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Title: | Properties of a hypothetical cold pulsar wind in LS 5039 |
Author: | Bosch i Ramon, Valentí |
Keywords: | Astronomia de raigs gamma Radiació Estels Gamma ray astronomy Radiation Stars |
Issue Date: | 13-Jan-2021 |
Publisher: | EDP Sciences |
Abstract: | Context. LS 5039 is a powerful high-mass gamma-ray binary that probably hosts a young non-accreting pulsar. However, despite the wealth of data available, the means by which the non-thermal emitter is powered are still unknown. Aims. We use a dynamical-radiative numerical model, and multiwavelength data, to constrain the properties of a hypothetical pulsar wind that would power the non-thermal emitter in LS 5039. Methods. We ran simulations of an ultrarelativistic (weakly magnetized) cold e±-wind that Compton scatters stellar photons and that dynamically interacts with the stellar wind. The effects of energy losses on the unshocked e±-wind dynamics, and the geometry of the two-wind contact discontinuity, are computed for different wind models. The predicted unshocked e±-wind radiation at periastron, when expected to be the highest, is compared to LS 5039 data. Results. The minimum possible radiation from an isotropic cold e±-wind overpredicts the X-ray to gamma-ray fluxes at periastron by a factor of ∼3. In the anisotropic (axisymmetric) wind case X-ray and ≳100 MeV data are not violated by wind radiation if the wind axis is at ≲20−40° from the line of sight (chance probability of ≲6−24%), depending on the anisotropic wind model, or if the wind Lorentz factor ∈102 − 103, in which case the wind power can be higher, but it requires e±-multiplicities of ∼106 and 109 for a 10−2 s and 10 s pulsar period, respectively. Conclusions. The studied model predicts that a weakly magnetized cold pulsar e±-wind in LS 5039 should be strongly anisotropic, with either a wind Lorentz factor ∈102 − 103 and very high multiplicities or with a fine-tuned wind orientation. A weakly magnetized, cold baryon-dominated wind would be a possible alternative, but then the multiplicities should be rather low, while the baryon-to-e± energy transfer should be very efficient at wind termination. A strongly magnetized cold wind seems to be the most favorable option as it is consistent with recent research on pulsar winds and does not require fine-tuning of the pulsar wind orientation, and the wind multiplicity and Lorentz factor are less constrained. |
Note: | Reproducció del document publicat a: https://doi.org/10.1051/0004-6361/202039666 |
It is part of: | Astronomy & Astrophysics, 2021, vol. 645, p. 86 |
URI: | http://hdl.handle.net/2445/175202 |
Related resource: | https://doi.org/10.1051/0004-6361/202039666 |
ISSN: | 0004-6361 |
Appears in Collections: | Articles publicats en revistes (Física Quàntica i Astrofísica) |
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709004.pdf | 2.17 MB | Adobe PDF | View/Open |
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