Download High Energy Emission  from GRBs HAWC

High Energy Emission from GRBs
Brenda Dingus, LANL
HAWC
What are GRBs?
• Cosmological distance • Typical observed z>1
• Energy released is up to few times the rest mass of Sun (if isotropic) in a few seconds => narrow beam
• Most of the energy is emitted in ‐ rays
• Relativistically expanding fireball • Shocks between shells of different velocity • Shocks created when fireball decelerates into external medium
• Central Engine
• Collapse of massive, rotating star? (long GRBs)
• Coalescence of binary neutron stars? (short GRBs)
• Final Product is Black Hole (probably)
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High‐Energy Emission from GRB (Past)
Gonzalez et al. Nature 2003
• EGRET observations of delayed HE gamma‐ray emissions
– It is not straightforward to explain by conventional electron synchrotron models
– Proton acceleration? Origin of UHECR?
BATSE
EGRET/TASC
14 – 47s
47 – 80s
Hurley et al. Nature 1994
Two γ >GeV @~T0
-18 – 14s
18 GeV γ @ ~T0+75 min
80 – 113s
113 – 211s
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/22
Fermi LAT Detected Bursts
Granot, astroph 1003.2425
Highest Energy Requires Large Bulk Lorentz Factor
• Gamma Rays attenuated at the source by  +  ‐‐> e‐ + e+
• peak cross section when E1 E2 ~ 4 me2 c4 / (1‐cos )
• Density of photons is high as inferred from source distance & rapid variability
• No attenuation if emission is from fireball with large bulk Lorentz
factor
• Decrease Energy of Gamma‐Rays
• Reduce Number of Photons
• Increase the source size
• Bulk Lorentz factor, , required to give opacity
of 1 for the highest E -ray observed
• For reference, AGN jets have 
Lithwick
26‐Mar‐10 & Sari 2001
[email protected]
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GRB Bulk Lorentz Factors > ~1000
Extragalactic ‐ray Absorption •
•
•
e-
~TeV 
e+
~eV 
High energy gamma rays pair produce with the infrared to UV extragalactic background light (EBL)
EBL not well constrained by direct measurements due to zodiacal light, but is constrained by galaxy and star formation history
Low ‐ray absorption possibly explained by axions?
EBL evolves with redshift
Kneiske, et al. 2004 A&A
Optical Depth evolves with redshift
Highest Energy Gamma‐Rays vs EBL models
080916, 13 GeV
090902, 33 GeV
090510, 31 GeV
Fundamental Physics with ‐rays
• Test of Lorentz Invariance which is predicted by some quantum gravity theories
v= c(1 ± E /EQG+ O[(E /EQG)2])
• EQG ~ Planck mass ~ 1019 GeV
• Compare light curve at different energies
• Need several sources at different redshift to disentangle effects of ‐ray production in the source
• However, a single observation can give a limit on EQG
If EQG= MPlanck , then a GRB @ 1017 light seconds, and
E = 100 GeV=10-17MPlancshould arrive 1 s late.
GRB090510
This short GRB rules out theories of violation of Lorentz invariance which are linear in E /EQG where EQG < mplanck
Going to Higher Energies from the Ground
• Atmospheric Cherenkov Telescopes (VERITAS, HESS, MAGIC)
– Low duty cycle of 5‐10% due to moonless, cloud free night time observations
– Require notification to look in direction of GRB
– Prompt Localizations by Fermi GBM have larger uncertainty than the field of view of the ACT
– Slew times of tens of seconds are too long for short GRBs
+ Excellent sensitivity to lower energies • Extensive Air Shower Observatories (Milagro, ARGO, HAWC)
– Worse sensitivity at lower energies
+ 24 hours/day, 7 days/week operation with > 95% duty factor
+ Large field of view of 2sr (~1/6 the sky)
+ Online analysis to send alerts if transient source is detected HAWC
High Altitude Water Cherenkov
HAWC Sensitivity is 15x Better than Milagro’s
(a) Larger Effective Area at Lowest Energies
(b) Improved Background Rejection
(c) Better Angular Resolution
=> 10‐15 x improvement in flux sensitivity
=> (10‐15)2 = 100‐200 x faster to observe same flux HAWC’s Low Energy Response
• Monte Carlo Simulation which has been confirmed with Milagro observations.
• Gamma‐ray air showers with angular reconstruction better than 1.5 degrees. Extensive Air Shower Development
4100m
2600m
• Higher Altitude means fewer radiation lengths and more particles
• Fluctuations in first interaction means more particles
For example 5% of events (e-3=5%) will have 5 x more particles
HAWC & Fermi > 10 GeV Sensitivity
Source Spectrum is dN/dE = E‐2
and is cutoff by absorption with the EBL model of Gilmore, 2009 HAWC’s Field of View
= 2.6 sr
= 1.8  sr
HAWC GRB Capability
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•
•
•
•
GRB090510
Z=0.9
Highest Observed Energy 33 GeV
HAWC will detect with 5 sigma significance if spectrum extends to 50 GeV
If spectrum extends to 125 GeV (and is attenuated by EBL model of Gilmore), then HAWC would detect 200 gamma‐
rays Measuring the Max Energy with HAWC + Fermi
Future Prospects are Exciting
• More GRBs from Fermi to come (~1/month)
• Possible Afterglow or Long GRB detection by ACTs
• Likely Detection of Prompt Emission by HAWC
• HAWC is ready to go
1st Tank
Site is Ready
Active Galactic Nuclei Flares Milagro’s 9 Mrk421
Milagro flux
• Correlations with x-rays, optical, radio to determine emission mechanisms
• Discovery potential for orphan TeV flares producing neutrinos and UHECR
Quadratic or Linear?
Synchrotron Self
Compton or External
Compton?
1 month
Crab Flux X-ray flux