Abstract
The arrival directions of cosmic rays detected by the Pierre Auger Observatory (Auger) with energies above 39 EeV were recently reported to correlate with the positions of 23 nearby starburst galaxies (SBGs): in their best-fit model, 9.7% of the cosmic-ray flux originates from these objects and undergoes angular diffusion on a 12.9o scale. On the other hand, some of the SBGs on their list, including the brightest one (M82), are at northern declinations outside the Auger field of view. Data from detectors in the northern hemisphere would be needed to look for cosmic-ray excesses near these objects. In this work, we tested the Auger best-fit model against data collected by the Telescope Array (TA) in a 9-year period, without trying to re-optimize the model parameters for our dataset in order not to introduce statistical penalties. The resulting test statistic (double loglikelihood ratio) was – 1.00, corresponding to 1.1σ significance among isotropically generated random datasets, and to – 1.4σ significance among ones generated assuming the Auger best-fit model. In other words, our data is still insufficient to conclusively rule out either hypothesis. The ongoing fourfold expansion of TA will collect northern hemisphere data with much more statistics, improving our ability to discriminate between different flux models.
Highlights
We will briefly illustrate the main features of the analysis by the Pierre Auger Collaboration [1], which we tried to replicate using Telescope Array data
In Ref. [1], the candidate sources were selected from a list of 64 starburst galaxies (SBGs) outside the Local Group searched by Fermi-LAT [2] for gamma-ray emission
The corresponding flux map is shown in figure 2. This model is favoured at the 4.0σ level over an isotropic null hypothesis and at the 3.0σ level over the hypothesis that the UHECR emissivity is proportional to the overall matter density in the nearby extragalactic Universe
Summary
We will briefly illustrate the main features of the analysis by the Pierre Auger Collaboration [1], which we tried to replicate using Telescope Array data. [1], the candidate sources were selected from a list of 64 starburst galaxies (SBGs) outside the Local Group searched by Fermi-LAT [2] for gamma-ray emission (which was only significantly detected from 4 of them in that work). [1] selected the 23 objects whose radio flux at 1.4 GHz is at least 0.3 Jy (figure 1). Their UHECR luminosity was assumed to be proportional to their radio luminosity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
