EMISSION OF HIGH ENERGY PHOTONS FROM GRB AND OBSERVATION WITH MAGIC TELESCOPE

1. HE photons from GRB • Emission mechanism • The MAGIC telescope • Conclusions Summary: EMISSION OF HIGH ENERGY PHOTONS FROM GRB AND OBSERVATION WITH MAGIC TELESCOPE Alessandro Carosi Lucio Angelo Antonelli Susanna Spiro INAF-Astronomical Observatory of Rome & University of Siena

2. EMISSION OF HIGH ENERGY PHOTONS FROM GRB – HYSTORICAL HINTS: GRBs have their peak energy usually in the 100 keV – 1 MeV energy range EGRET(GRB940217) MILAGRITO(GRB970417a) GRAND(GRB971110) “hystorical” hints of high energy photons (> GeV) MILAGRITO (500 GeV-20 TeV) GRB970417a EGRET (20 Mev-30 GeV) GRB940217 • News! • Observations by LAT@Fermi Gamma Ray Observatory: • 14 photons > GeV (up to 15 GeV) from GRB080916c • few GeV from GRB090323 A. Carosi

3. HIGH ENERGY EMISSION FROM GRB: The internal shock scenario provides several non thermal mechanism which can explain the emission of high energy photons. Leptonic component • Synchrothron emission (dominant process in the sub-Mev range)‏ • Inverse Compton Hadronic component • Proton syncrothron • decay 0 SSC in internal shock: 1-50/100 GeV (Guetta&Granot 2003; Galli&Guetta 2007; Zhang & Meszaros 2007) P-g interactions: MeV- TeV (Gupta & Zhang 2007) SSC in RS, keV-GeV (Granot & Guetta 2003, Kobayashi et al. 2007) SSC in FS, MeV-TeV (Galli & Piro 2007) p-γ interaction in FS, GeV – TeV A. Carosi

4. e,b,p: Energy equipartition parameters : Bulk Lorentz factor L: Burst Luminosity tv: Variability time scale of the burst The break energies are: Essa =Self absorption energy Em =Minimum injection energy Ec =Cooling break energy = F Physical parameter of the fireball HIGH ENERGY PROMPT EMISSION FROM GRB: Syncrotron emission Internal shocks Fermi Mechanism Power law distribution for particle: General assumptions (for all emission processes)‏ The shape of the spectrum is a four segment broken power law (from Gupta & Zhang 2007): (fast cooling)‏ (Slow cooling)‏ A. Carosi

5. HIGH ENERGY PROMPT EMISSION FROM GRB: Synchrotron Self Compton Using the synchrotron spectrum as the source of seed photons it is possible to compute the resulting inverse Compton emission. IC scattering amplifies the energy of photons by a factor e so if synchrotron radiation is the dominant process in the sub-MeV range, SSC photons can reach the GeV-TeV domain 2 (slow cooling)‏ (fast cooling)‏ The shape of the spectrum is very similar to the primary synchrotronspectrum. SSC Component can be approximated by a multi segment broken power law. A new break In the photon spectrum appears when the Klein Nishina effect becomes important. Klein-Nishina condition A. Carosi

6. Proton synchrotron: Since protons are poor emitters we only consider the scenario of slow-cooling in the proton spectrum. Pions decay: Typically  carry out 20% of the proton energy from p interaction (E>10 TeV)‏ 0 HIGH ENERGY PROMPT EMISSION FROM GRB: Hadronic emission component 20 As for the electrons, shock can accelerate protons to high energy (10 eV) Protons lose their energy by synchrotron emission and photoproduction of neutral and charged pions produced in the interaction with low energy photons (Inverse Compton is a neglegible process for protons - p>>pT)‏ Minimum energy of g from p decay: 12 TeV A. Carosi

7. OBSERVABILITY OF GRB IN DIFFERENT ENERGY RANGE: e=0.45 ; B=0.1 ; p=0.45 =600 ; T90=20s ;z=0.2 Liso=10 erg/s ; Eiso=10 erg Epeak=10 KeV ; Ecutoff=150 GeV 53 52 Leptonic component (usually) dominant. Syn.: < MeV IC: >10 MeV A. Carosi

8. OBSERVABILITY OF GRB IN DIFFERENT ENERGY RANGE: Most probably candidates for high energy emission: (XRF) (G > 500) Very Important: Multiwavelenght Observation

9. GAMMA RAY ASTRONOMY EXPERIMENTAL TECHNIQUE: Secondary detection Energy range > 60-100 GeV Eff. Area: ~10 /10 m Duty cycle 10% FOV: ~ 0.01 sr Low economic costs Detection of the “primary” gamma Energy range < 100 GeV Eff. Area= ~ m Duty cycle 100% FOV: ~ 1 sr High economic costs 4 5 2 g rays are 0.1% of cosmic radiation, but they keep the “memory” of the incoming direction Space based instruments (pair production telescopes) Ground based instruments (detector Cherenkov) A. Carosi

10. THE MAGIC TELESCOPE: MAGIC I : Diameter: 17m Energy range: 60 GeV-20 TeV Fast slewing:30-40 s (30x wrt IACT) Camera:3.5°FoV–575 PMT (QE 30%) Trigger threshold: 60 GeV (25 GeV) Sensitivity: 1.6% Crab (50h) Energy resolution: 20% - 30% MAGIC is now the best IACT for the observation of GRB Roque de los Muchachos, 2200m asl • And for the (next) future…. • MAGIC II : • 3x improve sensitivity • High QE for PMT (>50%) • Stereoscopic reconstruction • (better angular resolution and • energy estimation) A. Carosi

11. GRB080430: • Zenith angle: 22°-30° • Delay: 1h 19m • Redshift: 0.767 No evidences of emission above the reconstructed threshold energy Ethr = 100 GeV A. Carosi

12. UPPER LIMITS AND SKY PLOTS: GRB080430 A. Carosi

13. CONCLUSIONS: • Inside the fireball, several non thermal emission processes are able to give high energy photons (>MeV)‏ . For a “standard” burst the emission is dominated by electron synchrotron radiation while SSC become important at higher energy. Hadronic emission component is generally negligible or active for E>PeV (pion • decay)‏ • For a GRB with >500 MAGIC is able to detect high energy emission component from SSC. A positive detection would constrain the models on the emission mechanism and the range of the source distance. • MAGIC telescope(s), thanks to the used technical solutions, is (probably!) the best Imaging Atmospheric Cherenkov Telescope for the study of GRB. The performances of the instrument allow to observe high energy photons both during the prompt phase and the early afterglow. Multiwavelenght observations in the HE regime can discriminate between different emission models and can provide constraints to the different physical parameters which describe the fireball. • GRBs are “difficult business” for IACT. At present time, there is no evidences of VHE emission above 80-100 GeV, upper limits are calculated….still waiting for a near GRB!