[en] Here we reanalyze the archival Chandra data for the central parts of the Centaurus A radio galaxy, aiming for a systematic investigation of the X-ray emission associated with the inner radio lobes in the system, and their immediate surroundings. In particular, we focus on four distinct features characterized by the soft excess with respect to the adjacent fields. Those include the two regions located at kiloparsec distances from the nucleus to the west and east, the extended bow-shock structure to the south, and a fragment of a thin arc north of the center. The selected north, west, and south features coincide with the edges of the radio lobes, while the east structure is seemingly displaced from the radio-emitting plasma. Our X-ray spectral analysis reveals (i) a power-law emission component with photon index Γ ∼ 2 in the north, east, and south regions, and (ii) a dense (number density ∼0.3 cm⁻³) and relatively cold (temperature ∼ 0.2 keV) gas in the east and west regions. The power-law emission is consistent with the synchrotron continuum generated at the edges of the radio structure, and implies that the efficiency of the electron acceleration at the terminal bow shock does not vary dramatically over the inner lobes’ extension. The presence of gaseous condensations, on the other hand, could possibly be understood in terms of a massive outflow from the central regions of the galaxy.

[en] In this work, we study the distribution of temporal power-law decay indices, α, in the gamma-ray burst (GRB) afterglow phase, fitted for 176 GRBs (139 long GRBs, 12 short GRBs with extended emission, and 25 X-ray flashes) with known redshifts. These indices are compared with the temporal decay index, α _W, derived with the light-curve fitting using the Willingale et al. model. This model fitting yields similar distributions of α _W to the fitted α, but for individual bursts a difference can be significant. Analysis of (α, L _a) distribution, where L _a is the characteristic luminosity at the end of the plateau, reveals only a weak correlation of these quantities. However, we discovered a significant regular trend when studying GRB α values along the Dainotti et al. correlation between L _a and the end time of the plateau emission in the rest frame, $T_a^{\ast <!--\; ???\; -->}$, hereafter LT correlation. We note a systematic variation of the α parameter distribution with luminosity for any selected $T_a^{\ast <!--\; ???\; -->}$. We analyze this systematics with respect to the fitted LT correlation line, expecting that the presented trend may allow us to constrain the GRB physical models. We also attempted to use the derived correlation of $\mathrm{\alpha <!--\; ??\; -->}(T_a)$ versus $L_a(T_a)$ to diminish the luminosity scatter related to the variations of α along the LT distribution, a step forward in the effort of standardizing GRBs. A proposed toy model accounting for this systematics applied to the analyzed GRB distribution results in a slight increase of the LT correlation coefficient.

[en] We present a detailed analysis of the best-quality multiwavelength data gathered for the large-scale jet in the core-dominated quasar 3C 273. We analyze all the archival observations of the target with the Chandra X-ray Observatory, the far-ultraviolet observations with the Hubble Space Telescope, and the 8.4 GHz map obtained with the Very Large Array. In our study, we focus on investigating the morphology of the outflow at different frequencies, and therefore we apply various techniques for the image deconvolution, paying particular attention to a precise modeling of the Chandra and Hubble point-spread functions. We find that the prominent brightness enhancements in the X-ray and far-ultraviolet jet of 3C 273—the “knots”—are not point-like, and can be resolved transversely as extended features with sizes of about $\simeq <!--\; ???\; -->0.5\mathrm{k}\mathrm{p}\mathrm{c}$. Also, the radio outflow is wider than the deconvolved X-ray/ultraviolet jet. We have also found circumstantial evidence that the intensity peaks of the X-ray knots are located systematically upstream of the corresponding radio intensity peaks, with the projected spatial offsets along the jet ranging from $\lesssim <!--\; ???\; -->0.2\mathrm{k}\mathrm{p}\mathrm{c}$ up to $\simeq <!--\; ???\; -->1\mathrm{k}\mathrm{p}\mathrm{c}$. We discuss our findings in the wider context of multi-component models for the emission and structure of large-scale quasar jets, and speculate on the physical processes enabling an efficient acceleration of the emitting ultrarelativistic electrons along the entire jet length that exceeds 100 kpc.

[en] We present the results of our power spectral analysis for the BL Lac object PKS 0735+178, utilizing the Fermi -LAT survey at high-energy γ -rays, several ground-based optical telescopes, and single-dish radio telescopes operating at GHz frequencies. The novelty of our approach is that, by combining long-term and densely sampled intra-night light curves in the optical regime, we were able to construct for the first time the optical power spectrum of the blazar for a time domain extending from 23 years down to minutes. Our analysis reveals that: (1) the optical variability is consistent with a pure red noise, for which the power spectral density can be well approximated by a single power law throughout the entire time domain probed; (2) the slope of power spectral density at high-energy γ -rays (∼1) is significantly flatter than that found at radio and optical frequencies (∼2) within the corresponding time variability range; (3) for the derived power spectra, we did not detect any low-frequency flattening, nor do we see any evidence for cutoffs at the highest frequencies down to the noise floor levels due to measurement uncertainties. We interpret our findings in terms of a model where the blazar variability is generated by the underlying single stochastic process (at radio and optical frequencies), or a linear superposition of such processes (in the γ -ray regime). Along with the detailed PSD analysis, we also present the results of our extended (1998–2015) intra-night optical monitoring program and newly acquired optical photo-polarimetric data for the source.