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