GRB s CENTRAL -ENGINE & FLARes WARSAW Guido Chincarini & Raffaella margutti 1WARSAW 2009

2 From a serene garden To A violent universe WARSAW 2009

WE WILL SHOW GRBs generalities & Optical follow up at ESO & in preparation for publication Characteristic time of the central engine activity is about 1000 s. The energy on flare – residuals activity is about erg. Rest Frame – keV. We estimate an activity time [ ~ 20 s ] and the time the central engine is active compared to the total time of the afterglow. WARSAW 20093

GENERALITIES WARSAW 20094

What is a Gamma –Ray Burst ? (1) Hubble Deep Field EXTRA –galactic events GRB Host Galaxy At cosmological distances (z=6.7) Local Universe (z<0.1) 5WARSAW 2009

What is a Gamma –Ray Burst ? (2) EXPLOSIONS linked to the death of stars E  erg 6

Here we will be dealing with long GRBs. That is the prompt emission lasts generally more than two seconds. The Host Galaxy is a late type with rather high specific star formation rate. Short GRBs occur in early and late type Galaxies 7WARSAW 2009

What is a Gamma –Ray Burst ? (3) TRANSIENTNON-PERIODIC events with duration between s (prompt gamma emission)  -ray emission VELA Swift AGILE INTEGRAL Fermi ….. MAXI 8WARSAW 2009

What is a Gamma –Ray Burst ? (4) MULTI-WAVELENGTH LONG- LASTING emission (months, years) Swift TRIGGER!!!!TRIGGER!!!! Afterglow REM Robotic Telescopes 9WARSAW 2009

Swift – XRT – SERVICE - OPT Follow UP – UNIQUE PI ASI INAF REM ESO TNG ASDC MISTICI CIBO OAB IASF_PA IASF_MI WARSAW

11WARSAW 2009 GRB080329B – See eventually Movie - STOP Show – VLC – Open in GRB - Plot Here the real challenge for the future Time since BAT trigger in seconds

Log(Time) Log (Flux) t break1 t break2  t-1 t-1 t-1 t-1  t-2 t-2 t-2 t-2  t-3 t-3 t-3 t-3 Prompt Afterglow A long GRB explosion Black Hole 12WARSAW 2009

Light Curve Morphology - Time Flux old intruments t -  1 t -  2 t -  3 t break Many afterglows have a typical pattern Steep – flat – steep Prompt Emission Tail External shock ? Afterglow 13WARSAW 2009 WE ADD FLARES

A is behind the shock front of the amount d = R/  2 14WARSAW 2009

Light Curve Morphology - Time Flux old intruments t -  1 t -  2 t -  3 In the Swift era – Base for the analysis t break Many afterglows have a typical pattern Steep – flat – steep Prompt Emission Tail Active Engine Old type Afterglow 15WARSAW 2009 ADD FLARES

Norris 2005Kocevski, Ryde,Liang 2003 (Norris 1996) (Kobayashi) Et al WARSAW

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WARSAW GRB and Flare activity To keep the sample very controlled we disregarded in this work the flares observed in SGRBs. However to illustrate a classical example we show the light curve of GRB and a possible empirical interpretation of the early decay and of the late flare. All fits have been applied using the Norris 2005 function.

GRB We show a possible fitting of the background light curve and the various flares fitted by a norris 2005 function WARSAW

WARSAW GRB051117A

GRB not used. Late flare activity rather unusual and evolutionary effects may be important. The effect on the mean light curve is shown in any case later on. WARSAW

Light curve from GRB flares WARSAW

The sample – 36 GRB s Margutti – Bernardini – et al. Long GRBs – For instance no GRB Only GRBs with spectroscopic redshift. Flares must be detectable by naked eye. The analysis has been done on the GRB rest frame. The standard light curve has been subtracted. The common energy interval to all flares is finally from to keV. 23WARSAW 2009

GRB FLARES CONCLUSIONS WARSAW Charecteristic time of the central engine activity is about 1000 s. The energy on flare activity is about erg. Full agreement with previous indipendent analysis [COSPAR] – However here proper energy band rest frame We estimate an activity time [ ~ 20 s ] and the time the central engine is active compared to the total time since the alert of the GRB. Energy to power the flares noy yet known. Accretion, spinning down pf msgnetar, …….. TBD ….

Back up WARSAW

WARSAW Figure from Kumar & Mahon 2008

Syn. cooling & curvature Kumar&Panaitescu Dermer Sari et al. This equation is quite robust. It is valid for both the forward and reverse shock and it is independent of whether the reverse shock is relativistic or Newtonian. Fennimore et al. Width = k E If we assume the main factor is the curvature effect we have the following [The Observer way, however see later more formal derivation by Lazzati & Perna: 27WARSAW 2009

 +  t ej +  t ej t ej External Lazy t ej  t flare 28WARSAW 2009

11 22 pp w rr  d WARSAW 2009

30 GRB060526

31WARSAW 2009 <>= 0.29 ± 0.53

32WARSAW 2009

33 Slope 1.79

Note I have the same type of graph with TAU increasing with WIDTH slope 0.78 ± WARSAW 2009

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36WARSAW 2009 <> = 0.36 ± 0.2

WARSAW Norris 2005

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39WARSAW 2009 Correlation Mean width Energy. To this the BAT data for Flares in common are being added.

40WARSAW 2009

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42WARSAW 2009 Log versus Log GRB T90 = 8.4 s – z =0.44 See GCNs GRB short

THESE ARE SOME OF THE HYPOTHESIS & PROBLEMS SEE A FEW EXAMPLES Do we need to subtract the background underlying curve always? If yes we should know where it is coming from – BAT observations. Is the precursor having any role? Is it always the last flare for the early XRT slope or a combination of spikes or something else. Decay slope and cooling – How to approach it best. WARSAW

WARSAW GRB A

Do we need the underlying power law light Curve? WARSAW GRB A - S

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GRB – See also Krimm et al., 2007, ApJ WARSAW

Light Curve Morphology - Time Flux old intruments t -  1 t -  2 t -  3 In the Swift era – Base for the analysis t break Many afterglows have a typical pattern Steep – flat – steep Prompt Emission Tail Active Engine Old type Afterglow 48WARSAW 2009

49

Mechanism producing the jets? The observed flares have similarities to the variability observed during the prompt emission. They must be related to the activity of the central engine at time at which the flares are observed. Conversion of internal energy into bulk motion with hydrodynamic collimation. Energy deposition from neutrinos. Energy released from rapidly spinning newly born magnetar and magnetic collimation and acceleration. 50WARSAW 2009

# GRB s Analyzed– April GRBs83 with z7 - No spectra Not early observ 66 OK 15 no steep decay 7 single power law 44 steep decay or flare 26 with flare 11 No steep decay 15 steep8 1 spectrum 5 many spectra  const 2 spectral evolution 18 no flares 10 only 1 spectrum 4 More than 1 same  4 spectral evolution 164 no z10 One PL41 Flares 75 no Flares Various Fits 31 low stat or late Obs 7 No lc 51 IN 4 bands and TOT WARSAW 2009

Flares [UPDATE ] 47 GRBs67 Flares 29 Redshift No z C07 33 – 77 F07 52WARSAW 2009

NORRIS 2005 CH 1 25 – 50keV CH 2 50 – 100 CH – 300 CH > 300 WARSAW

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GRB050502B - Three components 55WARSAW 2009