Very-high-energy observations of the Seyfert galaxy NGC 4151 with MAGIC -- Indication of another gamma-ray obscured candidate neutrino source

TL;DR

This study presents the first VHE gamma-ray observations of NGC 4151 with MAGIC, finding no gamma-ray excess and providing upper limits that suggest the source may be gamma-ray obscured, impacting neutrino production models.

Contribution

First VHE gamma-ray observational constraints on NGC 4151, informing models of neutrino production and gamma-ray obscuration in Seyfert galaxies.

Findings

No gamma-ray excess detected from NGC 4151.

Established upper limits on VHE gamma-ray flux.

Results imply gamma-ray obscuration affecting neutrino emission.

Abstract

Seyfert galaxies are emerging as a promising source class of high-energy neutrinos. The Seyfert galaxies NGC 4151 and NGC 1068 have come up respectively as the most promising counterparts of a 3$\sigma$ and of a 4.2$\sigma$ neutrino excesses detected by IceCube in the TeV energy range. Constraining the very-high-energy (VHE) emission associated with the neutrino signal is crucial to unveil the mechanism and site of neutrino production. In this work, we present the first results of the VHE observations ($\sim$29 hours) of NGC 4151 with the MAGIC telescopes. We detect no gamma-ray excess in the direction of NGC 4151, and we derive constraining upper limits on the VHE gamma-ray flux. The integral flux upper limit (at the 95% confidence level) above 200 GeV is $f = 2.3 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$. The comparison of the MAGIC and IceCube measurements suggests the presence of a gamma-ray obscured accelerator, and it allows us to constrain the gamma-ray optical depth and the size of the neutrino production site.