Kumar Santorini05

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In this talk I am going to describe a puzzling phenomenon we have know for about 30 years and only in the last few years we have began to understand their nature. • • • • • Some basic results. Unsolved problems. Outline: GRB Parameter Determination Using Multi-wavelength Data How do we determine GRB parameters. Santorini, September 1, 2005 Pawan Kumar

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Evidence for Relativistic outflow 030329 was at a redshift of 0.1685; da =589 Mpc. Superluminal motion in 030329: Rt ~ 3x1017cm at 25d  vt =Rt/t=5c  ≈7 at 25 days (Taylor et al. 2004). • •

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Gamma-ray bursts are narrow jets: j < 10o What Have We Learned About GRBs? Energy in relativistic jet is ~ 1051 ergs (~SNe energy) & the density of the surrounding medium is ~ 1 cm-3. In most cases the CSM density is uniform. GRB ejecta is magnetized (at least in two cases). The number of e per proton in GRB ejecta is not large. • • • • •

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Dynamics (4R3/3) n0 (mpc22) = Eiso tobs= R/22    tobs-3/8

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At early time: G-1 ≤ q At late time: G-1 ≥ q Area visible to observer = (R/G)2 Area visible to observer = p (Rq )2  (R/G)2 (q G)2  (R/G)2 t -3/4 t ~ -1 t ~ -1 t ~ -2 t ~ -2 R R

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Determining Jet opening Angle Break in afterglow LC occurs when G = q -1  Substituting G = q -1 in the dynamics equation: q =o(n0/Eiso,52)1/8(tjet/1day)3/8 (4R3/3) n0 (mpc22) = Eiso • • We find:

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Panaitescu & Kumar (2000)

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Determining density structure of CSM For a windy CSM n(r)  r-2 Dynamics: r2  Eiso    tobs-1/4 This modifies flux scaling. For instance, the flux at m<< c is  tobs-(3p-1)/4 Whereas for a uniform CSM f  tobs-(3p-3)/4 • • • (instead of r32  Eiso)

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Example: Swift burst 050128 (Campana et al. 2005) This implies a uniform CSM for 050128!

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Steepening of LC due to a jet for s=0 and s=2 media Kumar & Panaitescu 2000 s=2 s=0  f  tobs-

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Parameters we want to determine  qn, p, e , B Example: A Recent Swift GRB The spectral slope between optical & x-ray determines c The ratio of optical to radio flux upper limit determines m From c & m we determine n (0.1/cc) & B (0.1). • • •

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 We determine the parameters  qn, p, e , B by a multi-wavelength LC fitting numerically.

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(1) (2) (3) 2 2 ' 2 ) cos v 1 ( ) , ( 3 4 1 d f q e p n n - G + = t r d z r L (4) Light-curve modeling (Panaitescu & Kumar, 2001) The dynamics is determined by the following equations: • • The observed flux is: • We have selected those GRBs which have observations covering x-ray, optical and radio bands, and thus provide the best constraint on various burst and post-shock gas parameters. • We determine energy, jet angle, •

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Panaitescu & Kumar (2000)

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Light curve fit for 8 GRBs 980519, 990123, 990510, 991208, 991216 000301c, 000926 & 010222 Panaitescu & Kumar, 2001

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Energy in Relativistic Ejecta, Jet Opening Angle and ISM Density (Panaitescu & Kumar, 2002) Berger et al. Claim (Nature, 2004, 430, 648) The energy of nearly GRBS -- 980425, 0301203 (z=.105) etc. -- is smaller than classical GRBs by a factor ~10. And the energy in the relativisitc component of Sne Ib/Ic is a factor 103 smaller. Berger et al. (2004) find the energy in the highly relativisitic outflow for 2 bursts to be ~ 5x1049 ergs, but the total energy to be ~ 1051 ergs.

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The early optical flash seen in several bursts is believed to come from shock heated ejecta predicted by Sari & Piran, 1999. Determining GRB-ejecta compostion • • • The composition/property of the ejecta can be deter- mined from the radiation it emits when heated by the reverse shock at early times. •

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Li et al. 2003 (GRB021211) ROTSE 1999 (GRB990123) The early afterglow combined with later afterglow – which originates in the forward shock in the ISM – provides a handle on GRB ejecta composition†. †The jecta property could undergone substantial changes by the time it is heated by the RS e.g., B could have decayed, baryons entrained, leptons generated or decayed etc..

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Optical Data for 021211 • Reverse shock flux = Forward shock flux at 10.8 min • R-band flux at 90s (RS) --- 7.2 mJy (14.1 mag) • R-band Forward shock flux at 10.8 min --- 0.2 mJy • The peak flux (FS) at 10.8 min > 0.2 mJy • The peak frequency at 10.8 min < 4.3x1014 Hz • The deceleration time ~ 3 s. if = 37 t-3/2 /A kev Fpf = 0.2 Af mJy (s=0) Fpf = 5.4 Af t-1/2 mJy (s=2)

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Reverse shock emission • The peak flux from forward shock at deceleration • Peak flux from reverse shock • The observed flux from reverse shock (extrapolated to td) ~ 1Jy (9 mag) 0.2 d mJy 3 d mJy • And the peak frequency is: 7 d-2 kev; if B in RS same as FS) These together imply that B ,RS >> B ,FS (Zhang et al. 2003 find similar result for 990123) B ,RS = B ,FS (GRB 021211)

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The simultaneous modeling of early (RS) and late (FS) emissions for 990123 & 021211 shows that: the magnetic field in the ejecta is much larger than in the FS by a factor of ~10 – 102 (Kumar & Panaitescu, 2003; Zhang et al. 2003). These results suggest that some GRBs produce magnetized outflow. Blandford & Lyutikov, Spruit, Drenkhahn… have a series of interesting papers investigating GRB energy carried outward by poynting outflow and its implications. • • • Magnetized Outflow? Moreover, for poynting outflow the -ray emission could arise from the decay of magnetic field and we should therefore look for differences in the radiation property during the burst and the afterglow phases. The total magnetic energy in the shock heated Ejecta is a good fraction of GRB energy.

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Long duration GRBs are associated with collapse of a massive star (at least in several cases!). Summary of Results 4. Mean Kinetic energy in relativistic ejecta = 7x1050erg (this is similar to supernova KE release); the energy dispersion is small – a factor 3 – but there might be some outliers. . Note: This is an animation slide. You need to click on the mouse several times to display all the texts. 3. The afterglow radiation over a very wide range of EM spectrum, and time interval, is in quantitative agreement with the external relativisitc shock model. 2. The outflow from the explosion is highly collimated (jet angle of 2 – 10 degrees), and has high Lorentz factor (~100).

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4. No firm evidence for r-2 density structure (except perhaps in 1 or 2 cases). And very low density found in several cases is puzzling. 5. The mechanism for -ray generation is poorly known. 3. The nature of the central engine is not understood. Unsolved Problems 2. Is the energy from the explosion carried outward by magnetic field, e±, or baryonic material? 1. What are Short duration GRBs?

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AGILE (an Italian mission) 30 Mev – 30 Gev & 10 – 40 kev is expected to launch in 2005. ICECUBE, ANTARES, NESTER will explore Neutrino emission from GRBs: 10 Gev – 105Tev. AMANDA: at the south pole has an effective area of 10^4 m^2, and its sensitivity is about 3-orders of magnitude below the expected neutrino flux from GRBs (neutrino energy between 100 Tev And 10^7 Tev). Kilometer-cube size detectors are needed to detect neutrinos from GRBs. ICECUBE: is a one-cube-kilometer neutrino observatory being built in the clear deep ice on the South Pole. ANTARES: detectors in sea water, Mediterrarian sea, the expected size is several-cubic-kilometer. NESTER: is also a sea based detector. GLAST: anticipated launch is 2007. It will cover Energy range of 10 Kev to 300 Gev. GALST/LAT Will have a field of view of 2.5 stradians, and 50 times The sensitivity of CGRO/EGRET at 100 Mev and better At higher energies; the limiting flux is 10^{-9} photons/cm^2/s. It should be able to locate sources to better than 5 arc-min. INTEGRAL: International Gamma-ray Astrophysics Laboratory an ESA mission was launched on October 17, 2002 using a Soviet proton launcher in a 72 hr orbit. It has instruments covering 15 kev to 10 Mev; the mission cost 330M Euros. It will have a sensitivity of 10^{-6} photons/cm^2/s in 10-100 kev range for an integration time of 10^6 s, & 10^{-7} photons at 10 Mev. The imaging instrument has a resolution of 12 arc-minutes. AGILE: is an Italian mission which will have an energy range of 30Mev to 50Gev & 10-40 kev with 2 steradian field of view. AGILE is a small mission (weighing 80 kg!) which will be placed in an equatorial orbit at about 550 km height. The X-ray camera (10-40 kev) should have an angular resolution Of about 5 arc-min, and the gamma-ray telescope 35 arc-min. Sensitivity at 100Mev is expected to be 6x10^{-9} photons/cm^2/s for 10^6s integration time, and 4x10^{-11} at 1Gev, and the timing accuracy is 25-micro-sec. The spectral resolution in gamma-rays is expected to be about 1 i.e. dE/E~1. Future Missions EGRET energy range was 30Mev to 10Gev. GLAST, due for launch in 2007, will cover 10 Kev – 300 Gev, and detect > 200 GRBs yr-1. Gravitational waves from GRBs? • •

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Polarization Granot & Konigl (ApJL, 2003, 594, L83) suggest an ordered magnetic field (part of total B) to explain polarization observations. Structured jet model Polarization measurement potentially are powerful tool to study jets. However, the we have had only limited success in this thus far. Observations don’t fit the simplest possible model; and we need either structured jets or some ordered magnetic field to fit the polarization data.

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Superluminal motion in GRB 030329 (Taylor et al., 2004, 609, L1)  ≈ 50 Solid line: Spherical outflow in a uniform ISM; E52/n0 =1 Dashed line: jet model with tj =10 days & E52/n0 =20. VLBI observations Were carried out Between 8.4 and 15.3 GHz.

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GRB light-curves Fishman & Meegan, 1995 (Ann. Rev. A&A) The CGRO was launched in 1991 and removed from orbit on June 4, 2000. It detected a total of 2704 GRBs during the 9 year period. The energy range for COMTEL was 1-30 Mev; EGRET energy range was 20 Mev to 30 Gev. And the BATSE had detectors covering energy range of 25-50 kev, 50-100 kev and 100-300 kev.

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Summary of -ray Observations for 021211 • Duration: ~ 3s • Peak of the spectrum (f): 47 kev • Flux at the peak: ~ 4 mJy • Low energy spectral slope (f): 0.24  0.12 (Crew et al. 2003)

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Jet dynamics

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The Internal-External Fireball Model Piran et al. 1993; Rees & Meszaros 1994; Paczynski & Xu 1994

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The low and constant density ISM is puzzling in the context of the collapsar model. Very Low density and constant n medium GRBs 990123 & 021211 seem to have gone off in a Low density medium: n 10-2 cm-3. A number of different lines of arguments support this conclusion. For instance, at higher densities the RS cooling- falls below the optical band shortly after the deceleration time, and the RS emission would have decayed much more rapidly than observed. The density in the CMB appears to be uniform. • • •