1. The ATIC Experiment ( Exploding Stars, Cosmic Rays and Antarctica) John P. Wefel Louisiana State University For the ATIC Collaboration June, 2006

2. 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. Adams 2, H.S. Ahn 3, G.L. Bashindzhagyan 4, K.E. Batkov 4, J. Chang 6,7, M. Christl 2, A.R. Fazely 5, O. Ganel 3 R.M. Gunasingha 5, T.G. Guzik 1, J. Isbert 1, K.C. Kim 3, E.N. Kouznetsov 4, M.I. Panasyuk 4, A.D. Panov 4, W.K.H. Schmidt 6, E.S. Seo 3, N.V. Sokolskaya 4, J. Watts, J.P. Wefel 1, J. Wu 3, V.I. Zatsepin 4

6. Standard Model of Cosmic Ray Acceleration Supernova shock waves may accelerate cosmic rays via first order Fermi process –Model predicts an upper energy limit E max ~ Z x 10 14 eV  composition growing heavier with increasing energy

7. 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

8. Energetics: – CR energy density  1eV/cm 3 – Residence time in the galaxy  2.6x10 7 yrs  Power required ~2.5X10 47 ergs/yr –A Type II Supernova yields ~10 53 ergs Almost all of it goes into neutrinos 10 51 ergs in the blast wave –SN rate  2/century  2X10 49 ergs/yr Blast wave must convert ~1% of its energy into cosmic rays. –Diffusive Shock Acceleration required

10. Standard picture of cosmic ray acceleration in expanding supernova shocks

11. 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

12. 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

13. ATIC energy range

16. 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 m 2 sr; S1-S3-BGO 6: 0.24 m 2 sr; S1-S3-BGO 8: 0.21 m 2 sr

18. 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’

19. Antarctica is a continent for Science Geology / Geophysics Marine Biology Glaciology Volcanology Life in Extreme Environments Environmental / Atmospheric Science Astrophysics

20. 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

22. LDB Facilities (new)

23. 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 1 st recovery flight of ATIC-1

24. All particle spectrum: ATIC, emulsion, and EAS data RUNJOB JACEE CASA-BLANCA Tibet KASKADE TUNKA ATIC-2

25. Charge resolution in the p-He group EBGO > 50 GeVEBGO > 500 GeVEBGO > 5 TeV

28. Deconvolution Primary Energy Spectra (E 0 ) Instrument Response Measured Energy Deposit Spectra (E d ) += (must solve the inverse problem) A(E 0,E d ) = response matrix Obtained from FLUKA model of instrument

30. Cosmic Ray Propagation 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 Some weak re-acceleration in turbulent magnetic fields seems likely And,

31. Cosmic Ray Propagation Diffusion Model: Osborne and Ptuskin (1988) proposed : where R 0 = 5.5 GV Spectral index ~2.6 at high energy 

34. Charge resolution in the CNO-group C O EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV

35. Charge resolution in the Ne-Si group Ne Mg Si S EBGO > 50 GeV EBGO > 250 GeV EBGO > 1 TeV

36. Charge resolution in the Fe group Fe S Ca EBGO > 50 GeVEBGO > 250 GeVEBGO > 1 TeV

37. 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 Leaky Box Model

38. Energy spectra of abundant nuclei C O/10 Ne/100 Mg Si/10 Fe/100 HEAO-3-C2 CRN ATIC-2

42. 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)

43. 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 electrongamma

44. 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

45. 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

46. 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

47. 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 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

48. Electron Spectrum from ATIC-2

49. Comparing with electron models Absolute electron spectrum spectrum comparison with calculated model by a diffusion coefficient of D=2.0X10 29 (E/TeV) 0.3 cm 2 s -1 and a power index of injection spectrum 2.4 T. Kobayashi, et al.; Astrophys. J. 601, 340 (2004)

51. 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