Transcript Exploding Stars, Cosmic Rays and Antarctica

The ATIC Experiment
(Exploding Stars, Cosmic Rays and
Antarctica)
John P. Wefel
Louisiana State University
For the ATIC Collaboration
June, 2006
The ATIC Collaboration
J.H. Adams2, H.S. Ahn3, G.L. Bashindzhagyan4, K.E. Batkov4,
J. Chang6,7, M. Christl2, A.R. Fazely5, O. Ganel3
R.M. Gunasingha5, T.G. Guzik1, J. Isbert1, K.C. Kim3,
E.N. Kouznetsov4, M.I. Panasyuk4, A.D. Panov4,
W.K.H. Schmidt6, E.S. Seo3, N.V. Sokolskaya4, J. Watts,
J.P. Wefel1, J. Wu3, V.I. Zatsepin4
1.
2.
3.
4.
Louisiana State University, Baton Rouge, LA, USA
Marshall Space Flight Center, Huntsville, AL, USA
University of Maryland, College Park, MD, USA
Skobeltsyn Institute of Nuclear Physics, Moscow State University,
Russia
5. Southern University, Baton Rouge, LA, USA
6. Max Plank Institute für Space Physics, Lindau, Germany
7. Purple Mountain Observatory, Chinese Academy of Sciences, China
Standard Model of Cosmic Ray Acceleration
• Supernova shock waves may accelerate cosmic rays via first order
Fermi process
– Model predicts an upper energy limit Emax ~ Z x 1014 eV
 composition growing heavier with increasing energy
Supernovae and Cosmic Rays
• Since 1960’s SN associated with CR
…….why?
• Energetics – take energy density in cosmic
rays and a lifetime of 10-100 million years,
to obtain the power needed to sustain CR
in the galaxy. Ask what objects can
produce such a power?
Answer was/is Supernovae explosions
Energetics:
– CR energy density  1eV/cm3
– Residence time in the galaxy  2.6x107 yrs
Power required ~2.5X1047 ergs/yr
– A Type II Supernova yields ~1053ergs
• Almost all of it goes into neutrinos
• 1051 ergs in the blast wave
– SN rate  2/century  2X1049ergs/yr
• Blast wave must convert ~1% of its energy into
cosmic rays.
– Diffusive Shock Acceleration required
Standard picture of cosmic ray acceleration in
expanding supernova shocks
Exploding Stars
• Novae, Supernovae, Hypernovae/Collapsars ….
– Hypernovae/Collapsars may give rise to gamma-ray bursts and
may involve a black hole.
– Supernovae are explosions of massive stars, say > 5 solar
masses which lead to neutron star (pulsar) or black hole
remnants.
Types I, IA, II, III and variations
Classified by Radio emission and Optical spectra
– Novae are explosions of small stars leading to ring nebulae, for
example.
Remnants
Advanced Thin Ionization Calorimeter (ATIC)
Science Objectives
• Investigate the nature of the cosmic ray
accelerator
– Look for evidence of more than type of source
– Test diffusive shock acceleration models
• Investigate galactic confinement
– Test “leaky box” and “diffusion” models
– Investigate cosmic ray leakage from the Galaxy
– Investigate the role of re-acceleration
• Examine the electron spectrum for evidence of
nearby cosmic ray sources
ATIC
energy
range
ATIC Instrument Details
•Si-Matrix: 4480 pixels each 2 cm x 1.5 cm
mounted on offset ladders; 0.95 m x 1.05 m
area; 16 bit ADC; CR-1 ASIC’s; sparsified
readout.
•Scintillators: 3 x-y layers; 2 cm x 1 cm cross
section; Bicron BC-408; Hamamatsu R5611
pmts both ends; two gain ranges; ACE ASIC. S1
– 336 channels; S2 – 280 channels; S3 – 192
channels; First level trigger: S1-S3
•Calorimeter: 8 layers (10 for ATIC-3); 2.5 cm x
2.5 cm x 25 cm BGO crystals, 40 per layer, each
crystal viewed by R5611 pmt; three gain ranges;
ACE ASIC; 960 channels (1200 for ATIC-3).
Data System: All data recorded on-board; 70 Gbyte disk (150 Gbyte for ATIC-3); LOS data rate –
330 kbps; TDRSS data rate – 4 kbps (6+ kbps for ATIC-3); Underflight capability (not used).
Housekeeping: Temperature, Pressure, Voltage, Current, Rates, Software Status, Disk status
Command Capability: Power on / off; Trigger type; Thresholds; Pre-scaler; Housekeeping
frequency; LOS data rate, Reboot nodes; High Volt settings; Data collection on / off
Geometry Factors: S1-S3: 0.42 m2sr; S1-S3-BGO 6: 0.24 m2sr; S1-S3-BGO 8: 0.21 m2sr
Antarctica
• ATIC is constructed as large as possible
and must be flown for as long as possible
to obtain events in the up to 100 TeV
energy region.
• Long Duration Ballooning (LDB) from
McMurdo Station, Antarctica gives the
longest possible flights.
• So, take ATIC to the ‘frozen continent’
Antarctica is a continent for
Science
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Geology / Geophysics
Marine Biology
Glaciology
Volcanology
Life in Extreme Environments
Environmental / Atmospheric Science
• Astrophysics
Astrophysics (Long History)
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McMurdo Neutron Monitor Station
IR Telescope at Pole (upgrade to 10 m)
Meteorite collection
Spase/Amanda  IceCube/IceTop
Long Duration Balloon Flights
– Cosmic Microwave Background
– Solar Observations
– Infrared Astronomy
– Cosmic Ray Studies
LDB Facilities (new)
Flight and Recovery
The good ATIC-1 landing on 1/13/01 (left) and the not so good
landing of ATIC-2 on 1/18/03 (right)
Launch of ATIC-2 in Dec. 2002
ATIC is designed to be
disassembled in the field
and recovered with Twin
Otters. Two recovery
flights are necessary to
return all the ATIC
components. Pictures
show 1st recovery flight
of ATIC-1
All particle spectrum: ATIC, emulsion, and EAS data
RUNJOB
JACEE
CASA-BLANCA
Tibet
KASKADE
TUNKA
ATIC-2
Charge resolution in the p-He group
EBGO > 50 GeV
EBGO > 500 GeV
EBGO > 5 TeV
Deconvolution
Primary Energy
Spectra
(E0)
+
Instrument
Response
=
Measured Energy
Deposit Spectra
(Ed)
(must solve the inverse problem)
A(E0,Ed) = response matrix
Obtained from FLUKA model of instrument
Cosmic Ray Propagation
Leaky Box Model:
N p (E) 
Qp ( E )  esc ( R)
1  esc ( R) /  p
where
 esc ( R)  esc ( R) /(v   )
from HEAO-3-C2:
esc (R)  34.1 R0.6 g / cm2
for R > 4.4 GV
Qp (E)  E  with  = 2.23 for Z > 2
But, esc  R0.6 at high energy leads to conflict with anisotropy
measurements
And, Some weak re-acceleration in turbulent magnetic fields
seems likely
Cosmic Ray Propagation
Diffusion Model:
Osborne and Ptuskin (1988) proposed:
esc  xeff  4.2  (R / R0 )1/ 3  (1 (R / R0 )2 / 3 ) g / cm2
where R0 = 5.5 GV

Spectral index ~2.6 at high energy
Charge resolution in the CNO-group
EBGO > 50 GeV
O
C
EBGO > 250 GeV
EBGO > 1 TeV
Charge resolution in the Ne-Si group
EBGO > 250 GeV
EBGO > 50 GeV
Mg
Ne
Si
S
EBGO > 1 TeV
Charge resolution in the Fe group
EBGO > 50 GeV
Fe
S
Ca
EBGO > 250 GeV
EBGO > 1 TeV
Energy spectra of abundant nuclei
C
Mg
O/10
Si/10
Mg
C
Fe/100
Si
O
Ne/100
Fe
Ne
HEAO-3-C2
CRN
ATIC-2
Leaky
Box
Model
Energy spectra of abundant nuclei
Mg
C
O/10
Si/10
Fe/100
Ne/100
HEAO-3-C2
CRN
ATIC-2
Electrons ( negatrons + positrons )
• Electrons are both Primary (source produced) and secondary
(produced by interactions in ISM
• Electrons are accelerated in Supernovae Remnants (SNR)
• Electrons lose energy by Synchrotron Radiation, Compton collisions
and Bremstrahlung
• Electron Energy Loss proportional to E^2
– Protons, in comparison, lose E proportional to log E
– Thus, at very high Energy, electrons do not last a long time
• Cannot get here from very far away (‘local source’)
• Source (accelerator) must be relatively young
• High energy (TeV) electrons may show nearby SN source(s)
ATIC can Measure High Energy Electrons
Typical (p,e,γ) Shower image in ATIC (from Flight data)
3 events, energy deposit in BGO is about 250 GeV
Electron and gamma-ray showers are narrower than the proton shower
Gamma-ray shower: No hits in the top detectors around the shower axis
Proton
electron
gamma
Shower width (r.m.s. ) distribution
of protons and electrons in BGO2
Solid line from 150 GeV electrons,
Dashed line from protons with comparable energy deposit in the BGO block
Simulation
CERN calibration
F= (E10/Sum)*(r.m.s.)2 distribution in BGO10
Solid line is from 150 GeV electrons
Dashed line is from protons with comparable E deposit in BGO
Simulation
CERN
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Background Level (inferred from the CERN beam test)
8741 proton events with energy deposit comparable to that of the electron
events: Only 3 protons mimic electrons for a cut at 80% of the electrons.
A proton deposits on average about 40% of its energy in ATIC
Rejection power = 8741/3*2.5^1.7 ~ 13000 (for a proton spectral index of –2.7)
Expected Balloon Observation
Single charge good geo. >50GeV
After step 1
The method to select
electron events:
1. Rebuild the shower image,
get the shower axis, and get the
charge from the Si-detector
(χ2<1.5)
2. Shower axis analysis
In Carbon to reject γ and
Proton (its first interaction
point is not in carbon)
3. Shower width analysis in
BGO1 and BGO2
4. Shower F value analysis in
BGO7 and BGO8
After step 2
After step 2
After step 3 4
After step 3 4
Electron Spectrum from ATIC-2
Comparing with electron models
Absolute electron spectrum spectrum comparison with calculated model by a diffusion
coefficient of D=2.0X1029(E/TeV)0.3cm2s-1 and a power index of injection spectrum 2.4
T. Kobayashi, et al.; Astrophys. J. 601 , 340 (2004)
Summary
• ATIC is providing new data in an unmeasured region of
the spectrum and is finding new features
– Not pure power law spectra
– H and He are different (why?)
– Galactic transport changes in this region leading to spectral
changes with energy
– Multiple source models will, almost assuredly, be required
(Exploding Stars of different types + ? )
• ATIC has the most significant measurement of the high
energy electron spectrum
– Feature in the spectrum at 400-500 GeV
• Evidence for nearby Supernovae source ?
• Evidence for Dark Matter annhilation ?
– No evidence for trans-TeV electron flux