A method to constrain the characteristic angular size of the brightest cosmic-ray sources observed above 57 × 1018 eV P. W. Younk 1Physics Dept., Colorado State University, Fort Collins, Colorado 80523-1875, USA 2Physics Dept., University of Siegen, Walter Flex Str. 3, 57068 Siegen, Germany 3Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Received: 08 Feb 2011 – Revised: 19 Aug 2011 – Accepted: 05 Sep 2011 – Published: 20 Sep 2011
Abstract. We introduce a method to constrain the characteristic angular size of the brightest cosmic-ray sources
observed above 57 × 1018 eV.
By angular size of a source, we mean the effective angular extent over
which cosmic-rays from that source arrive at earth.
The method is based on
the small-scale (<10°) self-clustering of cosmic-ray arrival directions.
The method is applicable to sparse data sets in which
strong localizations of CR* directions are not yet observed.
We show that useful constraints on the source size can be made
in the near future and that these constraints are not strongly dependent
on the assumed
spatial distribution and luminosity function of the cosmic-ray sources.
We suggest that an indication of the source size is quite telling.
For example, an indication of the source size can be
used to infer limits on the particle charge and intervening magnetic fields (not independently),
both of which are not well constrained so far. This is possible because the source size
is similar in scale to the magnetic deflection.
Citation: Younk, P. W.: A method to constrain the characteristic angular size of the brightest cosmic-ray sources observed above 57 × 1018 eV, Astrophys. Space Sci. Trans., 7, 403-410, doi:10.5194/astra-7-403-2011, 2011.