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
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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, ...)
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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.
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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
Naked-Eye Burst SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
Naked Eye Burst:optical vs gamma
Optical and gamma plateau are correlated!
Corr=0.82, SL=5*10-7
Naked-Eye Burst SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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 shellProton shell
Proton shell
Proton shellProton shell
Proton shell
Naked-Eye Burst SAO RAS, 2009
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 SAO RAS, 2009
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 SAO RAS, 2009
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