Dr Patrick Reichherzer

Abstract:

Ultraluminous infrared galaxies (ULIRGs) have infrared luminosities LIR ≥ 1012L⊙, making them the most luminous objects in the infrared sky. These dusty objects are generally powered by starbursts with star formation rates that exceed 100 M⊙ yr−1, possibly combined with a contribution from an active galactic nucleus. Such environments make ULIRGs plausible sources of astrophysical high-energy neutrinos, which can be observed by the IceCube Neutrino Observatory at the South Pole. We present a stacking search for high-energy neutrinos from a representative sample of 75 ULIRGs with redshift z ≤ 0.13 using 7.5 yr of IceCube data. The results are consistent with a background-only observation, yielding upper limits on the neutrino flux from these 75 ULIRGs. For an unbroken E−2.5 power-law spectrum, we report an upper limit on the stacked flux ${{\rm{\Phi }}}_{{\nu }_{\mu }+{\bar{\nu }}_{\mu }}^{90 \% }=3.24\times {10}^{-14}\,{\mathrm{TeV}}^{-1}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}\,{(E/10\,\mathrm{TeV})}^{-2.5}$ at 90% confidence level. In addition, we constrain the contribution of the ULIRG source population to the observed diffuse astrophysical neutrino flux as well as model predictions.

Abstract:

We present an all-sky 90% confidence level upper limit on the cosmic flux of relativistic magnetic monopoles using 2886 days of IceCube data. The analysis was optimized for monopole speeds between 0.750 c and 0.995 c , without any explicit restriction on the monopole mass. We constrain the flux of relativistic cosmic magnetic monopoles to a level below 2.0 × 10 − 19     cm − 2   s − 1   sr − 1 over the majority of the targeted speed range. This result constitutes the most strict upper limit to date for magnetic monopoles with β ≳ 0.8 and up to β ∼ 0.995 and fills the gap between existing limits on the cosmic flux of nonrelativistic and ultrarelativistic magnetic monopoles.