Universality of coronal properties in accreting black holes across mass and accretion rate

Through their radio loudness, lack of thermal UV emission from the accretion disk and power-law dominated spectra, Low Luminosity AGN (LLAGN) display similarity with the hard state of stellar-mass black hole X-Ray Binaries (BHBs). In this work we perform a systematic hard X-ray spectral study of a carefully selected sample of unobscured LLAGN using archival $NuSTAR$ data, to understand the central engine properties in the lower accretion regime. We analyze the $NuSTAR$ spectra of a sample of 16 LLAGN. We model the continuum emission with detailed Comptonization models. We find a strong anti-correlation between the optical depth and the electron temperature of the corona, previously also observed in the brighter Seyferts. This anti-correlation is present irrespective of the shape of the corona, and the slope of this anti-correlation in the log space for LLAGN (0.68-1.06) closely matches that of the higher accretion rate Seyferts (0.55-1.11) and hard state of BHBs ($\sim$0.87). This anti-correlation may indicate a departure from a fixed disk-corona configuration in radiative balance. Our result, therefore, demonstrates a possible universality in Comptonization processes of black hole X-ray sources across multiple orders of magnitude in mass and accretion rate.Comment: 9 pages, 3 figures. Shortened abstract. Accepted for publication in A&A Letter

A multiwavelength study of the hard and soft states of MAXI J1820+070 during its 2018 outburst

We present a comprehensive multiwavelength spectral analysis of the black hole (BH) X-ray binary MAXI J1820+070 during its 2018 outburst, utilizing AstroSat far-UV, soft X-ray, and hard X-ray data, along with (quasi-)simultaneous optical and X-ray data from the Las Cumbres Observatory and NICER, respectively. In the soft state, we detect soft X-ray and UV/optical excess components over and above the intrinsic accretion disk emission (kT in ∼ 0.58 keV) and a steep X-ray power-law component. The soft X-ray excess is consistent with a high-temperature blackbody (kT ∼ 0.79 keV), while the UV/optical excess is described by UV emission lines and two low-temperature blackbody components (kT ∼ 3.87 and ∼0.75 eV). Employing continuum spectral fitting, we determine the BH spin parameter (a = 0.77 ± 0.21), using the jet inclination angle of 64° ± 5° and a mass spanning 5–10 M ☉. In the hard state (HS), we observe a significantly enhanced optical/UV excess component, indicating a stronger reprocessed emission in the outer disk. Broadband X-ray spectroscopy in the HS reveals a two-component corona, each associated with its reflection component, in addition to the disk emission (kT in ∼ 0.19 keV). The softer coronal component dominates the bolometric X-ray luminosity and produces broader relativistic reflection features, while the harder component gets reflected far from the inner disk, yielding narrow reflection features. Furthermore, our analysis in the HS suggests a substantial truncation of the inner disk (≳51 gravitational radii) and a high disk density (∼1020 cm−3)

Palladium-catalysed regioselective aroylation and acetoxylation of 3,5-diarylisoxazole via ortho C–H functionalisations

The higher directing ability of N over O in 3,5-diarylisoxazole is demonstrated during the construction of C–C and C–O bonds. Out of the four ortho sp² C–Hs and one internal sp² C–H in 3,5-diarylisoxazoles, regioselective aroylation and acetoxylation take place at one of the ortho-C–Hs proximal to the N atom using Pd(OAc)₂ as the catalyst in the presence of suitable oxidants and solvents

Cu(II) catalyzed imine C–H functionalization leading to synthesis of 2,5-substituted 1,3,4-oxadiazoles

A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C–H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)₂. This is the first example of amidic oxygen functioning as a nucleophile in a Cu-catalyzed oxidative coupling of an imine C–H bond. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis

Four tandem C–H activations: a sequential C–C and C–O bond making via a Pd-catalyzed Cross Dehydrogenative Coupling (CDC) approach

An unprecedented aroylation at the ortho C–H bond with respect to a directing group has been accomplished via a Pd(II)-catalyzed cross dehydrogenative coupling approach using alkylbenzene as the synthetic equivalent of an aroyl moiety. The reaction proceeds through sequential C–C and C–O bond making at the expense of four consecutive C–H bond cleavages (three sp³ benzylic C–H’s and one sp² arene C–H) to selectively install an aroyl functionality at the proximal site of substrates containing various directing groups