X-Ray Spectra of Intermediate-Luminosity, Radio-Loud Quasars

We present new hard X-ray spectra of three radio-loud AGNs of moderately high X-ray luminosity (L_x ~ 10^45 erg/s; PKS 2349-01, 3C 323.1, and 4C 74.26) obtained with ASCA and BeppoSAX. The X-ray continua are described in all three cases with a power law model with photon indices of Gamma~1.85, modified at low energies by absorption in excess of the Galactic, which appears to be due to neutral gas. At higher energies, an Fe Ka emission line is detected in PKS 2349-01 and 4C 74.26, and is tentatively detected in 3C 323.1. The equivalent widths of the lines are consistent, albeit within large uncertainties, with the values for radio-quiet AGN of comparable X-ray luminosity. The Fe Ka line is unresolved in 4C 74.26. In the case of PKS 2349-01, however, the inferred properties of the line depend on the model adopted for the continuum: if a simple power-law model is used, the line is resolved at more than 99% confidence with a full width at half maximum corresponding to approximately 50,000 km/s and a rest-frame equivalent width of 230 +/- 120 eV, but if a Compton "reflection" model is used the line is found to be a factor of 2 weaker, for an assumed full width at half maximum of 50,000 km/s. In 4C 74.26, a strong Compton "reflection" component is detected. Its strength suggests that the scattering medium subtends a solid angle of 2pi to the illuminating source. Overall, the spectral indices of these radio-loud quasars are remarkably similar to those of their radio-quiet counterparts. On the other hand, if the absorber is indeed neutral, as our results suggest, this would be consistent with the typical properties of radio-loud AGNs.Comment: To appear in ApJ, v.575, Aug 10, 2002. 14 pages, including 3 tables and 6 figures. Uses emulateapj5.st

Exploring the disc/jet interaction in the radio-loud quasar 4C +74.26 with Suzaku

We report on a 90 ks Suzaku observation of the radio-loud quasar 4C +74.26. The source was observed in its highest flux state to date, and we find that it brightened by about 20 per cent during the observation. We see evidence of spectral hardening as the count rate increases and also find that the rms variability increases with energy up to about 4 keV. We clearly detect a broadened Fe line but conclude that it does not require any emission from inside about 50 r_g, although a much smaller inner radius cannot be ruled out. The large inner radius of our best fit implies that the inner disc is either missing or not strongly illuminated. We suggest that the latter scenario may occur if the power-law source is located high above the disc, or if the emission is beamed away from the disc.Comment: 11 pages, 9 figures. Accepted for publication in MNRA

Global impact of COVID-19 restrictions on the surface concentrations of nitrogen dioxide and ozone

Social distancing to combat the COVID-19 pandemic has led to widespread reductions in air pollutant emissions. Quantifying these changes requires a business-as-usual counterfactual that accounts for the synoptic and seasonal variability of air pollutants. We use a machine learning algorithm driven by information from the NASA GEOS-CF model to assess changes in nitrogen dioxide (NO2) and ozone (O3) at 5756 observation sites in 46 countries from January through June 2020. Reductions in NO2 coincide with the timing and intensity of COVID-19 restrictions, ranging from 60 % in severely affected cities (e.g., Wuhan, Milan) to little change (e.g., Rio de Janeiro, Taipei). On average, NO2 concentrations were 18 (13-23) % lower than business as usual from February 2020 onward. China experienced the earliest and steepest decline, but concentrations since April have mostly recovered and remained within 5 % of the business-as-usual estimate. NO2 reductions in Europe and the US have been more gradual, with a halting recovery starting in late March. We estimate that the global NOx (NO + NO2) emission reduction during the first 6 months of 2020 amounted to 3.1 (2.6-3.6) TgN, equivalent to 5.5 (4.7-6.4) % of the annual anthropogenic total. The response of surface O3 is complicated by competing influences of nonlinear atmospheric chemistry. While surface O3 increased by up to 50 % in some locations, we find the overall net impact on daily average O3 between February-June 2020 to be small. However, our analysis indicates a flattening of the O3 diurnal cycle with an increase in nighttime ozone due to reduced titration and a decrease in daytime ozone, reflecting a reduction in photochemical production. The O3 response is dependent on season, timescale, and environment, with declines in surface O3 forecasted if NOx emission reductions continue

Structural, electrochemical, and spectroscopic characterization of a redox pair of sulfite-based polyoxotungstates: α-[W₁₈O₅₄(SO₃)₂]^4- and α-[W₁₈O₅₄(SO₃)₂]^5-

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr<sub>4</sub>N)<sub>4</sub>{α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]}2CH<sub>3</sub>CN and the one-electron reduced form (Pr<sub>4</sub>N)<sub>5</sub>{α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]}·2CH<sub>3</sub>CN has been achieved. α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup> αwas obtained as a Pr<sub>4</sub>N<sup>+</sup> salt by reducing the "Trojan Horse" [W<sub>18</sub>O<sub>56</sub>(SO<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>8-</sup> cluster via a template orientation transformation. Acetonitrile solutions of pure α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup> also were prepared electrochemically by one-electron bulk reductive electrolysis of α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>4-</sup>. Cyclic voltammetry of α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>4-</sup> and α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup> in CH<sub>3</sub>CN (0.1 M Hx<sub>4</sub>NClO<sub>4</sub>) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten-oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH<sub>3</sub>CN exhibit the expected sign and magnitude of the steady-state limiting current values for the α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>4-/5-/6-</sup> series and confirm the existence of a stable one-electron reduced species, α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup>. Employment of the Randles-Sevcik (cyclic voltammetry) and Levich (rotating disk electrode) equations at a glassy carbon electrode (d = 3 mm) enable diffusion coefficient values of 3.7 and 3.8 × 10<sup>-6</sup> cm<sup>2</sup> s<sup>-1</sup> to be obtained for α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>4-</sup> and α-[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup>, respectively. The tungsten polyoxometalates are highly photoactive, since measurable photocurrents and color changes are detected for both species upon irradiation with white light. EPR spectra obtained from both acetonitrile solution and solid samples, down to temperatures as low as 2.3 K, of the chemically and electrochemically prepared one-electron reduced species provided evidence that the unpaired electron in -[W<sub>18</sub>O<sub>54</sub>(SO<sub>3</sub>)<sub>2</sub>]<sup>5-</sup> is delocalized over a number of atoms in the polyoxometalate structure, even at very low temperatures