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Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions (and discussions) from:

ESTREMO/WFXRT: GRB science / cosmology and requirements for the WFM. Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions (and discussions) from:

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Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions (and discussions) from:

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  1. ESTREMO/WFXRT: GRB science / cosmology and requirements for the WFM Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions (and discussions) from: N. Auricchio, S. Campana, E. Caroli, L. Colasanti, A. Corsi, G. Cusumano, M. Feroci, A. Galli, C. Labanti, M. Marisaldi, L. Piro, J. Stephen, G. Tagliaferri. J.J.M. in ‘t Zand Meeting on Scientific requirements for ESTREMO/WFXRT Bologna, May 4-5

  2. Summary of presentations concerning GRB • L. Piro: science with ESTREMO/WFXRT (yesterday) • A. Corsi: use of GRBs afterglows for WHIM studies (yesterday) • L. Amati: GRB science/cosmology with ESTREMO/WXRT and requirements for the Wide Field Monitor (WFM) • A. Galli: GRBs and XRFs X-ray logN-logS • S. Campana: GRB local absorption high resolutions spectroscopy • M. Marisaldi (first part): WFM - From scientific requirements to design and SDC+CsI. • M. Feroci: WFM – extending superAGILE capabilites

  3. Outline • GRBs: a brief introduction • brief review of GRB cosmology and science with ESTREMO/WXRT focal plane instruments • requirements for the Wide Field Monitor (WFM): general working scheme, main constraints & inputs • minimum requirements for the use of GRBs as beacons for WHIM • improved GRB science and cosmology: extended requirements for the Wide Field Monitor (WFM) • the foreseen international scenario

  4. GRBs: basic information

  5. The GRB phenomenon(very briefly !) • prompt emission

  6. The GRB phenomenon • 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 (2025 cm2) covering a 4p FOV

  7. The GRB phenomenon • 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

  8. afterglow emission

  9. Standard picture and basic physics • afterglow emission: power-law decay WFC (prompt) NFI (afterglow) Frontera 2002 Costa et al., A&AS, 1999

  10. Standard picture and basic physics • afterglow emission: power-law spectrum GRB 000210 GRB 010222 In ‘t Zand et al., ApJ, 2001 Costa et al., Nature, 1997 Piro et al., ApJ, 2000 Frontera 2002

  11. 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

  12. 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

  13. Afterglow light curve breaks -> collimation

  14. 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

  15. Standard picture and basic physics • Internal (between shells of the fireball expaning at different velocities), external shocks (with the circum-burst environment), reverse shock

  16. Unvealing the progenitors • . • dark GRBs (X-ray afterglow but no optical counterpart: high z ? high oscuration by dust ? inefficient external shock due to low density medium ? Guidorzi et al., A&A, 2003 Rol et al., ApJ, 2002

  17. Adding pieces to the puzzle • 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. A&A, 2004 Kippen et al. 2001

  18. 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

  19. Adding pieces to the puzzle • 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

  20. Adding pieces to the puzzle • GRB990123: first detection (by ROTSE) of optical emission simultaneous to a GRB • optical light curve does not follow high energy light curve: evidence for a different origin (reverse shock ?) GRB990123, Akerloff et al.,Nature, 1999 ; Maiorano et al., A&A, 2005

  21. Spectrum Reverse Shock Emission Forward Shock Emission frequency Optical Light Curve Reverse Shock Emission Forward Shock Emission time t~ sec - min t ~ few hours

  22. Adding pieces to the puzzle • GRB041219 (RAPTOR) contrary to GRB990123, the optical light curve follows the high energy light curve: evidence for same origin (internal shocks ?) • GRB050401 (ROTSE)the optical light does not follow the high energy light curve and is consistent with optical afterglow light curve: evidence of early afterglow ? GRB050401

  23. Unvealing the progenitors • evidence of a GRB - SN connection: GRB980425 / SN1998bw • GRB 980425, a normal GRB detected and localized by WFC and NFI, but in temporal/spatial coincidence with a type Ic SN at z = 0.008 (chance prob. 0.0001)

  24. Unvealing the progenitors • further evidences of a GRB/SN connection: bumps in optical afterglow light curves and optical spectra resembling that of GRB980425 GRB 030329, Hjorth et al., Nature, 2003 GRB 030329, Stanek et al., ApJ, 2003

  25. 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.

  26. Adding pieces to the puzzle • 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

  27. Adding pieces to the puzzle • 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

  28. Adding pieces to the puzzle • flat decay: probably “refreshed shocks”, due either to: • Long duration ejection (t ~ tflat ) • Short ejection (t ~ t), but with range of 

  29. Adding pieces to the puzzle • Flares: could be due to: • Refreshed shocks • IC from reverse shock • External density bumps • Continued ctrl. engine activity: late internal shocks • in some cases, missed part of a flare can explain early steep decay

  30. Unvealing the progenitors • host galaxies long GRBs: blue, usually regular and high star forming, GRB located in star forming regions • host galaxies of short GRBs (very recent): elliptical, irregular galaxies, away from star forming region (but still unclear) Long Short GRB 050509b

  31. 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

  32. Unique GRB science and cosmology with the ESTREMO/WFXRT telescopes

  33. GRBs as beacons for WHIM study Structure simulation from Cen & Ostriker (1999)  Simulations of WHIM absorption features from OVII as expected from filaments (at different z, with EW=0.2-0.5 eV) in the l.o.s. toward a GRB with fluence=410-6 as observed with ESTREMO (in 100 ksec). About 10% of GRB (10 events per year per 3 sr) with ~ 4106 counts in the TES focal plane detector

  34. simulations • 2eV res. S=4e-6erg cm-21eV res. S=4e-6erg cm-2

  35. New X-ray cosmology with GRB • Study the evolution of metals & star formation with z • Identify high-z GRB and their obscured host galaxies (X-rays and gamma-rays pierce through) at z=7-20 when the first stars & galaxies formed

  36. 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 NH in Giant Molecular clouds

  37. Expected distributions Galaxy (cumulative) MC (differential)

  38. Cumulative distributions KS test: MC: 0.65 Galaxy: 10-11 (incl. Upper limits)

  39. Simulations of X-ray edges produced by metals (Si, S, Ar, Fe) by a medium with column density NH=5 1022 cm-2 and solar-like abundances in the host galaxy of a bright GRB at z=5., as observed ESTREMO with an observation starting 60 s after the main pulse and lasting 60 ksec -> Map the metal evolution vs z Ar S Fe Si

  40. Spectroscopy of High-z GRBs • Swift is providing a rich return of high redshift (z > 4) • bright and flaring rest-frame light curves -> low metallicity ? -> metallicity evolution with z • high resolution X-ray spectroscopy only way to estimate z at very high redshift (optical spectroscopy limited by Lyman a dump) and of dark GRBs

  41. Fast slew: sensitive study of prompt-afterglow connection • new features seen by Swift in X-ray afterglow light curvesX-ray spectrscopy of X-ray flares ~ -3 ( 1 min ≤ t ≤ hours ) 10^5 – 10^6 s ~ -0.7 ~ - 1.3 ~ -2 10^2 – 10^3 s 10^4 – 10^5 s

  42. Sensitive study of SN shock break-out ? • Shock break-out in GRB060218/SN2006aj detected by Swift

  43. Requirements for the Wide Field Monitor: working scheme, basic constraints and inputs, assumptions

  44. Main goal of WFM : detect and localize ( ~ 1-3 arcmin) at least 30 GRBs /year bright (beacons for WHIM, etc.) Minimum requirements forWFM Basic WFM concept, with minimum performances and impact Weight, volume, power, electronics, OBDH, simplicity and other constraints Enabling technologies (CZT, SDC+scint., improved super-agile, other), state of art, know how and expertise Improved WFM design and trade off between different technologies (CZT, SDC+scint, improved super-agile, other) Desirable and new, (with respect to present and forseen experiments) scientific goals for GRB science Desirable requirements from X-Ray Transients WG GRB science with X-ray telescope and focal plane instruments GRB science with ESTREMO

  45. Main constraintsfor WFM • mass budget: 150 kg (preliminary) • power budget: 120 W (preliminary) • low impact on costs and simplicity • Other basic inputs • low (~600 km ) Earth equatorial orbit (e.g. SAX, AGILE) • satellite fast slew capability (~60° in 1 min.) • GRB occurrence rate: ~1000/year in the full sky • GRB/XRR/XRF ratios (based on HETE-2): 1/3,1/3,1/3

  46. Assumptions: GRB spectral shape • 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

  47. Assumptions: background • HEAO-1 diffuse background (CXB)from Grueber et al. (1997) • internal background: of course depends on mass and volumes distributions of the detectors and satellite structure -> will need MC simulations. • for these preliminary estimates, scaled from internal BKG of BeppoSAX WFC in 2-28 keV and PDS/GRBM at energies >30 keV)

  48. Use of GRB as cosmological beacons: minimum requirements for the WFM

  49. requiredafterglow 2-10 keV fluence (60s < 7 < 60 ks) > 4 x 10-7 erg/cm2 and a FOV of ~3 sr (see yesterday’s talk by A. Corsi)

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