Can we constrain GRB shock parameters using the Gamma Ray Large Area Space Telescope? Eduardo do Couto e Silva SLAC/KIPAC SABER Workshop Mar 15, 2006
The Main Questions Is there any connection between the SABER program and the GRB science with GLAST? Can we create an environment similar to that of the shock dissipation phase in GRBs? see poster (Stochastic( wake field particle acceleration in Gamma Baribiellini et al Stochastic wake field particle acceleration in Gamma-Ray Bursts, et al) Can we quantify the relative importance of magnetic fields during the shock dissipation phase in GRBs?
Outline Overview of the GLAST Observatory two high energy gamma ray telescopes Introduction to Gamma Ray Bursts (GRB) focus mostly high energy emissions (> GeV) Can we measure shock parameters related to Gamma Ray Bursts? phenomenological approach within the fireball scenario List expectations for this Workshop
GLAST Observatory : Overview GLAST will measure the direction, energy and arrival time of celestial estial γ rays LAT will record gamma-rays in the energy range ~ 20 MeV to >300 GeV Principal Investigator: Peter Michelson Orbit 565 km, circular GBM will provide correlative observations of transient events in the energy range ~10 kev 25 MeV Observing modes All sky survey Pointed observations Re-pointing Capabilities Autonomous Rapid slew speed (75 in < 10 minutes) Will follow on the measurements by its predecessor (EGRET) with unprecedented capabilities Inclination 28.5 o Lifetime 5 years (min) Launch Date Sep 2007 Launch Vehicle Delta 2920H-10 Launch Site Kennedy Space Center
GLAST Burst Monitor: Overview NaI and BGO counters exposed to the entire sky LAT FoV Principal Investigator: Charles Meegan GBM FoV NaI crystals (12) low-energy spectral coverage ~10 kev to ~1 MeV rough burst locations BGO crystals (2) high-energy spectral coverage ~150 kev to ~30 MeV Spectral Measurements measures spectra for bursts connects with LAT measurements GBM 10 kev to ~ 25 MeV Correlative observations of transient phenomena Afterglows in Gamma Ray Bursts Wide Sky Coverage (8 sr) autonomous repoint for exceptionally bright bursts that occur outside LAT field of view Connections to the Ground Network of Telescopes burst alerts to the LAT and ground telescopes within seconds
Principal Investigator: Peter Michelson Silicon Microstrip Tracker ~ 80 m 2 of silicon 8.8 x 10 5 readout channels Strip pitch = 228 µm xy layers interleaved with W converters ~1.5 X 0 Calorimeter Hodoscopic array Array of 1536 CsI(Tl) crystals in 8 layers ~8.5 X 0 Anti-Coincidence Detector 89 scintillator tiles Segmented design Large Area Telescope: Overview The LAT is a pair-conversion telescope of 16 towers surrounded by plastic scintillators γ e + e LAT 3000 kg, 650 W (allocation) 1.8 m 1.8 m 1.0 m 20 MeV 300 GeV Currently there is no other telescope covering this energy range Silicon Microstrip Tracker Measures γ direction γ identification Calorimeter Measures γ energy Shower imaging Anti-Coincidence Detector Rejects background of charged cosmic rays segmentation removes selfveto effects at high energy
LAT Integration @ SLAC Calorimeter module Tracker module LAT Integration & Test Team Anti Coincidence Detector being integrated with 16 towers
LAT Data from Tests at SLAC From A. Borgland Muon candidates Most of the 500 Hz of triggers recorded are muons Photon Candidates? ~20% of cosmic ray showers are not muons
Energy Peak effective area Field of view Sensitivity (1yr) 30 MeV - 30 GeV 1500 cm² 0.5 sr ~ 10-7 γ cm -2 s -1 Localization (bright source) Deadtime 15 100 ms 20 MeV - 300 GeV Comparison of Instrument Performance LAT Simulation EGRET LAT 3 rd EGRET Catalog E > 100 MeV Pointing All sky 1991-2001 2007 -? 5 yr operation requirement 10 yr operation goal E > 100 MeV Improvement > 8000 cm² > 5 > 2.0 sr > 4 < 6 10-9 γ cm -2 s -1 > 20 < 0.5 > 30 < 30 μs > 1000 Large area Low instrumental background
All Sky Monitoring with Improved Sensitivity Fraction of the 100 γ ray sec sky observed within 2 min 1 orbit ~ 90 min 100 sec - GRB940217 (100sec) - PKS 1622-287 flare - 3C279 flare - Vela Pulsar All-sky survey: sensitivity after O(1) day to detect the weakest EGRET sources at (5σ) level! zenith-pointed 1 ~ day 1 day EGRET Flux - Crab Pulsar - 3EG 2020+40 (SNR γ Cygni?) - 3EG 1835+59-3C279 lowest 5σ detection - 3EG 1911-2000 (AGN) - Mrk 421 - Weakest 5σ EGRET source rocking all-sky scan: alternating orbits point above/below the orbit plane
Some GRB Experimental Facts Intensity, location, rate Typical fluences 10-4 4 to -7 ergs cm -2 Cosmological distances Rate z ~ 1 1 /Myrs/ Myrs/galaxy Energy Spectrum Non-thermal emission up to γ rays (3 GeV) 940217 (Hurley 1994) Temporal properties Rapid flux variations miliseconds Range of burst durations few seconds to hours Transients are hard to catch!
Delayed High Energy Emission in GRB940217 LAT Large effective Area (can probe smaller fluxes) Extends spectral coverage to higher energies GBM will cover down to few kev GRB 940217 (Hurley 1994)
Fireball Model Kobayashi, Piran & Sari 1999 ζ=43 E=10 52 ergs η=50 R =3 10 10 cm U Int to U Kin U kin to U ISM Plethora of models Shells thin or thick Shocks Relativistic or Newtonian External Medium ISM or wind like COLD Fireball External Shock HOT Reverse shock HOT Forward shock ISM COLD ISM
Shock Plasma Parameters Can we use GLAST measurements to help constrain these parameters? Fraction of Magnetic Energy Density behind the shock ε B ~ 1 to 10-5 Ratio of peaks in Spectral Energy Density (GLAST + X ray Detector) Fraction of Thermal Electron Energy Density behind the shock ε e ~ 1 to 10-5 Ratio of peaks in Spectral Energy Density (GLAST + X ray Detector) Energy distribution of accelerated electrons p (power law index) ~ 2 to 3 Fits from Spectral Energy Density (GLAST + X ray Detector) Are p, ε B ε e time independent? (Paitanescu and Kumar 2001)
High Energy Emission Models Leptonic Models No definitive answer yet Hadronic models Shocks: Internal/ External? Hard to model IC (Pe erer Waxman 2005) KN regime HE EM cascades Large τ from e+- Proton Synchrotron pp, pn, pγ Forward/ Reverse? Meszaros & Zhang 2001 IC Synchroton
Mechanisms for High Energy Emission Meszaros & Zhang 2001 Inverse Compton scattering of low energy photons off energetic electrons most likely the answer to GRB940217? requires small ε B denser medium helps to increase the flux Proton-synchroton radiation maybe too faint for a GLAST detection if detected may provide hints that the medium density is constant requires large ε B very interesting because it may connect UHECR with GRBs
Which model should we choose? Region I Proton synchroton hard with GLAST large ε B Region II Inverse Compton good for GLAST denser medium helps small ε B :internal shocks Region III Electron synchroton not in GLAST range Typical from afterglows (Painatescu & Kumar 2001) (Painatescu & Kumar 2002) Zhang Zhang & & Meszaros Meszaros 2001 2001
We need DATA! Region I Proton synchroton hard with GLAST large ε B Zhang & Meszaros 2001 z = 0.1 z = 1 GRB 940217 (Hurley 1994) Region II Inverse Compton good for GLAST denser medium helps Region III Electron synchroton maybe hard with GLAST ε B= 10-4 ε e= 0.5
Back to the Main Questions Is there any connection between the SABER program and the physics interests of GLAST? Can we simulate in the laboratory an environment similar to that of the shock dissipation phase in GRBs? Can we quantify the relative importance of magnetic fields during the shock dissipation phase in GRBs? A deeper question: Are B fields generated locally or at the central engine?
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Gamma Ray Bursts: GBM and LAT GBM Huge field of view (8sr) Measure spectra for bursts from 10 kev to 30 MeV LAT Wide field of view (>2sr) Extends spectral coverage to higher energies GLAST Can be re-pointed to catch exceptionally bright bursts that occur outside the LAT field of view GLAST all-sky monitoring will be follow transient phenomena to a wide range of time scales from ~ 30 µs (GRB, solar flares) to hours or longer (AGN) Simulated GBM and LAT response to time- integrated flux from bright GRB 940217 Spectral model parameters from CGRO wide-band fit 1 NaI (14 º) ) and 1 BGO (30 º) + NaI BGO LAT
Multiple scattering Thin Thick GLAST/LAT performance Slide from N. Omodei Intrinsic resolution of the tracker Energy Resolution: ~10% (~5% off-axis) PSF (68%) at 100 MeV ~ 5 o PSF (68%) at 10 GeV ~ 0.1 o Field Of View: 2.4 sr Point Source sens. (>100 MeV): 3x10-9 cm -2 s -1 Thin converters (3%) Thin Thick Full Tkr Thick converters (18%) No converters F.o.V.: 2.4 sr
High Energy Emission in GRB 941017 Where is the high-energy peak? Is there a cut-off? Compare data from EGRET and BATSE: high-energy component has different time behavior than sub MeV component! Low Energy < 3 MeV E peak ~ 0.5 MeV Duration ~ 100s -18 to 14 s internal or external shocks? 14 to 47 s high energy component start to develop High Energy > 3 MeV dn/de ~ E -1 Duration ~ 200s hadrons or electrons? Is the spectral index timedependent? 47 to 80 s 80 to 113 s How common is this GRB? 113 to 211 s Gonzalez et al 2003 Need GLAST data!! BASTE-LAD EGRET-TASC
Modeling High Energy Emission for GRB941017 Two models used External shock (Pe erer &Waxmann 2004) e- accelerated in FS IC scatter γ from RS SSA is important Internal Shock (Granot & Guetta 2003) e- in FS IC scatter γ whlle RS is going on SSC from RS (depends on spectal index) e B ~ 10-7 Δt = 10-5 Pe er & Waxman 2004 E = 3 10 54 ergs, n = 0.10 cm -3, Γ i = 300, ε B,r =10-1, ε B,f = 10-6, z = 0.10 E = 1 10 55 ergs, n = 0.10 cm -3, Γ i = 200, ε B,r =10-3, ε B,f = 10-5, z = 0.10 E = 1 10 54 ergs, n = 0.03 cm -3, Γ i = 220, ε B,r = 0.2, ε B,f = 10-6, z = 0.06 E = 3 10 52 ergs, n = 0.10 cm -3, Γ i = 1500, ε B,r =10-7, ε B,f = 10-7, z = 0.15 Flux between 100 and 200 s after the burst High Energy data constrains Total energy, Lorentz factor and ambient density Data from Gonzalez et al 2003 GRB941017 GBM LAT Δt = 10-5
Multiwavelength Observations to Constrain Models Model Prompt emission from internal shocks in relativistic wind Spectra as high as 10 GeV Flux has a strong dependence on Γ Measure cut-offs with GLAST! Ratio of peaks in kev/gev can be used to constrain ratio of ε B / ε e LAT + GBM? Swift + GLAST? Pe er & Wazman 2004 100 kev 1 GeV l < 10 Γ = 600 Δt = 10-4 ε B = 0.33 ε B = 0.01 ε B = 0.0001 Caveat: single shell collisions
Can we constrain p and Γ from GRB940217? Model Prompt emission from internal shocks in relativistic wind Γ = 600 Γ = 350 Γ = 200 Guetta & Granot 2003 300 kev 1 GeV SSC dominates above 100 MeV Power law index > 2 GLAST can constrain p 30 MeV Parameters Γ= = 600, Δt = 0.1 ms, E p = 200 KeV Should we expect variability smaller that 0.1 ms? Δt = 10 ms Δt = 1 ms Δt = 0.1 ms
GBM Performance The GLAST Burst Monitor for GLAST, A. von Kienlin et al., in Proc of the SPIE-Conference, Glasgow 2004 GBM NaI Location 6 in the equatorial plane 4 at 45 o 2 at 20 o GBM BGO Location 2 in opposite sides of the spacecaft GBM GBM Trigger compare count rates for 2 of the modules same same as BATSE GBM GBM Trigger Sensitivity < < 1 ph cm -2 s -1 BATSE: BATSE: 0.2 ph cm - 2 s -1 (5σ) GBM GBM Burst Localization < < 15 o within 1.8s (on board) can can be used as a LAT trigger if if outside LAT FOV possible to repoint to catch delayed emissions < < 5 o within 5s (ground) < < 3 o within 1 day (ground)
GLAST and GRBs Slide from N. Omodei (GLAST GRB SWG) Full sky survey every 3 hours Number of Bursts GBM ~ 200 bursts/yr > 60 bursts within FoV of the LAT 1 burst/month ~ 100 photons Alert and Localization Alert to GCN ~ 10 s GBM < 15 0 initially, update 5 0 LAT > 10 arcmin depending on the burst Downlink and Communications near real-time (TDRSS) full science data ~ 6-86 8 times a day Downlink and Communications Intense burst: GLAST can repoint keep LAT in the FoV Dwell time: 5 hr (adjustable)
GLAST and SWIFT era GLAST can provide alerts to GRBs Swift can point for follow on observations. Precise measurements of the position will be given by Swift! Slide from N. Omodei (GLAST GRB SWG) GLAST will frequently scan the position of the bursts hours after r the Swift alerts monitoring for High energy emission. In these cases, we will have a broad spectral coverage of the GRB B spectrum (from 0.1 kev to hundreds of GeV > 9 decades!!). Swift is seeing 100 bursts per yr: ~ 20/yr will be in the LAT FoV ~2020 2007 XRT BAT GBM LAT 2005 0.1 kev 10 kev 100 KeV 1 MeV 30 MeV 300 GeV
Duration of GRBs 160 Short Long If there is a compact object at the inner engine, the source must also be active for a long time (e.g stellar mass BH accreting from a massive disk, rotating NS driving Poynting flux) NUMBER OF BURSTS 120 80 40 Compact Mergers? (ISM) 1 cm -3 Collapsar Model? (wind) 10 3-4 cm -3 0 0.01 0.1 1 10 100 1000 DURATION, SECONDS
X ray Flares GRB050502b Falcone 2005 Giant X-ray X Flare 500 times higher amplitude Can we detect IC from X ray flares?