Central engine activity as seen in Naked-Eye Burst prompt emission G.Beskin, S.Karpov, S.Bondar, A.Guarnieri, C.Bartolini, G.Greco, A.Piccioni

Gamma-Ray Bursts: origin E= erg — comparable to the rest-energy of the Sun the collimation is necessary — so, let there be jets Compact objects merging and formation of black hole NS+NS, NS+BH Orbital motion -> collimation Old objects in halos of old galaxies Massive star collapse towards the black hole Msun stars Rotation -> collimation of the ejecta Young objects in star formation regions Supernova imprints on late stages of the afterglow

Gamma-Ray Bursts: fireball model

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 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 Network coordinates 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 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: m  Detectors: PMT (< 1us)‏  FOV: square degrees  Angular resolution: 5-30 arcmin  Limit: up to 18 m 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 > 20 o x 20 o Small telescopes with large D/F Temporal resolution < 0.1 c and fast detectors Limiting magnitude > 10 m

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 2003 Built in collaboration with IPI and IKI (Moscow), supported by CRDF grant

Naked-Eye Burst SAO RAS, 2009 TORTORA system: overview TORTORA - Telescopio Ottimizzato per la Ricerca dei Transienti Ottici Rapidi Two-telescope complex: - independent detection - automatic study La-Silla, Chile mounted on REM since 2006 Team: SAO RAS, IPI (Russia), Bologna University, REM (Italy) Telescopio Ottimizzato per la Ricerca dei Transienti Ottici Rapidi Two-telescope complex: - independent detection - automatic study TORTORA

Naked-Eye Burst SAO RAS, 2009 TORTORA system: technical details Objective Diameter:120 mm Focal length:150 mm D/F:1/1.2 Field of view:32x24 o Image Intensifier type: S20 diameter: 90 mm amplification: 120 downscale: 4.5/1 Q.E.: 10% CCD type:SONY 2/3'' IXL285 size:1388х1036 exposures:0.128 — 10 sec scale:80''/pixel limit:~10.5 m for 0.13с Data flow rate — 20 Mb/s, per night— 600 Gb, ~ frames

Naked-Eye Burst SAO RAS, 2009 Wide-field monitoring systems: TORTORA

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 s magnitude – 4.6 m 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 Pointing after 59 seconds Limit B > 12.4 with 12.8 s effective exposure Limit for sinusoidal variable component B > 16.5 in Hz frequency range GRB Pointing after 92 seconds Limit B > 11.3 with 12.8 s effective exposure Limit for sinusoidal variable component B > 14.0 in Hz frequency range GRB Pointing after 118 seconds Limit B > 11.3 with 12.8 s effective exposure Limit for sinusoidal variable component B > 16.4 in Hz frequency range

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: the stars – they are falling GRB a: T 0 = 05:45:41 UT, T 90 ~40 s, R~21 m GRB b: T 0 = 06:12:49 UT, T 90 ~60 s, V~5.5 m GRB c: T 0 = 12:25:55 UT, T 90 ~20 s, R~17 m GRB d: T 0 = 17:05:19 UT, T 90 ~24 s, V~19 m GRB : T 0 = 04:37:38 UT, T 90 ~25 s, I' ~23 m

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: burst in real time

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: triumph of monitoring systems

Naked-Eye Burst SAO RAS, 2009 Naked-Eye Burst: observations, observations...

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: general information – spectrum

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: general information — light curve GRB b Swift, Konus-Wind, Integral E iso = 1.32  erg, E opt,iso = 6  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 s Rise ~ t 3.5 Fall ~ t -5 Variability: - 2 parts (2 x ~20 s) with intensity ratio of 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 T = 9.4  0.8 s, SL=10 -15

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: periodicity Four nearly equidistant peaks  T 1-2 = 8.7  0.4 s  T 2-3 = 9.0  0.3 s  T 3-4 = 8.2  0.5 s Periodic behaviour of central engine? Kocevski et al (2003)

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: power spectra

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 = 1.14  0.06 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 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 collisions R ~ cm Residual collisions R~10 16 cm Gamma emission Optical emission Г +/- dГ AfterglowAfterglow

Naked-Eye Burst SAO RAS, 2009 Naked Eye Burst: neutron-rich internal shocks  -rays Regular internal shocks at ~10 13 cm: powering gamma-ray emission The beta-decay radius : Natural explanation of fluxes ratio (opt- gamma) ~ 1000 Secondary internal shocks at ~10 16 cm – result of collisions of late proton shells with products of the early neutron beta- deckay: powering UV/optical emission 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 Gravitomagnetic Prcession T ~ 0.5 sec Toy model Newly born black hole M ~ 3 Msun Massive accretion disk Mdisk ~ Msun Neutrino-driven viscous instability Rstop ~ 30 Rg Viscous Instability T ~ 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 ~ 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

Naked-Eye Burst SAO RAS, 2009 See you in nine years! Naked-Eye Burst