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Cosmology and physics with GRB spectra

Cosmology and physics with GRB spectra. Lorenzo Amati (INAF - IASF Bologna, Italy). ESTREMO meeting - March 22th, 2006. Outline GRB spectra and energetics Cosmology with spectral-energy correlations GRB physics with spectral energy correlations

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Cosmology and physics with GRB spectra

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  1. Cosmology and physics with GRB spectra Lorenzo Amati (INAF - IASF Bologna, Italy) ESTREMO meeting - March 22th, 2006

  2. Outline • GRB spectra and energetics • Cosmology with spectral-energy correlations • GRB physics with spectral energy correlations • GRB and SN physics with prompt X-ray spectra • Some basic requirements

  3. GRB spectra and energetics

  4. GRBs spectra • smoothly broken power-law spectra typically described by the empirical Band function with parameters a= low-energy index, b= high-energy index, E0=“roll over” energy • Ep = E0 x (2 + a) = peak energy of the nFn spectrum

  5. . • CGRO/BATSE (25-2000 keV): Ep values distibuted around 200 keV • BeppoSAX (2-700 keV) and HETE-2 (2-400 keV) measurements show that the Ep distribution is broader and extending towards low energy than inferred from BATSE Kippen et a., Woods Hole 2001, AIP Proc. Sakamoto et al., ApJ, submitted

  6. . • substantial spectral evolution, typically hard to soft during the whole event • in some cases, Ep tracks the light curve, in others it monotonically evolves from high to low values

  7. . • spectra of short GRBs tend to be harder than those of long GRBs

  8. GRBs energetics • discovery of afterglow emission in 1997 -> detection and spectroscopy of optical counterparts and host galaxies -> GRB redshifts ! • all GRBs with measured redshift (more than 60) are long and (except for the peculiar GRB980425) lie at cosmological distances(z = 0.10 – 6.3) S. Klose • from distance, fluence and spectrum, it is possible to estimate the radiated energy assuming isotropic emission, Eiso

  9. the isotropic equivalent radiated energy spans over several orders of magnitude,from ~1051 (~1049 when including XRF020903 and the 2 peculiar sub-energetic events GRB980425 and GRB031203) up to more than ~1054 erg Amati 2006

  10. Bloom et al. , ApJ, 2001 • assuming jet angles derived from the break time of the optical afterglow light curve, the collimation-corrected radiated energy is clustered around ~1051 erg. Ghirlanda et al. , ApJ, 2004

  11. Standard scenario and basic physics • ms time variability + huge energy + detection of GeV photons -> plasma occurring ultra-relativistic (G > 100) expansion (fireball) • non thermal spectra -> shocks synchrotron emission (SSM) • fireball internal shocks -> prompt emission • fireball external shock with ISM -> afterglow emission

  12. LONG SHORT • energy budget up to >1054 erg • long duration GRBs • metal rich (Fe, Ni, Co) circum-burst environment • GRBs occur in star forming regions • GRBs are associated with SNe • naturally explained collimated emission • energy budget up to 1051 - 1052 erg • short duration GRBs (< 5 s) • clean circum-burst environment • GRBs in the outer regions of the host galaxy

  13. Cosmology with spectral - energy correlations

  14. The EP,i-Eiso (Amati) correlation (Amati et al. 2002) • based on a sample of 12 BeppoSAX GRBs with known z found a correlation between Ep,i = Ep x (2+a) and Eiso, highly significant (r = 0.949, chance prob. 0.005%) Ep,i= kEiso (0.52+/-0.06) Amati et al. , A&A, 2002

  15. Confirmation and extension of the Ep,i-Eiso correlation • by adding data from BATSE and HETE-2 of 10 more GRBs thecorrelation was confirmed and its significance increased • HETE-2 data shows that the Ep,i – Eiso correlation extends to XRFs, thus spanning 5 orders of magnitude in Eiso and 3 orders of magnitude in Ep,i Amati, ChJAA, 2003 Amati, MemSAIT, 2004

  16. analysis of the most updated sample of GRBs with firm estimates of z and Ep,i (43 events)gives a chance probability for the Ep-Eiso correlation < 10-9 • Swift GRBs with known z and Ep,i are fully consistent with the correlation • remark: the correlation is highly significant but characterized by a sample variance s(logEp,i) ~ 0.15 Amati 2006

  17. The Ep,i – Eg and Ep,i – Eiso – tb correlations

  18. by substituting Eiso with the collimation corrected energy Eg the correlation still holds, with a lower dispersion and a steeper slope of ~0.7(Ghirlanda et al. 2004, Dai et al. 2004) Nava et al.. , A&A, 2005 Dai et al., ApJ, 2004

  19. very recently, Liang et al. (2005) performed a multi-variable correlation analysis between various observables of prompt and afterglow • they found a tight correlation between Epi, Eiso and tb • with respect to Ep,i – Eg correlation it has the advantage of being model independent • differently from the Ep,i-Eiso correlation, the Ep,i-Eg and Ep,i-Eiso-tb correlations can be used for only a fraction of events (a firm estimate of tb is needed)

  20. use of the Ep,i-Eg and Ep,i-Eiso-tb correlations for the estimate of cosmological parameters, in a way similar to SN Ia Ghisellini et al., NCIM, 2005 Ghirlanda et al.,ApJ, 2004

  21. use of the Ep,i-Eg and Ep,i-Eiso-tb correlations for the estimate of cosmological parameters, in a way similar to SN Ia Liang & Zhang,ApJ, 2005

  22. use of the Ep,i-Eg and Ep,i-Eiso-tb correlations for the estimate of cosmological parameters, in a way similar to SN Ia Ghisellini et al. 2005

  23. cautions / problems • based on a still low number of events (and the Ep,i-Eg requires assumptions on the density and distribution of the circum-burst environment and on the kinematic to radiated energy conversion efficiency) • differently from the Ep,i-Eiso correlation, the Ep,i-Eg and Ep,i-Eiso-tb correlations can be used for only a fraction of events (a firm estimate of tb is needed) c) circularity problem d) physics underlying these correlations still not settled d) outliers, lack of jet breaks in Swift

  24. GRB physics with spectral - energy correlations

  25. GRB prompt emission models • physics of prompt emission still not settled -> various scenarios: SSM internal shocks, IC-dominated internal shocks, external shocks, photospheric emission dominated models, kinetic energy dominated fireball , poynting flux dominated fireball) • e.g., Ep,i G-2 L1/2 tn-1 for syncrotron emission from a power-law distribution of electrons generated in an internal shock, Ep,i G Tpk G2 L-1/4 for comptonized thermal emission from the photosphere • to be combined with the general assumption: L  Gb

  26. more in general,Ep,iGM and EisoGN , with M and N varying in each scenario and for different set of parameters within each scenario-> positive correlation between Ep,i – Eiso and its slope constrain parameters ranges in each scenario • also the extension of the correlation puts constraints on prompt emission models,showing that the distribution of Ep,i is much broader than thought before (e.g. zhang & Meszaros 2002, Asano & Kobayashi 2004) Zhang & Meszaros, ApJ, 2002

  27. jet and GRB/XRF unification models • the validity of the Ep,i– Eiso correlation from the brightest GRBs to XRFs puts severe constraints on jet and GRB/XRF unification models • uniform jet -> majority of GRBs with jet angles < 1° • universal structured jet -> too many XRFs • new hypothesis : quasi-universal structured jet ; Fisher-shape jet structured uniform

  28. Ep,i – Eiso correlation and off-axis scenarios • when the viewing angle exceeds the jet opening angle both Ep,i and Eiso decrease dramatically and we observe normal GRBs as very soft and weak events (i.e. XRFs), due to relativistic beaming and Doppler effects • extension to XRFs of the Ep,i-Eiso correlation Yamazaki et al. (2004): d=[g(1 - bcos(qv - Dq))]-1 DEp d , DEiso d(1+a) -> DEp DEiso(1+a) a=1÷2.3 -> Ep(qv)  Eiso(qv)0.5÷0.3 • other scenarios based on viewing angle include: ring shaped fireball (Eichler & Levinson 2004), multi component jets / subjets (e.g. Toma et al. 2005) cannonball model (Dar, Dado, De Rujula)

  29. the Ep,i – Eiso correlation, the GRB/SN connection and sub-energetic GRBs • the Ep and Eiso values of the GRB/SN prototype event GRB980425/SN1998bw (z=0.008) are inconsistent with the correlation • it has been claimed that this is true also for the other sub-energetic event GRB031203 / SN2003lw, but ISGRI Ep lower limit is debated, based on dust echo measured by XMM • the other GRB/SN events (e.g. GRB030329 /SN2003dh) are consistent with the Ep,i-Eiso correlation • GRB060218 / SN2006aj is consistent !

  30. the most common explanations for the (apparent ?) sub-energetic nature of GRB980425 and GRB031203 and their violation of the Ep,i – Eiso correlation are based on peculiar viewing conditions (e.g. Yamazaki et al. 2003, Ramirez-Ruiz et al. 2005) • double-peak interpretation (e.g. Dado and Dar 2004): in GRB980425 and GRB031203 we are seeing the high energy peak due to Compton up-scatter of UV photons by CR electrons accelerated by SN jets • in general: possible use of the Ep,i – Eiso plane to identify sub-classes ?

  31. Ep,i – Eiso correlation and short GRBs • only very recently, redshift estimates for short GRBs (1 by HETE-2, 3 by Swift) were available (in the range 0.16-0.72) • estimates of both Ep,i and Eiso are available for GRB050709 (HETE-2) and GRB051221 (Swift) and are inconsistent with Ep,i-Eiso correlation holding for long GRBs • low Eiso values and high lower limits to Ep,iindicate inconsistency also for the other three short GRBs • furher evidence for a different nature of short GRBs

  32. Ep,i – Eiso correlation as a tool • use of the Ep,i – Eiso to construct GRB redshift estimators (es. Atteia, 2003): pseudo-redshift of HETE-2 bursts published in GCN • use of the Ep,i – Eiso correlation to infer the star formation rate (SFR) evolution , e.g.Yonetoku et al., 2004 , Firmani et al. 2004) • use of the Ep,i – Eiso correlation to infer the jet angle probability distribution (e.g. Liang et al. 2004, Bosnjak et al 2004) • Ep,i – Eiso correlation is often used in GRB synthesis simulations as an input or a required output Atteia, A&A, 2003 Liang et al. 2004

  33. GRB and SN physics with prompt emission X-ray spectra

  34. Extending to X-rays: from BATSE… • major contribution came in the ’90s from the NASA BATSE experiment (25-2000 keV) onboard CGRO (1991-2000) • based on NaI scintillator detectors; 8 units covering a 4p FOV

  35. Extending to X-rays: … to BeppoSAX • BeppoSAX: • NFI (X-ray focusing telescopes, 0.1-10 keV + PDS, 15-200 keV) • WFC (2 units, proportional counters + coded mask, FOV 20°x20° each unit, 2-28 keV) • GRBM (4 units, CsI scintillators, large FOV, GRB triggering, 40-700 keV) • WFC and GRBMco-aligned

  36. Extending to X-rays: and HETE-2 • HETE-2: extending the sample of X-ray rich GRBs and XRFs • FREGATE: NaI crystal scintillators, 6-400 keV, FOV = 3 sterad • WXM: 2 units, gas proportional counters + 1-D codedmask, 2-25 keV , localization of few arcmin • SXC: 2 units, CCD + 1-D coded mask. 0.5 – 10 keV, ~30 arcsec • accurate localization (few arcmin) and fast position dissemination • study of prompt emission down to X-rays

  37. Extending to X-rays: light curves • pulse width as a function of energy: test of SSM • spectral lag – luminosity relation Frontera et al., ApJS, 2000 Piro et al./Feroci et al. , A&A, 1997/2001

  38. Extending to X-rays: spectra • many GRB spectra are consistent with syncrotron shock emission models down to X-rays • the extension to few keV allow a better estimate of low energy index and of Ep BATSE (Tavani, ApJ, 1995) BeppoSAX (Amati et al., 2001)

  39. Extending to X-rays: deviations from SSM • a fraction of GRB time resolved spectra are inconsistent with optically thin synchrotron emission (i.e. a > -0.67) From BATSE data From BeppoSAX

  40. Extending to X-rays: deviations from SSM • possible explanations: quasi-saturated comptonization, thermal component, Compton drags, synchrotron emission with small pitch angle, syncrotron self-absorption )

  41. Extending to X-rays: thermal component • evidences for a thermal component (from fireball photosphere ? SN ???) BATSE BeppoSAX

  42. Extending to X-rays: absorption features • BeppoSAX detection of a transient absorption feature in the first 13 s of GRB990705. Amati et al., Science, 2000

  43. Transient absorption feature in GRB990705: two possible interpretations: • K absorption edge of neutral Fe within a shell of material around the GRB site, photo-ionized by the GRB photons (Amati et al. 2000). Consequences: i. X-ray redshift (0.86±0.17) of the burst source, which was later confirmed by the optical redshift of the GRB host galaxy (Le Floc’h et al. 2002); ii. Iron relative abundance A/Asun≈75, typical of supernova explosions. iii. A large mass of Fe, unless Fe is clumped and a clump is along the line of sight (Boettcher et al. 2001). Amati et al. 2000

  44. Absorption line due resonant scattering of GRB photons off H-like Fe (transition 1s-2p, Erest = 6.927 keV) (Lazzati et al. 2001). Consequences: a) The redshift is still consistent with that of the HG; b) Fe mass required: ~0.2 Msun; c) Fe relative abundance ~10 Lazzati et al. 2001

  45. Variable NH from 2.5 x 1023 cm-2 to a value compatible with 1x1022 cm-2 which was observed during the late afterglow phase (Frontera et al. 2000) (Galactic value:1x1021 cm-2 ). The NH time behaviour is explained (Lazzati & Perna 2001) if the GRB event occurs in overdense regions within molecular clouds (Bok globules) Variable NH detected also in GRB000528 Variable intrinsic absorption in the prompt emission of GRB980329and GRB 000528 Frontera et al. 2000 Lazzati & Perna 2001

  46. Extending to X-rays: X-Ray Flashes • BeppoSAX discovers X-Ray Flashes (XRF): GRBs with only X-ray emission • distribution of spectral peak energies has a low energy tails Amati et al. Science, 2000

  47. Extending to X-rays: X.Ray Flashes • normal GRBs, XRRs and XRFs are found to be in the ratio 1:1:1 • recent XRF redshift estimates: z in the 0.1 – 1 range • GRBs, XRRs and XRFs form a continuum in the Ep – fluence plane: evidence of a common origin • most likely explanation: inefficient internal shocks due to low contrast of DG between colliding shells with respect to fireball bulk G

  48. Extending to X-rays: Swift • Swift: NASA mission dedicated to GRB studies launched 20 Nov. 2004 USA / Italy / UK consortium • main goals: afterglow onset, connection prompt-afterglow, substantially increase of conunterparts detection at all wavelengths (and thus of redshift estimates) • payload: BAT (CZT+coded mask, 15-350 keV, wide FOV, arcmin ang. res.), XRT (X-ray optics, 0.3-10 keV, arcsec ang.res.), UVOT (sub-arcsec ang.res. mag 24 in 1000 s) • spacecraft: automatic slew to target source in ~1 - 2 min.

  49. Extending to X-rays: Swift • new features seen by Swift in X-ray afterglow light curves: initial very steep decay, early breaks, flares;may occurr all together or only some of them ~ -3 ( 1 min ≤ t ≤ hours ) ~ -0.7 10^5 – 10^6 s ~ - 1.3 ~ -2 10^2 – 10^3 s 10^4 – 10^5 s

  50. Extending to X-rays: Swift • initial steep decay: in some cases matches end of prompt emission: continuation of prompt emission ? • in other cases inconsistent with prompt emission: mini break due to patchy shell, IC up-scatter of the reverse shock sinchrotron emission ? • may also be due to missed flare

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