Transcript Slide 1
Strategies in the search for astrophysical neutrinos
Yolanda Sestayo, MPI-k Heidelberg for the IceCube collaboration VLVνT 09, Athens
AMANDA/IceCube searches for extraterrestrial neutrinos
Energy Range
• AMANDA: E > 100 GeV • IceCube: E > ~ TeV
AMANDA
: operation period between 1997-2009 (Abbasi et al. 2009)
IceCube
• • • • 2006-2007: 9 strings (Finley et al. 2008ICRC) 2007-2008: 22 strings (Abbasi et al. 2009) 2008-2009: 40 strings 2009-2010: 59 strings (data is being analyzed) (taking data) 2006-2007: AMANDA DAQ integrated into IceCube DAQ (Gross et al. 2008ICRC)
IceCube + AMANDA
• IC22 strings + AMANDA (Portello-Roucelle et al. 2009ICRC) • IC40 strings + AMANDA (data is being analyzed) FUTURE:
IceCube + DeepCore
POINT SOURCE SEARCH STRATEGIES • Binned method: samples the sky in angular bins centered in a grid of points of 0.25
o x 0.25
o .
• Unbinned method: test the hypothesis of signal neutrinos from single point sources located at the positions of the grid. Constructs the likelihood assuming a signal pdf following a gaussian plus an energy term.
• Steady sources: No time dependence expected (supernova remnants, pulsar wind nebula, etc) • Time-varying sources: Analysis optimized by a priori information on the variability (micro-qso, blazars, etc)
SEARCH METHODS: ALL-SKY SEARCH
AMANDA 3.8 yrs
100 GeV < E < few PeV
Unbinned analysis IceCube 22 strings
~TeV < E < few PeV
Unbinned analysis
SEARCH METHODS: GALACTIC PLANE SCAN
Combined IceCube 22 strings + AMANDA analysis 100 GeV < E < few PeV Unbinned analysis
Galactic longitude
SEARCH METHODS: ALL-SKY SEARCH •
Best way to find neutrino sources without a known counterpart 1. Large statistical penalties (trial factors) 2. All-sky surveys are based on a point-source search over a grid covering all the sky model PSF only sensitive to emission within the 1. Promising sources are studied in separate analysis 2. Need to develop a method to study extended (non-point source) regions
Galactic Accelerators
Galactic accelerators always associated with regions of massive star formation: •
Supernova remnants
•
Micro-qso
•
Pulsar wind nebula
•
Massive stellar winds
Cas A, SNR Crab, PWN Microqso Wolf-Rayet star
SEARCH STRATEGIES: EXTENDED REGIONS • Angular resolution IceCube 80 strings ~ 1 o • IC22 ~ 2 o IceCube extended source: rather an extended region, comprising several point sources
Cygnus: 85 0 < l < 70 0 0 0 90 0 SUN 270 0 Motivation: extended regions in the galactic plane
Superposition of sources at different distances comprising a relatively large area in the sky
Cygnus Region
Cygnus
There is the compelling need to develop a
COMPTEL 1.809 MeV line Pluschke et al. 2001
method which can be applied efficiently to extended regions such as Cygnus!
Beacom & Kistler 2007 Abdo et al. 2007
EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS) GOALS:
To have a method which:
1) Is model independent
- number of sources/clusters unknown - shape and location of emission unknown (clustered + diffuse emission) 2) Takes advantage of the full signal content - sensitive to weaker neutrino PSs than std point source analyses if Nsrc > 1 Astrophysical neutrinos in the region increase the clustering of events Signal events (from astrophysical sources) Background events (atmospheric neutrinos)
Cygnus region Cygnus region SIGNAL CASE RANDOM CASE
EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS)
2-point correlation function: Quantifies clustering of events as function of the angular separation
Cygnus region MPS counts pairs of events
as function of the angular distance between the events in the pair Pair of events ≡ (event inside, event) Clustering of events increases the number of close pairs
MPS:
• • 2-point correlation function of the candidate neutrino events, where: Primaries: events inside the region Secondaries: all events
EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS)
MPS focuses on small scale clustering (close pairs)
EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS) Cygnus region
2-point binned sampling of the region at the locations of each of the neutrino events.
MPS treats every event inside the region as a point source
Single-point binned sampling 2-point binned sampling Companions per bin
ANALYSIS OF THE CYGNUS REGION USING IC22+AMANDA
72 o < l < 83 o , -3 o < b < 4 o
Selection of the region:
• Most intense γ -ray emission • 8 OB associations 72 o < l < 83 o , -3 o < b < 4 o
DISCOVERY POTENTIAL
Diffuse limit: MPS = binned search
Diffuse limit All-sky search
With IC22+AMANDA angular resolution we reach the diffuse limit with more than 4 point sources inside the region
RESULTS
UPPER LIMITS
Flux Upper Limit for the whole region of 11 o x 7 o : 7.29x10
-11 TeV cm -2 s -1
(90% CL)
RESULTS COMPATIBLE WITH A BACKGROUND FLUCTUATION