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Recent Results from the HiRes Experiment

Recent Results from the HiRes Experiment. Chad Finley UW Madison for the HiRes Collaboration TeV Particle Astrophysics II Madison WI 2006 August 28. HiRes Air-Fluorescence Detector. HiRes consists of two sites 12 km apart in the Utah desert (US Army Dugway Proving Ground)

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Recent Results from the HiRes Experiment

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  1. Recent Results from the HiRes Experiment Chad Finley UW Madison for the HiRes Collaboration TeV Particle Astrophysics II Madison WI 2006 August 28

  2. HiRes Air-Fluorescence Detector HiRes consists of two sites 12 km apart in the Utah desert (US Army Dugway Proving Ground) Rings of mirrors at each site observe night sky A cosmic ray induces a shower in the atmosphere which can be observed in UV fluorescent light by both sites. Operation on clear, moonless nights with good atmospheric conditions, so small duty cycle about 10% Chad Finley UW Madison

  3. HiRes Air-Fluourescence Detector • Stereo observations provide the sharpest angular resolution for searching for small-scale anisotropy • In simulations, 68% of events above 10 EeV are reconstructed within 0.6° of their true arrival direction • Monocular observations currently provide the largest exposure for measuring the energy spectrum • HiRes-I was built first and obtained almost three-years more data than HiRes-II Distribution of opening angles between true and reconstructed arrival directions for MC events. Chad Finley UW Madison

  4. I. BL Lac CorrelationsII. Energy Spectrum and GZK Effect

  5. BL Lacertae Objects Jet of active galaxy M87 (Hubble) BL Lacertae Object - special type of blazar, active galaxy with jet axis aligned with our line of sight. • Blazars are established sources of TeV -rays • Candidates for accelerating cosmic rays to EeV energies • Somewhat controversial recent history regarding correlations of UHECR with BL Lac objects: • Tinyakov and Tkachev, JETP 74 (2001) 445. • Tinyakov and Tkachev, Astropart. Phys. 18 (2002) 165. • Gorbunov et al., ApJ 577 (2002) L93. • Evans, Ferrer, and Sarkar, Phys.Rev. D67 (2003) 103005. • Torres et al., Astrophys.J. 595 (2003) L13. • Gorbunov et al., JETP Lett. 80 (2004) 145. • Stern and Poutanen, ApJ 623 (2005) L33. Chad Finley UW Madison

  6. BL Lac Correlations: Previous Claims • Previous correlations were found using AGASA and Yakutsk data. We test each claim with HiRes data: Tinyakov & Tkachev, JETP 74 (2001) 445. Tinyakov and Tkachev, Astropart. Phys. 18 (2002) 165. Gorbunov et al., ApJ 577 (2002) L93. No previous claims are confirmed. Chad Finley UW Madison

  7. Need to test with new data BL Lac Correlations: New Claim • Most recent claim by Gorbunov is based on published HiRes data. It uses a 10 EeV threshold, so it is a new claim. Gorbunov et al., JETP Lett. 80 (2004) 145. Chad Finley UW Madison

  8. BL Lac Objects BL Lacs Equatorial Coords. Chad Finley UW Madison

  9. BL Lac Objects and HiRes Events BL Lacs HiRes events (E>10 EeV) Equatorial Coords. Chad Finley UW Madison

  10. BL Lac Correlations: New Claim • The 0.8º angular bin size was optimized by Gorbunov et al. • It is preferable to perform an unbinned maximum likelihood analysis, using the individual errors of each event. • The test hypothesis is that the cosmic rays arrive from two distributions, a source distribution and an isotropic background distribution. The likelihood is maximized for the best estimate for ns , that is, the number of events from the source locations, assuming the remaining N-ns events are background. We find: • Estimated number of source events: ns = 8.0 (~ excess of events correlating with BL Lacs) • Fraction F of isotropic MC sets with stronger signal: F = 2×10-4 Chad Finley UW Madison

  11. BL Lac Correlations: New Claim • Charged primaries with energies ~ 10 EeV are expected to be deflected many degrees by the galactic magnetic field. • Correlations on the scale of the HiRes angular resolution (0.6º) imply that primary must be neutral (at least over most of its path through GMF). • But neutron decay length and photon mean free path are very short (~ few Mpc) at this energy, whereas BL Lacs are ~ 100 - 1000 Mpc distant Attenuation Length Torres & Anchordoqui, 2004 Chad Finley UW Madison

  12. BL Lac Correlations: Current Study • The Gorbunov et al. correlation was based on limited information (arrival directions only, for just the data set above 10 EeV) • Use the published sample of data up until 2004 January to decide a priori what will be tested before arrival directions of new data are analyzed • Consider: • Energy dependence • Source sample Chad Finley UW Madison

  13. BL Lac Correlations: Energy Dependence • If we perform the analysis on all the events below 10 EeV, there is correlation: ns = 22 with ln R = 3.10. • The fraction of isotropic MC sets with stronger signal is F = 6×10-3. • For the totalHiRes data set: • ns = 31 • F = 2×10-4 Chad Finley UW Madison

  14. BL Lac Correlations: Source Sample • Confirmed BL Lacs in the Veron Catalog are classified as “BL” or “HP” for high polarization. So far, only “BL” have been considered. • We perform the same analysis on the 47 “HP” BL Lacs, using the same m<18 cut as was used for “BL” • use HiRes events above 10 EeV • Result: ns = 3.0, with F = 6×10-3. • For the combined set of BL Lacs (i.e. “BL” + “HP”) with m<18, and HiRes events above 10 EeV, we find: • ns = 10.5, with F = 10-5. • The m<18 was originally tuned to optimize correlations with AGASA data. We have performed all of the same tests using BL Lacs with m>18, and no correlation is found. Chad Finley UW Madison

  15. TeV BL Lac Correlations • Six BL Lacs are confirmed sources of TeV g-rays. Five are in the northern hemisphere and well observed by HiRes. • We perform the maximum likelihood analysis on each source individually using all HiRes events: • For the TeV blazars taken as a set, the ML analysis yields: • All energies: ns = 5.6 with F = 10-3 Chad Finley UW Madison

  16. BL Lac Correlations: Summary of Results • Six results which we wish to test with independent data (all objects with m<18): • Note: • These are not independent results: the samples overlap. • Analysis has been a posteriori, so F values are not true probabilities. • Must be tested with independent data • Data taking through March 2006 has yielded an independent data set ~ 70% of the current sample size: Analysis is ongoing • R.U. Abbasi et al., Astrophys.J. 636 (2006) 680 [astro-ph/0507120] Fraction of MC sets with greater ln(R) value than data Chad Finley UW Madison

  17. I. BL Lac Correlations II. Energy Spectrum and GZK Effect

  18. HiRes-I and HiRes-II Data Sets • Current analysis of HiRes-I • May 1997 - June 2005 • Current analysis of HiRes-II • Dec. 1999 - Aug. 2004 • HiRes-I has more exposure than HiRes-II • Include only pure monocular statistics for HiRes-I when doing fits Chad Finley UW Madison

  19. HiRes-I and HiRes-II Data Sets • Current analysis of HiRes-I • May 1997 - June 2005 • Current analysis of HiRes-II • Dec. 1999 - Aug. 2004 • HiRes-I has more exposure than HiRes-II • Include only pure monocular statistics for HiRes-I when doing fits Chad Finley UW Madison

  20. Broken Power Law Fits • Fit Spectra to broken power law: • Allow break point to float • No break point: • Bad fit: c2=154 / 39 Chad Finley UW Madison

  21. Broken Power Law Fits • Fit Spectra to broken power law: • Allow break point to float • No break point: • Bad fit: c2=154 / 39 DOF • One break point: • Better fit: c2=67.0 / 37 DOF • Find Ankle at 4 EeV Chad Finley UW Madison

  22. Broken Power Law Fits • Fit Spectra to broken power law: • Allow break point to float • No break point: • Bad fit: c2=154 / 39 DOF • One break point: • Better fit: c2=67.0 / 37 DOF • Find Ankle at 4 EeV • Two break points: • Good fit: c2=40.0 / 35 DOF • Reduce c2 by 27 • HE break at 60 EeV Chad Finley UW Madison

  23. Statistical Significance • Significance of observed events beyond break point compared with expected: • Expect 44.9 events • Observe 14 • P(14 ; 44.9) = 7x10-8 • 5s is 3x10-7 • 6s is 1x10-9 Chad Finley UW Madison

  24. Statistical Significance • Significance of observed events beyond break point compared with expected: • Expect 44.9 events • Observe 14 • P(14 ; 44.9) = 7x10-8 • 5s is 3x10-7 • 6s is 1x10-9 Chad Finley UW Madison

  25. Is it the GZK Cutoff? • Compare integral spectrum to spectrum without cutoff Chad Finley UW Madison

  26. Is it the GZK Cutoff? • Compare integral spectrum to spectrum without cutoff Chad Finley UW Madison

  27. Is it the GZK Cutoff? • Compare integral spectrum to spectrum without cutoff • E½ is energy when measured integral is half expectation: • HiRes finds log10E½=19.73±0.07 • Berezinsky et al. prediction for GZK log10 E½= 19.72 Chad Finley UW Madison

  28. Expectation of GZK • Fit spectrum to a model: • Uniform source density for extragalactic sources • Energy losses Chad Finley UW Madison

  29. Expectation of GZK • Fit spectrum • Uniform source density for extragalactic sources • Energy losses • Use composition • Protons – Extragalactic • Iron – Galactic Chad Finley UW Madison

  30. Expectation of GZK • Fit spectrum • Uniform source density for extragalactic sources • Energy losses • Use composition • Protons – Extragalactic • Iron – Galactic Chad Finley UW Madison

  31. Expectation of GZK • Fit spectrum • Uniform source density for extragalactic sources • Energy losses • Use composition • Protons – Extragalactic • Iron – Galactic • Find good fit • Ankle from pair production losses • Indeterminate 2nd Knee Chad Finley UW Madison

  32. Conclusions • HiRes monocular data consistent with GZK suppression • Significance of HE suppression beyond 2nd break point: ~ 5s • Energy of break agrees with GZK predictions • The data is well fit by a uniform source density model. • Recently observed correlations between HiRes and BL Lacs must be tested with independent data: • Data taking through March 2006 has yielded an independent data set ~ 70% of the current sample size • Analysis is ongoing; independent test of BL Lac correlations will be performed Chad Finley UW Madison

  33. Chad Finley UW Madison

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