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)

GRB 080916C (Abdo et al. 2009)

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: 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

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)