A multi-wavelength view of the multi-messenger sources NGC 1068 and PKS 1502+1061

TL;DR

We address the uncertain origin of high-energy neutrinos from active galactic nuclei by performing a coordinated, multi-messenger study of two targets, NGC 1068 and PKS 1502+106, using X-ray observations from NICER and NuSTAR, archival Chandra data, gamma-ray data from Fermi-LAT, and IceCube ten-year neutrino measurements. The analysis tests leptohadronic and coronal/hidden-core models by fitting photon data and comparing predicted neutrino fluxes to IceCube constraints with SkyLLH across multiple spectral shapes. For PKS 1502+106, the hard-flare neutrino model is ruled out, while quiescent/soft-flare scenarios remain viable; for NGC 1068, LP-like spectra associated with coronal regions are broadly consistent with IceCube data, though some parameter choices require softer spectra or lower-energy constraints. Overall, the work demonstrates the power of integrating multi-wavelength photon data with neutrino observations to constrain AGN emission mechanisms and guide future MeV gamma-ray and low-energy neutrino studies.

Abstract

Multi-messenger astronomy offers a powerful approach to studying high-energy radiative processes in astrophysical sources. A notable example was seen in 2017, when the IceCube Neutrino Observatory detected a high-energy neutrino event that was found to coincide with a gamma-ray flare from a blazar. Since then, numerous multi-messenger studies combining neutrino and photon data have been conducted, yet the origin of neutrinos from active galactic nuclei (AGN) remains uncertain. In this work, we present the results of an X-ray observing program targeting two AGNs, NGC 1068 and PKS 1502+106. The multi-wavelength dataset includes new observations from NICER and NuSTAR from the observing proposal along with gamma-ray data collected using Fermi-LAT, and one archival observation from Chandra. Additionally, we derive the neutrino fluxes for both AGNs using ten years of IceCube data and neutrino spectra predicted by theoretical models. These results demonstrate the value of combining multi-messenger data in building and constraining theoretical models. They also highlight the importance of testing model predictions against observational data to refine measurements of both the neutrino flux and spectral shape.

Figures (7)

• Figure 1: Joint-fits for the NICER + NuSTAR observations of PKS 1502+106 made on MJD:60005 (top plot) and MJD:60170 (bottom plot).
• Figure 2: Joint-fit for the NICER + Chandra observation of NGC 1068 is shown here. The NICER observation is made on MJD:60314 and the Chandra observation was conducted on MJD:60313.
• Figure 3: Light Curve for PKS 1502+106 derived using the data collected by NICER (top panel), NuSTAR (middle panel) and Fermi-LAT (bottom panel) is shown here.
• Figure 4: Light Curve for NGC 1068 derived using the data collected by NICER (top panel) and Fermi-LAT (bottom panel) is shown here. The X-ray observations are taken between March 2023 (MJD:60004) to February 2024 (MJD:60341) while the Fermi-LAT light curve is derived using 4 week time bin periods from March 2022 (MJD:59639) to March 2025 (MJD:60735).
• Figure 5: The multi-wavelength observations of PKS 1502+106 are shown (Top: MJD:60005 and Bottom:MJD:60170, with the neutrino limits derived using SkyLLH and the theoretical models of Rodrigues_2021. No fitting is done in this case and the models are shown only for comparison. The photon data includes NICER + NuSTAR + 1-week Fermi-LAT observations.