Talk: GRBs – Recent developments from Fermi

Peter Mészáros (PSU)

  • Are the photons from leptonic or hadronic origin?  X-ray to radio: leptonic, MeV: probably leptonic; GeV: debated.
  • GRBs are a possible origin for ultra-high energy cosmic rays.  For gravitational waves, theoretically but not detected yet.
  • GRB 080916c: Adbo+ (2009, Science, 323, 1688): GeV photons “lag” behind MeV photons.  Why?
  • (Jacob & Piran 2008): Quantum gravity?  Energy-dependent dispersion of boson and fermion signals.  Can determine some lower-limit of a quantum gravity strength. M_QG(n=1) ≥ (1.50 ± 0.20) x 10^18 GeV/c^2 for GRB 080916c, a long burst.  For a short burst (GRB 090510), the lower limit was ~few x 10^19 GeV/c^2 ~ M_planck. Rules out n=1 term.
  • Do the internal or external shocks produce the GeV signals?  Which matter (leptonic, hadronic?) creates it?
  • GRB 080319B (naked-eye one): Had a very strong MeV component.  Can be explained through a hadronic origin.
  • (Beloborodov 2010, MNRAS 407, 1033): proton-neutron collisional dissipation to explain a “thermal” component.  It leads to pair-production to gamma-ray emission.
  • (Mészáros & Rees 2010, ApJ 715, 967): Pop III GRBs?  Their emission will be extended because of their high redshifts.  See (Toma+ 2011 ApJ 731, 127) for the afterglows.  Detectable with ICECUBE and Fermi.  However we can’t determine the distance of most GRBs without a spectrum.
  • (Gao+ 2011 PRD 83): Neutrinos should originate from the external shock of Pop III GRBs.  It is mass dependent!  Could be a way to constraint the Pop III IMF.  For a 30 solar mass star, it couldn’t be detectable by ICECUBE after 5 years.  However for a 300 solar mass star, it would be detectable at higher energies.
  • Advanced LIGO should find a few BH-NS NS-NS mergers per year, if they’re the source of short GRBs.  One can obtain the distance from the GW “chirp”.
  • (Ott+ 2011, PRL 106): Simulation of GWs from collapsars.  Determined that they are undetectable unless in the MW.  Debatable.
  • The neutrino flavor ratios (perhaps detectable by ICECUBE) depends on the production process.  A whole neutrino spectrum is generated by the expansion of the fireball with the higher energies coming later, especially when the jet breaks out.
  • (Kappes, NUSKY, June 2011): Adding up the emission of all northern sky GRBs and observing with ICECUBE, they found that the observed upper limit was a factor of 5 lower than what is predicted by models.  Must rethink the models.  Up to now, there’s no hint for neutrinos from GRBs.  However, they’re still a possible source!

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