Michael Baker

Using Time Dependent Methods for Neutrino Point Source Searcheswith IceCube

Michael Baker

Prelim PresentationJanuary 15, 2009

Major Professor: Teresa Montaruli

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Outline

Cosmic Rays

Astrophysical Neutrino Production

Multiwavelength Resources

IceCube Neutrino Observatory

IC-22 Point Source Results

Time-Dependent Analyses

-- Hotspot

-- Microquasars

-- Multi Wavelength Flare Search

Future Prospects

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Cosmic rays are highlyenergetic particles, mainlyprotons, which come fromouter space and collide withthe atmosphere.

The spectrum spans energiesup to that of a tennis ball

The differential energy fluxof cosmic rays exhibits a broken power-law spectrum.

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Fermi Acceleration

- Each time a particle crossesa shock it gains energy

- Regardless of which directionthe particle encounters the shock

- Results in approximately an E^-2 energy spectrum

Shocks found in Supernova remnants,also from GRBs and AGN jets

Shock

UpstreamDownstream

What do we think accelerates Cosmic Rays?

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“Below the knee”

Protons will be confined tothe galaxy for > 10^6 years

The flux of cosmic raysat these energies is about 0.1 of the energy believed to be released by supernovae in theMilky Way, so SNRacceleration is apossible explanation.

“The Ankle”

Above ~1PeV, firstprotons and heaviernuclei with increasingenergy will not be confined to our galaxy,so we need to find newsources.

AGN? GRB?

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Neutrino Production

1 : 2 : 0 1 : 1 : 1(after oscillations)

High energy particles can interact with nearby matter (or gammas)

Neglecting absorption, the flux of gamma rays from πºand neutrinos are proportional.

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Astronomy with Neutrinos

Charged particles are deflectedby magnetic fields in space, sothey don't point back to their source.

High Energy photons can be absorbedon the way from the source.

However, neutrinos will give us a lineof sight directly back to the sourceand aren't attenuated.

The problem is that they are hardto detect once they get to Earth dueto small cross-sections, so we need a big detector.

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About how big?

Here we have plots for the sensitivities for neutrino telescopesof different sizes and at different longitudes.

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Source Candidates

In a nutshell, our candidate sources are anything thatcould accelerate particles to very high energies...

← Supernova remnants

Active Galaxies ->

Microquasars ->

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Microquasars

Compact object in a binary systemwith a star with evidence for a radio jet.

The compact object will pull off matterfrom its companion, forming anaccretion disk.

Microquasar LS I +61 303 exhibitsperiodicity in all photon wavebands

Is there a periodicity in neutrinoemission?

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H.E.S.S (Imaging AtmosphericCherenkov Telescope) has seen TeV gamma emission from LS 5039

Gamma emission from πº decay?

If inelastic pp collisions make πº wealso expect charged pion productionin equal proportions

Ls I +61 303 has also been observedto be periodic in >400 MeV photonsfrom MAGIC (IACT)

From Ls I +61, Can expect 4 signal & 5 background events in 1 yr with full detector. (Torres and Halzen 2008)

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AGN and microquasarshave the same underlyingprinciple powering them

Difference is a matter ofscale of the jet, AGN havehigher Lorenz factors.

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Marscher 2008

Models of AGN acceleration

The matter distribution in AGN jets is clumpyand can be followed by radio interferometers

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The Spectral Energy Distribution (SED) for blazars has twobumps that fits the Synchrotron Self-Compton descriptionwith some contribution from the light emitted by the AGN's accretion disk. There are also models that use hadronic processes to explain the second bump.

This SED is from Markarian421 from 2005-6.

Multi Wavelength studies are useful to see what changes happen in thepeaks and relative heightsof the two bumps.

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Multi-Wavelength Resources

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WIYN 0.9 meter optical telescope

Campaign for monitoring blazarswith Whipple/VERITAS collaborators

Currently monitoring:Mrk 421, 1ES1959+650, H1426+428W Comae, 1ES0806+524

In previous years:1ES2344+514, Mrk 501, 1ES1218+304

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Whipple telescope:Imaging Atmospheric Cherenkov Telescope

Detects air showers from 100 GeV – 10 TeV photons

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Both the Swift BAT andAll Sky Monitor on XTE use acoded mask to get a widefield of view, so they scan theentire sky several times a day.

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LAT first Skymap

Fermi/GLAST

Recently launched Fermi LAT has a 1 steradianFOV constantly scanning the sky for photons inthe 100 MeV to 300 GeV energy range

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Multiwavelength measurements of Mrk 421; 2005-6

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NESTOR Pylos, Greece

ANTARESLa-Seyne-sur-Mer, France

BAIKAL Russia

DUMAND Hawaii

(cancelled 1995)

NEMOCatania, Italy

IceCube/AMANDA, South Pole, Antarctica

Cerenkov Neutrino Detectors

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Between 300-600 nm about 3.5 x 104 Cherenkov photons/m of a muon track

β 1 and θ∼ c 41∼ o

Natural radiator is low cost and allows huge instrumented regionsbut it takes time to know it well!Main systematic error source

wavefro

ntConcept of Neutrino Detector

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Neutrinos can create a lepton via chargedcurrent interactions, or an energetic showerby a neutral current interaction.

Neutrino Detection

Reno 2004

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Distorted from plane wave by scattering

θ c = 41º

Ĉerenkov Light

Moving charged particles disturb local matter

Light emitted interferes constructively toform a cone if v > c/n

Ice n=1.31

25Amundsen-Scott South Pole station

South PoleDome

Summer camp

AMANDA

road to work

1500 m

2000 m

[not to scale]

www.icecube.wisc.edu

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The goal is to have a cubic km ofice underneath the South Poleinstrumented with photo-multipliers.

The depth helps reduce downgoingmuons and external light.

Currently 5x strings in-ice, and thenew season of drilling is under way.

1x strings installed this season!

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IceCube Construction

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DOM – Digital Optical Module

10-Inch Hamamatsu PMT

Main boardDigitize waveform:

300 MHz for 400 ns40 MHz for 6.4 μs

Flasher board with 12 LEDs

separate high voltage

Time resolution: 2ns

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Example of an IC-22 event

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We only have good angular resolution with muons, so we findthe best-fit track for our reconstruction.

We have the time residual function to describe the probability of a photon arriving at a certain time at a certain distance from its production. The likelihood of the track is the product of these probabilities.

Iterate over all the hit DOMsand we minimize the negative log likelihoodfor the track.

Use the most probabletrack, and fit a paraboloidto the shape of the likelihoodspace to get the angularresolution of the track.

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Simulated events let us know if our reconstructedangular resolution is a good measure of the uncertaintyin the track direction.

Here we have the fraction ofevents reconstructed withina certain angular distance of the true direction.

Where it crosses 0.5 is the definition of the detector's angular resolution.

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See a deficit in CR shower-produced muons from 3 monthsof IC40 data. Shows our telescope can 'point' !

L. Gladstone

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The detector's stability is especially important for time dependent searches, so here we have the event ratesat Level 3 processing for IC22 data.

Here we still have 11 million events, so it is dominated by mis-reconstructed background, which has a strong seasonal variation.

We use a randomsample of these eventsto create equivalentsamples for timedependent analyses

Rate Stability Studies

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Unbinned Analysis

We use a signal Pdf based on the angular resolution of eachevent and an energy estimator based on the number of DOMs hit (Nchan)based on simulated neutrino events.

The background Pdf is based on density of events in a declinationband and the Nchan of the final data sample .

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Confidence level of the test is the fraction of scrambled background trials which yield higher values for the log likelihood.

Detection is for 5σ confidence level (p=5.73e-7)

The power is the fraction of trials with a particular level of signalwhich yield higher values of the log likelihood.

3σ

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IC22 Point Source Results

Hottest spot found at r.a. 153 , dec. +11est. nSrcEvents = 7.7 est. gamma = 1.65

est. pre-trial p-value: -log10(p): 6.14 (4.8 sigma)

If it's a steady source, we can confirm it in subsequent years of data

Concern that it could be due to a one-time occurrence.

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Time Dependent Analysis of the Hotspot

Time-Integratedlikelihood factors

Time-Dependentlikelihood factors

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Hotspot Analysis – Setup and Null Hypothesis

Identified the events near the spot as interesting

Still blind to timing information, so we can get an independent value

Fix the position and energy of the events, and simulate signal byclustering events in time.

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Hotspot Analysis – Discovery Potentials

I performed tests with and without using the energy weightsto fit a Gaussian to derive the best-fit mean and sigma that describes a flare

Use events which have S/B > 1 at the hotspot location

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Hotspot Analysis – Results

p-value ~ 0.5p-value ~ 0.3

Neither analysis finds any significant clustering of events in time

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Microquasar method

For the microquasar study, we take the same idea asthe hot spot and look for a Gaussian from the events'time modulo the period of the particular object, whichis known with good precision from other studies.

Here we have a plot of how precisely we can determinethe peak emission with differentemission widths and signal events

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Objects we looked at:

Object PeriodCygnus X1 5.600 daysCygnus X3 0.1997 daysGRO J0422 0.212 daysGRS 1915 30.8 daysLs I +61 303 26.496 daysSS 433 13.08 daysXTE J1118 0.1699 days

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Discovery Potentials

We found that the discovery potential is better than thetime-integrated analysis if the sigma of the emissionis less than one fifth of the period.

For wider emission widthsthe added degrees of freedommake the time-dependentsearch less powerful.

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Microquasar Results

The smallest p-value pretrial we got for the microquasar analysis is 0.06 for SS 433, which isn't significant given we looked at 7 objects

SS 433

Here are two examples of the 7 microquasars, the events are plottedin phase. Black is the events per bin, blue the space and energyin the bin, and red is the best-fit Gaussian reconstruction.

Ls I +61

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IC-22 Flares Intro

In addition to periodic sources, we are also interested inexamining outbursts from transient objects, mainly blazarsand microquasars.

For the IC-22 run, we took notes of Astronomer's Telegramalerts for objects in our source list. We used light curvesfrom other experiments to define a time window for each flare.

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IC-22 Flares Selection

3C 454.3 July 24-30 2007 (seen with Agile) Nov. 11-21 2007 (Agile and WEBT)

1ES 1959 Nov 25-28 2007 (Integral report)

Cygnus X1 August 8 2007 (Konus-Wind, ASM)

S5 0716+71 September 7-12 2007 (Agile, Radio) Oct 19-28 2007 (Agile, Radio)

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Flares Method

We compared two methods-- Fix a time window, events fall either inside or out-- Use the window to constrain the mean of a Gaussian

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Flares Method and Status

We find there is a range of widths of signal where the box does better, due to its fewerdegrees of freedom for the fit.

Still waiting for permission to,unblind, no results yet

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Future Prospects

IC 40 flare analysis

Prescription for general flare analysis

Program to utilize Fermi data & software tools

Other PS improvements-- mirror symmetry in some events-- Investigate different methods for calculating

angular resolution

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IC 40 Flares:Mrk 421 from April 30 – May 3 2008 Whipple sees up to ~10 Crab3C 454.3 has had several flares June 16, July 24, Nov 20S50716+714 on April 28 in x-rayAO 0235+16 Large radio outburst from Nov 7-11

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Conclusions

IceCube currently has 5x/80 strings in the ice

IC-22 analysis show the detector is working as expected and Moon shadow confirms pointing

We have new sources of astronomical data

There are many new opportunities in neutrino and multi-messenger astronomy

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With well-sampled photon data in the future, wewould like a method to define flares to single outand take a Pdf directly from that photon data.

We're testing a Maximum Likelihood Blocks algorithmto see how well it takes discrete measurements toa continuous function.

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To test the block method we need to simulate a satellite response

and use that for the analysis.

How much does the telescope sampling affect what we reconstruct?

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Here are samples of different trials to simulate ASM data

and their reconstructions. This will give a better sense of

how well blocks are representing the Pdf,

to make sure that the areas are largely in the same place.