Lyutikov, M, Temim, T, Komissarov, S orcid.org/0000-0003-4545-9774 et al. (3 more authors) (2019) Interpreting Crab Nebula’s synchrotron spectrum: two acceleration mechanisms. Monthly Notices of the Royal Astronomical Society, 489 (2). pp. 2403-2416. ISSN 0035-8711
Abstract
We outline a model of the Crab pulsar wind nebula with two different populations of synchrotron emitting particles, arising from two different acceleration mechanisms: (i) Component-I due to Fermi-I acceleration at the equatorial portion of the termination shock, with particle spectral index pI ≈ 2.2 above the injection break corresponding to γwindσwind ∼ 105, peaking in the ultraviolet (UV, γwind ∼ 102 is the bulk Lorentz factor of the wind, σwind ∼ 103 is wind magnetization); and (ii) Component-II due to acceleration at reconnection layers in the bulk of the turbulent Nebula, with particle index pII ≈ 1.6. The model requires relatively slow but highly magnetized wind. For both components, the overall cooling break is in the infrared at ∼0.01 eV, so that the Component-I is in the fast cooling regime (cooling frequency below the peak frequency). In the optical band, Component-I produces emission with the cooling spectral index of αo ≈ 0.5, softening towards the edges due to radiative losses. Above the cooling break, in the optical, UV, and X-rays, Component-I mostly overwhelms Component-II. We hypothesize that acceleration at large-scale current sheets in the turbulent nebula (Component-II) extends to the synchrotron burn-off limit of ϵs ∼ 100 MeV. Thus in our model acceleration in turbulent reconnection (Component-II) can produce both hard radio spectra and occasional gamma-ray flares. This model may be applicable to a broader class of high-energy astrophysical objects, like active galactic nuclei and gamma-ray burst jets, where often radio electrons form a different population from the high-energy electrons.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. Reproduced in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Mathematics (Leeds) > Applied Mathematics (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 06 Mar 2020 16:16 |
Last Modified: | 06 Mar 2020 16:16 |
Status: | Published |
Publisher: | Oxford University Press |
Identification Number: | 10.1093/mnras/stz2023 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:158137 |