Baker_prelim_v1.ppt - IceCube by yurtgc548

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									   Using Time Dependent Methods
   for Neutrino Point Source Searches
   with IceCube

        Michael Baker
        January 15, 2009




Michael Baker
Outline



   Cosmic Rays
   Astrophysical Neutrino Production
   IceCube Neutrino Observatory
   IC-22 Point Source Results
   Time-Dependent Analyses
   -- Hotspot
   -- Microquasars
   -- Multi Wavelength Flare Search




Michael Baker
                Cosmic rays are highly
                energetic particles, mainly
                protons, which come from
                outer space and collide with
                the atmosphere.

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




Michael Baker
What do we think accelerates Cosmic Rays?




 Fermi Acceleration

 - Each time a particle crosses
    a shock it gains energy

 - Regardless of which direction
    the particle encounters the
    shock
                                        Downstream           Upstream
 - Results in approximately an
    E^-2 energy spectrum                             Shock




Michael Baker
“Below the knee”              “The Ankle”

Protons will be confined to   Above ~1PeV, protons
the galaxy for > 10^6 years   will not be confined to
                              our galaxy, so we need
The flux of cosmic rays       to find new sources.
at these energies is about
0.1 of the energy believed    AGN? GRB?
to be released by
supernovae in the
Milky Way




  Michael Baker
Neutrino Production

 High energy particles can interact with nearby matter




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


       Neglecting absorption, the flux of gamma rays from πº
       and neutrinos are proportional




Michael Baker
 Astronomy with Neutrinos

                            Charged particles are deflected
                            by magnetic fields in space, so
                            they don't point back to their source.

                            High Energy photons can be absorbed
                            on the way from the source.

                            However, neutrinos will give us a line
                            of sight directly back to the source
                            and aren't attenuated.

                            The problem is that they are hard
                            to detect once they get to Earth, so we
                            need a big detector




Michael Baker
 Source Candidates

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



                ← Supernova remnants


                  Active Galaxies ->


                    Microquasars ->



Michael Baker
  Microquasars


                                      Compact object in a binary system
                                      with a star.

                                      The compact object will pull off matter
                                      from its companion, forming an
                                      accretion disk.




Microquasar LS I +61 303 exhibits
periodicity in all photon wavebands

Is there a periodicity in neutrino
emission?


  Michael Baker
Hess has seen TeV gamma emission
from LS 5039

--Evidence of πº decay?

If inelastic pp collisions make πº we
also expect charged pion production
in equal proportions

Ls I +61 303 has also been observed
to be periodic in >400 MeV photons
from MAGIC




  Michael Baker
AGN and microquasars
have the same underlying
principle powering them

Difference is a matter of
scale of the jet




Michael Baker
   Model of AGN acceleration

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




 Marscher
 2008

Michael Baker
          WIYN 0.9 inch optical telescope




                              (Add lightcurve from something)




Michael Baker
                Both the Swift BAT and
                All Sky Monitor on XTE use a
                coded mask to get a wide
                field of view, so they scan the
                entire sky several times a day.

Michael Baker
 Fermi/GLAST
                Recently launched Fermi LAT has a 1 steradian
                FOV constantly scanning the sky for photons in
                the 100 MeV to 300 GeV energy range




                                 LAT first Skymap




Michael Baker
 Whipple telescope:
 Imaging Atmospheric Cherenkov Telescope

 Detects air showers from 100 GeV – 10 TeV photons




Michael Baker
Multiwavelength measurements of Mrk 421




Michael Baker
   Neutrino Detection
   Neutrinos can create a lepton via charged
   current interactions, or an energetic shower
   by a neutral current interaction.




                             Reno 2004

Michael Baker
 Ĉerenkov Light

Moving charged particles disturb local matter

Light emitted interferes constructively to
form a cone if v > c/n                             Distorted from
                                                   plane wave by
                                                   scattering

                                                                   º
                                                                 41
                                                             =
                                                        θc



                                                                       }
                                                Ice n=1.31



  Michael Baker
         Cerenkov Neutrino Detectors
         ANTARES               BAIKAL
La-Seyne-sur-Mer, France          Russia




        NEMO                                     DUMAND
     Catania, Italy                               Hawaii
                                              (cancelled 1995)
            NESTOR
           Pylos, Greece


                              IceCube/AMANDA,
                            South Pole, Antarctica
                                            South Pole
                           road to
                                                         Dome
                                     work




 AMANDA

            1500 m                                        Summer camp




2000 m                         Amundsen-Scott South Pole station 21
          [not to scale]
                The goal is to have a cubic km of
                ice underneath the South Pole
                instrumented with photo-multipliers.

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




Michael Baker
 IceCube Construction




Michael Baker
   DOM – Digital Optical Module


   10-Inch Hamamatsu PMT

   Main board
   Digitize waveform:
        300 MHz for 400 ns
        40 MHz for 6.4 μs

   Flasher board with 12 LEDs

   separate high voltage

   Time resolution: 2ns




Michael Baker
Michael Baker
We only have good angular resolution with muons, so use a track
to find a best fit for our reconstruction.

We have the Pandel function to describe the probability of a photon
arriving at a certain time at a certain distance from its production.
The likelihood is the product of these probabilities.
                                             Iterate over all the hit DOMs
                                             and we minimize the
                                             negative log likelihood
                                             for the track.

                                             Use the most probable
                                             track, and fit a paraboloid
                                             to the shape of the likelihood
                                             space to get the angular
                                             resolution of the track.



Michael Baker
    Simulated events let us know if our reconstructed
    angular resolution is a good measure of the uncertainty
    in the track direction.




Michael Baker
Rate Stability Studies

The detector's stability is especially important for time
dependent searches, so here we have the event rates
at 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 start with a random
sample of these
as random background
times for the time
dependent analyses




Michael Baker
IC22 Point Source Results




Hottest spot found at r.a. 153 , dec. +11
est. 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.

Michael Baker
 Time Dependent Analysis of the Hotspot




   Time-Integrated                 Time-Dependent
   likelihood factors              likelihood factors




Michael Baker
 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 by
clustering events in time.




 Michael Baker
 Hotspot Analysis – Discovery Potentials

I performed tests with and without using the energy weights
to fit a Gaussian with best-fit mean and sigma to describe a flare

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




 Michael Baker
Hotspot Analysis – Results




                                                     p-value ~ 0.3
                p-value ~ 0.5




   Neither analysis finds any significant clustering of events in time

Michael Baker
Microquasar method

   For the microquasar study, we take the same idea as
   the hot spot and look for a Gaussian from the events'
   time modulo the period of the particular object.




Michael Baker
Discovery Potentials

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

 Wider than that and the
 added degrees of freedom
 make the time-dependent
 search less powerful.




Michael Baker
Microquasar Results

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


     Ls I +61                                   SS 433




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


Michael Baker
IC-22 Flares Intro



   In addition to periodic sources, we are also interested in
   examining outbursts from transient objects.

   For the IC-22 run, we took notes of Astronomer's Telegram
   alerts for objects in our source list. We used light curves
   once published to define a time window for each flare.




Michael Baker
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)




Michael Baker
Flares Method


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




Michael Baker
 Flares Method and Status

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

   Still discussing the analysis,
   haven't yet unblinded for results




Michael Baker
Future Prospects

 IC 40 flare sample

 Prescription for general flare analysis

 Other PS improvements
 -- mirror symmetry
 -- Cramer-Rao method for angular resolution




Michael Baker
        With well-sampled photon data in the future, we
        would like a method to define flares to single out
        and take a Pdf directly from that photon data.

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




Michael Baker
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?




  Michael Baker
        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.

Michael Baker
Michael Baker

								
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