Jun 23 – 28, 2014
Europe/Zurich timezone

Constraints on Sources and Composition of UHECRs

Jun 26, 2014, 4:30 PM
Room 4 (Tuschinski Theatre)

Room 4

Tuschinski Theatre

Presentation Cosmic Rays Cosmic Rays


Glennys Farrar (NYU)


- A simple and well-motivated modification of QCD at ultrahigh energy naturally explains the observed Xmax distribution above 10^18 eV, with a purely protonic composition. This removes the need for a fine-tuned source composition and very hard injection spectrum as required if UHECRs have a mixed composition, and eliminates the need to postulate an additional population of extragalactic protons filling in the spectrum below the ankle. (Time permitting, new stronger limits on a light Galactic component in the 10^17.5-18 eV range will be presented.) - It is shown that if UHECRs are protons, their sources must be transient. - Tidal Disruption Jets are shown to satisfy the three essential requirements for being the source of all UHECRs. Multi-wavelength observations and modeling of Swift J1644, a TDE jet observed in blazar mode, show that the product of field strength and characteristic size of the jet satisfies BR >~ 3 10^17 G-cm, the Hillas criterion for accelerating protons to 10^20 eV. The total UHECR energy injection rate from TDE jets and the number of contributing sources within the GZK volume, can be estimated from the recently-measured TDE rate; both are ample to explain UHECR requirements. Thus TDE jets are a strong candidate for being the sources of all or most UHECRs.

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