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Gamma-Ray Bursts

Gamma-Ray Bursts. Luigi Piro Istituto Astrofisica Spaziale Fisica Cosmica - Roma INAF. Summary. GRB: the breakthroughs of the last decade Main theoretical and observational background Clues to the progenitors Open issues Cosmological Perspectives. BeppoSAX: GRB in the afterglow Era.

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Gamma-Ray Bursts

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  1. Gamma-Ray Bursts Luigi Piro Istituto Astrofisica Spaziale Fisica Cosmica - Roma INAF L. Piro - ILIAS meeting - 2008

  2. Summary • GRB: the breakthroughs of the last decade • Main theoretical and observational background • Clues to the progenitors • Open issues • Cosmological Perspectives L. Piro - ILIAS meeting - 2008

  3. BeppoSAX: GRB in the afterglow Era • Launch: Apr. 30, 1996 • End ops: April 30, 2002 • Discovery of the afterglows of GRB • Discovery of the extragalactic distances • Progenitor: Association with SN and star formation in distant galaxies • Dark GRB’s and X-ray flashes • Cosmology with GRB L. Piro - ILIAS meeting - 2008

  4. GRB970228: the 1st X-ray and O afterglow • Fast follow up with NFI in 8 hrs: a bright unknown X-ray source • A second pointing 3 days after the GRB: fading X-ray counterpart (Costa et al 1997) • Optical fading source (van Paradijs et al 1997) L. Piro - ILIAS meeting - 2008

  5. Internal vs external shock: prompt & afterglow emission • In contrast with the afterglow, the prompt emission is characterized by strong hard-to-soft spectral evolution from X- to Gamma rays (e.g. GRB960720 Piro et al 1997) L. Piro - ILIAS meeting - 2008

  6. g RB G2 X-ray afterglow G1 taft t-1 tGRB The fireball model 1016 cm 1013 cm 106 cm L. Piro - ILIAS meeting - 2008

  7. Galama et al 98 Afterglow spectrum: fireball model L. Piro - ILIAS meeting - 2008

  8. GRB970508: direct evidence of fireball • Discovery of the radio afterglow • Direct evidence of a relativistic expanding source by radio scintillation induced by electrons in the Galaxy ISM (3 uarcsec) L. Piro - ILIAS meeting - 2008

  9. Hypernovae/collapsar evolve much faster, going off in their formation site => “mass-rich environment” • NS- NS merging Collapsar The progenitors of GRB The nature of the progenitor can be inferred from the environment • NS-NS (BH-NS & BH-WD) travel far from their formation sites before producing GRB’s (Fryer et al 2000) => “clean environment” L. Piro - ILIAS meeting - 2008

  10. Progenitors and hosts Fryer, Woosley and Hartmann 1999 L. Piro - ILIAS meeting - 2008

  11. The fading OT of GRB990123 L. Piro - ILIAS meeting - 2008

  12. Host galaxies of long GRBs: Normal (spiral) showing star formation • most GRB within the half-light radius of the galaxy: star-formation sites and massive progenitors L. Piro - ILIAS meeting - 2008

  13. X-ray absorption in the GRB local environment X-ray absorption column densities in the afterglow: NH=1021-22 cm-2(Stratta et al 2000, Campana et al 2006) Consistent with Giant molecular clouds L. Piro - ILIAS meeting - 2008

  14. GRB-SN connection • GB980425: in the BeppoSAX error box: SN1998bw(Pian et al. 99,Kulkarni et al, Galama et al al 98). Exploded within 1 day from the GRB. Chance P=1E-4 L. Piro - ILIAS meeting - 2008

  15. GRB-Sn: 030329 • Sn contribution should appear when the power-law GRB afterglow has decreased (Bloom et al 98: GRB980326) • GRB030329: The nearest (and the brightest in HETE2 GRB) z=0.168 (Greiner et al, VLT) • SN spectrum (similar to 1998bw) emerging at about 10 days (Matheson et al 03, Hjorth et al 03). L. Piro - ILIAS meeting - 2008

  16. Sub energetic X-ray flashes XRF (low G) GRB (high G) Collapsar model L. Piro - ILIAS meeting - 2008 Woosley et al

  17. Jet vs spherical expansion: break in the afterglow light curve F The break must be achromatic G-1(t4)=q Spher. Jet t4 t q t1 t2 t3 t4 t5 L. Piro - ILIAS meeting - 2008

  18. Simultaneous O and X-ray light curves of GB990510 • Break in the O at t= 1day (Harrison et al 99) • BeppoSAX light curve compatible with break (Kuulkers et al 2000, Pian et al01) but not required (Piro et al.00) • SWIFT data show a variety of behaviour, achromatic breaks are a small fraction. 1 10 T-T0(days) L. Piro - ILIAS meeting - 2008

  19. X-ray flashes • A New class discovered by BSAX and confirmed by HETE2: about 40% GRB’s with no or very faint or gamma-ray emission • high redshift GRBs • off-axis events • Subenergetic events, more numerous than normal GRBs Heise et al 2001 L. Piro - ILIAS meeting - 2008

  20. XRF host galaxies • 2 of XRF localized by BSAX and followed up by Chandra, • more redshift by SWIFT at z<3 (Gendre, Galli, LP, 2007) XRF GRB L. Piro - ILIAS meeting - 2008

  21. g RB G2 X-ray afterglow G1 taft t-1 tGRB GRB seen off axis: GW trigger + orphan Opt/X-ray afterglows 1016 cm 1013 cm 106 cm L. Piro - ILIAS meeting - 2008

  22. Dark GRBs • BeppoSAX showed that >90% GRB are followed by X-ray afterglows. Confirmed by SWIFT. However only about 40% have optical afterglows. • High z (z>5) events ? L. Piro - ILIAS meeting - 2008

  23. About 25% of GRB’s have durations <1 sec,down to few msec. No counterpart so far. Different progenitors (NS-NS mergers)? T90=40 ms Short GRB’s GRB050509B Paciesas et al 99 L. Piro - ILIAS meeting - 2008 Gehrels et al 05

  24. Entering SWIFT L. Piro - ILIAS meeting - 2008

  25. HOST GALAXIES OF SHORT BURSTS: Elliptical AND Spiral GRB050509 GRB050709 GRB050724 GRB050906 GRB050813 L. Piro - ILIAS meeting - 2008

  26. Temporal evolution for mergers L. Piro - ILIAS meeting - 2008 Fryer, Woosley and Hartmann 1999

  27. Redshift distribution of long- & short-GRBs However, suggestions that at least 25% of short-GRBs are at z>0.7 (Berger et al. 2006) ( if they did not travel long distances from their HG) L. Piro - ILIAS meeting - 2008

  28. X-ray light curves of SHBs L. Piro - ILIAS meeting - 2008

  29. X-ray to prompt γ-ray fluence One explanation (but not unique): lower density in short GRBs L. Piro - ILIAS meeting - 2008

  30. THE GRB PROGENITORS The tell tale feature from GW 1) Electromagnetic window: • Afterglow: properties of the environment (host galaxy, density,..) • SN features • Long: Yes (outliers?) • Short. NO LONG=COLLAPSAR • 2) Gravitational waves by GRBs: • Binary merger: • in-spiral • b) merger, • c) ring down • For collapsars NO inspiral SHORT=NS-NS mergers L. Piro - ILIAS meeting - 2008

  31. Time delay GW-GRB • Collapsar case (e.g. Waxman and Meszaros 2003): • the jet inside the star can be subrelativistic • The jet stream needs to be maintained for several tens of seconds to overcome the pressure inside the star (cork effect) • NS-NS mergers • Much shorter L. Piro - ILIAS meeting - 2008

  32. GRBs by VIRGO and LIGO bh-ns m1=12 M m2 =1.4 M - - - in-spiral -  -merger ring-down Initial Virgo Upgraded Virgo 62 Mpc 280 Mpc GRB050709 D=650Mpc 2300 Mpc Collapsar m1= m2 =1 M - - - - merger Virgo Upgraded Virgo 23 Mpc 27 Mpc GRB 980425 d=40 Mpc GRB020618 D=130Mpc 110 Mpc L. Piro - ILIAS meeting - 2008

  33. Precursors, flares and central engine • X-ray precursor • Hard prompt emission • X-ray flare at 300 s with spectrum similar to the late afterglow b 1 0.5 0 Piro et al. 05, ApJ. L. Piro - ILIAS meeting - 2008

  34. The canonical X-ray light curve after SWIFT X-ray flares Prompt: IS Prompt: IS, curvature emission External shock (classical power law) Flattening: refreshed shocks, off axis jet, …. Jet break L. Piro - ILIAS meeting - 2008

  35. X-ray Flares SWIFT: Burrows et al (2005) BeppoSAX: Piro et al (2005) Signature of long duration activity of the central engine SWIFT: about 40% X-ray afterglows showing X-ray flares on time scales >100 sec (Chincarini et al 2007) L. Piro - ILIAS meeting - 2008

  36. GRBs in the dark Universe GRB050904: z=6.3 • Kawai et al 2005 • SWIFT X-ray data (Cusumano et al, Campana et al., Gendre et al) L. Piro - ILIAS meeting - 2008

  37. GRBs as cosmological beacons • measure the cosmic history of metals in GRB regions and their host galaxies • pinpoint the formation of early population of luminous sources ignited in the dark Universe (z>7) • Solve the missing baryon problem residing in the cosmic web filaments L. Piro - ILIAS meeting - 2008

  38. Conclusions • Progenitors • circumstantial evidence associating long events to Massive star (collapsar) and short events to mergers. • GW can be crucial • Central engine • Still to be really understood (BH+AD) • X-ray flares (and their GeV counterparts with AGILE and GLAST) as evidence of long duration engine (fragmented AD) • Fireball model • General agreement, but too simplistic: • Jet breaks not so common as expected • X-ray and optical appear to be decoupled • Cosmological Perspectives • GRB can probe throughout the Universe from present era to dark ages L. Piro - ILIAS meeting - 2008

  39. Conclusions for GW • GW provide direct information on the central engine • Good prospect of detections from nearby GRB with advanced LIGO/VIRGO using EM trigger • Rate should be 100 times larger than EM burst, due to collimation (EM counterpart: XRF and Orphan afterglows) • In the future GW could provide the trigger and coarse (1 deg position) to carry out fast follow up observations in X-rays with mission like EDGE to detect the orphan afterglows of GRB jets pointing away from earth L. Piro - ILIAS meeting - 2008

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