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Title: DETECTING THE RAPIDLY EXPANDING OUTER SHELL OF THE CRAB NEBULA: WHERE TO LOOK

We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emissions from high ionization lines that will not be emitted by the Crab's filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The near-NIR [Ne VI] {lambda}7.652 {mu}m line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV {lambda}1549 doublet is predicted to be the strongest absorption line from the shell, which is in agreement with Hubble Space Telescope observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually ''remember'' its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level ofmore » ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion.« less
Authors:
;  [1] ; ; ;  [2]
  1. Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States)
  2. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320 (United States)
Publication Date:
OSTI Identifier:
22133907
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 774; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; APPROXIMATIONS; CRAB NEBULA; EMISSION; EXPLOSIONS; HYDROGEN; MASS; PHOTOIONIZATION; RECOMBINATION; SIMULATION; STEADY-STATE CONDITIONS; SUPERNOVAE; TELESCOPES; VISIBLE RADIATION