Related papers: Testing redshift variation of the X-ray and ultrav…
The non-linear relation between the X-ray and ultraviolet (UV) luminosity in quasars has been used to derive quasar distances and to build a Hubble diagram at redshifts up to $z\sim$ 7. This cosmological application is based on the…
We compare, with data from the quasars, the Hubble parameter measurements, and the Pantheon+ type Ia supernova, three different relations between X-ray luminosity ($L_X$) and ultraviolet luminosity ($L_{UV}$) of quasars. These three…
We construct a three-dimensional and redshift-evolutionary X-ray and ultraviolet ($L_X-L_{UV}$) luminosity relation for quasars from the powerful statistic tool called copula, and find that the constructed $L_X-L_{UV}$ relation from copula…
We present a new catalogue of ~2,400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM-Newton. The sample can be used to investigate the non-linear relation between the UV and X-ray…
We use measurements of 59/58 quasars (QSOs), over a redshift range $0.0041\leq z \leq 1.686$, to do a comparative study of the radius--luminosity ($R-L$) and X-ray$-$UV luminosity ($L_X-L_{UV}$) relations and the implication of these…
A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in Active Galactic Nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence…
Quasars could serve as standard candles if the relation between their ultraviolet and X-ray luminosities can be accurately calibrated. Previously, we developed a model-independent method to calibrate quasar standard candles using the…
We explore the evolution of the X-ray luminosity function of quasars and the intrinsic correlation between the X-ray and 2500\AA $\,$ ultraviolet luminosities, utilizing techniques verified in previous works and a sample of over 4000…
Proceeding of the "HACK100" Conference, 6-10 June 2022, Trieste, Italy - In recent years, quasars have been shown to be reliable standardizable candles, thanks to the non-linear relation between their X-rays and ultraviolet luminosity.…
In this paper we address the question whether the non-linear relation between the X-ray and UV emission of quasars can be used to derive their distances. In previous works of our group, we demonstrated that such a relation does not show any…
The non-linear relation between X-ray and UV luminosity in quasars can be used to estimate their distance. Recently, we have shown that despite the large dispersion of the relation, a Hubble Diagram made of large samples of quasars can…
In the past few years, we built a Hubble diagram of quasars up to redshift z$\sim$7, based on the nonlinear relation between quasars' x-ray and UV luminosities. Such a Hubble diagram shows a >4$\sigma$ deviation from the standard flat…
In Khadka et al. (2023), a sample of X-ray-detected reverberation-mapped quasars was presented and applied for the comparison of cosmological constraints inferred using two well-established relations in AGN -- the X-ray/UV luminosity…
The recently-finished Edinburgh UVX quasar survey at B < 18 is used together with other complete samples to estimate the shape and evolution of the optical luminosity function in the redshift range 0.3 < z < 2.2. There is a significantly…
The recent compilation of quasar (QSO) X-ray and UV flux measurements include QSOs that appear to not be standardizable via the X-ray luminosity and UV luminosity ($L_X-L_{UV}$) relation and so should not be used to constrain cosmological…
The non-linear relation between the UV and X-ray luminosity in quasars has been studied for decades. However, as we lack a comprehensive model able to explain it, its investigation still relies on observational efforts. This work focuses on…
We use six different cosmological models to study the recently-released compilation of X-ray and UV flux measurements of 2038 quasars (QSOs) which span the redshift range $0.009 \leq z \leq 7.5413$. We find, for the full QSO data set, that…
The goal of the present paper is to assess the usefulness of quasars as cosmological distance indicators. We calibrate, in a model-independent way, the non-linear relation between X-ray and UV emission to derive quasar luminosity distances.…
In this paper, we use quasars calibrated from type Ia supernova (SN Ia) to constrain cosmological models. We consider three different X-ray luminosity ($L_{X}$) - ultraviolet luminosity ($L_{UV}$) relations of quasars, i.e., the standard…
In this paper, we present a cosmological model-independent test for the cosmic opacity at high redshifts ($z\sim5$). We achieve this with the opacity-dependent luminosity distances derived from nonlinear relation between X-ray and UV…