The nature of the longest gamma-ray bursts
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The nature of the longest gamma-ray burstsAndrew LevanUniversity of Warwick
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Burst durations
Swift 1644+57
Very long bursts are often image triggers (1000+s)
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Correction from Swift observed rates to astrophysical rates (at Swift limits) could be a factor 10
Not as rare as you think…….
For same integrated fluence, more difficult to detect long events
Data courtesy J. Kennea
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Should they be different?Some very long bursts probably are the “tail” of
the “normal” GRB distributionOthers 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)
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GRB 101225A
Visibility from Bethlehem
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X-ray spectrum = Powerlaw + blackbody (1 keV)
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Optical afterglow
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Scenario I: Galactic
Tidal shredding of asteroid mass body around a NSCampana et al. 2011
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Scenario II: Collapsar
Fryer et al. 1999; Thoene et al. 2011
Supernova?He-NS merger
Bang
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Thoene et al. 2011
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HST and late time observations
Note: No proper motion in 6 months (v < 250 km/s/kpc)If host the afterglow is “on” the nucleus
HST ACS/F435W (Jan) Gemini GMOS (July) g-band
Significant host contribution at ~1 month, but not resolved
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Host constraints
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GRB 111209A
10000s
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OIII (4959) OIII (5007)
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X-ray afterglow
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X-ray afterglow
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Supernova search
HST grism spectrumJ-band
u-band
VLT + Gemini
Clear reddening, no obvious SN. Host? Chromatic afterglow?
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HST observations
WFC3/F336W WFC3/F110W
Host galaxy still largely unresolved (<800pc), very compact if bright
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SummaryVery 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.
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SGRs
TDEs?
Galactic sources (SGR, LMXB, HMXB, micro-quasar, gamma-ray pulsar)
LLGRBs
SGRBsLGRB
unknown