We present a study of quasars with very redward asymmetric (RA) ultraviolet (UV) broad emission lines (BELs). An excess of redshifted emission has been previously shown to occur in the BELs of radio loud quasars and is most extreme in certain blazars. Paradoxically, blazars are objects that are characterized by a highly relativistic blue-shifted outflow towards Earth. We show that the red emitting gas resides in a very broad component (VBC) that is typical of Population B quasars that are defined by a wide H$β$ BEL profile. Empirically, we find that RA BEL blazars have both low Eddington rates ($\lesssim1\%$) and an inordinately large (order unity) ratio of long term time averaged jet power to accretion luminosity. The latter circumstance has been previously shown to be associated with a depressed extreme UV ionizing continuum. Both properties conspire to produce a low flux of ionizing photons, two orders of magnitude less than typical Population B quasars. We use CLOUDY models to demonstrate that a weak ionizing flux is required for gas near the central black hole to be optimally ionized to radiate BELs with high efficiency (most quasars over-ionize nearby gas, resulting in low radiative efficiency). The large gravitational redshift and transverse Doppler shift results in a VBC that is redshifted by $\sim 2000 -5000$~km~s$^{-1}$ with a correspondingly large line width. The RA BELs result from an enhanced efficiency (relative to typical Population B quasars) to produce a luminous, redshifted VBC near the central black hole.
The first measurements from the CIBER experiment of extragalactic background light (EBL) in near-infrared (NIR) band exhibit a higher intensity than those inferred through $γ$-ray observations. Recent theoretical-EBL intensities are typically consistent with the very high energy (VHE) $γ$-ray observations. Yet, it is possible that the excess NIR radiation is a new component of EBL and not in tension with the TeV spectra of distant blazars, since the hypothetical axion-like particle (ALP) may lead to a reduced opacity of the Universe for VHE $γ$-rays. In order to probe whether the excess compon…
Soft X-ray emission (0.5--2.0 keV) plays a pivotal role in regulating the optical and UV emission in the AGNs. We collected a sample of 1811 AGNs from the SDSS database and obtained various parameters of Balmer lines, optical continuum, MgII line \& UV continuum and studied their dependencies on soft X-ray luminosity. Based on the linear regression analysis, we found that FWHM$_{\text{MgII}}$ $\propto$ FWHM$_{\text{H}β}^{0.554}$ suggesting that UV emission is arising from a region relatively outside the broad line region (BLR) associated to the H$β$ emission and found a strong correlation betw…
AstroSat has surveyed M31 with the UVIT telescope during 2017 to 2019. The central bulge of M31 was observed in 2750-2850 A, 2000-2400 A, 1600-1850 A, 1450-1750 A, and 1200-1800 A filters. A radial profile analysis, averaged along elliptical contours which approximate the bulge shape, was carried out in each filter. The profiles follow a Sersic function with an excess for the inner 8" in all filters, or can be fit with two Sersic functions (including the excess). The ultraviolet colours of the bulge are found to change systematically with radius, with the center of the bulge bluer (hotter). We…
The flat spectrum radio quasars (FSRQs) are a sub-class of blazars characterised by prominent optical emission lines and a collimated large-scale jet along the observer line of sight. An X-ray spectral flattening has been reported in FSRQs (at relatively high redshifts), attributable to either absorption from gas along the line of sight or intrinsic jet based radiative processes. We study a sample of 16 high redshift FSRQs (z of 1.1 -- 4.7; rest frame energy upto 50 keV) observed with XMM-Newton and Swift satellites spanning 29 epochs. The X-ray spectra are fit with a power law including free …
High-redshift blazars are among the most powerful objects in the Universe. The spectral and temporal properties of thirty-three distant blazars ($z>2.5$) detected in the high energy $γ$-ray band are investigated by analyzing the {\it Fermi}-LAT and {\it Swift} UVOT/ XRT data. The considered sources have soft time averaged $γ$-ray spectra ($Γ_{\rm γ}\geq2.2$) whereas those that have been observed in the X-ray band have hard X-ray spectra ($Γ_{\rm X}=1.01-1.86$). The $γ$-ray flux of high-redshift blazars ranges from $4.84\times10^{-10}$ to $1.50\times10^{-7}\:{\rm photon\:cm^{-2}\:s^{-1}}$ and t…
The Stripped-Star Ultraviolet Magellanic Cloud Survey (SUMS): The UV Photometric Catalog and Stripped Star Candidate Selection
University of Toronto（多伦多大学）；KU Leuven（荷语鲁汶大学）；Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）；Perimeter Institute for Theoretical Physics（理论物理珀西默研究所）
