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In this talk I am going to describe a puzzling phenomenon we have know for about

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. GRBs : Recent progress and new mysteries. Outline:. •. Summary of main results. •. Prompt and afterglow emissions. •.

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In this talk I am going to describe a puzzling phenomenon we have know for about

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  1. 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. GRBs: Recent progress and new mysteries Outline: • Summary of main results. • Prompt and afterglow emissions. • (our current understanding or lack there of) • • Unsolved problems. Ohio, September 26, 2007

  2. Short burst Long burst Gamma-ray bursts are short pulses of radiation that come from random directions a few times a day. GRB Duration Note 1: To return back to the original slide, click on the underlined headline at the top of the slide. Note 2: The distribution is bimodal; most of what we know is about long duration bursts.

  3. Swift GRB mission Swiftwas launched on Nov 20, 2004. Swift has accurate localization (~2’) rapid response (~1 min) and excellent temporal coverage for a few days. • Determine the nature of short duration GRBs. • Find GRBs at high z • The transition from -ray prompt to afterglow emission. Swift is in an orbit at 600km altitude which is inclined 22-degree wrt equator. The spacecraft weighs 1450 kg and consumes 1040 W of power. BAT: 15-150 kev band with resolution of about 7 kev and 1-4 arc-min positional accuracy and detector area of 5440 cm^2. XRT: 0.2-10 kev, resolution of 190 ev at 10 kev and 50ev at .1 kev, angular resolution of 5-arcsec, and effective area of 110 cm^2, field of view of 23-arcmin. UVOT: 30 cm diameter telescope with 0.3-arcsec resolution and 170-600 nm wavelength sensitivity of B=24-mag in 1000s integration time.

  4. What Have We Learned About GRBs? Long duration GRBs: • Energy: ~ 1051 erg (wide dispersion) • The outflow is collimated: j ~ 3o 30o • Occur in late type galaxies and associated with star formation. • At least a few of them have SNa Ic associated with them; these supernove were more energetic than average Ic. • Medium is uniform (often) with density a few/cc • Median redshift for Swift bursts is ~ 2.5; the lowest Z is 0.033 & the highest is 6.29 The smallest z =0.0331 for Swift burst was for 060218 -- a XRF which had A spectroscopic evidence for a Sna. The burst duration was ~ 1000s!

  5. Peak luminosity of SNIa is ~ 10^{43} erg/s Short duration GRBs Swift has detected 15 and HETE 1 short bursts: • 5 GRBs are located near early type galaxies whereas 2 are in late type galaxy; theoffset varies from 0.3 to 13 Rg & SFR < 0.1 Mo yr-1 for two of the host galaxies (Nakar , 2007). • Very stringent limit on any underlying SN for two GRBs (L<4x1040 erg/s) between 7-20 days (Fox et al.). • Low density of the circum-stellar medium; For 2 of the GRBs n< 10-2 cm-3; Panaitescu (2006) • Lower Eiso (E) by ~ 103 (10) & median z  0.25. Associated with older stellar population, possibly binary n-star (but we lack a firm proof). Low z is consistent with V/V_max ~ 0.4 The 5 short GRBs are: 050509B, 050709 (HETE), 050724, 050813 & 051114 050709 & 050724 had x-ray and optical afterglows; 050509B & 050813 had x-ray AG and 05115 had no afterglow detection. Only half of the SHBs have host galaxy identification. This might be a selection effect in the sense that bursts going off in a low density medium will have weak afterglow that might not be detected. The typical star formation rate for hosts of long-GRB is about 10 M_sun/year * (L/L*)-1. (a long-GRB galaxy is a star forming dwarf field galaxy i.e. not in cluster.)

  6. Nakar, 2007

  7. Early afterglow: emission from shock heated ejecta >200 at ~100s for 990123 & 021211 Soderberg & Ramirez-Ruiz, 2002; KP 2003. • • Afterglow modeling gives >4.5 at 1 day for 10 bursts (Panaitescu & Kumar, 2002). • Diffractive scintillation quenched at 30d for 970508  R~1017cm  V~R/t~C; Goodman 1997; Frail et al. Evidence for Relativistic outflow • Superluminal motion in 030329:Rt ~ 3x1017cm at 25d  vt =Rt/t=5c  ≈7 at 25 days (Taylor et al. 2004). • 030329 was at a redshift of 0.1685; da =589 Mpc.

  8. Synchrotron from FS fits late afterglow data Panaitescu & Kumar EGRB ~ 1051 erg; qjet Uniform ISM; nISM ~ 10 cm-3

  9. Early Afterglow Results for Swift Bursts • Rapidly decaying flux in the x-ray; likely the remnant of decaying -ray source (before the onset of FS emission). • Slowly decaying lightcurve in the x-ray.

  10. Nousek et al. 2005 Sudden increase in flux (flare) during the “afterglow” (long lived central engine activity) Because of smearing due to curvature dt/t ~ 1 in FS. Many of the flares have t/t << 1 which suggests late time engine activity. (these bursts did not have redshift determination) The big flare of 050502b, at 650s (peak), had slightly higher fluence than the main burst And delta T/T <<1. 050607 had a flare peaking at 310s, fluence during the flare was ~ 15% of the burst fluence and delta T/T ~ 0.2.

  11. Some of the basic unanswered questions about GRBs • How does the central engine operate: accretion, B-Z…? The central engine is hidden -- opaque to EM signals. So our best hope is to try to model the -ray emission and the x-ray flares. • How is the relativistic jet produced? • Is the GRB outflow baryonic or magnetic? Understanding the-ray emission mechanism and detecting RS emission from GRB-ejecta would help.

  12. Factor ~ 103 drop in flux! Prompt -ray generation mechanism O’Brien et al., 2006 • • The early time data from Swift shows that -rays are produced by a distinct - short lived - source. • We exploit this steep falloff to determine -ray source distance from the center of explosion.

  13. fn t The fastest decay of LCs (Off-Axis Emission) (Kumar & Panaitescu 2000) p t -1 f t -2- t =Rq 2/2 q t =RG-2/2 G-1 R t ~ -1 t~ -2-b

  14. Nousek et al. 2005

  15. Gamma-ray Generation (distance) • The distance from the center of the explosion where -rays are produced, R , can be determined from the early x-ray lightcurve: ct1 ≈ R/202 ; ct2 ≈ Rfs/2fs2 Since fs < 0  R > (t1/t2) Rfs Rfs = [3ct2Eiso/2mpc2n0]1/4 fs: forward shock LF at t2 0: -ray source Lorentz factor t2: time when steep x-ray decline ends. t1: time when-ray emission ends,

  16. • For 10 Swift bursts (t2/t1) is between 5 & 25 ; the mean is ~ 14  same for FRED & non-FREDs.  -ray source lies within a factor ~10 of FS radius. • • Or -rays are produced at a distance of ~ 1016 cm from the center of explosion. This distance is much larger than what was expected for internal shocksand of order the distance suggested for poynting model.

  17. Afterglow g-rays Inner Engine Relativistic Outflow Internal Shocks External Shock 1016-1018cm 106cm 1013-1015cm The Internal-External Fireball Model Piran et al. 1993; Rees & Meszaros 1994; Paczynski & Xu 1994

  18. (Kumar et al. 2007) Understanding -ray emission Synchrotron & IC from a relativistic source emission can be completely described by 5 parameters:

  19. We also use the flux/upperlimits in early x-ray & optical when available. Constraints • Flux • spectral index below the peak of spectrum • frequency at peak of spectrum • burst/pulse duration 5 unknowns and 3 constraints gives 2-D solution surface.

  20. -rays produced via the synchrotron process? (Ep =100kev; flux=1mJy; t=1s; low energy spectral index -ve)

  21. Synchrotron solution is also ruled out when f+ve • Synchrotron peak frequency = 100 kev  Bi2 = 1013 • Electron cooling: c/i ~ 10-17 i3 /tGRB(1+Y) Compton Y ~ eci  c/i ~ 10-9 [i/(tGRB e)]1/2 Therefore, c/i<<1  f-1/2

  22. -rays produced via the SSC process? (Ep =100kev; flux=1mJy; t=1s)

  23. SSC gives consistent solutions. It predicts bright, prompt, optical which we see in a few cases: 041219 ~ 14 mag. • Is the GRB jet that produces -rays baryonic or poynting outflow? • For baryonic outflow we should see RS emission. 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.

  24. • Ejecta ISM Forward shock Reverse shock Ejecta ISM Reverse shock emission? • One of the things Swift was going to do is find many more bright optical flashes like GRB 990123  where are they? • Roming et al. 2006 •

  25. Panaitescu et. Al, 2007 O’Brien et al. 2006 New puzzles posed by Swift data Flares lasting for hours - short and long GRBs Chromatic plateau In x-ray LCs Do we have the FS AG right? (Problem when you have good data!) RS emission? Jet breaks? Do we have the FS AG right?

  26. A sudden drop in x-ray flux in a few cases! Troja et al. astro-ph/0702220

  27. Summary of Results • Long duration GRBs are associated with collapse • of a massive star (at least in several cases!). 2. The short GRBs have much less energy and are associated with old stellar population. 3. The rapid fall off of the early x-ray afterglow suggests that -ray emission is produced by a short lived source; we find that it is most likely SSC at a distance of ~ 1016 cm baryonic jets have a few problems. 4. X-ray lightcurves show flares on time scale of minutes to a day suggesting that the central engine of GRBs can be active for a period of order ~ 1 day. Note: This is an animation slide. You need to click on the mouse several times to display all the texts.

  28. Unsolved Problems 1.The nature of the central engine is not understood. 2.Is the energy from the explosion carried outward by magnetic field, e±, or baryonic material? 3. 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. 4. Collisionless shocks, particle acceleration, magnetic field generation etc. poorly understood.

  29. ≈7 v=3c v=5c Superluminal motion in GRB 030329 (Taylor et al., 2004, 609, L1) VLBI observations Were carried out Between 8.4 and 15.3 GHz.  ≈ 50 Solid line: Spherical outflow in a uniform ISM; E52/n0 =1 Dashed line: jet model with tj =10 days & E52/n0 =20.

  30. Nakar, 2007 Host of short-GRBs)

  31. t-2.4 t-0.72 Tagliafferi et al. 2005 Break in the LC at 2.6 days implies: j ~ 3o E ~ 4x1051 erg

  32. Determining Jet Angle from Break in LC (Rhoads 1999, Sari et al. 1999, Kumar & Panaitescu 2000) q G-1 q G-1 At late time: G-1≥ q At early time: G-1≤ q R R 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

  33. Future Missions 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. GLAST, due for launch in 2008, will cover 10 Kev – 300 Gev, and detect > 200 GRBs yr-1. EGRET energy range was 30Mev to 10Gev. 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 (an Italian mission) 30 Mev – 30 Gev & 10 – 40 kev is expected to launch in 2005. 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. • ICECUBE, ANTARES will explore Neutrino emission from GRBs: 10 Gev – 105Tev. • Gravitational waves from GRBs? 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 (seems like it has been canceled)

  34. GRB 021004 (HETE II: Shirasaki et al.) Absorption lines at different velocities Temporal fluctuations (spectrum at ~ 1 day -- McDonald HET) Bersier et al. 2002, astro-ph/0211130 Schaefer et al. 2002 Nakar & Piran, 2003, ApJ 598, 400 (similar velocity features are also seen in 050505; Berger et al.) 021004 was at z=2.3; absorption features are seen at 3000 km/s, 560 km/s Wolf-Rayet wind velocity is 1000-3000 km/s, mass loss rate of ~ 10^{-5} M_sun/yr And this phase lasts for a few times 10^5 years. O-star main sequence wind has a Similar speed, but ~ 10 times smaller mass loss rate. And red supergiant wind speed Is of order 10-100 km/s, mass loss rate of upto 10^:-4} M_sun/yr and this phase Could last for upto 10^5 years.

  35. Stanek et al., 2003, ApJ 591, L17; Hjorth et al, 2003, Nature 423, 847 Emission lines of CII, OII and OIII Long GRBs - collapse of massive stars (Woosley and Paczynski) GRB 030329/SN2003dh SN 2003dh/ GRB 030329: z=0.166 (afterglow-subtracted) SN 1998bw: local, energetic, core-collapsed Type Ic Stanek et al., Chornock et al. Eracleous et al., Hjorth et al., Kawabata et al. According to Mazzali et al. (2003) the energy in this hypernova was 2x10^{52} erg, The velocity & mass of ejecta 25000 km/s and 8 M_sun. Matheson et al. (2003) suggest that SN lightcurve Peaked at about 20 days, and the luminosity of 030329 SN was similar to SN-98BW. GRB 031203 (an x-ray flash) at z=0.105 was also found to be associated with a Sne This was based on both the spectrum and the LC which peaked at ~ 20 days and then Declined -- similar to the spectrum & LC of 98bw -- except that it was brighter than 98bw By about 50%! (Malesani, Tegliaferri et al/astro-ph-0405449 is a good paper). X-ray flash 020903 also seems to show a spectrum like 98bw at 25 days after the burst (Soderberg astro-ph/0502553).

  36.       Detectability of Bursts at high Z The peak flux for GRB 050904 was ~ 3x10-8 erg cm-2 s-1 (BAT sensitivity, 15-150 kev, is 0.25 photons cm-2 s-1 or 1.2x10-8 erg cm-2 s-1 for f -1/2) So Swift can detect bursts like 050904 to Z~10. Price et al. (2005) claim that 8 out of 9 Swift bursts (at z>1) could be detected at z=6.3 and 3 of these could be detected at z~20.  

  37. Detectability of Afterglows at high Z 10 min after GRB 050904 the 0.2-10 kev flux was ~ 10-9 erg cm-2 s-1 and the luminosity (isotropic equivalent) was ~ 1050 erg s-1 (the flux at earlier time scaled as t-2).  Swift/XRT detection limit is 10-13 erg cm-2 s-1 for 100s integration time.  At 1 hr the J-band flux was 17th-mag and the luminosity (isotropic equivalent) was ~ 1047 erg s-1  Negative k-correction helps: f(t)  - t- (~1 and ~1-3 at early times)

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