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Astrophysical implications of external triggers, GRB030329 in particular
External Triggers subgroup

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GRB astrophysics is still very uncertain Associated GW emission: even more uncertain Interpret our observations in the simplest terms
Easy to re-cast in terms of specific models Provides some astrophysical context which is readily interpretable

Probable: The GRB field will need GW observations to fully understand GRB progenitor astrophysics

Nov 10, 2003

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Short and Long GRBs...

BATSE data

Prejudices: Long GRBs are Collapsars (2 events) Short GRBs are compact inspirals
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Burst categories associated with GRBs
1. Short (~1ms) GW bursts SN-like core bounces, including collapsars (the long-GRB SM)
· Plausible for GRB030329

The astrophysical modeling can serve only as a guide of signal character, not to be taken literally Gaussians, sine-gaussians ZM or DFM or ? Main focus of current analyses in ExtTrig group 2. Must also consider longer duration, sinusoid-like bursts: Interesting core dynamics: bar-instabilities, core fragmentation Large ang. mom., lumpy, accretion torus (van Putten)
The most specific model (and potentially prolific GW producer)

Binary inspirals (the "leading" candidates for short GRBs)
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Determining an astrophysically relevant limit

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Trigger inputs: event position on sky (assume a point with errors here) event time to <1s distance (z) if known from afterglow measurements Assume a waveform h(t) and polarization A "surrogate" waveform (G or SG, for example), or a modeled waveform (e.g. ZM) Can specify polarization, if predicted. (Assume unpol. for now.) Inject series of such waveforms into pipeline upper limit

Nov 10, 2003

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Relate observed h(t) to GW Energy...

for an observation (or limit) made at a luminosity distance d from a source.

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For example, consider an upper limit corresponding to a gaussian signal (hO, ) with a specified polarization and orientation, then:

Nov 10, 2003

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a) Assume there exists some mechanism which converts non-spherical mass into GW:

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Minimal astrophysical assumptions Isotropic GW emission Short, core-collapse-like bursts

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Note: For d=100 Mpc, the GRB rate is about 1/yr for a GRB beaming angle of 2°
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b) If we can assume a GRB is associated with a truly SN-like core collapse, then we might estimate GW energy based on SN calculations. E.g., assuming axisymmetry, a max. efficiency is 7в10-4 , then

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1.4 MO at this efficiency d=5 Mpc 1.4 MO and d=10Mpc = 0.4 %

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Waveforms...
· Surrogates Gaussian:

Sine-gaussian: · For waveforms such as ZM or DFM: · Determine h_peak and f2h(f)2 df for each waveform whose hrss corresponds to the observed limit · Form distribution of derived M_ns, etc For putative long duration waveforms, the limits improve for comparable strain amplitudes... this work in progress.

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Idea is to include these calculations as standard part of injection/analysis pipeline; implement as a Matlab script, for example
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GRB030329
H1-H2 only antenna attenuation factor 0.37 (assuming unpolarized) d z(c/Ho)(1 + z/4) , for =1 z=0.1685 d=800Mpc , for Ho=66 km/s/Mpc Using sine-gaussian limit for Q=8.9, f=250 Hz, 90% eff: hO= 6.8в10-20 M_ns = 2.0 MO (d/100Mpc) 125 MO (1 / 0.37) = 340 MO
2

Nov 10, 2003

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Prospects example

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GRB980425: d=35Mpc, assuming GRB030329 H1-H2 sensitivity and optimal orientation:

M_ns = 0.24 MO

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Astrophysical Models Considered 1. Collapsars ("standard" GRB progenitor model) ­ Collapse of massive (>20M ), rapidly rotating (,non-H) star to a black hole; star shell is blown off ("hypernova"); accretion inflow produces relativistic (200) outflow ("fireball") which gets beamed by interaction with asymmetric shell, producing photons GRB. Time scales for collapse and accretion-jet are both 1 ms. derives from v Nov 10, 2003 Frey 11


Astrophysical Models (contd.) 2. Cannonball GRB model ­ Progenitors are ordinary core-collapse SNe. Infall of stellar shell remnant onto core highly relativistic (103) "cannonball" pair highly beamed GRB 1 s (requires clarification) T and waveforms: use DFM 3. GW emission from the relativistic jet (fireball/cannonball) itself Produces "burst with memory"; G 4 m h= 2 requires further study c d 4. Binary inspirals BH formation; accretion disk GRBs. Leading candidates for short (<2 s) duration GRBs. Not clear that triggers are helpful... is there a study? No current plans to pursue this explicitly.

Nov 10, 2003

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Parameters Summary

1-a Collapsar, "SN-like" core collapse 1-b Collapsar, with core bar instability 1-c Collapsar, with core fragmentation 1-d Collapsar, with unstable torus (van Putten) 2 3 4 Cannonball GW from the GRB jets Binary inspiral
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wf waveform z redshift G gaussian () SG sine gaussian (,f0)