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					                Status of CELESTE
Cherenkov Low Energy Sampling & Timing Experiment
[E. Paré et al., 2002, Nuclear Instruments and Methods, A490, 71-89]

                            12th May 2003
             Centre de Physique de Particules de Marseille




  Javier Bussons Gordo, Groupe d'Astroparticules de Montpellier (France)
Detection principle: sampling and
             timing




    Pulses (1 Ghz FADCs)




                           Intensities   Arrival times
Trigger                                             Trigger rate
Cherenkov pulse (a few ns):
S ~ 3 p.e. / heliostat at 30 GeV
Night sky background:
B ~ 1 p.e. / heliostat / ns

Trigger multiplicity:
3/5, now 4/6 groups above a given threshold:
                      4 p.e. / heliostat
Helps reject hadrons
Rate ~ 20 Hz (mostly from cosmic background)
Must take care of electronics dead time



                                                                     Threshold setting




                                       Jan 2002:
                                       40 heliostats (5 groups) => 53 heliostats (6 groups)
Energy Threshold and Collection Area

                          Eth ~ sqrt(B) / S ~ sqrt{ Fns Omega T }
                                                     A EFFpm,opt
                                           2          -5
                           Omega = pi   RFOV   = 8 x 10 sr

                           RFOV = 5 mrad

                           CELESTE lowers threshold via large A

                           (PHYSICAL) COLLECTION AREA:
                          CELESTE: 53 x 54 ~ 2800 m2
                          STACEE: 64 x 39 ~ 2500 m2
                          CAT: 16 m2
                          HESS: 4 x 113 ~ 450 m2
Veto
Pointing configurations:
SINGLE: all heliostats at 11 km
DOUBLE: half at 11 km, half at 25 km
now VETO: 41 at 11km and 12 as veto

Normal heliostats point at shower max
Veto heliostats point 150m to the side
Better hadron rejection at lower energies


                                            d=150m
Crab Nebula detection
[M. De Naurois, Holder et al., ApJ 566, 343-357 (2002)]




                             integral rate on a differential plot
Pulsars
[Emmanuel Durand's thesis approved January 2003]
7 EGRET pulsars, none seen by IACTs
6 seen at E>100MeV (3 in N hemisphere)
Cutoffs expected at 10 – 100GeV
Polar cap (super-exponential cutoff model)
Outer gap (exponential cutoff model)
E0 polar cap < E0 outer gap
                  Crab            PSR1951                 RUN SELECTION
Distance [kpc]        2              2.5
Period [ms]           33.4           39.5                 Duration > 7 mins (most runs 18 mins)
Age [yrs]             949            10000                Rate:    Crab              PSR1951
L [1034 erg/s]        44             15
B [1012 G]            3.8            0.5                  3/5      20 - 30 Hz        12 - 17 Hz
Object [SNR]          Crab Nebula    CTB80                4/5      6 - 16 Hz         5 - 10 Hz
                                                          Rate stability
  OPTICAL CRAB                                            Hour angle:        -2 h < H < +2 h
  Check barycentering, phase calculation and GPS timing
  Optical peaks aligned with radio peaks => OK            Remaining data (Crab):
                                                          Set 1: SP, trigger 3/5     48 runs (16.02 h)
                                                          Set 2: SP, trigger 4/5     21 runs (7.78 h)
                                                          Set 3: DP, trigger 3/5     29 runs (8.91 h)
                                                          Remaining data (PSR1951):
                                                          Set 1: SP, trigger 3/5     22 runs (6.66 h)
                                                          Set 2: DP, trigger 3/5     19 runs (5.93 h)
                                                          Set 3: DP, trigger 4/5     24 runs (7.71 h)
                                                          * SP [DP]: single [double] pointing
                        Crab results
Further cut in hour angle:
-3/4h < h < 3/4h
Set 1: signal but < 5
Compatible with p1<p2 w/bridge
[2-100keV, 100keV-10MeV]
Incompatible with p2>p1 no bridge
[0.5-2keV, >100MeV]
EGRET favourable: P2, bridge, TW1, LW2
Profile compatible with EGRET extrapolation
Assume flux from this lot:
< 2 sigma expected in other lots,
+ result not incompatible with – result sets 2,3
Need to master:     acceptance at low energies
                atmosphere effects

Set 2: no signal         Set 3: no signal
Upper limit (SP, 3/5, H cut)
A[E] => A[ (1 0.30)E ]; 0.7 most conservative
Inf                                     Nul
                        B
[A(E) k
0
            E -g e-(E/Eo)dE    =
                                        Tfe
f =phase interval, e = dead time
B=1 (Outer Gap) or B=2 (Polar Cap)
Integrate and find E0 (cutoff energy)
PSR1951: no signal
UL compatible with both models



                                      E0<57GeV
                          E0<80GeV    exp
                          exp




                          E0<75GeV
                          super-exp   E0<62GeV
                                      super-exp
E0< 26GeV [ApJ]           Crab Pulsar (Limit or Flux?)
                  LIMIT
                          (comparing ApJ to ED's thesis)
                          Exponential cutoff model:
                          14 < E0 < 57GeV for A(1.3E) > A > A(0.7E)
                               E0= 25GeV at nominal A(E)
                          2.7  /min [5.4  /min instantaneous]
                          Super-exponential cutoff model:
                          19 < E0 < 60GeV for A(1.3E) > A > A(0.7E)
                          E0= 31GeV at nominal A(E)

                          FLUX
Energy resolution
 E resolution varies smoothly with E
 Unbiased above threshold
 12% < (Em - E) / E < 24%



Spectrum derivation

Energy bins: 50 - 100 - 200 - 400 GeV
Separate acceptance from energy resol
 Max likelihood fit (over all events):

f(Em|E0)=[dE dP/dE (1/sqrt(2pi s2))
            x exp(-(Em-E)2 / 2 s2)

        dP/dE=P0 exp(-E/E0)

yields mean true energy in each bin.
    [ A(E) Eg dE    ON-OFF
 A=              F=
       [ Eg dE      A T dE

 Assume power-law spectrum
 Iterate to find g
Crab Nebula E>50GeV
       Cuts:
       4/5 majority
       #peaks > 10
2000   2001   Mrk421 E>70GeV
Seasonal effects
                    Rate vs DewPoint




   o Mrk421
   + Mrk501                                    We understand trigger rate variations:
                                               large for Mrk501 (warm, humid season)
                                               small for Mrk421 (cold, dry season)


 Rate vs Pressure                      Rate vs Temperature    Rate vs Elevation
 ATMOSPHERE
 LIDAR + CCD photometry + radiometry + pseudo-photometry (star track runs)
 Monte Carlo parameters: atmospheric profile, absorption table
   height
     Radiosounding data => customised profiles by month

                       August ~ mid-latitude summer

                                                                     STREAMER transmission
                                                                        vs CCD measurements
                                               Cherenkov light density
        January ~ mid-latitude winter
                                                               Rayleigh

                                                                 Rayleigh + Mie



                Overburden

 Uncertainty in estimated energy and
acceptance due to choice of atmosphere
   Aerosol distrib at Themis (boundarylayer)
LIDAR   Laser: Nd-YAG
        rep rate 10 Hz
        =1064, 532, 355 nm
        pulse width =4ns
        pulse E=180mJ (532nm)
                   70mJ (355nm)
        beam divergence 0.5mrad
        Optics: Cassegrain + dichroic splitter
        primary mirror Ø 60cm ,f=102cm
        secondary      Ø 8cm, f=10cm
        reflectivity(300-600nm) = 80%
        PMTs: Philips XP2020
        Acquisition:
        12-bit, 5000-word card, 2 inputs
        25 Mhz (40ns/sample)
        Pointing:
        azimuth 0-359°
        elevation 36-89°
             encoder step 0.14°
        _ http: //doc.in2p3.fr/themis/LIDAR
PREDICTIONS (Cherenkov light density on ground)
 Attenuation (50GeV photon):
[25%]                         40%               70%
[std atmosphere]              +aerosols            +clouds
 Seasonal variations: 20% at mid-latitude sites

GOALS
 Select good quality data
 Model Thémis atmosphere with CORSIKA (extinction)
 Correct for seasonal variations
                                extinction (scattering + absorption)
LIDAR EQUATION (  unknowns)  backscattering
P = Po Leff O (R) T2              R
                                                                              gas + particles
                                                       [
                         Transmittance T=I/I0=exp(- (r) dr)                  Rayleigh + Mie
 R: range; O : solid angle; Leff = c                0

                 Nightly shots, quicklook by observer (sky quality, run selection)
         FFT-cleaned, solid-angle-corrected                          Signal in lidarists form
                                                              Slope Method



                    range(km)
[G. Debiais, B. Fabre (Univ. Perpignan)]
Kramers-Kronig analysis (n+ik)             Two-colour difference (aerosol respo


                Refrective index




                                                            green

                                                   violet




          Optical index (absorption)                  Aerosols 0 - 10 km
Flux predictions for neutralino annihilation
[A. Falvard et al., submitted to Astroparticle Physics, astro-ph/0210184
Supersymmetric dark matter in M31: can one see neutralino annihilation with CELESTE?]


                                                     The DRACO case:
                                                     Dwarf spheroidal
                                                     M/L ~ 200

                                                     November 2001:
                                                     evidence for extended DM halo

                                                     April 2002:
                                                     observation proposal with CELESTE

                                                     Possible detection
                                                     if DM spike near black hole
MY MESSAGE:

New results on Crab pulsar: marginal detection & cut-off
Other pulsars: PSR1951 cut-off

Two spectra: Crab (E>50GeV) & Mrk421(E>70GeV)
Two spectra: Crab (E>50GeV) & Mrk421(E>70GeV)
Operating at 50 GeV (hit by bad weather)

Working on understanding our systematics
Attention to best shots next season
Ready to shut down in July 2004
THE END

				
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