Magnetic deflections of ultra-high energy cosmic rays from Centaurus A

The origin and mass composition of ultra-high energy cosmic rays (UHECRs) are among the mysteries of particle astrophysics. Since UHECRs are mostly or entirely charged particles, they will be deflected in cosmic magnetic fields on their way to Earth. UHECR deflections in the Galactic magnetic fields (GMF) should be considered to identify their origin and nature. The calculated Galactic magnetic deflections of UHECRs from a source strongly depend on the GMF model. I use the recent GMF model of Jansson and Farrar (JF12), a 35-parameter model which includes coherent, striated and random components and is constrained by WMAP7 Galactic synchrotron emission map and more than forty thousand extragalactic rotation measures. I develop a new method of implementing a random field using a Kolmogorov spectrum and scale it with the JF12 random component strengths. Simulated UHECRs are propagated through the GMF using the publicly available propagation code CRT. These particles are simulated from Centaurus A, which is the nearest AGN to Earth. I identify the expected arrival direction loci of UHECRs in the JF12 GMF model for different rigidities (energy divided by charge) between 2 and 100 EV (1 EV ≡ 1018 V) to determine whether Centaurus A could be a significant source of the UHECR excess reported by Pierre Auger Observatory. I calculate the excess of event arrival directions, with respect to isotropic expectations, for cases of pure protons, pure iron, and a mixture. I also develop a method for identifying the mass composition of UHECRs under specific source and GMF hypotheses. Comparing Auger observations with simulations of different rigidities leads to the identification of the charges of the events. Consistent simulated rigidities are found for each Auger event based on their overlap probabilities. The charge of each event is the measured energy divided by the rigidity of the most consistent simulation. Including a Kolmogorov random field component to the JF12 regular component does not significantly change the results of propagation at high rigidities whereas at low rigidities it smears the arrival distributions of events to such an extent that deflection studies can become difficult

Galactic magnetic deflections of UHECRs including realistic random fields

We present the results of a study that simulates trajectories of ultra-high energy cosmic rays from Centaurus A to Earth. The arrival directions are characterized to assess whether Cen A can be identified as a source of cosmic rays based on observing departures from isotropy. We analyze separately particles originating from the central engine as well as from the north and south radio lobes of the Cen A complex. Simulations are performed for particle rigidities from E/Z 2 = EV to 100 EV, thus covering the possibility of primary particles as heavy as Fe nuclei with energies exceeding 50 EeV. The Galactic magnetic field is modeled using the recent work of Jansson and Farrar (JF12) which fitted its parameters to match extragalactic Faraday rotation measures and WMAP7 synchrotron emission maps. We also discuss the effects of an additional turbulent magnetic field on the cosmic ray deflections

X-Ray Follow-Up of Extragalactic Transients

Most violent and energetic processes in our universe, including mergers of compact objects,explosions of massive stars and extreme accretion events, produce copious amounts of X-rays. X-ray follow-up is an efficient tool for identifying transients: (1) X-rays can quickly localize transients with large error circles; (2) X-rays reveal the nature of transients that may not have unique signatures at other wavelengths. Here, we identify key science questions about several extragalactic multi-messenger andmulti-wavelength transients, and demonstrate how X-ray follow-up helps answer these questions