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1. chinaXiv:201808.00172 [pdf]

A Phenomenological Model for the Light Curve of three Quiescent Low-inclination Dwarf Novae and one Pre-Cataclysmic Variable

Dai, zhibin; Szkody, Paula; Kennedy, Mark; Su Jie; Medagangoda, N. Indika; Robinson, Edward L.; Garnavich, Peter M.; De Silva, L. Malith M.
Subjects: Astronomy >> Astrophysics

We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS\,J0632+2536 (J0632+2536), RZ\,Leo, TW\,Vir and the pre-CV WD\,1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ\,Leo and TW\,Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD\,1144+011 can explain its single-hump modulation and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of $\sim0.11$. The disk model of RZ\,Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ\,Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW\,Vir and WD\,1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semi-empirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy.

submitted time 2018-09-12 Hits10302Downloads1139 Comment 0

2. chinaXiv:201711.02302 [pdf]

A systematic study on the cosmic ray antiproton ?ux

Su-Jie Lin; Xiao-Jun Bi; Jie Feng; Peng-Fei Yin; Zhao-Huan Yu
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Recently the AMS-02 collaboration has published the measurement of the cosmic antiproton to proton ratio p?/p and the p? ?ux with a high precision up to ? 450 GeV. In this work, we perform a systematic analysis of the secondary antiproton ?ux generated by the cosmic ray interaction with the interstellar gas. The uncertainty of the prediction originates from the cosmic ray propagation process and the hadronic interaction models. Although the cosmic ray propagation parameters have been well controlled by the AMS-02 B/C ratio data for a speci?ed model, di?erent propagation models can not be discriminated by the B/C data. The p? ?ux is also calculated for several hadronic interaction models, which are generally adopted by the cosmic ray community. However, the results for di?erent hadronic models do not converge. We ?nd the EPOS LHC model, which seems to ?t the collider data very well, predicts a slightly lower p?/p ratio than the AMS-02 data at the high energy end. Finally we derive the constraints on the dark matter annihilation cross section from the AMS-02 p?/p ratio for di?erent propagation and hadronic interaction models.

submitted time 2017-11-10 Hits1392Downloads759 Comment 0

3. chinaXiv:201711.02306 [pdf]

Perspective on the cosmic-ray electron spectrum above TeV

Kun Fang; Bing-Bing Wang; Xiao-Jun Bi; Su-Jie Lin; Peng-Fei Yin
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The AMS-02 has measured the cosmic ray electron (plus positron) spectrum up to ?TeV with an unprecedent precision. The spectrum can be well described by a power law without any obvious features above 10 GeV. The satellite instrument Dark Matter Particle Explorer (DAMPE), which was launched a year ago, will measure the electron spectrum up to 10 TeV with a high energy resolution. The cosmic electrons beyond TeV may be attributed to few local cosmic ray sources, such as supernova remnants. Therefore, spectral features, such as cuto? and bumps, can be expected at high energies. In this work we give a careful study on the perspective of the electron spectrum beyond TeV. We ?rst examine our astrophysical source models on the latest leptonic data of AMS-02 to give a self-consistent picture. Then we focus on the discussion about the candidate sources which could be electron contributors above TeV. Depending on the properties of the local sources (especially on the nature of Vela), DAMPE may detect interesting features in the electron spectrum above TeV in the future.

submitted time 2017-11-10 Hits1321Downloads747 Comment 0

4. chinaXiv:201711.02308 [pdf]

Excesses of Cosmic Ray Spectra from A Single Nearby Source

Wei Liu; Xiao-Jun Bi; Su-Jie Lin; Bing-Bing Wang; Peng-Fei Yin
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays (p, e+) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary (p, e?) and secondary (e+, ?p/p) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.

submitted time 2017-11-10 Hits1203Downloads642 Comment 0

5. chinaXiv:201609.00921 [pdf]

Implications for dark matter annihilation from the AMS-02 $\barp/p$ ratio

Su-Jie Lin; Xiao-Jun Bi; Peng-Fei Yin; Zhao-Huan Yu
Subjects: Physics >> Nuclear Physics

The AMS-02 collaboration has just released the cosmic antiproton to proton ratio?p?/p?with a high precision up to??450?GeV. In this work, we calculate the secondary antiprotons generated by cosmic ray interactions with the interstellar medium taking into account the uncertainties from the cosmic ray propagation. The?p?/p?ratio predicted by these processes shows some tension with the AMS-02 data in some regions of propagation parameters, but the excess is not significant. We then try to derive upper bounds on the dark matter annihilation cross section from the?p?/p?data or signal regions favored by the data. It is shown that the constraint derived by the AMS-02 data is similar to that from Fermi-LAT observations of dwarf galaxies. The signal region for dark matter is usually required?mχ?O(10)?TeV and?$\left<\sigma v\right>\sim\mathcal{O}(10^{-23})~\cm^3~\sec^{-1}$.

submitted time 2016-09-13 Hits1413Downloads705 Comment 0

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