Searching for Correlations between HiRes Stereo

Events and Active Galactic Nuclei

Gordon Thomson

Rutgers University

Outline

• Introduction

• HiRes stereo data

• AGN’s from the Veron-Cetty catalog

• Comparisons with the Auger correlation signal

• Search in HiRes data

Introduction• Auger published a Science paper describing the correlation between

their events and AGN’s from the Veron-Cetty catalog, 12th Ed.• Their correlation signal was maximized for the following parameter

set:– Log(Emin) = 19.75– zmax = 0.018– θmax = 3.1º

• This set of parameters is self-consistent.• The parameters were determined from a scan using ½ of their data,

then they used the other half to test the correlation. • In the second half, 8/13 events were correlated, with random

expectation = 2.7 events.• We tested our data with these parameters.• We are scanning our data to find the best parameter set, and the

strength of the correlation.

• We used Bill Hanlon’s reconstruction with cuts for anisotropy, not spectrum determination (looser bracketing).

• 6636 events resulted.• Bill used a consistent set of

dE/dx(s) and <dE/dx> values, so his energy scale is 10% lower than HiRes 1 mono (as it should be).

HiRes Stereo Data

Exposure and Spectrum

• Bill calculates an exposure for this data set of 3200 km2 sr yr.

• His spectrum is above the HiRes mono spectra.

• This is not consistent. • His exposure must be

low by 10-20%.

AGN Catalog

• We used the Veron-Cetty catalog, 12th Ed.

• They may have used QSO’s as well as AGN’s, since they plotted them on their sky map.

• We did not use QSO’s.

Comparing the Energy Scales• For energies above log(E) = 19.75,

– Auger sees 28 events with exposure of 9000 km2 sr year.– HiRes sees 13 events with exposure of 3200-4000 km2 sr year.– Auger events/exposure = 3.1±0.6 per 1000 km2 sr year.– HiRes events/exposure = 3.2±0.9 - 4.1±1.1 per 1000 km2 sr year.– The whole HiRes range is consistent with Auger.

• What is the energy scale difference?– Auger has a nonlinearity since they see E-2.6 above the ankle, rather

than E-2.8

– Auger nonlinearity raises their energy scale at higher energy.– Bill Hanlon’s energy scale is 10% lower than mono.

The energy scales are pretty much the same. In any case we cannot determine the difference.

HiRes Result at the Auger Point

• We found 2 events correlated out of 13, with 3 expected randomly; i.e., no effect is seen in our data.

• Peter Tinyakov and Igor Tkachev checked our numbers and agree exactly.

• JAJM sent us the Auger analysis of AGASA, and no particular correlations are seen.

• Add together HiRes + Auger data: 10 correlated events out of 26, with 6 expected randomly: a 1σ effect.

Scan in Emin around Auger Point

Emin ncorr total random excess(σ)

19.2 59 198 46.2 1.7

19.3 37 129 30.1 1.2

19.4 28 93 21.7 1.1

19.5 17 61 14.2 0.7

19.6 12 39 9.1 0.9

19.7 7 22 5.1 0.7

19.75 2 13 3.0 -0.7

19.8 1 9 2.1 -1.1

19.9 0 4 0.9 -0.9

What do the HiRes Data (alone) Tell Us?

• Divide the data into two random halves (actually throw random numbers), scan on first half, test with second.

• This is the same procedure as Auger followed, so we have to do it too.

• In addition we are scanning our half1, half2, and whole data sets, to determine chance probabilities including statistical penalties.

Conclusions

• The HiRes data do not confirm the Auger finding of correlations with AGN’s.

• The HiRes data have equal statistics to the Auger test sample.

• The “world’s data” show a 1σ effect.

• Stay tuned for more results in a day or two.

• Our draft has been sent far and wide.