Probing Neutrino Emission from X-ray Blazar Flares observed with Swift-XRT
Résumé
Blazars are the most extreme subclass of active galactic nuclei with relativistic jets emerging from
a supermassive black hole and forming a small angle with respect to our line of sight. Blazars
are also known to be related to flaring activity as they exhibit large flux variations over a wide
range of frequency and on multiple timescales, ranging from a few minutes to several months. The
detection of a high-energy neutrino from the flaring blazar TXS 0506+056 and the subsequent
discovery of a neutrino excess from the same direction have naturally strengthened the hypothesis
that blazars are cosmic neutrino sources. While neutrino production during gamma-ray flares has
been widely discussed, the neutrino yield of X-ray flares has received less attention. Motivated by
a theoretical scenario where high energy neutrinos are produced by energetic protons interacting
with their own x-ray synchrotron radiation, we make neutrino predictions over a sample of X-ray blazars. This sample consists of all blazars observed with the X-ray Telescope
(XRT) on board Swift more than 50 times from November 2004 to November 2020. The statistical
identification of a flaring state is done using the Bayesian Block algorithm to the 1 keV XRT light
curves of frequently observed blazars. We categorize flaring states into classes based on their
variation from the time-average value of the data points. During each flaring state, we compute the
expected muon plus anti-muon neutrino events as well as the total signal for each source using the
point-source effective area of Icecube for different operational seasons. We find that the median
of the total neutrino number (in logarithm) from flares with duration < 30 d is 0.02 events