Gamma-Ray Bursts prospects for GLAST

GRBs I Basic phenomenology Flashes of high energy photons in the sky (typical duration is few seconds). Isotropic distribution in the sky Cosmological origin accepted (furthest GRBs observed @ z ~ 7 – billions of light-years). Never seen two GRBs from the same location (destructive phenomenon?). Extremely energetic and short:the greatest amount of energy released in a short time (not considering the Big Bang). Sometimes x-rays and optical radiation observed after days/months (afterglows).

GRB observations First detected... ... in early ‘70 by military satellites (Vela). Originally connected with Neutron Stars (NSs) in the Milky Way. Then CGRO came... EGRET (10 MeV-10 GeV): ~ 1 burst per year. BATSE (10 keV-10 MeV): ~ 1 burst per day. Distribution in the sky found to be isotropic. Cosmological origin? The afterglow era... BeppoSax: X-ray afterglows -> Direct observation of the “host galaxy” A “smoking gun” for extragalactic origin! Keck: optical afterglow. And the Swift Era… On going mission Dedicated to GRB (x-ray follow up) New understanding of GRB afterglow…more open questions? The GLAST era High energy emission Connection to low energy New discovery window: region of the EM spectra previously uncovered

GRB 940217 This bursts remains an enigma, and it is a perfect “key study” for GLAST

Another enigma “Extra component” BATSE + EGRET joint analysis: 2 separate components Independent time evolution (extended HE emission) Spectral index of the HE component: -1 Cut-off at higher energies: where? How common in GRB? Very promising picture for GLAST!

The GLAST mission (Gamma-ray Large Area Space Telescope) The GLAST satellite has two telescopes: Large Area Telescope: Pair Conversion Detect photons between 20 MeV - 300GeV Tracking system: Silicon Strip Detectors Calorimeter: CsI Cristals (8.5 r.l., hodoscopic) Anticoincidence: Segmented ACD Tracker ACD Calorimeter Grid LAT g e+ e- Launch Vehicle Delta II – 2920-10H Launch Location Kennedy Space Center Orbit Altitude 565 Km Orbit Inclination ~24.5 degrees Orbit Period 95 Minutes Launch Date Late 2007

The GLAST mission (Gamma-ray Large Area Space Telescope) Glast Burst Monitor 12 Sodium Iodide (NaI) Scintillation detectors Wide Field of View Burst trigger Coverage of the typical GRB spectrum (10 keV-1 MeV) 2 Bismunth Germanate (BGO) Scintillation detectors Spectral overlap with the LAT (150 keV-30 MeV) 10-4 10-5 10-6 10-7 10-8 10-9 10-10

GLAST & GRB GLAST TDRSS White Sands GCN Users community Operational modes Sky survey (full coverage every 3 hours) Pointing mode GBM and LAT will both have triggers! GBM will detect ~ 200 burst per year >60 burst per year within the FoV of the LAT detector Alert to GCN ~ 10 seconds GBM < 15o initially, update <5o LAT > ~10 arcmin depending on burst Downlink and communications Bursts alerts sent on ground in near real-time (TDRSS) TDRSS: full science data downlink (~ 8 times a day) Autonomous repoint In case of intense bursts GLAST can repoint to keep the burst in the LAT FoV. Dwell time: initially 5 hr (adjustable) GLAST TDRSS Users community White Sands GCN

GRB data flow... ISOC ISOC BAP GCN S/C GIOC 1) GBM & LAT trigger GBM GCN notice (10s) BAP GBM gnd analysis GCN notice (30min) GCN Alert message Alert message LAT GCN notice (15 s) L1 processing 24 hours GBM ground analysis circular? (36 hours) S/C GIOC 4-12 hours GCN notice (6-14 hours) Final GBM analysis Full Downlink GCN Report (24-72 hours) GBM GRB Catalog LAT Ground analysis circular (24-48 hours) 1) GBM & LAT trigger 4-12 hours L1 processing 1 hour ISOC ASP follow-up LAT analysis (spectra, localisation, lc, afterglow etc) Manual follow-up LAT analysis GRB LAT catalog Joint LAT/GBM analysis Joint LAT/GBM catalog ISOC

Manual follow-up LAT analysis GRB data flow... GBM GCN notice (10s) BAP GBM gnd analysis GCN notice (30min) GCN Alert message Alert message LAT GCN notice (15 s) L1 processing 24 hours GBM ground analysis circular? (36 hours) S/C GIOC GCN notice (6-14 hours) No LAT GRB found! 4-12 hours Final GBM analysis Full Downlink GBM GRB Catalog 2) GBM trigger only... 4-12 hours L1 processing 1 hour ISOC ASP follow-up LAT analysis (searching for GRB...) Manual follow-up LAT analysis Searching... Upper limit Around 30-50% of the time, the GBM alert will be spurious. Source Deoccultation, CR precipitation, Solar Flares Similar Procedure for any non-LAT trigger (Swift) ISOC

Manual follow-up LAT analysis GRB data flow... GBM GCN notice (10s) BAP GBM gnd analysis GCN notice (30min) GCN Alert message Alert message LAT GCN notice (15 s) L1 processing 24 hours GBM ground analysis circular? (36 hours) S/C GIOC 4-12 hours GCN notice (6-14 hours) Final GBM analysis Full Downlink GCN Report (24-72 hours) GBM GRB Catalog LAT Ground analysis circular (24-48 hours) 3) GBM trigger only... 4-12 hours L1 processing 1 hour ISOC ASP follow-up LAT analysis (searching for GRB...) Manual follow-up LAT analysis Searching... Found! Analyze it! Similar Procedure for any non-LAT trigger (Swift) Joint LAT/GBM analysis Joint LAT/GBM catalog ISOC

LAT GRB Sensitivity Phenomenological model for GRB simulations: From BATSE energy to LAT energy Sampling observables form BATSE distribution See the LAT response Comparison with the BATSE catalog: Bimodal distribution in duration and fluences for long and short bursts Fluence - Duration correlation

Study the LAT GRB sensitivity The numbers depend on the assumed model: here we are extrapolating from BATSE to LAT energies! (MeV - GeV) Reasonable model: LAT can detect prompt emission from GRB (some per year) IRF dedicated to GRB (see next): double the number of low energy photons! (update sensitivity/plots… coming soon!)

On Board Science Most of the detected photons have on-board tracks Onboard Reconstruction available GRB alert algorithms: Clustering Histogram rate (in different region of the sky) Advanced trigger alg based on spatial and temporal clustering First Localization estimation => First GCN via TDRESS!

High energy emission... SSC component not in the BATSE energy range Possible detection by EGRET (?) 941017, 940217

Connection between X-Ray flashes and Gamma-Ray Emisison... Galli and Piro, 2006 Predictions in the context of External-Shock model: Gamma-Flares as IC from X-Ray Flashes Possible target for GLAST (and maybe Seen by EGRET The 17th February 1997) Simulations for the GLAST/LAT See Galli’s Talk

Other on going activities… Quantum Gravity and GRBs. Scargle, Norris, Bonnell Pair Attenuation Signatures in Evolving Gamma-Ray Burst Spectra. Matthew G. Baring and Brenda L. Dingus Time Dependence of Pair Opacity in GRB Internal Shocks. Johann Cohen-Tanugi, Jonathan Granot, Eduardo Do Couto e Silva

Conclusions Gamma-Ray Burst is a very promising Scientific Target for GLAST GBM and LAT simultaneous observations GBM: “Peak energy” determination Cosmology with GRB (Amati and Ghirlanda relations) LAT: IC, but mainly a new “Discovery Window” GRB Science Group: good in shape! Simulations Preparation to the analysis Theory, predictions, and Speculations... ISOC Support Infrastructure, Science Operations Multi-frequency approach: Near IR telescope (Afterglow follow-up) X-ray afterglow (Swift) Synergy with TeV telescopes TeV emission? Absorption for cosmological attenuation Rapid response (MAGIC)

…GeV-TeV synergy ACTs: 10% duty cycle, 5˚ fov. Some of them can slew in few minutes (20% of the sky) need ~1˚ location accuracy (LAT only) Some back-of-the-envelope calculations: Joint observation: Number of LAT alerts * duty cycle * sky coverage ACT: 50 * 0.1 * 0.2 ~ 1 GRB/yr suitable for combined GeV-TeV observations EAS: 50 * 1 * 0.2 ~ 10 GRB/yr suitable for combined GeV-TeV observations

GRB analysis 7 decades in energy Data Challenge 2, Service Challenges Spectral analysis and light curves for GBM and LAT 7 decades in energy Combined signal from GBM (B0 N0) and LAT detectors

GRB hybrid model LAT and GBM joint spectral fit with BB+BPL+Exp cut-off. Possibility to obtain GBM and LAT simulation simultaneously

Model “Independent” studies Systematic variation of the parameters Trigger request: 5 photons and TS=25. Most of the GRB are in the “Background free” regime! Support the study for new IRFs