Gamma-ray burst afterglows in pulsar-wind bubbles

Arieh Königl, Jonathan Granot

Research output: Contribution to journalArticlepeer-review


We propose to identify pulsar-wind bubbles (PWBs) as the environment in which the afterglow emission in at least some gamma-ray burst (GRB) sources originates. Such bubbles could naturally account for both the high fraction of the internal energy residing in relativistic electrons and positrons (∈e) and the high magnetic-to-internal energy ratio (∈ B) that have been inferred in a number of sources from an interpretation of the afterglow emission as synchrotron radiation. GRBs might occur within PWBs under a number of scenarios: in particular, in the supranova model of GRB formation a prolonged (months to years) period of intense pulsar-type wind from the GRB progenitor precedes the burst. Focusing on this scenario, we construct a simple model of the early-time structure of a plerionic supernova remnant (SNR), guided by recent results on the Crab and Vela SNRs. The model is based on the assumption of an "equipartition" upper bound on the electromagnetic-to-thermal pressure ratio in the bubble and takes into account synchrotron-radiation cooling. We argue that the effective upstream hydrogen number density for a relativistic shock propagating into the bubble is given by nH,equiv = [4p + (B′ + ℰ′) 2/4π]/mpc2, where B′ and ℰ′ are, respectively, the comoving magnetic and electric fields, and p is the particle pressure. We show that, for plausible parameter values, n H,equiv spans the range inferred from spectral fits to GRB afterglows and that its radial profile varies within the bubble and may resemble a uniform interstellar medium, a stellar wind, or a molecular cloud. We consider how the standard expressions for the characteristic synchrotron spectral quantities are modified when the after-glow-emitting shock propagates inside a PWB instead of in a uniform interstellar medium and demonstrate that the predictions for the empirically inferred values of ∈e and ∈B are consistent with the observations. Finally, we outline a self-consistent interpretation of the X-ray emission features detected in sources such as GRB 991216 in the context of the supranova/PWB picture.

Original languageEnglish
Pages (from-to)134-154
Number of pages21
JournalAstrophysical Journal
Issue number1 I
StatePublished - 20 Jul 2002
Externally publishedYes


  • Gamma rays: bursts
  • MHD
  • Pulsars: general
  • Pulsars: individual (Crab Nebula, Vela pulsar)
  • Shock waves
  • Supernova remnants


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