Are all grbs of merger origin? FJV, Zhang, o’brien , troja , 727, 109 (2011)

Francisco J Virgili Prompt GRB Conference, 2011 March 5, 2011; Raleigh, NC Are all grbs of merger origin?FJV, Zhang, o’brien, troja, 727, 109 (2011)

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) Intrinsic v. empirical

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 080916C (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? I. Short hard bursts as mergers

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: pop synthesis/log • Twin model(Belczynski 2007) • Regular and logarithmic do not

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

Mixed models 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) • 090510 of massive star origin? (Panaitescu 2010) Conclusions

Are all grbs of merger origin? FJV, Zhang, o’brien , troja , 727, 109 (2011)