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Lack of thermal energy in superbubbles: hint of cosmic rays?

Gupta, Siddhartha and Nath, Biman B and Sharma, Prateek and Eichler, David (2018) Lack of thermal energy in superbubbles: hint of cosmic rays? In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 473 (2). pp. 1537-1553.

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Official URL: http://dx.doi.org/10.1093/mnras/stx2427

Abstract

Using analytic methods and 1D two-fluid simulations, we study the effect of cosmic rays (CRs) on the dynamics of interstellar superbubbles (ISBs) driven by multiple supernovae (SNe)/stellar winds in OB associations. In addition to CR advection and diffusion, our models include thermal conduction and radiative cooling. We find that CR injection at the reverse shock or within a central wind-driving region can affect the thermal profiles of ISBs and hence their X-ray properties. Even if a small fraction (10-20 per cent) of the total mechanical power is injected into CRs, a significant fraction of the ram pressure at the reverse shock can be transferred to CRs. The energy transfer becomes efficient if (1) the reverse shock gas Mach number exceeds a critical value (M-th greater than or similar to 12) and (2) the CR acceleration time-scale tau(acc) similar to k(cr)/v(2) is shorter than the dynamical time, where k(cr) is a CR diffusion coefficient and v is the upstream velocity. We show that CR affected bubbles can exhibit a volume-averaged hot gas temperature 1-5 x 10(6) K, lower by a factor of 2 -10 than without CRs. Thus, CRs can potentially solve the long-standing problem of the observed low ISB temperatures.

Item Type: Journal Article
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Depositing User: Id for Latest eprints
Date Deposited: 02 Mar 2018 14:55
Last Modified: 02 Mar 2018 14:55
URI: http://eprints.iisc.ac.in/id/eprint/59061

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