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The nature of the longest gamma-ray bursts

The nature of the longest gamma-ray bursts. Andrew Levan University of Warwick. Burst durations. Very long bursts are often image triggers (1000+s). Swift 1644+57. Not as rare as you think……. For same integrated fluence , more difficult to detect long events.

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The nature of the longest gamma-ray bursts

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  1. The nature of the longest gamma-ray bursts Andrew Levan University of Warwick

  2. Burst durations Very long bursts are often image triggers (1000+s) Swift 1644+57

  3. Not as rare as you think……. For same integrated fluence, more difficult to detect long events Correction from Swift observed rates to astrophysical rates (at Swift limits) could be a factor 10 Data courtesy J. Kennea

  4. Should they be different? Some very long bursts probably are the “tail” of the “normal” GRB distribution Others are low luminosity GRBs (shock breakout?) Some initially classified as GRBs are clearly different (e.g. GRB 110328A/Swift 1644+57 – Burrows talk) Jet breakout time – longer GRBs could mean bigger stars? Suggestion of longer lived central engines, perhaps powered by outer layers of stars (e.g. Quataert et al. 20122; Woosley & Heger 2012) Two more recent examples discussed here (101225A, 111209A)

  5. GRB 101225A Visibility from Bethlehem

  6. X-ray spectrum = Powerlaw + blackbody (1 keV)

  7. Optical afterglow

  8. Scenario I: Galactic Tidal shredding of asteroid mass body around a NS Campana et al. 2011

  9. Scenario II: Collapsar Supernova? He-NS merger Bang Fryer et al. 1999; Thoene et al. 2011

  10. Thoene et al. 2011

  11. HST and late time observations HST ACS/F435W (Jan) Gemini GMOS (July) g-band Significant host contribution at ~1 month, but not resolved Note: No proper motion in 6 months (v < 250 km/s/kpc) If host the afterglow is “on” the nucleus

  12. Host constraints

  13. GRB 111209A 10000s

  14. OIII (4959) OIII (5007)

  15. X-ray afterglow

  16. X-ray afterglow

  17. Supernova search VLT + Gemini J-band HST grism spectrum u-band Clear reddening, no obvious SN. Host? Chromatic afterglow?

  18. HST observations WFC3/F336W WFC3/F110W Host galaxy still largely unresolved (<800pc), very compact if bright

  19. Summary Very long GRBs are more astrophysically common that we might expect. (but too long for Swift and too faint for BATSE, GBM etc). The longest bursts appear to have distinct prompt, afterglow (and host?) properties from the majority of GRBs. They are probably cosmological, but evidence for SN within them remains weak Understanding the nature of the longest gamma-ray transients should remain an important task.

  20. LGRB SGRBs TDEs? LLGRBs unknown SGRs Galactic sources (SGR, LMXB, HMXB, micro-quasar, gamma-ray pulsar)

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