The Blazar TXS 0506+056 Associated with a High-energy Neutrino: Insights into Extragalactic Jets and Cosmic-Ray Acceleration

Abstract

A neutrino with energy ∼290 TeV, IceCube-170922A, was detected in coincidence with the BL Lac object TXS0506+056 during enhanced gamma-ray activity, with chance coincidence being rejected at ∼3σ level. We monitored the object in the very-high-energy (VHE) band with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes for ∼41 hr from 1.3 to 40.4 days after the neutrino detection. Day-timescale variability is clearly resolved. We interpret the quasi-simultaneous neutrino and broadband electromagnetic observations with a novel one-zone lepto-hadronic model, based on interactions of electrons and protons coaccelerated in the jet with external photons originating from a slow-moving plasma sheath surrounding the faster jet spine. We can reproduce the multiwavelength spectra of TXS 0506+056 with neutrino rate and energy compatible with IceCube-170922A, and with plausible values for the jet power of 10 4 10 erg s 45 46 1 -´-. The steep spectrum observed by MAGIC is concordant with internal γγ absorption above ∼100 GeV entailed by photohadronic production of a ∼290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton upscattering of external photons by accelerated electrons. The X-ray and VHE bands provide crucial constraints on the emission from both accelerated electrons and protons. We infer that the maximum energy of protons in the jet comoving frame can be in the range ∼10 14 -10 18 eV.

Patterns in the Multiwavelength Behavior of Candidate Neutrino Blazars

“…Britzen et al (2019) use radio data to suggest a possible collision of two jets in TXS 0506+056. However, Ros et al (2019) exclude the presence of a secondary jet core with higher resolution radio data, but find signs of a spine-sheath structure of the jet, which could be relevant for neutrino production see also (see also Ghisellini et al 2005;Tavecchio et al 2014;Ansoldi et al 2018).…”

“…Software: Fermi-LAT Science Tools (v11r04p00), fermipy (v0.17.4; Wood et al 2018), astropy (Astropy Collaboration et al 2013, 2018, IRAF (Tody 1986(Tody , 1993, ISIS (Alard & Lupton 1998;Alard 2000), XSPEC (Arnaud 1996) The green region in panel 1 marks the quiescent state and vertical red, cyan and black lines mark three flaring states, which are accompanied by X-ray and optical flares, selected for a dedicated gamma-ray spectral analysis (see Tab. 5 and Fig.…”

“…Furthermore, those hidden source scenarios (Murase et al 2016) are inconsistent with the association of IC-170922A with a strong gamma-ray flare from TXS 0506+056 (e.g. Gao et al 2019;Ansoldi et al 2018;Cerruti et al 2019). There are however attempts to explain both observations in one single model by and Liu et al (2019), which come at the cost of assuming more complex geometries.…”

The redshift and the host galaxy of the neutrino candidate 4FGL J0955.1+3551 (3HSP J095507.9+355101)

“…The modeling of the sources requires the knowledge of their distance, which in the case of BLL, is hard to establish, because by definition of the class the spectral lines are absent or very weak (equivalent width, EW < 5Å). In the past several years some of us have been studying optical spectra of BLL with resolution and signalto-noise ratio (S/N) optimized to detect such weak features (Landoni et al 2014;Paiano et al 2017aPaiano et al ,b,c, 2019a Ansoldi et al 2018;Giommi et al 2020b, and references therein) with BLL, which are a blazar sub-class. These neutrinos permit to shed light on the most energetic processes, which, as mentioned above, are otherwise screened off by the EBL.…”

A self-consistent leptonic–hadronic interpretation of the electromagnetic and neutrino emissions from blazar TXS 0506+056

“…The high-energy component is often interpreted as the inverse Compton (IC) upscattering of ambient soft photons by the accelerated electrons (e.g., Böttcher 2007). The soft photons can be either synchrotron photons within the jet( the synchrotron self-Compton, SSC, process, Maraschi et al 1992;Bloom and Marscher 1996), or the photons external to the jet ( the External Compton, EC, process). These external photons may be the UV accretion disk photons (Dermer & Schlickeiser 1993), the accretion disk photons reprocessed by broad-line region clouds (Sikora et al 1994), or infrared photons from the dust torus (Blaźejowski et al 2000).…”