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1. chinaXiv:201609.01015 [pdf]

Dynamic changes of emitting electron distribution in the jet of 3C 279: signatures of acceleration and cooling

Dahai Yan; Jianjian He; Jinyuan Liao; Li Zhang; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

We study the dynamic changes of electron energy distribution (EED) through systematically analysing the quasi-simultaneous spectral energy distributions (SEDs) of the flat spectrum radio quasar 3C 279 in different states. With Markov chain Monte Carlo (MCMC) technique we model fourteen SEDs of 3C 279 using a leptonic model with a three-parameter log-parabola electron energy distribution (EED). The 14 SEDs can be satisfactorily fitted with the one-zone leptonic model. The observed?γ?rays in 13 states are attributed to Compton scattering of external infrared photons from a surrounding dusty torus. The curved?γ-ray spectrum observed during 2-8 April 2014 is well explained by the external Compton of dust radiation. It is found that there is a clear positive correlation between the curvature parameter?b?of the EED and the electron peak energy?γ′pk. No clear correlation between?b?and the synchrotron peak frequency?νs?is found, due to the varied product of Doppler factor and fluid magnetic field from state to state. We interpret the correlation of?b?γ′pk?in a stochastic acceleration scenario. This positive correlation is in agreement with the prediction in the stage when the balance between acceleration and radiative cooling of the electrons is nearly established in the case of the turbulence spectral index?q=2.

submitted time 2016-09-14 Hits857Downloads489 Comment 0

2. chinaXiv:201609.01014 [pdf]

Galaxy alignment as a probe of large-scale filaments

Yu Rong; Yuan Liu; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

The orientations of the red galaxies in a filament are aligned with the orientation of the filament. We thus develop a location-alignment-method (LAM) of detecting filaments around clusters of galaxies, which uses both the alignments of red galaxies and their distributions in two-dimensional images. For the first time, the orientations of red galaxies are used as probes of filaments. We apply LAM to the environment of Coma cluster, and find four filaments (two filaments are located in sheets) in two selected regions, which are compared with the filaments detected with the method of \cite{Falco14}. We find that LAM can effectively detect the filaments around a cluster, even with?3σ?confidence level, and clearly reveal the number and overall orientations of the detected filaments. LAM is independent of the redshifts of galaxies, and thus can be applied at relatively high redshifts and to the samples of red galaxies without the information of redshifts. We also find that the images of background galaxies (interlopers) which are lensed by the gravity of foreground filaments are amplifiers to probe the filaments.

submitted time 2016-09-14 Hits569Downloads316 Comment 0

3. chinaXiv:201609.01004 [pdf]

The evolution of the magnetic inclination angle as an explanation of the long term red timing-noise of pulsars

Shu-Xu Yi; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

We study the possibility that the long term red timing-noise in pulsars originates from the evolution of the magnetic inclination angle?χ. The braking torque under consideration is a combination of the dipole radiation and the current loss. We find that the evolution of?χ?can give rise to extra cubic and fourth-order polynomial terms in the timing residuals. These two terms are determined by the efficiency of the dipole radiation, the relative electric-current density in the pulsar tube and?χ. The following observation facts can be explained with this model: a) young pulsars have positive?ν¨; b) old pulsars can have both positive and negative?ν¨; c) the absolute values of?ν¨?are proportional to??ν˙; d) the absolute values of the braking indices are proportional to the characteristic ages of pulsars. If the evolution of?χ?is purely due to rotation kinematics, then it can not explain the pulsars with braking index less than 3, and thus the intrinsic change of the magnetic field is needed in this case. Comparing the model with observations, we conclude that the drift direction of?χ?might oscillate many times during the lifetime of a pulsar. The evolution of?χ?is not sufficient to explain the rotation behavior of the Crab pulsar, because the observed?χand?χ˙?are inconsistent with the values indicated from the timing residuals using this model.

submitted time 2016-09-14 Hits821Downloads470 Comment 0

4. chinaXiv:201609.00999 [pdf]

Super Strong Magnetic Fields of Neutron Stars in Be X-Ray Binaries Estimated with New Torque and Magnetosphere Models

Chang-Sheng Shi; Shuang-Nan Zhang; Xiang-Dong Li
Subjects: Physics >> Nuclear Physics

We re-estimate the surface magnetic fields of neutron stars (NSs) in Be X-ray binaries (BeXBs) with different models of torque, improved beyond Klus et al. (2014). In particular, a new torque model (Dai \& Li 2006) is applied to three models of magnetosphere radius. Unlike the previous models, the new torque model does not lead to divergent results for any fastness parameter. The inferred surface magnetic fields of these NSs for the two compressed magnetosphere models are much higher than that for the uncompressed magnetosphere model. The new torque model using the compressed-magnetosphere radius (Shi, Zhang \& Li 2014) leads to unique solutions near spin equilibrium in all cases, unlike other models that usually give two branches of solutions. Although our conclusions are still affected by the simplistic assumptions about the magnetosphere radius calculations, we show several groups of possible surface magnetic field values with our new models when the interaction between the magnetosphere and the infalling accretion plasma is considered. The estimated surface magnetic fields for NSs BeXBs in the Large Magellanic Cloud, the Small Magellanic Cloud and the Milk Way are between the quantum critical field and the maximum "virial" value by the spin equilibrium condition.

submitted time 2016-09-14 Hits960Downloads539 Comment 0

5. chinaXiv:201609.00997 [pdf]

Parameter constraints in a near-equipartition model with multifrequency NuSTAR, Swift, and Fermi-LAT data from 3C 279

Dahai Yan; Li Zhang; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs of \emph{Swift} and \emph{NuSTAR} observations, are analyzed using a near-equipartition model. We apply a one-zone leptonic model with a three-parameter log-parabola electron energy distribution (EED) to fit the \emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and \emph{Fermi}-LAT γ-ray data. The Markov Chain Monte Carlo (MCMC) technique is used to search the high-dimensional parameter space and evaluate the uncertainties on model parameters. We show that the two spectra can be successfully fit in near-equipartition conditions, defined by the ratio of the energy density of relativistic electrons to magnetic field ζe being close to unity. In both spectra, the observed X-rays are dominated by synchrotron-self Compton photons, and the observed γ rays are dominated by Compton scattering of external infrared photons from a surrounding dusty torus. Model parameters are well constrained. From the low state to the high state, both the curvature of the log-parabola width parameter and the synchrotron peak frequency significantly increase. The derived magnetic fields in the two states are nearly identical (?1\ G), but the Doppler factor in the high state is larger than that in the low state (?28 versus ?18). We derive that the gamma-ray emission site takes place outside the broad-line region, at ? 0.1 pc from the black hole, but within the dusty torus. Implications for 3C 279 as a source of high-energy cosmic-rays are discussed.

submitted time 2016-09-14 Hits899Downloads489 Comment 0

6. chinaXiv:201609.00993 [pdf]

Perspective of monochromatic gamma-ray line detection with the High Energy cosmic-Radiation Detection (HERD) facility onboard China’s space station

Xiaoyuan Huang; Anna S. Lamperstorfer; Yue-Lin Sming Tsai; Ming Xu; Qiang Yuan Jin Chang; Yong-Wei Dong; Bing-Liang Hu; Jun-Guang L╱; Le Wang; Bo-Bing Wu; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

HERD is the High Energy cosmic-Radiation Detection instrument proposed to operate onboard China's space station in the 2020s. It is designed to detect energetic cosmic ray nuclei, leptons and photons with a high energy resolution (?1%?for electrons and photons and?20%?for nuclei) and a large geometry factor (>3m2sr?for electrons and diffuse photons and?>2m2sr?for nuclei). In this work we discuss the capability of HERD to detect monochromatic?γ-ray lines, based on simulations of the detector performance. It is shown that HERD will be one of the most sensitive instruments for monochromatic?γ-ray searches at energies between??10?to a few hundred GeV. Above hundreds of GeV, Cherenkov telescopes will be more sensitive due to their large effective area. As a specific example, we show that a good portion of the parameter space of a supersymmetric dark matter model can be probed with HERD.

submitted time 2016-09-14 Hits977Downloads549 Comment 0

7. chinaXiv:201609.00960 [pdf]

Correlation Analysis between Tibet AS-$\gamma$ TeV Cosmic Ray and WMAP Nine-year Data

Qian-Qing Yin; Shuang-Nan Zhang
Subjects: Physics >> Nuclear Physics

The Wilkinson Microwave Anisotropy Probe (WMAP) team subtracted template-based foreground models to produce foreground-reduced maps, and masked point sources and uncertain sky regions directly; however, whether foreground residuals exist in the WMAP foreground-reduced maps is still an open question. Here, we use Pearson correlation coefficient (PCC) analysis with AS-γ?TeV cosmic ray (CR) data to probe possible foreground residuals in the WMAP nine-year data. The correlation results between the CR and foreground-contained maps (WMAP foreground-unreduced maps, WMAP template-based and MEM foreground models) suggest that: (1) CRs can trace foregrounds in the WMAP data; (2) at least some TeV CRs originate from the Milky Way; (3) foregrounds may be related to the existence of CR anisotropy (loss-cone and tail-in structures); (4) there exist differences among different types of foregrounds in the declination range of?<15?. Then, we generate 10,000 mock CMB sky maps to describe the cosmic variance, which is used to measure the effect of the fluctuations of all possible CMB maps to the correlations between CR and CMB maps. Finally, we do correlation analysis between the CR and WMAP foreground-reduced maps, and find that: (1) there are significant anticorrelations; and (2) the WMAP foreground-reduced maps are credible. However, the significant anticorrelations may be accidental, and the higher signal-to-noise ratio (SNR) Planck SMICA map cannot reject the hypothesis of accidental correlations. We therefore can only conclude that the foreground residuals exist with???95\% probability.

submitted time 2016-09-13 Hits818Downloads458 Comment 0

8. chinaXiv:201609.00952 [pdf]

Modeling the evolution and distribution of the frequency's second derivative and the braking index of pulsar spin

Yi Xie; Shuang-Nan Zhang; Jin-Yuan Liao
Subjects: Physics >> Nuclear Physics

We model the evolution of the spin frequency's second derivative?ν¨?and the braking index?n?of radio pulsars with simulations within the phenomenological model of their surface magnetic field evolution, which contains a long-term power-law decay modulated by short-term oscillations. For the pulsar PSR B0329+54, a model with three oscillation components can reproduce its?ν¨?variation. We show that the "averaged"?n?is different from the instantaneous?n, and its oscillation magnitude decreases abruptly as the time span increases, due to the "averaging" effect. The simulated timing residuals agree with the main features of the reported data. Our model predicts that the averaged?ν¨?of PSR B0329+54 will start to decrease rapidly with newer data beyond those used in Hobbs et al.. We further perform Monte Carlo simulations for the distribution of the reported data in?|ν¨|?and?|n|?versus characteristic age?τc?diagrams. It is found that the magnetic field oscillation model with decay index?α=0?can reproduce the distributions quite well. Compared with magnetic field decay due to the ambipolar diffusion (α=0.5) and the Hall cascade (α=1.0), the model with no long term decay (α=0) is clearly preferred for old pulsars by the p-values of the two-dimensional Kolmogorov-Smirnov test.

submitted time 2016-09-13 Hits930Downloads519 Comment 0

9. chinaXiv:201609.00007 [pdf]

Do we expect to detect electromagnetic radiation from merging stellar mass black binaries like GW150914? No

Shuang-Nan Zhang; Yuan Liu; Shuxu Yi; Zigao Dai; Chaoguang Huang
Subjects: Physics >> Nuclear Physics

Context: The LIGO consortium announced the first direct detection of gravitation wave event GW150914 from two merging black holes; however the nature of the black holes are still not clear. Aims: We study whether electromagnetic radiation can be detected from merging stellar mass black binaries like GW150914. Methods: We briefly investigate the possible growth and merging processes of the two stellar mass black holes in the merging event of GW150914 detected by aLIGO, as clocked by a distant external observer. Our main results are: (1) The description of the black hole growth using stationary metric of a pre-existing black hole predicts strong electromagnetic radiation from merging black holes, which is inconsistent with GW150914; (2) Only gravitational wave radiation can be produced in the coalescence of two black holes such as that in the GW150914 event, if the black hole growth is described using time-dependent metric considering the influence of the in-falling matter onto a pre-existing black hole, as clocked by a distant external observer. Conclusions: Future high sensitivity detections of gravitational waves from merging black holes might be used to probe matter distribution and space-time geometry in the vicinity of the horizon. Perhaps the GW150914-like events can be identified with traditional astronomy observations only if the black holes are embedded in extremely dense medium before their final merge, when very strong electromagnetic radiation is produced and can escape from the system.

submitted time 2016-09-01 Hits783Downloads441 Comment 0

10. chinaXiv:201608.00197 [pdf]

Testing Einstein's Equivalence Principle With Gravitational Waves

Xue-Feng Wu; He Gao; Jun-Jie Wei; Xi-Long Fan; Peter M?esz?aros; Bing Zhang; Zi-Gao Dai; Shuang-Nan Zhang; Zong-Hong Zhu
Subjects: Physics >> Nuclear Physics

A conservative constraint on the Einstein Equivalence Principle (EEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the EEP are mainly based on the observed time delays of photons with different energies, and it is highly desirable to develop more accurate tests involving different types of particles. The detection by the advanced LIGO/VIRGO systems of gravitational waves (GWs) will provide attractive candidates for constraining the EEP, which would further extend the tested particle species to the gravitons, with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals can potentially probe the EEP to an accuracy of 10?11, which is several orders of magnitude tighter than previous limits.

submitted time 2016-08-30 Hits760Downloads455 Comment 0

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