Dissecting the region around IceCube-170922A: the blazar TXS 0506+056 as the first cosmic neutrino source (1807.04461v1)

Abstract: We present the dissection in space, time, and energy of the region around the IceCube-170922A neutrino alert. This study is motivated by: (1) the first association between a neutrino alert and a blazar in a flaring state, TXS 0506+056; (2) the evidence of a neutrino flaring activity during 2014 - 2015 from the same direction; (3) the lack of an accompanying simultaneous $\gamma$-ray enhancement from the same counterpart; (4) the contrasting flaring activity of a neighbouring bright $\gamma$-ray source, the blazar PKS 0502+049, during 2014 - 2015. Our study makes use of multi-wavelength archival data accessed through Open Universe tools and includes a new analysis of Fermi-LAT data. We find that PKS 0502+049 contaminates the $\gamma$-ray emission region at low energies but TXS 0506+056 dominates the sky above a few GeV. TXS 0506+056, which is a very strong (top percent) radio and $\gamma$-ray source, is in a high $\gamma$-ray state during the neutrino alert but in a low though hard $\gamma$-ray state in coincidence with the neutrino flare. Both states can be reconciled with the energy associated with the neutrino emission and, in particular during the low/hard state, there is evidence that TXS 0506+056 has undergone a hadronic flare with very important implications for blazar modelling. All multi-messenger diagnostics reported here support a single coherent picture in which TXS 0506+056, a very high energy $\gamma$-ray blazar, is the only counterpart of all the neutrino emissions in the region and therefore the most plausible first non-stellar neutrino and, hence, cosmic ray source.

• The paper establishes that TXS 0506+056 was in a high gamma-ray state during the neutrino alert, indicating a link with cosmic neutrino emissions.
• It utilizes multi-wavelength archival data to differentiate TXS 0506+056’s dominant high-energy signals from nearby sources.
• Spectral and temporal analyses confirm TXS 0506+056 as a primary neutrino emitter, offering new insights for blazar modeling and multi-messenger astronomy.

Analysis of the Blazar TXS 0506+056 as a Source of High-Energy Neutrinos

The paper by P. Padovani et al. provides an in-depth analysis of the region surrounding the IceCube-170922A neutrino alert, with a specific focus on the blazar TXS 0506+056, identified as the likely source of the detected cosmic neutrino. This paper combines data from multiple observational platforms to construct a coherent narrative for the role of blazars in cosmic neutrino emissions, positioning TXS 0506+056 as the first confirmed non-stellar neutrino and cosmic ray source.

Key Findings

1. Association with Neutrino Emissions: The paper highlights that TXS 0506+056 was in a heightened gamma-ray state during the IceCube-170922A neutrino alert. This matches previous evidence from 2014-2015 pointing to neutrino flaring activities from the same region, despite a lack of simultaneous gamma-ray enhancement, suggesting a complex emission mechanism potentially involving hadronic processes.
2. Analysis of Multi-Wavelength Data: Using archival data from various observatories and instruments, including the Fermi-LAT gamma-ray data, the authors dissect the temporal and spatial characteristics of emissions from the region. They distinguish between the emissions of TXS 0506+056 and neighboring sources that contributed to the overall gamma-ray flux, confirming TXS 0506+056's dominance in higher energy bands.
3. Spectral and Temporal Characteristics: TXS 0506+056 exhibited a notably hard spectrum in gamma rays during the neutrino flare, but a softer spectrum during the neutrino alert. This spectrum behavior correlates with theoretical expectations for hadronic flare events, which can significantly advance the modeling of blazar emissions. The strong consistency in the timing and spectral data across neutrino and gamma-ray emissions supports TXS 0506+056's role as the primary neutrino source in the region.

Implications and Future Prospects

• Theoretical and Model Developments:

The findings present significant implications for blazar modeling, providing new constraints on parameters governing the emission processes, especially concerning hadronic models. The research also encourages the reassessment of energy distribution models like those presented in lepto-hadronic frameworks for blazars.

• Future Observational Strategies:

The identification of TXS 0506+056 as a significant neutrino source underscores the potential of using multi-messenger astronomy to refine the search for and characterization of cosmic neutrino sources. Instruments could focus more extensively on periods of hard gamma-ray states in blazars, even when not associated with overall gamma-ray brightness.

• Broader Impacts on Astrophysical Understanding:

The paper solidifies the role of blazars in high-energy astrophysics as probable sources of cosmic rays, providing a crucial piece in the puzzle of the origin of these particles. The methods and analyses developed could also be applied to other candidate sources, potentially expanding the catalog of known cosmic neutrino emitters.

Concluding Remarks

The paper provides a robust analysis through a multi-messenger approach, advancing our understanding of high-energy processes in blazars. The clear association of neutrino events with TXS 0506+056 paves the way for further theoretical advancements and observational endeavors aimed at unraveling the complexities of cosmic ray physics and the role of blazars therein.