We report the Imaging X-ray Polarimetry Explorer (IXPE) polarimetric andsimultaneous multiwavelength observations of the high-energy-peaked BL Lacertae(HBL) object 1ES 1959+650, performed in 2022 October and 2023 August. In 2022October IXPE measured an average polarization degree $\Pi_{\rm X}=9.4\;\!\%\pm1.6\;\!\%$ and an electric-vector position angle $\psi_{\rm X}=53^{\circ}\pm5^{\circ}$. The polarized X-ray emission can be decomposed into a constantcomponent, plus a rotating component, with rotation velocity $\omega_{\rmEVPA}=(-117\;\!\pm\;\!12)$ ${\rm deg}\;\!{\rm d}^{-1}$. In 2023 August, duringa period of pronounced activity of the source, IXPE measured an average$\Pi_{\rm X}=12.4\;\!\%\pm0.7\;\!\%$ and $\psi_X=20^{\circ}\pm2^{\circ}$, withevidence ($\sim$0.4$\;\!\%$ chance probability) for a rapidly rotatingcomponent with $\omega_{\rm EVPA}=(1864\;\!\pm\;\!34)$ ${\rm deg}\;\!{\rmd}^{-1}$. These findings suggest the presence of a helical magnetic field inthe jet of 1ES 1959+650 or stochastic processes governing the field inturbulent plasma. Our multiwavelength campaigns from radio to X-ray revealvariability in both polarization and flux from optical to X-rays. We interpretthe results in terms of a relatively slowly varying component dominating theradio and optical emission, while rapidly variable polarized componentsdominate the X-ray and provide minor contribution at optical wavelengths. Theradio and optical data indicate that on parsec scales the magnetic field isprimarily orthogonal to the jet direction. On the contrary, X-ray measurementsshow a magnetic field almost aligned with the parsec jet direction. Confrontingwith other IXPE observations, we guess that the magnetic field of HBLs onsub-pc scale should be rather unstable, often changing its direction withrespect to the VLBA jet.
Blazars, supermassive black hole systems (SMBHs) with highly relativisticjets aligned with the line of sight, are the most powerful long-lived emittersof electromagnetic emission in the Universe. We report here on a radio togamma-ray multiwavelength campaign on the blazar BL Lacertae with unprecedentedpolarimetric coverage from radio to X-ray wavelengths. The observations caughtan extraordinary event on 2023 November 10-18, when the degree of linearpolarization of optical synchrotron radiation reached a record value of 47.5%.In stark contrast, the Imaging X-ray Polarimetry Explorer (IXPE) found that theX-ray (Compton scattering or hadron-induced) emission was polarized at lessthan 7.4% (3sigma confidence level). We argue here that this observationalresult rules out a hadronic origin of the high energy emission, and stronglyfavors a leptonic (Compton scattering) origin, thereby breaking the degeneracybetween hadronic and leptonic emission models for BL Lacertae and demonstratingthe power of multiwavelength polarimetry to address this question. Furthermore,the multiwavelength flux and polarization variability, featuring an extremelyprominent rise and decay of the optical polarization degree, is interpreted forthe first time by the relaxation of a magnetic "spring" embedded in the newlyinjected plasma. This suggests that the plasma jet can maintain a predominanttoroidal magnetic field component parsecs away from the central engine.
Boreal forests represent one of the most important carbon (C) sinks globally. Current climate change could have unpredictable effects on the processes that regulate the dynamics of C allocation in boreal forests and, consequently, on the terrestrial C balance. In these extremely nutrient-poor ecosystems, symbioses between plant roots and ectomycorrhizal fungi play a crucial role in enhancing nutrient uptake by plants. It was therefore hypothesised that, in a mature Pinus sylvestris boreal forest, there is a phenological and environmental control on C and N exchange. For this reason, at the Hyytiälä Forest Research Station (SMEAR II), equipped with an Eddy-covariance tower for measuring net fluxes of C between the atmosphere and the ecosystem, the seasonal dynamics of C and N allocation along the soil-ectomycorrhiza-host-plant continuum were studied, and the possibility of using the natural abundances of the stable isotopes of C (δ¹³C) and N (δ¹⁵N) as tracers to investigate these processes was evaluated. On the basis of NEE (Net Ecosystem Exchange) and GPP (Gross Primary Productivity) data, three sampling dates from June to October were selected and chemical-isotopic analyses were performed on soil, rhizosphere, mycorrhizal root tips (ECM), roots and leaves. The collected data show a synchronised C allocation towards ECM and xylogenesis, driven by the strong increase of NEE during the spring-summer period. Furthermore, seasonal variations in C and N concentrations along the soil-ECM-plant continuum suggest a close interaction between the cycles of these nutrients. These results agree with the model that, under nutrient-limited conditions, an increased allocation of C to symbiotic fungi would favour an immobilisation of N by the fungi to support their development and metabolism. Conversely, a decrease in C supply to the mycorrhizal fungi would lead to an increase in the amount of N released to the host plant. This hypothesis is supported by δ¹³C and δ¹⁵N analyses that show an isotopic fractionation associated with the exchange of C and N between symbiont fungus and host plant. The results obtained may therefore have significant implications for understanding nutrient exchange within a boreal forest.