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

Chad Finley UW MadisonTeV II 2006 Aug 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 MadisonTeV II 2006 Aug Distribution of opening angles between true and reconstructed arrival directions for MC events. 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

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

Chad Finley UW MadisonTeV II 2006 Aug BL Lacertae Objects 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) Torres et al., Astrophys.J. 595 (2003) L13. Gorbunov et al., JETP Lett. 80 (2004) 145. Stern and Poutanen, ApJ 623 (2005) L33. Jet of active galaxy M87 (Hubble) BL Lacertae Object - special type of blazar, active galaxy with jet axis aligned with our line of sight.

Chad Finley UW MadisonTeV II 2006 Aug 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 MadisonTeV II 2006 Aug 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. Need to test with new data

Chad Finley UW MadisonTeV II 2006 Aug BL Lac Objects BL Lacs Equatorial Coords.

Chad Finley UW MadisonTeV II 2006 Aug BL Lac Objects and HiRes Events BL Lacs HiRes events (E>10 EeV) Equatorial Coords.

Chad Finley UW MadisonTeV II 2006 Aug 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 n s, that is, the number of events from the source locations, assuming the remaining N-n s events are background. We find: Estimated number of source events:n s = 8.0 (~ excess of events correlating with BL Lacs) Fraction F of isotropic MC sets with stronger signal: F = 2×10 -4 BL Lac Correlations: New Claim

Chad Finley UW MadisonTeV II 2006 Aug 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 ~ Mpc distant Attenuation Length Torres & Anchordoqui, 2004

Chad Finley UW MadisonTeV II 2006 Aug 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 MadisonTeV II 2006 Aug BL Lac Correlations: Energy Dependence If we perform the analysis on all the events below 10 EeV, there is correlation: n s = 22 with ln R = The fraction of isotropic MC sets with stronger signal is F = 6× For the total HiRes data set: –n s = 31 –F = 2×10 -4

Chad Finley UW MadisonTeV II 2006 Aug 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: n s = 3.0, with F = 6× For the combined set of BL Lacs (i.e. “BL” + “HP”) with m<18, and HiRes events above 10 EeV, we find: n s = 10.5, with F = The m 18, and no correlation is found.

Chad Finley UW MadisonTeV II 2006 Aug Six BL Lacs are confirmed sources of TeV  -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: n s = 5.6 with F = TeV BL Lac Correlations

Chad Finley UW MadisonTeV II 2006 Aug 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/ ] BL Lac Correlations: Summary of Results Fraction of MC sets with greater ln(R) value than data

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

Chad Finley UW MadisonTeV II 2006 Aug HiRes-I and HiRes-II Data Sets Current analysis of HiRes-I –May June 2005 Current analysis of HiRes-II –Dec Aug HiRes-I has more exposure than HiRes-II Include only pure monocular statistics for HiRes-I when doing fits

Chad Finley UW MadisonTeV II 2006 Aug HiRes-I and HiRes-II Data Sets Current analysis of HiRes-I –May June 2005 Current analysis of HiRes-II –Dec Aug HiRes-I has more exposure than HiRes-II Include only pure monocular statistics for HiRes-I when doing fits

Chad Finley UW MadisonTeV II 2006 Aug Broken Power Law Fits Fit Spectra to broken power law: –Allow break point to float No break point: –Bad fit:  2 =154 / 39

Chad Finley UW MadisonTeV II 2006 Aug Broken Power Law Fits Fit Spectra to broken power law: –Allow break point to float No break point: –Bad fit:  2 =154 / 39 DOF One break point: –Better fit:  2 =67.0 / 37 DOF –Find Ankle at 4 EeV

Chad Finley UW MadisonTeV II 2006 Aug Broken Power Law Fits Fit Spectra to broken power law: –Allow break point to float No break point: –Bad fit:  2 =154 / 39 DOF One break point: –Better fit:  2 =67.0 / 37 DOF –Find Ankle at 4 EeV Two break points: –Good fit:  2 =40.0 / 35 DOF –Reduce  2 by 27 –HE break at 60 EeV

Chad Finley UW MadisonTeV II 2006 Aug Statistical Significance Significance of observed events beyond break point compared with expected: –Expect 44.9 events –Observe 14 –P(14 ; 44.9) = 7x  is 3x  is 1x10 -9

Chad Finley UW MadisonTeV II 2006 Aug Statistical Significance Significance of observed events beyond break point compared with expected: –Expect 44.9 events –Observe 14 –P(14 ; 44.9) = 7x  is 3x  is 1x10 -9

Chad Finley UW MadisonTeV II 2006 Aug Is it the GZK Cutoff? Compare integral spectrum to spectrum without cutoff

Chad Finley UW MadisonTeV II 2006 Aug Is it the GZK Cutoff? Compare integral spectrum to spectrum without cutoff

Chad Finley UW MadisonTeV II 2006 Aug Is it the GZK Cutoff? Compare integral spectrum to spectrum without cutoff E ½ is energy when measured integral is half expectation: –HiRes finds log 10 E ½ =19.73±0.07 –Berezinsky et al. prediction for GZK log 10 E ½ = 19.72

Chad Finley UW MadisonTeV II 2006 Aug Expectation of GZK Fit spectrum to a model: –Uniform source density for extragalactic sources –Energy losses

Chad Finley UW MadisonTeV II 2006 Aug Expectation of GZK Fit spectrum –Uniform source density for extragalactic sources –Energy losses –Use composition Protons – Extragalactic Iron – Galactic

Chad Finley UW MadisonTeV II 2006 Aug Expectation of GZK Fit spectrum –Uniform source density for extragalactic sources –Energy losses –Use composition Protons – Extragalactic Iron – Galactic

Chad Finley UW MadisonTeV II 2006 Aug 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 2 nd Knee

Chad Finley UW MadisonTeV II 2006 Aug Conclusions HiRes monocular data consistent with GZK suppression –Significance of HE suppression beyond 2nd break point: ~ 5  –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 MadisonTeV II 2006 Aug