Shiho Kobayashi (Liverpool JMU)

GW burst-GRB delayGW burst-GRB delay

Time delay between GW signal and GRB trigger

• GRB-trigger search for GWs by LIGO/Virgo targets both the chirp signal in the case of short GRBs and short unmodeled pulses of GWs.

• On-source time windows of few mines (Long GRBs) and few seconds (Short GRBs)

• Any astrophysical implications?

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Collapsar Model for Long GRBs

Massive Star Core collapse

relativistic jet

accreting disk

4

GRB Progenitor GW Signals: Collapsar

breakup (optimistic) d=270 Mpc, solar mass blobs at disk size r=107 cm

Dashed: adv LIGO sensitivity

(b)

(Solid: dot-dash: merger; circle :bar inst; spike: ring-down); shaded : rate/dist uncertainty

(S.K. & Mészáros 2003)

Long GRBs• The time delay is possibly dominated by the time

necessary for the jet to push through the stellar envelope.

• For low luminosity GRBs, the break time is longer, and the head velocity is newtonian: beta <<1

• Possible Correlation between GRB luminosity and time delay(GW-GRBs)– Luminosity, temporal profile (shock breakout), spectrum

5

6

Low luminosity GRB

7

R

t

GW burst

observer’sworld linerel

ativis

tic je

t

10^13-14cm 10^16-17cm

prompt gamma-raysInternal shock model

onset of afterglowExternal shock

~hr

~week

Time delay: EM and GW

almost

null

geodes

ic

€

Δt = R /cΓ2

€

c Δt = c Rcβ ⎛ ⎝ ⎜

⎞ ⎠ ⎟≈ 1+ 1

2Γ 2

⎛ ⎝ ⎜

⎞ ⎠ ⎟R

€

Δtobs ≈ R2cΓ2

Two photons from a source with relativistic velocity　

photon1 photon1photon2

R

€

1st photon propagates

Separation:

€

≈R

2Γ 2

Arriving time difference:

2R

Summary

• Possible Correlation between GRB luminosity and time delay(GW-GRBs)– Luminosity, temporal profile (shock breakout), spectrum

• Other contributions to the delay between GW burst and GRB?– Precursor, some GRBs : dimmer peaks at the beginning– Uncertainty in GW production: GW and jet form together?

9