1. Erik Strahler Ph.D. Thesis Defense 6/26/2009
Searches for Neutrinos from Gamma Ray Bursts with the AMANDA-II and IceCube Detectors
Erik Strahler
Ph.D. Thesis Defense
6/26/2009

2. Outline Motivation Neutrinos from Gamma Ray Bursts Detection
AMANDA-II Analysis
IceCube Analysis
Discussion and Outlook

3. Why Neutrinos? Neutrinos from GRBs Magnetic Fields Absorption source
Charged particles are deflected, photon can be absorbed in opaque materials or highly suppressed at high energy due to CMB photon pair production. Neutrinos are neutral and low cross-section. Also a signature of hadronic interactions.
source

4. The Cosmic Ray Connection
Sources of the highest energy cosmic rays are unknown. Need either very large B fields or spatial extent in order for acceleration mechanisms to work. GRBs are one of the few source candidates.

5. GRBs : A History Nuclear tensions led to the Vela satellite system
Discovery in 1969 of short duration, highly energetic bursts of gamma rays coming from space
70’s and 80’s – a Dark Age for GRB physics
Many theories without observational backing
1991 – Launch of CGRO
BATSE begins large scale observation of GRBs
Comets colliding in the Oort cloud, neutron star collapse in the galaxy.
Thought must be galactic due to energy requirements.

6. GRB Observations Isotropic Highly Variable Extremely Energetic
X-ray/Optical Afterglows
So what are GRBs? Extremely high energy, widely time variable on short time scales, short duration. Isotropic -> cosmological -> very very high energies

7. Compactness Problem dt ≈ 10-2 s implies Rs = cdt ≈ 3000 km
g’s may pair produce if
Given typical GRB parameters  tgg ≈ 1013
At odds with observed non-thermal photon spectra
Relativistic emission: E  Eobs / G, Rs G2cdt
With G≈102, gives tgg < 1
Average optical depth. FD^2 comes from total burst energy
E^-a observed spectrum. Fraction that can pair produce drops by Gamma^-2a
Yields Tau = 10^13 / Gamma^(4+2a) (Tau goes like 1/R^2)

8. Fireball Model Relativistically expanding plasma of e+, e-, g, (p?)
Initially optically thick
G increases with time, until tgg < 1
Kinetic Energy dissipated via shocks
Internal between shells with varying G
Prompt emission
External with ISM
Afterglow emssion

9. Photon Emission Shocks accelerate electrons which then produce photons
Synchrotron
Inverse compton
Empirically fit
Band function
GRB030329

10. Prompt GRB Neutrinos
Assume shock accelerated protons with same spectrum as electrons (~ E-2)
A fraction fp ~ 0.20 of the proton energy is given to the pion
 En ~ 0.05 Ep
Traces the observed photon spectrum
Further break due to p and m synchrotron losses

11. see Razzaque, Meszaros, and Waxman: Phys.Rev. D68 (2003) 083001
Precursor Neutrinos
Before prompt emission, jet must drive through stellar envelope
Possibility for ‘choked’ GRBs
pp and pg interactions with thermalized jet photons, cold stellar nucleons and jet protons.
Photon interactions highly suppressed due to magnetic fields and subsequent synchrotron radiation
see Razzaque, Meszaros, and Waxman: Phys.Rev. D68 (2003)

12. Afterglow Neutrinos Same processes as prompt spectrum
Lower energy afterglow photon field
Neutrinos up to 1019 eV
Large shock radii reduce synchrotron loss effect

13. Neutrino Spectra
Gamma emission from Syncrotron, Inverse Compton off of accererated charged particles. Precursor emission from shocks in the fireball before it becomes optically thin. Oscillations between source and earth lead to ratio 1:1:1

14. Swift Satellite Launched in November 2004 BAT (Burst Alert Telescope)
1.4 sr field-of-view
~100 bursts / yr.
Slew within 20-75s
arcsec positioning
XRT, UVOT
Afterglow measurements
Coded mask is transparent above 150 KeV

15. Neutrino Detection
charged current
Cherenkov effect

16. Detector Concept Array of optical sensors
High energy muon emits Cherenkov light
Record light arrival times, amplitudes

17. Antarctic Physics
AMANDA-II
station
south pole
IceCube

18. Neutrino Detectors Detector 19 strings 677 optical modules
Operated
dfasdfsadf 59
m deployment. Depth block atmospheric background. Neutrinos interact in the ice to produce muons/electrons. Muons track through detector giving off cherenkov light.

19. Reconstruction Arrival times / Intensities Spatial Resolution
AMANDA: 2-3 degrees
IceCube: < 1 degree
Energy Resolution
0.3 in ln(Ereco/Etrue)
1.5 – 2.5 degrees. ~x2 in energy
.3-.4 in log(E) vs in log(E)

20. Detection Challenges I
Down-going muons from CR showers misreconstructed as up-going

21. Detection Challenges II
Up-going atmospheric neutrinos from CR showers on other side of Earth
Isotropically distributed
Softer energy spectrum than GRB signal

22. Current Status
Previous searches for neutrino-induced muons (Achterberg A. et al. 2008, ApJ, 674, 357) and cascades (Achterberg A. et al. 2007, ApJ, 664, 397) saw no events and set upper limits on GRB neutrino fluxes

23. AMANDA-II Analysis
data sample contains 85 northern hemisphere bursts that pass all detector stability criteria.
Largest sample in the post-BATSE era.
Search for prompt phase emission assuming Waxman-Bahcall spectra for all bursts

24. Upgoing filter, rescaled to GRB on-time
GRB Advantages
Time, Position of predicted signal known.
Drastic reduction in background rate
Use of data for background estimation
Removes many sources of systematic error
Reduces reliance on simulation
Upgoing filter (reconstructed track > 80 degrees), 386 days livetime
Upgoing filter, rescaled to GRB on-time
~10M
1703.9

25. Event Selection Angular offset from GRB position
Angular resolution of tracks
Timing coincidence with gamma emission
Likelihood ratio of upgoing reconstruction vs. downgoing reconstruction
Data
Downgoing Muons
Atm. Neutrinos
GRB Neutrinos

26. Final Sample

27. 0 events in the GRB emission windows survive final cuts
Results
Expected
90% C.L. Limit
Upgoing filter
Final Cut Level
data
1703.9
GRB signal
0.501
0.166
Discovery Potential
1 event: 3s
2 events: 5s
Observed
0 events in the GRB emission windows survive final cuts
05-06 Limit: 14.7 * Prompt flux

28. IceCube-22 Analysis Analysis of 22 String Configuration (6/07 – 4/08)
41 Northern Sky GRBs that pass data quality considerations
prompt, precursor, and extended window searches
Different Approach
Incorporate individual burst information
Unbinned analysis, using likelihood ratio test, and incorporating event energy

29. Burst Modeling

30. Event Selection ~77 M events all-sky, all-year
~1 event on-time

31. Likelihood Method
Probability that each event belongs to signal or background distribution
Test statistic is Likelihood ratio
Maximize LLH ratio by varying ns
Likelihood function:
Null hypothesis:
Likelihood Ratio:

32. Probability Distributions

33. 108 background randomizations
Sensitivity
108 background randomizations

34. Improvement Complementary binned analysis on same data
flux factor
Complementary binned analysis on same data
Factor ~1.8 more powerful at 5s, P=0.5

35. IC-22 Results
Test statistic consistant with the null hypothesis for all searches
Checks with looser cuts reveal no signal-like events

36. Summary
While none of the analyses are able to place constraints on the leading models of neutrino emission, we have:
Demonstrated that highly significant discoveries of transient sources can be made with only 1-2 observed events
Shown that significant gains are achieved by considering the energy information of individual events in a likelihood analysis
Set a precedent for the modeling of fluxes on a per burst basis for stacked GRB searches

37. Outlook Fermi satellite began operations in July 2008
Triple observation rate
IC-40 data run complete
GRB analysis underway
~2 events expected (WB)
IC-86 complete in 2011
Discovery within one year of operations (~150 GRBS)

38. Conclusion
Continued aggregation of GRBs pushes limits closer to model predictions
Rapid increases in detector effective areas and satellite observation rates mean we will very soon see astrophysical high energy neutrinos from Gamma-ray bursts or will set meaningful limits on such emission

39. The End

40. Systematics
Remove many sources of error by using off-time data to estimate the background
Ice Properties
Optical Module Efficiency
Seasonal Atmospheric Variation
error
mag.
Cross-section
±3%
Muon propagation
±2%
Reconstruction bias
+5%
Ice simulation
±5%
Timing resolution
OM efficiency
+6%
Background rate
<1%
Total
+10%, -7%

41. Fermi Acceleration