francisco j virgili prompt grb conference, 2011 march 5, 2011; raleigh, nc
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ARE ALL GRBS OF MERGER ORIGIN?FJV, ZHANG, O’BRIEN, TROJA, 727, 109 (2011)
Francisco J VirgiliPrompt GRB Conference, 2011March 5, 2011; Raleigh, NC
Short: smaller energy budget? Energy injection?
Eichler et al. (1989), Paczynski (1986), Narayan et al. (1992) propose merger scenario as possible progenitor
Supported by hostobservations, lack ofSN
INTRINSIC V. EMPIRICAL
Short-hard and long-soft Nomenclature based on the observational
properties of the burst Type I and Type II
Based on the intrinsic progenitor of the burst
Type I = compact object (e.g. merger progenitor)
Type II = massive star (e.g. stellar core collapse)
Short burst Long Burst (Evans et al 2007)
sGRB + Extended Emiss. (long-short?) Barthelmy 2007
High z long burst, but intrinsically short? (Zhang et al. 2009)
I. SHORT HARD BURSTS AS MERGERS Observational evidence supports a
merger model as possible progenitor Tricky nomenclature…but boils down to:
Are all short-hard bursts consistent with a merger progenitor?
MONTE CARLO SIMULATIONS
Test the underlying luminosity function, redshift distribution (including the merger time delay) and validity of the assumption that SHBs are of type I origin by comparison with the observational sample through multiple criteria:
1D z and L 2D z-L log N – log P (BATSE) log N – log P (Swift)
MERGER TIMESCALE DISTRIBUTION
Constant + scatter (SD = 0.3, 1.0) (Nakar and Gal-yam, 2006; Guetta and Piran, 2006)
Logarithmic (Piran 1992, Guetta and Piran 2006)
Population Synthesis (Belczynski et al. 2008, 2007)
MERGER TIMESCALE DISTRIBUTION
No delay Mix (Population
synthesis + Type II population)
Use to gauge the amount of contamination from different burst populations
RESULTS: NO DELAY
Extreme case: All SHB are Type II (related to massive stars)
Small area of consistency with L-z constraints, LNLP incompatible
Need SOME delay
RESULTS: CONSTANT MTD
Large delay (>2 Gyr) models not favored by most LNLP constraints and not supported by host galaxy observations
Smaller (esp. 2 Gyr model) passes all tests
RESULTS: MIXED MODELS
Both fully merger and no delay models ruled out by current observations of short-hard bursts
100% type II model (as modeled in FJV 2009 and Liang et al 2007) ruled out in L-z consideration but consistent with slope of BATSE log N-log P
Consider a model with mixing of a type I population (with a merger time delay that follows the twin population synthesis distribution) and a population that follows the Type II luminosity function
CONCLUSIONS Constant delay ~2 GYR (plus scatter)
At odds with Galactic NS-NS binary observations
Different origin? (e.g. AIC – (Qin et al. 1998, Dermer & Atoyan 2006))
Mixing High z – High L GRBs Type II? (Zhang et al.
2009) Off-axis emission? (Lazzati et al. 2010) 090510 of massive star origin? (Panaitescu
2010)
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