1/52 An Untriggered Search for High Energy Neutrinos From Gamma Ray Bursts Brennan Hughey University of Wisconsin - Madison April 11th, 2007

2/52 High Energy Neutrino Astronomy and AMANDA GRBs and GRB neutrinos Rolling Search for GRBs IceCube Overview

3/52 Questions High Energy Neutrino Astronomy Can Help Address Cosmic ray acceleration sites?Cosmic ray acceleration sites? –TeV gamma-ray sources? –Gamma-ray bursts? “GZK” cutoff?“GZK” cutoff? Dark matter? Supersymmetry?Dark matter? Supersymmetry? What’s out there that we haven’t even conceived of yet?What’s out there that we haven’t even conceived of yet?

4/52 Photons can be absorbed by Interstellar matter Charged particles are deflected by magnetic fields in space Neutrinos interact only through the weak force, and even then only rarely This makes them uniquely useful astrophysical messengers (and makes them hard to see) Neutrinos as Astrophysical Messengers

5/52 PMT noise: ~1 kHz AMANDA-B10 (inner core of AMANDA-II) 10 strings 302 OMs Data years: Optical Module AMANDA-II 19 strings 677 OMs Trigger rate: 80 Hz Data years: The AMANDA Detector Antarctic Muon And Neutrino Detector Array

6/52 Neutrino interacts with particle in ice Secondary particles emit Cherenkov radiation which is detected by optical modules

7/52 Dark sector AMANDA IceCube Skiway South Pole Station South Pole

8/52 High Energy Neutrino Telescope Projects NESTOR Pylos, Greece BAIKAL Russia DUMAND Hawaii (cancelled 1995) AMANDA, IceCube also ANITA, RICE, AURA Antarctica NEMO Catania, Italy ANTARES La-Seyne-sur-Mer, France

9/52 Measurements: in-situ light sources atmospheric muons Dust Logger Average optical ice parameters : abs ~ nm sca ~ nm Scattering Absorption optical WATER parameters : abs ~ nm sca ~ nm

10/52 Better Pointing Resolution Larger Effective Area Muon-neutrino CC interactions Half-sky coverage Better Energy Resolution Better Background Rejection All Flavor Detection Full-sky coverage Two Detection Channels Muon ChannelCascade Channel

11/52 Backgrounds Downgoing events from Atmosphere Upgoing events through Earth Atmospheric Muons - ~6 million events per day - Cascade events separated by topology - Muon events separated by direction Atmospheric Neutrinos - ~10 3 events per year - Created by cosmic rays - penetrate Earth - Useful for calibration While searching for Astrophysical Neutrinos AMANDA and IceCube must deal with two primary backgrounds:

12/52 Significance map AMANDA II data from (1001 live days) 4282 from northern hemisphere No significant excess observed Highest excess: 17 events on a background of 5.8 events Time scrambled Data Search for neutrino clusters in the northern sky

13/52 event selection optimized for both dN/dE ~ E -2 and E -3 spectra source nr. of events (5 years) expected background (5 years) flux upper limit  90% (E >10 GeV) [10 -8 cm -2 s -1 ] Markarian M ES SS Cygnus X Cygnus X Crab Nebula C2738(1yr)4.72(1yr)0.99 No significant excess observed Search for neutrinos from interesting sky spots crab Mk421 Mk501 M87 Cyg-X3 1ES1959 Cyg-X1 SS433 3C273

14/52 Diffuse Limits Sum of total neutrino flux over full sky (or half sky in the case of muon analyses) Individually unresolvable sources

15/52 Neutralino dark matter searches (WIMPs in sun or Earth) Supernova searches (rise in noise rates from MeV ’s Ultra High Energy searches: focuses on area near horizon searching >PeV events Galactic plane analysis Search for new physics (i.e. Lorentz invariance violations) with atmospheric neutrino sample Magnetic Monopoles Cosmic ray composition (with SPASE array) Gamma-ray astronomy with downgoing muons (SGR in 2004) Studies of temperature variation using downgoing muons Other AMANDA analyses

16/52 Discovered by military satellites in the 1960’s Occur isotropically, therefore extragalactic in origin Most violent, energetic explosions in known universe: at least ergs Observationally divided into two classes due to bimodal distribution (although additional classes have been postulated) Duration measured by T 90 : time over which central 90% of gamma-ray flux occurs Gamma Ray Bursts Data from BATSE Catalog,

17/52 - GRBs are very non-uniform - Rapid variability on the order of a few milliseconds GRB Light Curves Light curves from Swift satellite

18/52 Central Engine Rapid variability implies compact object Central engine cannot be directly observed Currently favored models: Collapsar: massive star forming black hole Supported by evidence from satellites (e.g. GRB and GRB060218) Merger between two objects: Black Hole -Black Hole, Black Hole -Neutron Star, et cetera Chandra X-ray image of NGC

19/52 Gamma Ray Emission Regardless of central engine, GRBs are best described by the fireball shock model - Plasma of electrons, positrons, gamma rays rapidly expands until it becomes optically thin - Particles accelerated in collisions of mildly relativistic shock fronts GRB believed to emit in jets rather than isotropically - Direct evidence from breaks in observed optical afterglow spectra - Reduces total energy requirement to a more believable level - Means we can only see GRBs that are on-axis Ref: Peter Meszaros

20/52 Neutrinos from Gamma Ray Bursts  + p →  + →  + →  + +  → e + + e +   +  p-p interactions also possible in certain mechanisms, resulting in equal ratio of neutrinos and antineutrinos e :  :  flavor ratio is thus 1:2:0 at source After oscillations, ratio becomes 1:1:1 at Earth (although neutrino to antineutrino ratio is not the same for each flavor) Flavor ratio at source becomes 0:1:0 at very high energies (>PeV) due to energy losses in  + Resulting flavor ratio at Earth becomes 1:1.8:1.8

21/52 Prompt Emission: Collapsar Model Neutrino spectrum can be extrapolated from observed gamma-ray spectrum Band function fit Gamma-Ray Spectrum Neutrino Spectrum Sample burst: GRB HETE data

22/52 Prompt Emission: Diffuse Flux Limits Waxman-Bahcall limit obtained for “diffuse” flux of GRB neutrinos using typical burst parameters – assumed as signal spectrum in rolling analysis as well as most triggered GRB searches conducted with AMANDA [E. Waxman and J. Bahcall, Phys. Rev. Lett. 80, ] Murase and Nagataki Model A yields a similar spectrum from somewhat different assumptions [K. Murase and S. Nagataki, Physical Review D 73, ] Supranova Model neutrinos result if a massive supernova precedes the burst by ~1 week, creating a field of matter with which the GRB jet interacts. This model is currently strongly disfavored due to observations by the Swift satellite [S. Razzaque, P. Meszaros and E. Waxman Phys. Rev. Lett. 90, ]

23/52 Additional Diffuse Flux Limits Precursor neutrinos: produced by the GRB jet while it is still within the stellar progenitor ~ seconds before the burst. Choked bursts, which have no prompt gamma or neutrino emission but can still produce the equivalent of precursor neutrinos, could outnumber conventional GRBs by as much as a factor of 100 [E. Waxman and J. Bahcall, Astrophysics Journal 541, ] Afterglow neutrinos: occur Through interactions of the GRB jet with interstellar matter around the burst. [S. Razzaque, P. Meszaros and E. Waxman Physical Review D, 68, ] Thermal neutrinos (not shown) are emitted isotropically at an earlier stage of burst formation. They are in the MeV range and not likely to be detectable outside of our own galaxy.

24/52 10 min Blinded Window -1 hour +1 hour Triggered AMANDA GRB Searches Background is measured off-time at location of burst 10 minute window is kept blinded, but time examined for neutrino signal is T 90 +U 90 +1s. Searches performed in coincidence with 312 BATSE and 91 IPN bursts with muon channel 73 burst search performed with cascade channel (year 2000) Precursor search performed for No on-source on-time events observed so far

25/52 Rolling Search Method The rolling search method uses a rolling window to search for a statistically significant cluster of events which still remain after all data selection criteria have been applied. Disadvantages: -Less sensitive due to increased backgound -Cluster analysis rather than counting analysis Advantages: - Can identify bursts missed by gamma-ray satellites - Can potentially identify flux from hidden sources and un-modeled transients - Will not miss neutrino flux if there is an offset relative to prompt emission BATSE

26/52 2 time windows: 1 and 100 seconds Uses cascade channel Rolling Search Color indicates time of hit (red earliest, violet latest) Diameter of circle proportional to intensity Fits performed on each event in analysis: - “direct walk” muon first guess - “Center of gravity” cascade first guess - Maximum Likelihood reconstructions for muons and cascades

27/52 Data Reduction 1.High energy filter removes events with fewer than 160 hit optical modules and events with less than 72% of hit optical modules having two or more hits 2. Flare checking cuts, which Remove “unphysical” events 3. Cut on “number of direct hits” variable 4. Six variable support vector machine cut

28/52 Flare Checking Plots

29/52 Cut Variables Real DataSimulated SignalSimulated Background

30/52 Final Cut Final cut is determined by Support Vector Machine: Support Vector Machine finds optimal cut in multidimensional cut space created by six input variables Operates by using a mathematical kernel function to translate six-dimensional phase space of variables into higher dimensional space where cut is a linear function of variables Support vector machine is trained with 5 days of real data as background and ANIS computer simulation weighted to broken power law as signal Tighter or looser cuts can be obtained by adjusting a variable called the cost factor

31/52 Optimization Optimization of analysis performed using Monte Carlo simulation of entire 3-year ensemble of bursts (1240 bursts based on BATSE rate and adjusting for livetime) Analysis optimized for N large, the largest number of events observed in any time window throughout the year Account for variations in event rate due to distance from Earth, overall fluence, spectral shape, Earth shadowing effect, et cetera using predictions from actual bursts When looking for an event cluster, one strong source is better than multiple weaker ones Two time windows (1 and 100 seconds) optimized separately Predicted events for real bursts from BATSE catalog Astro-ph/ >

32/52 Optimization Two methods of selecting optimal support vector machine cut: Model Discovery Potential: Finds cut such That one has a 90% chance of observing a signal at a 5 sigma confidence level. Model Rejection Potential: Finds cut such that, in the absence of an observed signal, the best possible 90% confidence level limits can be placed on the astrophysical neutrino flux This analysis was optimized for discovery, but this is not too far from the best choice under limit-optimization

33/52 Data Stability Data is consistent with Poissonian hypothesis and shows consistent rates throughout year

34/52 Results N large for the 100 second window was 3, N large for the 1 second window was 2. Number Observed Number Expected 2 event windows in short burst search ±18 2 event windows in long burst search ±32 3 event windows in long burst search ±4.8 Additionally, the distribution of bins with 2 or 3 events Is consistent with simulations Assuming Poissonian background

35/52 Limit Calculations Limits constructed using Feldman Cousins method (90% confidence level) 90% confidence belts constructed for each discrete signal flux Ordering principle is likelihood ratio L(N large at this flux)/ L(maximum probability at any flux) Flux upper limits read off for each value of N large

36/52 50% for ice properties: Modeled clear, average and dusty ice and took spread as uncertainty (conservative approach and worse for cascades than muons) 20% for other modeling: Distribution of events among various bursts is model-dependent 5% for neutrino cross section Uncertainties incorporated as nuisance parameters Each treated as separate flat error, numerator in likelihood ratio integrated over PDF of possible range of real signal strengths In practice this is done numerically as part of the monte carlo simulation Systematic Uncertainties Conrad, Botner, Hallgren and Perez del Los Heros (hep-ex/ ) and Hill (physics/ )

37/52 Limits Limits were derived using the Feldman Cousins maximum likelihood ratio ordering method, with systematic uncertainties included as nuisance parameters Limits shown for central 90% Energy ranges. Limits for various Models are shown for the rolling search and triggered cascade analysis Waxman-Bahcall Spectrum (W03) Murase-Nagataki (MN06) Precursor/choked burst (MW01) Supranova (R03b) Solid black lines – rolling search Dashed black lines – triggered cascade search (2000)

38/52 Back of the Envelope Sensitivity Check 90% chance of seeing signal = 10% chance of not seeing signal With ~425 bursts during livetime, this means an average of.9946 probability of not seeing each burst. 5 or more events from a burst would exceed the 90% sensitivity bound, so the probability of not seeing each burst means four or fewer events ~1.1 events per burst~734 events per year Scaling between predicted number of events From reference WB flux, we obtain the flux to which we are sensitive Correcting for detector deadtime, we get the original prediction of 1.3 X GeV/cm 2 ssr Taking the simplified assumption of a flat distribution wherein all bursts are equal and the 2001 data subsample our algorithm yields a Sensitivity of 1.3 X GeV/cm 2 ssr

39/52 Effective Area Spike at 6.3 PeV Is due to Glashow Resonance (antineutrino- electron interaction) Earth is not opaque to high energy tau neutrinos due to tau regeneration

40/52 Expected Energy Distribution Folding effective area with predicted spectrum gives distribution of expected energies. This is shown for Waxman Bahcall spectrum (above) and atmospheric neutrino spectrum (right) All plots have arbitrary normalization

41/52 Sphere of Sensitivity Other way to look at limit: Distance at which burst could be observed given certain assumptions (e.g. bulk Lorentz factor of burst normalized to ~300, ΛCDM cosmology assumed) Closest observed redshift so far is z~.009, although this was an anomalous burst

42/52 The Future Current analysis results of both cascade channel GRB searches to be published in July 2007 Astrophysical Journal Rolling search can be extended to muon channel, possibly taking advantage of point source search datasets Coincidence studies with other detectors – neutrinos, gamma-rays, gravitational waves? Extension to other sources – mildly relativistic supernova Substantially improved limits with IceCube Order of magnitude improvement with little effort Improved background rejection techniques should bring much greater improvements

43/52 IceTop InIce Air shower detector Threshold ~ 300 TeV planned 80 strings of 60 optical modules 17m between modules 125m string separation 1km 3 instrumented volume : 1 string : 8 strings AMANDA 19 strings 677 modules Completion by : 13 strings deployed IceCube First data in 2005 first upgoing muon: July 18, 2005 Altogether: 22 strings 52 surface tanks

44/52  signature  signature eV (10 TeV) ~90 hits 6x10 15 eV (6 PeV) ~1000 hits Multi-PeV   +N  +...  ± (300 m!)   +hadrons AMANDA Event Signatures in IceCube

45/52 Hose reel Drill tower IceTop tanks

46/52 Drilling and Deployment

47/52 Photomultiplier tube Mu metal magnetic shield Glass sphere Active PMT base Mainboard

48/52 Digital Optical Module Testing Each DOM taken through extensive battery of tests Every test run at sequence of temperatures: +25 C, -45 C, -20 C, +25 C, -45 C (-55 C runs included for IceTop DOMs since temperatures will be lower on the surface than in deep ice) Tests run over period over ~3 weeks in batches of 60 DOMs each Tests include - Optical Sensitivity tests - Time resolution - Local coincidence chain testing - Long term spike monitoring - High gain monitoring - Various mainboard performance tests - Reboot tests

49/52 Mean time between failures ~= 2 million DOM hours 76 DOMs589 DOMs “Liljeholmen” stops communicating properly “Rowan” stops communicating properly Plot credit: Mark Krasberg

50/52 GRB Triggered Analysis Scenario Events/ Burst Flat Model 1 Event Realistic 1 Event Flat Model 3 events Real Model 3 events Muon Predicted Muon WB bound Cascades Predicted Cascades WB bound )Could take several years to observe GRB (or we could get lucky) 2)Not much difference between assuming bursts are all equivalent and modeling realistic distribution (although difference is statistically significant) Number of bursts required (90% C.L.) Note that bursts which can be studied by cascade channel occur at 2X rate

51/52 Conclusions AMANDA is currently the most sensitive high energy neutrino physics experiment and will continue to operate as a lower energy sub-array within IceCube The rolling search method adds another approach to the search for astrophysical neutrinos which complements previous strategies IceCube will produce dramatically improved limits relative to AMANDA analyses and stands to be high energy neutrino astrophysics’ first discovery instrument The End Acknowledgements: I would like to thank the whole IceCube collaboration for support: Albrecht Karle, Kael Hanson, Ignacio Taboada, Francis Halzen, Gary Hill, Mike Stamatikos, Teresa Montaruli and many others

52/52 Backup Slides

53/52 Murase Nagataki flux

54/52 Flavor Ratio ____ Predicted flavor ratio % C.L. for  % C.L. for  E 0,  is energy at which cooling time is equal to decay time (~1 PeV)

55/52 SPASE/AMANDA 12° SPASE AMANDA x= m y= m z= m South Pole Air Shower Experiment Uses surface air shower array in coincidence with AMANDA as a muon detector in order to determine Composition and energy of cosmic rays

56/52 Bursts of low-energy (MeV) ν e from SN simultaneous increase of all PMT count rates (~10s) Since 2003: AMANDA supernova system includes all AMANDA-II channels Recent online analysis software upgrades –can detect 90% of SN within 9.4 kpc Part of SuperNova Early Warning System (with Super-K, SNO, LVD, …) AMANDA-II AMANDA-B10 IceCube 30 kpc Supernova Search

57/52 Neutralino-induced neutrinos qq  l + l -   W, Z, H “down” “up” Searches for WIMPS with AMANDA Weakly Interacting Massive Particles - Leading dark matter candidate - Collect in center of sun and Earth - May produce > 10 GeV neutrinos through WIMP-antiWIMP annihilation

58/52 Limits on muon flux from EarthLimits on muon flux from Sun Solar and Earth WIMP Limits

59/52 Diffuse Analyses Sum of total neutrino flux over full sky (or half sky in the case of muon analyses) Individually unresolvable sources Best available limit from muon neutrino analysis Final energy-related cut shown on right