We present results based on the systematic analysis of currently available Chandra archive data on the brightest galaxy in the Draco constellation, NGC 6338, in order to investigate the properties of the X‐ray cavities. In the central ∼6 kpc, at least two, possibly three, X‐ray cavities are evident. All these cavities are roughly of ellipsoidal shape and show a decrement in surface brightness of several tens of per cent. In addition to these cavities, a set of X‐ray bright filaments are also noticed which are spatially coincident with the Hα filaments over an extent of 15 kpc. The Hα emission‐line filaments are perpendicular to the X‐ray cavities. Spectroscopic analysis of the hot gas in the filaments and cavities reveals that the X‐ray filaments are cooler than the gas contained in the cavities. The emission‐line ratios and the extended, asymmetric nature of the Hα emission‐line filaments seen in this system require a harder ionizing source than that produced by star formation and/or young, massive stars. Radio emission maps derived from the analysis of 1.4‐GHz Very Large Array Faint Images of the Radio Sky at Twenty‐Centimeters survey data failed to show any association of these X‐ray cavities with radio jets; however, the cavities are filled by radio emission. The total power of the cavities is 17 × 1042 erg s−1 and the ratio of radio luminosity to cavity power is ∼10−4, implying that most of the jet power is mechanical.
The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V-band and NIR J, H and K s bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using crosscorrelation techniques, we found delayed responses of the J, H and K s light curves to the V-band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be 27.1 +13.5 −12.0 days (V vs. J), 30.4 +13.9 −12.0 days (V vs. H) and 34.6 +12.1 −9.6 days (V vs. K s). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the τ-M V plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN.
Recent simulations and observations have shown large scale filaments in the cosmic web connecting nodes, with accreting materials (baryonic and dark matter) flowing through them. Current high sensitivity observations also show that the propagation of shocks through filaments can heat them up, and make filaments visible between two or more galaxy clusters or around massive clusters, based on optical and/or X-ray observations. We are reporting here the special case of the cluster A3017 associated with a hot filament. The temperature of the filament is 3.4 −0.77 +1.30 keV and its length is ∼ 1 Mpc. We have analysed its archival Chandra data and report various properties. We also analysed GMRT 235/610 MHz radio data. Radio observations have revealed symmetric two-sided lobes which fill cavities in the A3017 cluster core region, associated with central AGN. In the radio map, we also noticed a peculiar linear vertical radio structure in the X-ray filament region which might be associated with a cosmic filament shock. This radio structure could be a radio phoenix or old plasma where an old relativistic population is re-accelerated by shock propagation. Finally we put an upper limit on the radio luminosity of the filament region.
We present results based on the systematic analysis of \textit{Chandra} archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991 with an objective to investigate properties of the X-ray cavities hosted by this system. The unsharp masked image as well as 2-d $\beta$ model subtracted residual image of Abell 1991 reveals a pair of X-ray cavities and a region of excess emission in the central $\sim$12 kpc region. Both the cavities are of ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray surface brightness compared to that in the undisturbed regions. Spectral analysis of X-ray photons extracted from the cavities lead to the temperature values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and $1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial temperature profile derived for Abell 1991 reveals a positive temperature gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec region of Abell 1991 reveals relatively cooler three different knot like features that are about 10\arcsec off the X-ray peak of the cluster. Total power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum, while the X-ray luminosity within the cooling radius is found to be 6.04 $\times 10^{43}$ \lum, comparison of which imply that the mechanical energy released by the central AGN outburst is sufficient to balance the radiative loss.Comment: 29 pages, 12 figures and 3 tables, accepted for publication in Astrophysics and Space Scienc
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