Central engine activity as seen in Naked-Eye Burst prompt emission G.Beskin, S.Karpov, S.Bondar,...

Central engine activityas seen in Naked-Eye

Burstprompt emission

G.Beskin, S.Karpov, S.Bondar, A.Guarnieri, C.Bartolini, G.Greco, A.Piccioni

Gamma-Ray Bursts:origin

E=1051-1054 erg — comparable to the rest-energy of the Sun

the collimation is necessary — so, let there be jetsCompact objects merging and formation of black holeNS+NS, NS+BHOrbital motion -> collimationOld objects in halos of old galaxies

Massive star collapse towards the black hole100-150 Msun starsRotation -> collimation of the ejectaYoung objects in star formation regionsSupernova imprints on late stages of the afterglow

Gamma-Ray Bursts:fireball model

cm 10100

15

r cm 10110

17

r

Naked-Eye Burst SAO RAS, 2009

Gamma-Ray Bursts:what can variability tell?

• Activity of central engine – Periods– Flares

• Dynamics of ejecta– Internal shocks– Instabilities (density fluctuations, magnetic field

reconnections…)– Interaction with surrounding medium

• Temporal properties of prompt emission– Stochastic components are distorted (instabilities,

interactions, ...)– Periodic components (have to, can, could) reflect internal

engine behaviour?

Gamma-Ray Bursts:temporal properties – key for the central

engine nature

About 80% of GRBs light curves are structured The gamma variability timescale is down to ~10-4 s (close to the timescale near horizon events) No periodicity! What about optical prompt emission?

Bi-modal distribution of durations~40% are shorter than 2 seconds


Gamma-Ray Bursts:open questions about optical emission

• When does it start and when does it end?

• Transition from prompt emission to afterglow

– several hundreds of afterglows, but only about ten prompts

• Temporal variability

– gamma is highly variable down to 10-4 s, what about optics?

• Relation to gamma emission

– are they correlated?

– what is the temporal lag between them? who is the first?

• Prompt emission from the short bursts

– afterglows are basically the same, what about prompts?

All this require the detection of very first moments of the burst

and, obviously, high temporal resolution of observations


Gamma-Ray Bursts:time is money

GRB Coordinates Networkcoordinates after ~10 seconds

For 50% of events optical prompt emission is lost!

Up to now found ~350 afterglows and ~ 20 prompts (~40 upper limits from 8 to 23 mag) ratio of papers - 0.2 RESPONSE TIME OF ALERT-BASED SYSTEMS IS TOO LARGE


Independent search for optical prompt emission:

requirements for a general-purpose system

• Need wide field of view

– the shorter the focus the better

• Need good detection limit

– the larger the diameter the better

• Need high temporal resolution

– short exposures and fast read-out

– low read-out noise

• Need real-time processing software

– real-time detection and classification of transients


Independent search for optical prompt emission :

crazy ideas of the past• Large telescopes with «bad» mirrors

Beskin et al (1999)

Size: 10-30 m Detectors: 10-1000 PMT (< 1us) FOV: 10-20 square degrees Angular resolution: 5-30 arcmin Limit: up to 18m for 1ms

Cerenkov telescopes

(MAGIC, H.E.S.S., VERITAS...)

Solar concentrators

(PETAL, ...)


Gamma-Ray Bursts:prompt optical emission

You need to look at the burst position before it appears!

Systematic monitoring of all sky (or its large parts) with high temporal resolution

Selection of parameters – contradictory requirements

Wide field of view

Large objective diameter

High time resolution

Optimal parameters: DECISION

Field of view > 20o x 20o Small telescopes with large D/F

Temporal resolution < 0.1 c and fast detectors

Limiting magnitude > 10m


Wide-Field Monitoring:systems currently in operation

Only general-purpose systems are listed. There are also a lot of specialized (like meteor cameras) or narrow-field (like LINEAR) monitoring projects around the world.


FAVOR & TORTORA systems:overview

FAVOR (FAst Variability Optical Registrator) camera — SAO RAS, since 2003Built in collaboration with IPI and IKI (Moscow), supported by CRDF grant


TORTORA system:overview

La-Silla, Chilemounted on REMsince 2006Team: SAO RAS, IPI (Russia), Bologna University, REM (Italy)

Telescopio Ottimizzato per la Ricerca deiTransienti Ottici Rapidi

Two-telescope complex:- independent detection- automatic studyT

OR

TO

RA


TORTORA system:technical details

Objective

Diameter: 120 mmFocal length: 150 mmD/F: 1/1.2Field of view: 32x24o

Image Intensifier

type: S20diameter: 90 mmamplification: 120downscale: 4.5/1Q.E.: 10%

CCD

type: SONY 2/3'' IXL285size: 1388х1036exposures: 0.128 — 10 secscale: 80''/pixellimit: ~10.5m for 0.13с

Data flow rate — 20 Mb/s, per night— 600 Gb, ~200.000 frames


Wide-field monitoring systems:TORTORA


TORTORA – real-time analysis

Decision scheme Analysis of objects on separate frames

Merging them into events

Automatic classification of events transient known astrophysical object satellite meteor

Conclusion on event nature in 0.4 s

Example of fast optical transient

duration – 0.4 smagnitude – 4.6m

identification – satellite


Wide-field monitoring systems:TORTORA

Two-telescope complex — observations in triggered mode Bursts outside FOV Fast REM repointing on GCN alerts Data acquisition and analysis with high time resolution

GRB 060719Pointing after 59 seconds

Limit B > 12.4 with 12.8 s effective exposure

Limit for sinusoidal variable component B > 16.5 in 0.01 - 3.5 Hz frequency range

GRB 061202Pointing after 92 seconds

Limit B > 11.3 with 12.8 s effective exposure

Limit for sinusoidal variable componentB > 14.0 in 0.1 - 3.5 Hz frequency range

GRB 061218 Pointing after 118 seconds Limit B > 11.3 with 12.8 s effective exposure Limit for sinusoidal variable component B >

16.4 in 0.01 - 3.5 Hz frequency range


Naked Eye Burst:the stars – they are falling

• GRB 080319a: T0 = 05:45:41 UT, T

90~40 s, R~21m

• GRB 080319b: T0 = 06:12:49 UT, T

90~60 s, V~5.5m

• GRB 080319c: T0 = 12:25:55 UT, T

90~20 s, R~17m

• GRB 080319d: T0 = 17:05:19 UT, T

90~24 s, V~19m

• GRB 080320: T0 = 04:37:38 UT, T

90~25 s, I' ~23m


Naked Eye Burst:burst in real time


Naked Eye Burst:triumph of monitoring systems


Naked-Eye Burst:observations, observations...


Naked Eye Burst:general information – spectrum


Naked Eye Burst:general information — light curve

GRB 080319bSwift, Konus-Wind, IntegralE

iso = 1.321054 erg, E

opt,iso = 61051 erg

z=0.937(VLT/UVES, 8.5 min since burst)


Naked Eye Burst:what timing may say

Starting at T ~ 0 sRise ~ t 3.5

Fall ~ t -5

Variability: - 2 parts (2 x ~20 s) with intensity ratio of 1.6 - 4 peaks (3-7 s)

Optical observations:- detailed rise and fall- variability (peaks) on seconds- optical/gamma correlation - ???


Naked Eye Burst:periodicity

T = 9.40.8 s, SL=10-15


Naked Eye Burst:periodicity

Four nearly equidistant peaks

• T1-2

= 8.7 0.4 s

• T2-3

= 9.0 0.3 s

• T3-4

= 8.2 0.5 s

Periodic behaviour of central engine?

Kocevski et al (2003)


Naked Eye Burst:power spectra


Naked Eye Burst:short time scales

Signs of a periodicity at last peak (40-50 s). A~10%, T~1.14

T = 1.140.06 s

SL= 0.01

A<10%A<15%

Precession of central engine / jet ???


Naked Eye Burst:optical vs gamma

Optical and gamma plateau are correlated!

Corr=0.82, SL=5*10-7


Naked Eye Burst:what theorists think about

Two-component jet (Racusin et al 2008)

Explains optical/x-ray late afterglow

Can't say anything about prompt emission and variability

Synchrotron-Self Compton model (Kumar & Panaitescu 2008)

Explains optical to gamma excess

No optical lag, or negative one

Overproduces GeV photons

Cannonball model (Dado, Dar & De Rujula 2008)

The same as SSC model

No predicted supernova bump one month since the burst

Optical and gamma emissions from internal forward-reverse shocks (Yu, Wang & Dai 2008)

Optics and gamma from the same region, simultaneous emission

No optical lag


Naked Eye Burst:residual collisions at large radii

Optical emission from residual collisions at large radii (Li & Waxman 2008)

Optical lag of ~1 s imply residual collisions radius of 1016 cm

Optical emission is of the same nature as gamma-ray one

Optics and gamma have the same modulation due to internal engine

Internal engine(single activity episode)modulated ejection of shells

Initial collisionsR ~ 1013 cm

Residual collisionsR~1016 cm

Gamma emission Optical emissionГ +/- dГAfterglow


Naked Eye Burst:neutron-rich internal shocks

-rays

Regular internal shocks at ~1013 cm: powering gamma-ray emission

The beta-decay radius :Natural explanation of fluxes ratio (opt-gamma) ~ 1000

Secondary internal shocks at ~1016 cm – result of collisions of late proton shells with products of the early neutron beta-deckay: powering UV/optical emission

Proton shellProton shell


Proton shell


Proton shell


Naked Eye Burst:insights from variability

Periodic activity of internal engine — accretion instability modulating the outflow?

One second period — signature of precession?


Naked Eye Burst:instability + precession

GravitomagneticPrcession T ~ 0.5 sec

Toy model

Newly born black hole

M ~ 3 Msun

Massive accretion disk

Mdisk ~ Msun

Neutrino-driven viscous instability

Rstop ~ 30 RgViscousInstabilityT ~ 5 sec

Masada et al, 2007


Naked Eye Burst:Summary

• First GRB to be seen completely simultaneously in optical/gamma

• Two scales of optical variability

– Periodicity of ~10 seconds for overall emission – four peaks

– One second period on the last peak (40-50 s)

• Optical/gamma spectral lag of ~2 seconds as evidence of different localizations ( distance ~ 1016 cm )

– Rules out inverse compton models of gamma emission

• Spectral lags and optical/gamma correlation (r~0.82) imply the same origin of emission variability – periodic activity of central engine


See you in nine years!

Naked-Eye Burst

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Central engine activity as seen in Naked-Eye Burst prompt emission G.Beskin, S.Karpov, S.Bondar,...

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