Francisco J Virgili Prompt GRB Conference, 2011 March 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 host observations, lack of SN

 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)

GRB C (Abdo et al. 2009) Zhang et al. (2009)

 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?

 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)

 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)

 No delay  Mix (Population synthesis + Type II population)  Use to gauge the amount of contamination from different burst populations

 Extreme case: All SHB are Type II (related to massive stars)  Small area of consistency with L-z constraints, LNLP incompatible  Need SOME delay

 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

 Twin model (Belczynski 2007)  Regular and logarithmic do not

 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

Population synthesis mix Twin model mix

 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)  of massive star origin? (Panaitescu 2010)