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Title: On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies

Abstract

Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of cosmic rays (CRs) with energies >57 EeV that suggests a correlation with the positions of active galactic nuclei (AGN) located within {approx}75 Mpc. However, this analysis does not take into account AGN morphology. A detailed study of the sample of AGN whose positions correlate with the CR events shows that most of them are classified as Seyfert 2 and low-ionization nuclear emission-line region (LINER) galaxies which do not differ from other local AGN of the same types. Therefore, the claimed correlation between the CR events observed by the Pierre Auger Observatory and local active galaxies should be considered as resulting from a chance coincidence, if the production of the highest energy CRs is not episodic in nature, but operates in a single object on long ({ge} Myr) timescales. Additionally, most of the selected sources do not show significant jet activity, and hence--in the framework of the jet paradigm--there are no reasons for expecting them to accelerate CRs up to the highest energies, {approx}10{sup 20} eV, at all. If the extragalactic magnetic fields and the sources of these CRs are coupled with matter, it ismore » possible that the deflection angle is larger than expected in the case of a uniform source distribution due to effectively larger fields. A future analysis has to take into account AGN morphology and may yield a correlation with a larger deflection angle and/or more distant sources. We further argue that Cen A alone could be associated with at least 4 events due to its large radio extent, and Cen B can be associated with more than 1 event due to its proximity to the Galactic plane and, correspondingly, the stronger Galactic magnetic field the ultra high energy CRs (UHECRs) encounter during propagation. If the UHECRs associated with these events are indeed accelerated by Cen A and Cen B, their deflection angles may provide information on the structure of the magnetic field in the direction of these putative sources. Future -ray observations (by, e.g., Gamma-Ray Large Area Space Telescope [GLAST], High Energy Stereoscopic System [HESS]) may provide additional clues to the nature of the accelerators of the UHECRs in the local Universe.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
928358
Report Number(s):
SLAC-PUB-13234
Journal ID: ISSN 0004-637X; ASJOAB; arXiv:0805.1260; TRN: US0804238
DOE Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Name: Astrophysical Journal; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; ANISOTROPY; CEN; DISTRIBUTION; GALAXIES; MAGNETIC FIELDS; MORPHOLOGY; NUCLEI; PRODUCTION; TELESCOPES; UNIVERSE; Astrophysics,ASTRO

Citation Formats

Moskalenko, Igor V, Stawarz, Lukasz, Porter, Troy A, and Cheung, Chi C. On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies. United States: N. p., 2008. Web. doi:10.1086/588425.
Moskalenko, Igor V, Stawarz, Lukasz, Porter, Troy A, & Cheung, Chi C. On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies. United States. doi:10.1086/588425.
Moskalenko, Igor V, Stawarz, Lukasz, Porter, Troy A, and Cheung, Chi C. Wed . "On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies". United States. doi:10.1086/588425. https://www.osti.gov/servlets/purl/928358.
@article{osti_928358,
title = {On the Possible Association of Ultra High Energy Cosmic Rays with Nearby Active Galaxies},
author = {Moskalenko, Igor V and Stawarz, Lukasz and Porter, Troy A and Cheung, Chi C},
abstractNote = {Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of cosmic rays (CRs) with energies >57 EeV that suggests a correlation with the positions of active galactic nuclei (AGN) located within {approx}75 Mpc. However, this analysis does not take into account AGN morphology. A detailed study of the sample of AGN whose positions correlate with the CR events shows that most of them are classified as Seyfert 2 and low-ionization nuclear emission-line region (LINER) galaxies which do not differ from other local AGN of the same types. Therefore, the claimed correlation between the CR events observed by the Pierre Auger Observatory and local active galaxies should be considered as resulting from a chance coincidence, if the production of the highest energy CRs is not episodic in nature, but operates in a single object on long ({ge} Myr) timescales. Additionally, most of the selected sources do not show significant jet activity, and hence--in the framework of the jet paradigm--there are no reasons for expecting them to accelerate CRs up to the highest energies, {approx}10{sup 20} eV, at all. If the extragalactic magnetic fields and the sources of these CRs are coupled with matter, it is possible that the deflection angle is larger than expected in the case of a uniform source distribution due to effectively larger fields. A future analysis has to take into account AGN morphology and may yield a correlation with a larger deflection angle and/or more distant sources. We further argue that Cen A alone could be associated with at least 4 events due to its large radio extent, and Cen B can be associated with more than 1 event due to its proximity to the Galactic plane and, correspondingly, the stronger Galactic magnetic field the ultra high energy CRs (UHECRs) encounter during propagation. If the UHECRs associated with these events are indeed accelerated by Cen A and Cen B, their deflection angles may provide information on the structure of the magnetic field in the direction of these putative sources. Future -ray observations (by, e.g., Gamma-Ray Large Area Space Telescope [GLAST], High Energy Stereoscopic System [HESS]) may provide additional clues to the nature of the accelerators of the UHECRs in the local Universe.},
doi = {10.1086/588425},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = ,
volume = ,
place = {United States},
year = {2008},
month = {5}
}