Investigating an angular correlation between nearby starburst galaxies and UHECRs with the Telescope Array experiment. (arXiv:1905.07994v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Matteo_A/0/1/0/all/0/1">Armando di Matteo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fujii_T/0/1/0/all/0/1">Toshihiro Fujii</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kawata_K/0/1/0/all/0/1">Kazumasa Kawata</a> (for the Telescope Array collaboration)
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 $12.9^circ$~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 log-likelihood
ratio) was $-1.00$, corresponding to $1.1sigma$ significance among
isotropically generated random datasets, and to $-1.4sigma$ 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.
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 $12.9^circ$~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 log-likelihood
ratio) was $-1.00$, corresponding to $1.1sigma$ significance among
isotropically generated random datasets, and to $-1.4sigma$ 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.
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