1. 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
HE photons from GRB
Emission mechanism
The MAGIC telescope
Conclusions
Summary:

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 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
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. (for all emission processes)‏
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)‏
The break energies are:
Essa =Self absorption energy
Em =Minimum injection energy
Ec =Cooling break energy
= F
e,b,p: Energy equipartition parameters
: Bulk Lorentz factor
L: Burst Luminosity
tv: Variability time scale of the burst
Physical
parameter
of the
fireball
A. Carosi

5. the resulting inverse Compton emission.
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 synchrotron spectrum. 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. Minimum energy of g from p decay:
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
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)‏
A. Carosi

7. OBSERVABILITY OF GRB IN DIFFERENT ENERGY RANGE:
Leptonic
component
(usually)
dominant.
Syn.: < MeV
IC: >10 MeV
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 52 53
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:
g rays are 0.1% of cosmic radiation, but they keep the “memory” of the incoming direction
Space based instruments
(pair production telescopes)
Detection of the “primary” gamma
Energy range < 100 GeV
Eff. Area= ~ m
Duty cycle 100%
FOV: ~ 1 sr
High economic costs 2
Ground based instruments
(detector Cherenkov)
Secondary detection
Energy range > GeV
Eff. Area: ~10 /10 m
Duty cycle 10%
FOV: ~ sr
Low economic costs 4 5
A. Carosi

10. MAGIC is now the best IACT for the observation of GRB
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 GeV, upper limits are calculated….still waiting for a near GRB!

14. THE GRB ALARM SYSTEM: Outside GCN Alert System MAGIC systems
Central Control
Communication:
web
Acoustic alarm
Outside
MAGIC systems
Developed by Nicola Galante. Very soon
INAF people will assume the responsabillity
of the alert system.
A. Carosi