The ATIC Experiment (Exploding Stars, Cosmic Rays and

Antarctica)

John P. WefelLouisiana State University

For the ATIC Collaboration

June, 2006

The ATIC Collaboration

1. Louisiana State University, Baton Rouge, LA, USA

2. Marshall Space Flight Center, Huntsville, AL, USA

3. University of Maryland, College Park, MD, USA

4. 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

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

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 yrsPower 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

• 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

Advanced Thin Ionization Calorimeter (ATIC)Science Objectives

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 statusCommand Capability: Power on / off; Trigger type; Thresholds; Pre-scaler; Housekeeping frequency; LOS data rate, Reboot nodes; High Volt settings; Data collection on / offGeometry 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

• Geology / Geophysics

• Marine Biology

• Glaciology

• Volcanology

• Life in Extreme Environments

• Environmental / Atmospheric Science

• Astrophysics

Astrophysics (Long History)

• 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 EnergySpectra

(E0)

InstrumentResponse

Measured EnergyDeposit Spectra

(Ed)+ =

(must solve the inverse problem)

A(E0,Ed) = response matrix

Obtained from FLUKA model of instrument

Cosmic Ray Propagation

pesc

escpp R

REQEN

/)(1

)()()(

)/()()( vRR escesc

26.0 /1.34)( cmgRResc

EEQp )(

Leaky Box Model:

where

from HEAO-3-C2:for R > 4.4 GV

with = 2.23 for Z > 2

But, at high energy leads to conflict with anisotropy measurements

6.0 Resc

Some weak re-acceleration in turbulent magnetic fields seems likely

And,

Cosmic Ray Propagation

Diffusion Model:Osborne and Ptuskin (1988) proposed:

23/20

3/10 /))/(1()/(2.4 cmgRRRRxeffesc

where R0 = 5.5 GV

Spectral index ~2.6 at high energy

Charge resolution in the CNO-group

C

O

EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV

Charge resolution in the Ne-Si group

Ne

Mg

Si

S

EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV

Charge resolution in the Fe group

Fe

SCa

EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV

Energy spectra of abundant nuclei

C

O

Ne

Mg

Si

Fe

HEAO-3-C2

CRN

ATIC-2

C

O/10

Ne/100

Mg

Si/10

Fe/100

LeakyBoxModel

Energy spectra of abundant nuclei

C

O/10

Ne/100

Mg

Si/10

Fe/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 ElectronsTypical (p,e,γ) Shower image in ATIC (from Flight data)3 events, energy deposit in BGO is about 250 GeVElectron and gamma-ray showers are narrower than the proton showerGamma-ray shower: No hits in the top detectors around the shower axis

Proton electron gamma

Simulation CERN calibration

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

F= (E10/Sum)*(r.m.s.)2 distribution in BGO10

Solid line is from 150 GeV electronsDashed line is from protons with comparable E deposit in BGO

Simulation CERN

• Background Level (inferred from the CERN beam test)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

After step 2

After step 3 4

After step 2

After step 3 4

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 analysisIn Carbon to reject γ andProton (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

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