Long Duration High Energy Transients

S. R. Kulkarni

AN INTERLUDE – COMPACTNESS PROBLEM

FROM SARI’S TALK (CIRCA 2000)

Energy

• We measure F~10-6 erg/cm2

• Cosmological: D ~ 1028cm

• E = 4D2F ~ 1051erg

Temporal Variability• dT<1s, T~100 N=T/dT>100

Implications of short timescale

dt=R/c

R/c

dT ~ 1ms R < 3•107 cm E ~ 1051ergs 1057 photons

high photon density(many above 500 keV).

Optical depth T n R~1015>>1 Inconsistent with the non thermal spectrum!

COMPACTNESS PROBLEM g + g e+ + e-

Spectrum:Optically thin

Size & Energy:Optically thick

? Paradox ?

A

C

BD

R

R

R

~1/g

Relativistic Time-Scales

• tB-tA ~ R (1-) / c ~ R/2g2c

• tC-tA ~ R(1-cos )/c ~ R/2g2c

• tD-tA ~ /c

Due to Relativistic Motion R = g2 c dT Eph (emitted) = Eph (obs) / g

tgg = g-(4+2a) nTR ~ 1015/g4+2a

(Goodman; Paczynski; Krolik & Pier; Fenimore; Woods & Loeb; Piran & Shemi; Lithwick & RS 01)

g > 100

The Solution:Relativistic Motion

Relativistic Motion

(Lithwick & RS 2001)

References

• F. J. Virigili et al. 2013 (ApJ 778)• A. J. Levan et al. 2013 (astroph)

GRB091024Az=1.09

Nuclear sources?

Need a long lived engine

• Collapsar model: What determines the duration of the engine?

• Tidal Disruption Event– Long duration nicely explained

• Magnetar powered?

Tidal Disruption Flare?

Movie!

Grand Overview

Observational difficulties

• Most GRB missions work on “triggers” – spikes of emission

• Such events are best seen in “imaging triggers”– But satellite must be pointed to the same piece of

sky for 1000 s (not the case with Swift)• I wonder how well has the BAT data been

analyzed for such objects (or for that matter WFC data)

Tests

• Does the object coincide with the nucleus?• Is there a 1998bw-like supernova associated

with the object?• What is the total energy loss? (relative to say

1052 erg)