TIME-INTEGRATED SEARCHES FOR POINT-LIKE SOURCES OF NEUTRINOS WITH THE 40-STRING IceCube DETECTOR

Abstract

We present the results of time-integrated searches for astrophysical neutrino sources in both the northern and southern skies. Data were collected using the partially completed IceCube detector in the 40-string configuration recorded between 2008 April 5 and 2009 May 20, totaling 375.5 days livetime. An unbinned maximum likelihood ratio method is used to search for astrophysical signals. The data sample contains 36,900 events: 14,121 from the northern sky, mostly muons induced by atmospheric neutrinos, and 22,779 from the southern sky, mostly high-energy atmospheric muons. The analysis includes searches for individual point sources and stacked searches for sources in a common class, sometimes including a spatial extent. While this analysis is sensitive to TeV-PeV energy neutrinos in the northern sky, it is primarily sensitive to neutrinos with energy greater than about 1 PeV in the southern sky. No evidence for a signal is found in any of the searches. Limits are set for neutrino fluxes from astrophysical sources over the entire sky and compared to predictions. The sensitivity is at least a factor of two better than previous searches (depending on declination), with 90% confidence level muon neutrino flux upper limits being between E 2 dΦ/dE ∼ 2-200 × 10 −12 TeV cm −2 s −1 in the northern sky and between 3-700 × 10 −12 TeV cm −2 s −1 in the southern sky. The stacked source searches provide the best limits to specific source classes. The full IceCube detector is expected to improve the sensitivity to dΦ/dE ∝ E −2 sources by another factor of two in the first year of operation.

Neutrino searches with the IceCube telescope

“…Both the north and the south hot spots have post-trial probabilities compatible with background fluctuations. The muon neutrino upper limits presented here are a factor ∼ 3.5 better than the latest published upper limits by IceCube [1] and are the most competitive neutrino limits to date over the majority of the sky.…”

“…The details of this event selection can be found in Ref. [1]. A multi-variate classification algorithm was used for the event selections in IC-59 and IC-79.…”

Search for a diffuse flux of astrophysical muon neutrinos with the IceCube 59-string configuration

“…To date, no cosmic high-energy neutrino sources have been found [4]. This motivates the complementary approach of a search for a diffuse flux of astrophysical neutrinos [5].…”

IceCube and ANTARES

“…Each point is the individual limit for a chosen candidate source. Already existing limits from Superkamiokande [31] and Amanda-II [32]) are compared to the most recent results from ANTARES [33] and IceCube (IC40 [34] and IC40+IC59 [27]). The shown limits are all for the muon channel, which has a better sensitivity in the point source search with respect to cascade events due to the superior angular resolution of muon events.…”