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1. Historically inconsistent productivity and respiration fluxes in the global terrestrial carbon cycle

   https://doi.org/10.1038/s41467-022-29391-5  

   Jian, Jinshi ; Bailey, Vanessa ; Dorheim, Kalyn ; Konings, Alexandra G. ; Hao, Dalei ; Shiklomanov, Alexey N. ; Snyder, Abigail ; Steele, Meredith ; Teramoto, Munemasa ; Vargas, Rodrigo ; et al ( December 2022 , Nature Communications)

   Abstract The terrestrial carbon cycle is a major source of uncertainty in climate projections. Its dominant fluxes, gross primary productivity (GPP), and respiration (in particular soil respiration, R S ), are typically estimated from independent satellite-driven models and upscaled in situ measurements, respectively. We combine carbon-cycle flux estimates and partitioning coefficients to show that historical estimates of global GPP and R S are irreconcilable. When we estimate GPP based on R S measurements and some assumptions about R S :GPP ratios, we found the resulted global GPP values (bootstrap mean $${149}_{-23}^{+29}$$ 149 − 23 + 29 Pg C yr −1 ) are significantly higher than most GPP estimates reported in the literature ( $${113}_{-18}^{+18}$$ 113 − 18 + 18 Pg C yr −1 ). Similarly, historical GPP estimates imply a soil respiration flux (Rs GPP , bootstrap mean of $${68}_{-8}^{+10}$$ 68 − 8 + 10 Pg C yr −1 ) statistically inconsistent with most published R S values ( $${87}_{-8}^{+9}$$ 87 − 8 + 9 Pg C yr −1 ), although recent, higher, GPP estimates are narrowing this gap. Furthermore, global R S :GPP ratios are inconsistent with spatial averages of this ratio calculated from individual sites as well as CMIP6 model results. This discrepancy has implications for our understanding of carbon turnover times and the terrestrial sensitivity to climate change. Future efforts should reconcile the discrepancies associated with calculations for GPP and Rs to improve estimates of the global carbon budget. 

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2. The variability patterns of the TeV blazar PG 1553 + 113 from a decade of MAGIC and multiband observations

   https://doi.org/10.1093/mnras/stae649  

   MAGIC_Collaboration ; Abe, H. ; Abe, S. ; Abhir, J. ; Acciari, V_A ; Agudo, I. ; Aniello, T. ; Ansoldi, S. ; Antonelli, L_A ; Arbet Engels, A. ; et al ( March 2024 , Monthly Notices of the Royal Astronomical Society)

   PG 1553 + 113 is one of the few blazars with a convincing quasi-periodic emission in the gamma-ray band. The source is also a very high energy (VHE; >100 GeV) gamma-ray emitter. To better understand its properties and identify the underlying physical processes driving its variability, the MAGIC Collaboration initiated a multiyear, multiwavelength monitoring campaign in 2015 involving the OVRO 40-m and Medicina radio telescopes, REM, KVA, and the MAGIC telescopes, Swift and Fermi satellites, and the WEBT network. The analysis presented in this paper uses data until 2017 and focuses on the characterization of the variability. The gamma-ray data show a (hint of a) periodic signal compatible with literature, but the X-ray and VHE gamma-ray data do not show statistical evidence for a periodic signal. In other bands, the data are compatible with the gamma-ray period, but with a relatively high p-value. The complex connection between the low- and high-energy emission and the non-monochromatic modulation and changes in flux suggests that a simple one-zone model is unable to explain all the variability. Instead, a model including a periodic component along with multiple emission zones is required.

    

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3. Multiwavelength analysis of Fermi -LAT blazars with high-significance periodicity: detection of a long-term rising emission in PG 1553+113

   https://doi.org/10.1093/mnras/stad3246  

   Peñil, P. ; Westernacher-Schneider, J. R. ; Ajello, M. ; Domínguez, A. ; Buson, S. ; Otero-Santos, J. ; Marcotulli, L. ; Torres−Albà, N. ; Zrake, J. ( November 2023 , Monthly Notices of the Royal Astronomical Society)

   Blazars display variable emission across the entire electromagnetic spectrum, with time-scales that can range from a few minutes to several years. Our recent work has shown that a sample of five blazars exhibit hints of periodicity with a global significance ${\gtrsim}2\, \sigma$ at γ-ray energies, in the range of 0.1 GeV < E < 800 GeV. In this work, we study their multiwavelength emission, covering the X-ray, ultraviolet, optical, and radio bands. We show that three of these blazars present similar periodic patterns in the optical and radio bands. Additionally, fluxes in the different bands of the five blazars are correlated, suggesting a co-spatial origin. Moreover, we detect a long-term (≈10 yr) rising trend in the light curves of PG 1553+113, and we use it to infer possible constraints on the binary black hole hypothesis.

    

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4. The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energetics

   https://doi.org/10.1093/mnras/stad942  

   Raiteri, C. M. ; Villata, M. ; Jorstad, S. G. ; Marscher, A. P. ; Acosta Pulido, J. A. ; Carosati, D. ; Chen, W. P. ; Joner, M. D. ; Kurtanidze, S. O. ; Lorey, C. ; et al ( March 2023 , Monthly Notices of the Royal Astronomical Society)

   In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid-2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarization degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time-scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time-scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time-scales are shortened by relativistic effects.

    

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5. The radio spectral turnover of radio-loud quasars at z > 5

   https://doi.org/10.1051/0004-6361/202142489  

   Shao, Yali ; Wagg, Jeff ; Wang, Ran ; Momjian, Emmanuel ; Carilli, Chris L. ; Walter, Fabian ; Riechers, Dominik A. ; Intema, Huib T. ; Weiss, Axel ; Brunthaler, Andreas ; et al ( March 2022 , Astronomy & Astrophysics)

   We present Karl G. Jansky Very Large Array S - (2–4 GHz), C - (4–8 GHz), and X -band (8–12 GHz) continuum observations toward seven radio-loud quasars at z  > 5. This sample has previously been found to exhibit spectral peaks at observed-frame frequencies above ∼1 GHz. We also present upgraded Giant Metrewave Radio Telescope (uGMRT) band-2 (200 MHz), band-3 (400 MHz), and band-4 (650 MHz) radio continuum observations toward eight radio-loud quasars at z  > 5, selected from our previous GMRT survey, in order to sample their low-frequency synchrotron emission. Combined with archival radio continuum observations, all ten targets show evidence for spectral turnover. The turnover frequencies are ∼1–50 GHz in the rest frame, making these targets gigahertz-peaked-spectrum or high-frequency-peaker candidates. For the nine well-constrained targets with observations on both sides of the spectral turnover, we fit the entire radio spectrum with absorption models associated with synchrotron self-absorption and free-free absorption (FFA). Our results show that FFA in an external inhomogeneous medium can accurately describe the observed spectra for all nine targets, which may indicate an FFA origin for the radio spectral turnover in our sample. As for the complex spectrum of J114657.79+403708.6 at z  = 5.00 with two spectral peaks, it may be caused by multiple components (i.e., core-jet) and FFA by the high-density medium in the nuclear region. However, we cannot rule out the spectral turnover origin of variability. Based on our radio spectral modeling, we calculate the radio loudness R 2500 Å for our sample, which ranges from 12 −1 +1 to 674 −51 +61 . 

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