Transcript pptx
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
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 Galyam, 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)