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ESTREMO/Wide Field Monitor: scientific requirements for GRB physics and cosmology

ESTREMO/Wide Field Monitor: scientific requirements for GRB physics and cosmology. Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions from:

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ESTREMO/Wide Field Monitor: scientific requirements for GRB physics and cosmology

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  1. ESTREMO/Wide Field Monitor: scientific requirements for GRB physics and cosmology Lorenzo Amati (INAF - IASF Bologna, Italy) with contributions from: N. Auricchio, S. Campana, E. Caroli, L. Colasanti, A. Corsi, G. Cusumano, M. Feroci, A. Galli, B. Gendre, G. Ghirlanda, C. Labanti, M. Marisaldi, L. Piro, J.B. Stephen, G. Tagliaferri, J.J.M. in ‘t Zand

  2. Outline • minimum requirements for the use of GRBs as beacons for WHIM X-ray spectroscopy • extended requirements for GRB physics • requirements for use of GRBs as cosmological standard candles • other possible reuirements and present/future GRB experiments • brief review of GRB cosmology and science with focal plane instruments

  3. 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

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

  5. 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

  6. Based on TES resp. and eff. simulations • S = GRB afteglow fluence in 2-10 keV in 60s < t < 60 ks • 2eV res. S=4e-6 erg cm-2 1eV res. S=4e-6 erg cm-2

  7. Minimum requirements for WFM design • FOV at least 3 sr (~1/4 of the sky) • source location accuracy of 1-3 arcmin for a 15-20 s source • energy band ~20-200 keV (where S/N for typical GRBs is optimal) • energy resolution: not important

  8. Baseline: coded mask instrument • fraction of coded mask that is open: 50% • coded mask area 4 times detector area • detector plane and mask connected by four passive shields • significance needed for source location accuracy of 1-2 ‘ : 15 – 20 sigma (based on discussion with hardware people) • CZT and SDC+scint have been proposed for the detectors, but also different concept proposed (e.g. by Feroci et al.)

  9. Assumptions: GRB spectral shape and rate • smoothly broken power-law spectra typically described by the empirical Band function with parametersa= low-energy index, b= high-energy index, E0=“roll over” energy • Ep = E0 x (2 + a) = peak energy of the nFn spectrum • low (~600 km ) Earth equatorial orbit (e.g. BeppoSAX) -> GRB occurrence rate: ~300/year in the full sky • GRB/XRR/XRF ratios (based on HETE-2): 1/3,1/3,1/3

  10. Assumptions: background • HEAO-1 diffuse background (CXB) from Grueber et al. (1997) • internal background: 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)

  11. requiredafterglow 2-10 keV fluence (60s < t < 60 ks) > 4 x 10-7 erg/cm2 and a FOV of ~3 sr

  12. ->afterglow 2-10 keV fluence (60s < 7 < 60 s) > 3 x 10-7 erg/cm2 ->20-200 keV prompt fluence > 2.5 x 10-6 erg/cm2(~35-40%) (based on correlations between afterglow 2-10 keV flux at 11hr and prompt emission X-ray and gamma-ray fluences)

  13. Preliminary estimates of minimum 20-200 keV effective area • assumed typical 25s long GRB with spectrum :a = -1 , b = -2.5 and E0 = Ep = 200 keV • required 15 s significance in 10 s integration time, in order to localize the source with at least 3’ accuracy and start to slew • this corresponds to a required 20-200 keV 5s sensitivity in 1 sof 2.5x10-7 erg/cm2/sor 2.3 ph/cm2/sor ~700mCrab • computation of effective areas (in cm2) performed for different n of units / FOV: #units [fov] 1 [3 sr] 2 [1.5 sr] 4 [0.75 sr] 6 [0.5 sr] Eff. Area of each unit 300 220 180 160 NOTE: assumed f_mask = 0.5

  14. reducing the FOV is not an dvantage, as expected given that in 20-200 keV the CXB is not the main component of the BKG and that we are talking of very bright sources ! • -> number of units driven by other design requirements (e.g. maximum number of pixels for each detecting unit, payload volume and mass distributions, need to cover a 3sr FOV including the telescopes FOV, etc.)

  15. Improved GRB science requirements: extending WFM energy band down to a few keV

  16. extending down to a few keV increases trigger sensitivity

  17. few keV low energy threshold allows a better determination of the spectral parameters (Swift/BAT is very sensitive but with an energy band 15-150 keV -> 80% of time averaged spectra can be fitted with simple power-laws !) • Ep -> very important for GRB physics and cosmology (discuss later) and understanding nature of XRFs (GRB/XRF unification)

  18. Based on GRB X-ray logN-logS BeppoSAX, 70% of GRBs have a 2-10 keV fluence > 10-7 erg/cm2/s

  19. Preliminary estimates of minimum 2-20 keV effective area for sensitive study of X-ray emission of normal GRB with 2-10 keV fluence > 10-7 erg/cm2 (~70% of GRBs) • assumed typical 25s long GRB with spectrum :a = -1 , b = -2.5 and E0 = Ep = 200 keV • required 10 s significance of2-20 keVtime integrated counts , in order to perform sensitive spectral continuum analysis • this corresponds to a required 2-20 keV 5s sensitivity in 1 s of~2.2x10-8 erg/cm2/s or ~1.8 ph/cm2/s or ~500 mCrab #units [fov] 1 [3 sr] 2 [1.5 sr] 4 [0.75 sr] 6 [0.5 sr] Eff. Area of 1 unit 390 220 135 100 NOTE: assumed f_mask = 0.5

  20. 2 – 3 keV at most is unavoidable if want to check the real existence of transient absorption/emission features detected by BeppoSAX

  21. more stringent requirements are needed for detection and study of transient X-ray absorption features in 2-10 keV • GRB990705 was a very bright event, the edge was very deep but it was detected only at ~3s c.l. and was detected only in the first 13 s • evidences of transient local nH in 2 other bright events (GRB030329 and GRB000528) and a possible transient absorption feature in GRB011211 (X-ray rich) • to make a sensitive search of these features, confirm BeppoSAX results -> require at least 10 s significance in 2-10 keV in 10 s for normal GRBs with fluence • energy resolution of ~5% at 6 keV would be very good

  22. Preliminary estimates of minimum 2-10 keV effective area for detection and study of transient X-ray absorption features in normal GRB with 2-10 keV fluence > 10-7 erg/cm2 (70%) • assumed typical 25s long GRB with spectrum :a = -1 , b = -2.5 and E0 = Ep = 200 keV • required 10 s significance of2-10 keVin 10 s • this corresponds to a required 2-10 keV 5s sensitivityin 1 s of6.x10-9 erg/cm2/sor0.8 ph/cm2/sor~250 mCrab #units [fov] 1 [3 sr] 2 [1.5 sr] 4 [0.75 sr] 6 [0.5 sr] Eff. Area of 1 unit 1400 800 450 320 NOTE: assumed f_mask = 0.5

  23. required energy resolution at energies < 10 keV can be achieved with existing technology (e.g. SDC, CZT)Simulation of the transient (13 s) absorption feature in GRB990705 (a bright GRB) as would by a CZT based detector, 3 mm thick, 400 cm2, FOV = 0.5 energy resolution of 5% at 6keV GRB990705 (Amati et al., Science, 2000) simulation

  24. Extending down the low energy allows detection, study and use of X-ray rich GRBs and in particular of X-Ray Flashes (XRFs)

  25. Specific Requirements for XRFs • weak and soft events, with Ep < 20 keV • correlation between XRF peak flux and Ep • need high sensitivity in the 2-20 keV energy band, especially if thinking of triggering in this energy band • enough statistics to estimate Ep -> very important for test of spectral energy correlations (see next) -> GRB physics and cosmology • have enough statistics to detect and localize XRFs, thus allowing fast pointing with NFIs for afterglow search and study (if off-axis events -> late afterglow onset) • HETE-2 -> 60% of XRFs have a 2-30 keV fluence > 1.5x10-7 erg/em2 -> 2-20 keV fluence > 1.2x10-7 erg/cm2

  26. Preliminary estimates of minimum 2-20 keV effective area for detection of sensitive spectral study of XRFs with 2-20 keV fluence > 1.2x10-7 erg/cm2 (60%) • assumed typical 25s long XRF with spectrum :a = -1 , b = -2.5 and E0 = Ep = 15 keV • required 10 s significance in 2-20 keV in 10 s • this corresponds to a required 2-20 keV 5s sensitivity in 1 s of8.2x10-9 erg/cm2/s or 0.8 ph/cm2/sor 200 mCrab #units [fov] 1 [3 sr] 2 [1.5 sr] 4 [0.75 sr] 6 [0.5 sr] Eff. Area of 1 unit 1900 1100 600 425 NOTE: assumed f_mask = 0.5

  27. Requirements for the cosmological use of GRBs as “standard candles” : extending to 1 MeV the WFM energy band for accurate estimate of Ep

  28. spectral-energy correlations: Ep,i-Eiso, Ep,i-Eg, Ep,i-Eiso-tb, Ep,i-Liso-T0.45

  29. 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

  30. 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

  31. Requirements: spectral-energy corr. • due to the broad and smooth roll-over that characterizes GRBs spectra, the estimate of Ep can be significantly affected by detector’s energy band (“data truncation effect”) and sensitivity as a function of energy • indeed, in several cases, for simultaneously detected events, BATSE (25-2000 keV), BeppoSAX (2-700 keV), HETE-2 (2-400 keV), Swift/BAT (15-350 keV) and Konus-Wind (15-5000 keV) provide significantly different values of Ep ! • if the energy band is not large enough, a fit with the Band function does not allow to constrain all the parameters and often a cut-off power-law is adopted (e.g. for HETE-2 and Swift/BAT)

  32. The Future of Cosmology with GRBs: Requires 1) Larger sample (only 3-5 over 13 (out of 51) GRBs with z, Ep from Swift in ~ 2yr) 2) Higher accuracy in measuring spectral parameters (e.g. below 10% on average, though flux-dependent) 2) Calibrate the correlations Instrumental energy band Lower energy extension:  detected # of bursts (down to few keV) (agrees with present pop studies) Upper energy extension: accuracy of spectral parameters (up to ~ MeV)

  33. A “minimal” Simulation 150 Fake GRBs 1) C-SFR (Porciani & Madau 1999) 2) F(L) (e.g. Firmani 2004) • Bursts satisfy the Ep-Eiso correlation (within its scatter) • Bursts satisfy the Ep-Eg correlation (withing its scatter) • Detectability: Fluence > 10-7 erg/cm2 in 2-400 keV (assuming a typical GRB spectrum) • Average parameter uncertainties: Fluence  10% Ep  20% Tb  20% The simulated sample has a peak energy distributed beteew 2keV and 1MeV Ghirlanda et al. 2006 A&A

  34. Ghirlanda et al.2006 A&A Ghirlanda et al. 2006 JOP Review, GRB Special Issue

  35. TEST on instr. energy range extension: The detection sensitivity is maximal for bursts with Ep within the instrumental energy range E. We should expect that for Ep  E (spec. param) is inversely related to E 43 GRBs with Ep=[25,200] keV 127 GRBs with Ep=[5,200] keV 150 GRBs with Ep=[2,1000] keV  (Ep)=60% , (F)=30%  (Ep)=40% , (F)=20%  (Ep)=20% , (F)=10% E1 = 15 – 300 keV E2 = 2 – 300 keV E3= 2 – 1000 keV Cosmological constraints are dominated by number of events and precision on parameter estimates

  36. Vary param. Uncert. by a factor 2 Vary #of GRBs by a factor 2

  37. Reasonable possible configurations • unique instrument with energy band from a few keV up to ~ 300-400 keV -> good number of Ep estimates but low accuracy in estimate of Ep (40%) and fluence (20%) • low energy instrument (from a few keV up 100-200 keV, few arcmin localization capabilites through mask) +high energy instrument (from ~20 keV to ~1 MeV , collimated or omnidirectional) -> optimal number of Ep estimates and high accuracy in estimate of Ep (20%) and fluence (10%) • performed estimates of required effective area in 2-20, 20-200 and 200-700 keV by considering a soft, average and hard GRB, respectively • accurate estimates of Ep for GRBs with 2-400 keV fluence > 3x10-7 erg/cm2

  38. Low energy detector (e.g. 2 – 150 keV): preliminary estimates of minimum 2-20 keV effective area for sensitive study of X-ray emission of normal GRB with 2-400 keV fluence > 3x10-7 erg/cm2 • assumed typical 25s long soft GRB with spectrum :a = -1.5 , b = -2.5 and E0 = 100 keV (Ep = 50 keV) • required at least 15s significance of2-20 keVtime integrated counts , in order to perform sensitive spectral continuum analysis • this corresponds to a required 2-20 keV 5s sensitivity in 1 s of~6x10-9 erg/cm2/s or ~0.75 ph/cm2/s or ~220 mCrab #units [fov] 1 [3 sr] 2 [1.5 sr] 4 [0.75 sr] 6 [0.5 sr] Eff. Area of 1 unit 2000 1250 650 450 NOTE: assumed f_mask = 0.5

  39. high energy detector (e.g. 30 – 1000 keV) • omnidirectional or weakly collimated (no imaging required -> no mask) scintillator detector (NaI, CsI, BGO, etc.) units with thousends cm2 area could do the job • e.g. half BATSE/LAD – like detector (NaI, 1000 cm2) would allow to estimate Ep with 20% accuracy for most 70% GRBs with Ep in the 100-600 keV energy range and 2-400 keV fluence > 5x10-7 erg/cm2 • smaller misaligned units in orther to optimize efficiency as a function of source detection, could be an alternative

  40. Other possible requirements for the WFM and present/future GRB experiments

  41. Other possible requirements: polarization • emission mechanisms: mainly sinchrotron -> polarization • but not ordered magnetic field -> should dump the detectable degree of polarization; but relativistic beaming effects -> a low degree (10-20%) towards the observer • detected in optical afterglow (lin., 1-3%); in X/gamma rays ? (there was a claim, not confirmed by re-analysis) • simulation performed for a CZT based detector, 5 – 10 mm thick, polarization > 20-30% should be detectable at least for the 1-2 brightest event in a year (CZT hardware people)

  42. Other possible requirements: timing • GRBs power spectra do not provide particurlarly relevant information • most efforts have been done on light curve variability, by defining different parameters for variability • most interesting uses: correlation between variability and peak luminosity -> redshift estimators • very recent developments: introduce a time variability parameter in spectral energy correlation -> improved cosmological use of GRBs • a time resolution of 1 ms would fit these requirements

  43. Summary of scientific requirements for WFM • FOV = 3 - 4 sr, 1 – 6 modules • other: 1-10 ms timing, 10-20% lin. pol.

  44. Main present GRB experiments • Swift: 15-150 keV, poor continuum determination, fits with power-law, Ep only in 20% cases, not much sensitive to XRFs, no X-ray features • HETE-2: 2-400 keV, XRFs, no detection of X-ray features (because of sensitivity of WXM worse than beppoSAX/WFC ?), low sensitivity at > 200 keV -> fits mostly cut-off power-laws • Konus/Wind : > 15 keV, no X-ray features, not much sensitive to XRFs, Ep determination for most events (but not disseminated because very slow ) • Suzaku/WAM: 50 keV – 5 MeV, no X-ray rich and XRFs, starting to provide reliable Ep estimates

  45. Some foreseen GRB experiments • AGILE and GLAST (2006, 2007) : study of GRBs up to tens or hundreds of GeV; miss low energy X-ray band, could complement measurements of ESTREMO/WFM is still operating after 2015 • ECLAIRs (2011-2016) : spectral study of prompt emission in 1-300 keV and optical observation of prompt emission • Lobster-ISS (2010-2014) : spectral study of GRB in the 0.3-500 keV enegy band (but probably with a gap between 3 and 15-20 keV)

  46. Further GRB science and cosmology with the ESTREMO X-ray telescopes

  47. 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

  48. 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

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

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

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