Singularity-free black holes in conformal gravity: new observational constraints

We consider the family of singularity-free rotating black hole solutions in Einstein's conformal gravity found in Bambi, Modesto & Rachwal (2017) and we constrain the value of the conformal parameter $L$ from the analysis of a 30 ks NuSTAR observation of the stellar-mass black hole in GS 1354-645 during its outburst in 2015. Our new constraint is much stronger than that found in previous work. Here we obtain $L/M < 0.12$ (99% confidence level, statistical uncertainty only).Comment: 6 pages, 3 figure

Constraints on the ultra-fast outflows in the narrow-line Seyfert 1 galaxy Mrk 1044 from high-resolution time- and flux-resolved spectroscopy

Ultra-fast outflows (UFOs) have been revealed in a large number of active galactic nuclei (AGN) and are regarded as promising candidates for AGN feedback on the host galaxy. The nature and launching mechanism of UFOs are not yet fully understood. Here we perform a time- and flux-resolved X-ray spectroscopy on four XMM-Newton observations of a highly accreting narrow-line Seyfert 1 (NLS1) galaxy, Mrk 1044, to study the dependence of the outflow properties on the source luminosity. We find that the UFO in Mrk 1044 responds to the source variability quickly and its velocity increases with the X-ray flux, suggesting a high-density ($10^{9}-4.5\times10^{12}\,\mathrm{cm}^{-3}$) and radiatively driven outflow, launched from the region within a distance of $98-6600\, R_\mathrm{g}$ from the black hole. The kinetic energy of the UFO is conservatively estimated ($L_\mathrm{UFO}\sim4.4\%L_\mathrm{Edd}$), reaching the theoretical criterion to affect the evolution of the host galaxy. We also find emission lines, from a large-scale region, have a blueshift of $2700-4500$ km/s in the spectra of Mrk 1044, which is rarely observed in AGN. By comparing with other sources, we propose a correlation between the blueshift of emission lines and the source accretion rate, which can be verified by a future sample study.Comment: 14 pages, 13 figures, 3 tables, accepted for publication in MNRA

The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy

© 2021. The American Astronomical Society. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.3847/1538-4357/abf430We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGN) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband (0.3\mbox{--}79 keV) spectrum shows the presence of a power-law continuum with a soft excess below $2$ keV, iron K$\alpha$ emission ($\sim 6.4$ keV), and a Compton hump (peaking at $\sim 20$ keV). We find that the soft excess can be modeled by two different possible scenarios: a warm ($kT_\mathrm{e}\sim0.2$ keV) and optically thick ($\tau\sim34$) Comptonizing corona; or with relativistically-blurred reflection off a high-density ($\log{[n_\mathrm{e}/\mathrm{cm}^{-3}]}>18.3$) inner disk. These two models cannot be easily distinguished solely from their fit statistics. However, the low temperature ($kT_\mathrm{e}\sim20$ keV) and the thick optical depth ($\tau\sim5$) of the hot corona required by the warm corona scenario are uncommon for AGNs. We also fit a 'hybrid' model, which includes both disk reflection and a warm corona. Unsurprisingly, as this is the most complex of the models considered, this provides the best fit, and more reasonable coronal parameters. In this case, the majority of the soft excess flux arises in the warm corona component. However, based on recent simulations of warm coronae, it is not clear whether such a structure can really exist at the low accretion rates relevant for ESO 362-G18 ($\dot{m}\sim0.015$). This may therefore argue in favor of a scenario in which the soft excess is instead dominated by the relativistic reflection. Based on this model, we find that the data would require a compact hot corona ($h\sim3\,R_\mathrm{Horizon}$) around a highly spinning ($a_\star>0.927$) black hole.Peer reviewe

RELXILL_NK: a relativistic reflection model for testing Einstein's gravity

Einstein's theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in the weak field regime. However, the strong field regime is largely unexplored, and there are many modified and alternative theories that have the same predictions as Einstein's gravity for weak fields and present deviations when gravity becomes strong. RELXILL_NK is the first relativistic reflection model for probing the spacetime metric in the vicinity of astrophysical black holes and testing Einstein's gravity in the strong field regime. Here we present our current constraints on possible deviations from Einstein's gravity obtained from the black holes in 1H0707-495, Ark 564, GX 339-4, and GS 1354-645.Comment: 8 pages, 6 figures. Talk given at the "International Conference on Quantum Gravity" (26-28 March 2018, Shenzhen, China). To appear in the conference proceeding

Ejection-accretion connection in NLS1 AGN 1H 1934-063

Accretion and ejection of matter in active galactic nuclei (AGN) are tightly connected phenomena and represent fundamental mechanisms regulating the growth of the central supermassive black hole and the evolution of the host galaxy. However, the exact physical processes involved are not yet fully understood. We present a high-resolution spectral analysis of a simultaneous \xmm\ and \nustar\ observation of the narrow line Seyfert 1 (NLS1) AGN 1H 1934-063, during which the X-ray flux dropped by a factor of $\sim6$ and subsequently recovered within 140 kiloseconds. By means of the time-resolved and flux-resolved X-ray spectroscopy, we discover a potentially variable warm absorber and a relatively stable ultra-fast outflow (UFO, $v_\mathrm{UFO}\sim-0.075\,c$) with a mild ionization state ($\log(\xi/\mathrm{erg\,cm\,s^{-1})}\sim1.6$). The detected emission lines (especially a strong and broad feature around 1\,keV) are of unknown origin and cannot be explained with emission from plasmas in photo- or collisional-ionization equilibrium. Such emission lines could be well described by a strongly blueshifted ($z\sim-0.3$) secondary reflection off the base of the equatorial outflows, which may reveal the link between the reprocessing of the inner accretion flow photons and the ejection. However, this scenario although being very promising is only tentative and will be tested with future observations.Comment: 15 pages, 17 figures, 1 table, accepted for publication in MNRA