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)