly energy dependent with a double-peaked profile from 3-7 keV and a single-peaked profile in hard X-rays above 7 keV. Combined with previous measure- ments, we find that GRO J1008-57 has undergone a spin-down trend from 1993 - 2009 with a rate of - 4.1 × 10^-5 s d^-1, and could have changed into a spin-up trend after 2009. We find a relatively soft spectrum in the early phase of the 2009 outburst with cutoff energy ~ 13keV. Above a hard X-ray flux of - 10^-9 erg cm^-2 s^-1, the spectra of GRO J1008-57 during outbursts need an enhanced hydrogen absorption with column density ~ 6 x 1022 cm-2. The observed dip-like pulse profile of GRO J1008-57 in soft X-ray bands could be caused by this intrinsic absorption. Around the outburst peaks, a possible cyclotron resonance scattering feature at - 74 keV is detected in the spectra of GRO J1008-57 which is consistent with the feature that was reported in MAXI/GSC observations, making the source a neutron star with the highest known magnetic field （- 6.6 × 10^12 G） among accreting X-ray pulsars. This marginal feature is supported by the present detections in GRO J1008-57 following the correlation between the fundamental line energies and cutoff energies in accret- ing X-ray pulsars. Finally we discovered two modulation periods at - 124.38 d and 248.78d using RXTE/ASM light curves of GRO J1008-57. Two flare peaks ap- pearing in the folded light curve had different spectral properties. The normal outburst lasting 0,1 of an orbital phase had a hard spectrum and could not be significantly de- tected below 3 keV. The second flare lasting ten days showed a very soft spectrum without significant detections above 5 keV. GRO J1008-57 is a good candidate of an accreting system with an equatorial circumstellar disk around the companion star. The neutron star passing the disk of the Be star near periastron and apastron produces two X-ray flares. The soft spectral properties in the secondary flares still need further detailed studies with soft X-ray spectroscopy.

A compiled catalog of rotation measures of radio point sources

We compiled a catalog of Faraday rotation measures （RMs） for 4553 extragalactic radio point sources published in literature. These RMs were derived from multi-frequency polarization observations. The RM data are compared to those in the NRAO VLA Sky Survey （NVSS） RM catalog. We reveal a systematic uncertainty of about 10.0± 1.5rad m^-2 in the NVSS RM catalog. The Galactic foreground RM is calculated through a weighted averaging method by using the compiled RM catalog together with the NVSS RM catalog, with careful consideration of uncertainties in the RM data. The data from the catalog and the interface for the Galactic foreground RM calculations are publicly available on the webpage： http：//zmtt.bao.ac.cn/RM/.

Study of grain alignment efficiency and a distance estimate for small globule CB4

We study the polarization efficiency（defined as the ratio of polarization to extinction） of stars in the background of the small, nearly spherical and isolated Bok globule CB4 to understand the grain alignment process. A decrease in polarization efficiency with an increase in visual extinction is noticed. This suggests that the observed polarization in lines of sight which intercept a Bok globule tends to show dominance of dust grains in the outer layers of the globule. This finding is consistent with the results obtained for other clouds in the past. We determined the distance to the cloud CB4 using near-infrared photometry（2MASS J H KScolors） of moderately obscured stars located at the periphery of the cloud. From the extinction-distance plot,the distance to this cloud is estimated to be（459 ± 85） pc.

Smoothing methods comparison for CMB E-and B-mode separation

The anisotropies of the B-mode polarization in the cosmic microwave background radiation play a crucial role in the study of the very early Universe. However, in real observations, a mixture of the E- mode and B-mode can be caused by partial sky surveys, which must be separated before being applied to a cosmological explanation. The separation method developed by Smith （2006） has been widely adopted, where the edge of the top-hat mask should be smoothed to avoid numerical errors. In this paper, we compare three different smoothing methods and investigate leakage residuals of the E-B mixture. We find that, if less information loss is needed and a smaller region is smoothed in the analysis, the sin- and cos-smoothing methods are better. However, if we need a cleanly constructed B-mode map, the larger region around the mask edge should be smoothed. In this case, the Gaussian-smoothing method becomes much better. In addition, we find that the leakage caused by numerical errors in the Gaussian-smoothing method is mostly concentrated in two bands, which is quite easy to reduce for further E-B separations.

Vector Magnetic Field Measurement of NOAA AR 10197

A set of two-dimensional Stokes spectral data of NOAA AR 10197 obtained by the Solar Stokes Spectral Telescope （S^3T） at the Yunnan Observatory are quafitatively analyzed. The three components of the vector magnetic field, the strength H, inclination 7 and azimuth X, are derived. Based on the three components, we contour the distributions of the longitudinal magnetic field and transverse magnetic field. The active region （AR） has two different magnetic polarities apparent in the longitudinal magnetic map due to projection effect. There is a basic agreement on the longitudinal magnetic fields between the S^3T and SOHO/MDI magnetograms, with a correlation coefficient PBl = 0.911. The transverse magnetic field of the AR has a radial distribution from a center located in the southwest of the AR. It is also found that the transverse magnetic fields obtained by Huairou Solar Observing Station （HRSOS） have a similar radial distribution. The distributions of transverse magnetic field obtained by S^3T and HRSOS have correlation coefficients, PAzimu = 0.86 and PBt =0.883, in regard to the azimuthal angle and intensity.