strategies in the search for astrophysical neutrinos

Strategies in the search forStrategies in the search forastrophysical neutrinosastrophysical neutrinos

Yolanda Sestayo, MPI-k Heidelbergfor 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 (data is being analyzed)• 2009-2010: 59 strings (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 0.25o x 0.25o.

• 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 SEARCHAMANDA 3.8 yrs

100 GeV < E < few PeVUnbinned analysis

IceCube 22 strings~TeV < E < few PeV

Unbinned analysis

SEARCH METHODS: GALACTIC PLANE SCAN

Unbinned analysis

Combined IceCube 22 strings + AMANDA analysis100 GeV < E < few PeV

Gal

actic

latit

ude

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 only sensitive to emission within the model PSF

1. Promising sources are studied in separate analysis2. 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

• Pulsar wind nebula

• Micro-qso

• Massive stellar winds

Cas A, SNR Crab, PWN Microqso Wolf-Rayet star

• Angular resolution IceCube 80 strings ~ 1o

• IC22 ~ 2o

IceCube extended source:

rather an extended region, comprising several point sources

SEARCH STRATEGIES: EXTENDED REGIONS

00

Cygnus: 850 < l < 700

SUN

900 2700

Motivation: extended regions in the galactic planeSuperposition of sources at different distances comprising a relatively large area in the sky

Cygnus Region

Cygnus

COMPTEL 1.809 MeV line Pluschke et al. 2001

Abdo et al. 2007

There is the compelling need to develop a method which can be applied efficiently to

extended regions such as Cygnus!

Beacom & Kistler 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

Cygnus region Cygnus region

Astrophysical neutrinos in the region increase the clustering of events

RANDOM CASE

Signal events (from astrophysical sources)

Background events (atmospheric neutrinos)

SIGNAL CASE

Cygnus region

EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS)2-point correlation function: Quantifies clustering of events as function of the angular separation

MPS:2-point correlation function of the candidate neutrino events, where:• Primaries: events inside the region• Secondaries: all events

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

EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS)

MPS focuses on small scale clustering(close pairs)

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

Cygnus region

EXTENDED REGIONS: MULTI POINT SOURCE ANALYSIS (MPS)

Single-point binned sampling 2-point binned sampling

Companions per bin

Rela

tive

freq

uenc

y

Rela

tive

freq

uenc

y

ANALYSIS OF THE CYGNUS REGION USING IC22+AMANDA

72o < l < 83o, -3o < b < 4o

72o < l < 83o, -3o < b < 4o

Selection of the region:

• Most intense γ-ray emission

• 8 OB associations

DISCOVERY POTENTIALDiffuse limit: MPS = binned search

With IC22+AMANDA angular resolution we reach the diffuse limit with more than 4 point sources inside the region

Diffuse limit

All-sky search

UPPER LIMITSFlux Upper Limit for the whole region of 11o x 7o: 7.29x10-11 TeV cm-2s-1 (90% CL)

RESULTS

PRELIMIN

ARY

RESULTS COMPATIBLE WITH A BACKGROUND FLUCTUATION

PREL

IMIN

AR

Y