Carla Distefano for the NEMO Collaboration

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Carla Distefanofor the NEMO Collaboration
WNNA 2007 Catania Febrary 15 16
LNS
Sensitivity of the NEMO detector to Galactic
microquasars
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Outline of the talk

• Possibility to detect microquasar neutrinos with
  the NEMO telescope
• Neutrino production in microquasar jets
• Monte Carlo simulation of the response of the
  NEMO-km3 telescope
• - Reconstructed events from
  microquasars
• - Expected atmospheric muon and neutrino
  background.
• Background rejection
• - Definition of the detector sensitivity
• - Optimisation of event selection.
• Results.

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Galactic Microquasars

• Galactic X-ray binary systems which exhibit
  relativistic radio jets
• persistent or bursting
• about 20 identified microquasars
• not extremely powerful sources but close to the
  Earth
• good sources to investigate astrophysical
  relativistic jets (AGN, GRB)
• jet composition
• possible TeV neutrino sources.
  
  

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Neutrino production via p? interaction in the jet
Semi-continuous jets with internal shocks
Plasma shells with different Lorentz factors
collide
p,e
Ep,max1016 eV
Internal shocks propagating along the jet
jet
Acceleration of p-e
IR, radio
plasma inhomogeneities
?1
?2
Photo pion production
?1lt ?2
neutrinos
X-ray
accretion disk
Levinson Waxman, Phys. Rev. Lett., 87.171101,
2001
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Neutrino production via p? interaction in the jet

• Levinson and Waxman (2001) model predicts a E-2
  neutrino flux in the energy range 1-100 TeV.
• Distefano et al. (2002) estimated the expected
  neutrino energy fluxes from known microquasars,
  considering both steady and bursting sources.
• Theoretical predictions are based on several
  source parameters
• model free parameters
• (particle acceleration efficiency)
• observational parameters
• (jet luminosity)

Distefano et al., ApJ, 575, 378, 2002
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Simulated NEMO-km3 detector
See R. Conigliones talk

• Simulated Detector Geometry
• square array of 81 NEMO towers
• 140 m between each tower
• 18 storeys for each tower
• vertical distance 40 m
• storey length 20 m
• 4 PMTs for each storey
• 5832 PMTs (10 diameter)

The detector is located at the Capo Passero site
PMT location and orientation
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Detector sensitivity to neutrino fluxes

• Calculation of the sensitivity energy flux
• we simulate the expected background b (atm. ?
  and ?) and we estimate the 90 c.l. sensitivity
  in counts lt?90(b)gt (Feldman Cousins)
• we calculate the sensitivity energy flux as

where f?th is the theoretical energy flux
producing N? counts in the detector
Feldman Cousins define the sensitivity as the
average upper limits for no true signal. It is
the maximum number of events that can be excluded
at a given confidence level.
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Event simulation
Atmospheric neutrinos are generated according
to the Bartol RQPM (highest prediction) flux
BartolRQPM 1 year
NBartolRQPM ? 4104 expected events/year
Events at the detector
Atmospheric muons are generated according to
the Okada parameterization, taking into account
the depth of the NEMO Capo Passero site (3500 m)
and the flux variation inside the detector
sensitive height ( 900 m) But only down-going
events!
Okada 1 year
NOkada ? 4108 expected events/year
Events at the detector
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Simulation of point-like neutrino sources
We use the ANTARES event generation code
(weighted generation) We simulated Ngen109
interacting neutrinos in the expected energy
range with a generation spectral index X1, for
each microquasar. Average number of
reconstructed events per microquasar
1.5105. The generated neutrino events are
weighted to the theoretical spectrum.
Aiello et al., submitted to Astrop. Phys.
(astro-ph/0608053)
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Rejection of the atmospheric background
At this level of the analysis procedure the
fraction of background events is too high also in
the case of the most intense microquasars.
SS433 (1 year) Counts in the plotted sky
region (considering only up-going events)
71 source events
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Event selection strategy

• quality cut
• The used reconstruction algorithm is a robust
  track fitting procedure based on a maximization
  likelihood method. The reconstruction may give
  more than one possible solutions
• - ?gt ?cut ? ? - log(L)/NDOF0.1(Ncomp-1)
• log(L)/NDOF ? log-likelihood per degrees of
  freedom
• Ncomp ? total number of compatible solutions
  (within 1?)
• (see ANTARES documentation)
• angular cuts
• - rejection of down-going tracks
• ??reclt??max ??rec ?
  reconstructed event direction
• - choice of the search bin size
• rltrmin r ? angular distance from
  source position

The optimal values of ?cut, ??max and rmin are
chosen minimizing the detector sensitivity.
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Detector sensitivity (1 year data taking)
Sensitivity vs. declination
The sensitivity is calculated for a ??-? neutrino
spectrum with ? 2 and ?? 1-100 TeV.
Average sensitivity 5?10-11 erg/cm2 s search
bin radius 0.5-1
Aiello et al., submitted to Astrop. Phys.
(astro-ph/0608053)
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Microquasar neutrinos selected events (1 year)
Steady microquasars
Average number of selected events from source Nµm
and of background Nµb in 1 year observation time.
Microquasars SS433 and GX339-4 NEMO could detect
neutrinos in 1 year of data taking or strongly
constrain source physical parameters
(acceleration efficiency, energy content )
Aiello et al., submitted to Astrop. Phys.
(astro-ph/0608053)
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Microquasar neutrinos selected events
Bursting microquasars
We assume that transient sources cause 1 burst
per year N?m calculated for 1 burst, N?b
calculated in 1 year.
Improvement considering time correlation with
source bursts (multi-messenger analysis) N?b10-3
events per burst Cumulative analysis of
considered bursts N?m3.4?9.0 events
N?b0.04 events
Improvement integrating over more bursts per
microquasar (mandatory knowledge of the duty
cycle) GRS 1915105 and GRO J1655-40 may show
more than 1 burst per year Cir X-1 periodic
bursts (T17 days ? 1.5 evt/year).
Aiello et al., submitted to Astrop. Phys.
(astro-ph/0608053)
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Summary

• We simulated the proposed NEMO detector (9x9
  array 5832 PMT and Capo Passero Site
  environmental parameters) using the ANTARES
  software tools.
• We studied the possibility to detect microquasar
  neutrinos
• we simulated the response of the NEMO-km3
  telescope and we computed
• - the number of reconstructed events from
  microquasars
• - the number of expected atmospheric muon and
  neutrino events.
• we applied an event selection to reject the
  background
• - optimisation of event selection optimizing the
  detector sensitivity
• - average sensitivity (1 year) 5?10-11
  erg/cm2 s search bin radius 0.5-1
• we computed the number of events surviving the
  selection
• - NEMO could detect several ? events from
  microquasars in 1 year
• - evidence of astrophysical ? fluxes is expected
  in a few years.

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Microquasars with Wolf-Rayet stars
Microquasar Cygnus X-3

• Neutrons resulting from photo-disintegration of
  accelerated nuclei produce neutrinos after
  interactions with matter in
• the inner disk (Reg. II)
• the proximity of the WR star surface (Reg. III).
• Region I analogue to LW scenario

Accelerated nuclei spectrum ?A-?
Bednarek ApJ 631, 466, 2005
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Microquasar LS 5039
HESS observed TeV ?-rays from LS 5039
Aharonian et al. Science 309, 746, 2005
??(?0.25 TeV) 5.1 ? 0.810-12 ph/cm2 s ? 2.12
? 0.15
Fast radiative cooling (Sync. and Compton) which
prevents the electrons from reaching multi-TeV
energies ? hadronic origin of TeV ?-rays (pp
interaction)
Expected neutrino energy flux
f?(?0.1 TeV) 10-10 erg/cm2 s
Aharonian et al. astro-ph/0508658
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Other models in literature

• windy microquasars
• - HE ? and ?-ray production from interaction of
  jet relativistic p with the stellar wind
• - 3-5 TeV muon neutrinos per km2 per year
  expected from LS I 61 303
• - LS I 61 303 is outside the field of view of a
  Mediterranean telescope
• - The model can be applied to other sources as LS
  5039, Cygnus X-1, Cygnus X-3
• strongly misaligned jets with respect to the
  perpendicular to the orbital plane
• - The jet could collide with the stellar wind,
  producing HE ? and ?-rays
• - The expected neutrino fluxes are in general too
  low to be detected by a km3 telescope
• These models are not considered in this work.

Christiansen et al. astro/ph-0509214
Romero Orellana, AA, 439, 237, 2005
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Simulation of point-like neutrino sources (1 year)
Number of reconstructed muon events from LS 5039
considering different values of the spectral
index ? and of the energy cutoff ??max of the
neutrino spectrum.
f?(?0.1 TeV) 10-10 erg/cm2 s
Aharonian et al. astro-ph/0508658
Number of reconstructed muon events from Cygnus
X-3 considering different values of the spectral
index ? and of the energy cutoff ?Amax of the
nuclei spectrum.
Bednarek ApJ 631, 466, 2005
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Detector sensitivity microquasar LS 5039
??min 0.1 TeV
Muon energy spectra of selected events. Spectra
are weighted to the energy neutrino flux f?(?0.1
TeV) 10-10 erg/cm2 s (flux predicted by
Aharonian et al., 2005)
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Microquasar neutrinos selected events
Average number of selected events from source Nµm
and of background Nµb in 1 year observation time.
Neutrino flux predicted by Aharonian et al., 2005
Neutrino fluxes predicted by Bednarek, 2005
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Simulation of atmospheric neutrino background
We use the ANTARES event generation code
(weighted generation) We simulated a power law
interacting neutrino spectrum
X2 for 102 GeV lt ?? lt 108 GeV Ngen 7109
interacting neutrinos 4? isotropic angular
distribution
Nrec ? 3.7105 reconstructed events
BartolRQPM 1 year
The atmospheric neutrino events are weighted to
the Bartol RQPM (highest prediction) flux
Events at the detector
NBartolRQPM ? 4104 expected events/year
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Simulation of atmospheric muon background
The events are generated at the detector,
applying a weighted generation technique. We
simulate a broken power law spectrum (compromise
between the requirement of high statistics and
CPU time consumption)
Okada 1 year
X1 for ?? lt 1 TeV Ngen 3107 events X3 for
?? gt 1 TeV Ngen 2.5107 events
Nrec ? 3.8106 reconstructed events
Events at the detector
The atmospheric muon events are weighted to the
Okada parameterization (Okada, 1994), taking into
account the depth of the NEMO Capo Passero site
and the flux variation inside the detector
sensitive height ( 900 m)
Okada 1 year
NOkada ? 4108 expected events/year tgen ? 4 days
Events at the detector
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Atmospheric muon background for a point-like
source
Distribution of equatorial coordinates of the
reconstructed atmospheric muons.

• The statistics of generated events corresponds
  to a few days.
• Reconstructed events have a RA flat
  distribution.
• We can project the full sample of simulated
  events in a few degrees bin ?RA, centered in the
  source position.
• We get statistics of atmospheric muons
  corresponding to a time of 1 year for each
  microquasar.