Identifying the Sources of Ultrahigh Energy Cosmic Rays

1
Identifying the Sources of Ultra-high Energy
Cosmic Rays

• Tonia Venters
• The University of Chicago
• International Astroparticle Physics Symposium -
  May 7, 2008

2
The ultra-high energy sky is anisotropic.
Sources of UHECRs are likely to be nearby
astrophysical objects.
3
The Search for Sources Idea 1

• Correlation scans using different catalogs
  (source type? possible counterpart emission?)
• Does the correlation improve (exhibit more
  significant deviation from isotropy) or get worse
  (exhibit less significant deviation from
  isotropy)?

The only recourse at the 1 event per source limit.
4
Problems with a Makeshift Catalog

• The VCV catalog is a patched up catalog
• Comprised of objects that have been reported in
  the literature to be AGNs
• No selection criterion applied
• Objects from many different surveys all with
  their own sensitivities and goals and all looking
  at different parts of the sky
• Includes objects that are no longer thought to be
  AGNs

Interpretation is not so obvious!!!
5
Source density?

• Sparse catalogs
• Harder for isotropic events to hit objects
• Harder for real events to hit objects
• Why is the catalog sparse? - Property of objects?
  Survey(s) not very sensitive?
• Dense catalogs
• Easier for isotropic events to hit objects
• Easier for real events to hit objects
• How do we distinguish isotropy from anisotropy?

6
The Search for Sources Idea 2

• Catch the culprits red-handed
• Wait for clusters of events - Auger source
  catalog
• Source positions
• Source significances
• Source fluxes
• Source spectra
• Request help from our lower energy friends -
  Multiwavelength campaigns

7
Lessons from HE Astronomy - Background

• Claim source significance as a fluctuation of the
  background
• Claim source fluxes - maximum likelihood fit of
  background source of flux F to observations
• Model of the background critical!
• Non-existent at the highest energies
• Dominant at lower energies

8
Lessons from HE Astronomy - Error Circles

• Point Spread Function - based on instrument and
  well understood
• PSF -
• Dominated by magnetic fields that are not very
  well constrained
• Different for different parts of the sky
• Doesnt peak at the center
• Large error circles problematic for source
  identification? - Get help!!! - Multi-wavelength
  campaigns
• Maybe we can do this As I said before -
  catalogs, please!
• Bursting sources - Aarrrgghh!!!

9
Doublets

• 4 doublets - 8 events within 3.2º error circles
• 1 Auger year of data
• Within another year - 83 events from them (if
  real sources)

Hinthint
10
Hot spots?
Hinthint
11
Not just excess of events

• Lack of events where there are a lot of sources!
• Is it significant?
• If real, what does it mean?
• Object Properties?
• Confinement?
• Shield?

Hinthint
12
The Future

• Auger South (complete)
• Running for several years - more statistics
• More hot spots
• Continue looking at Virgo Centaurus
• Auger North (bigger)
• Better statistics
• More sources
• Look at Virgo
• Multi-wavelength Campaigns
• More complete uniform catalogs
• Campaigns on Auger excesses/deficits

13
The Beginnings of UHECR Astronomy!!!