Unveiling Sub-Pc supermassive black hole binary candidates in active galactic nuclei

The elusive supermassive black hole binaries (SMBHBs) are thought to be the penultimate stage of galaxy mergers, preceding a final coalescence phase. SMBHBs are sources of continuous gravitational waves, possibly detectable by pulsar timing arrays; the identification of candidates could help in performing targeted gravitational wave searches. Due to SMBHBs\u2019 origin in the innermost parts of active galactic nuclei (AGN), X-rays are a promising tool for unveiling their presence, by means of either double Fe K\u3b1 emission lines or periodicity in their light curve. Here we report on a new method for selecting SMBHBs by means of the presence of a periodic signal in their Swift Burst Alert Telescope (BAT) 105 month light curves. Our technique is based on Fisher\u2019s exact g-test and takes into account the possible presence of colored noise. Among the 553 AGN selected for our investigation, only the Seyfert 1.5 galaxy Mrk 915 emerges as a candidate SMBHB; from subsequent analysis of its light curve we find a period P0 = 35 \ub1 2 months, and the null hypothesis is rejected at the 3.7\u3c3 confidence level. We also present a detailed analysis of the BAT light curve of the only previously X-ray-selected binary candidate source in the literature, the Seyfert 2 galaxy MCG+11-11-032. We find P0 = 26.3 \ub1 0.6 months, consistent with the one inferred from previously reported double Fe K\u3b1 emission lines

The current state of disk wind observations in BHLMXBs through X-ray absorption lines in the iron band

International audienceThe presence of blueshifted absorption lines in the X-ray spectra of Black Hole Low Mass X-ray Binaries is the telltale of massive outflows called winds. These signatures are found almost exclusively in soft states of high-inclined systems, hinting at equatorial ejections originating from the accretion disk and deeply intertwined with the evolution of the outburst patterns displayed by these systems. In the wake of the launch of the new generation of X-ray spectrometers, studies of wind signatures remain mostly restricted to single sources and outbursts, with some of the recent detections departing from the commonly expected behaviors. We thus give an update to the current state of iron band absorption lines detections, through the analysis of all publicly available XMM-$Newton$-PN and $Chandra$-HETG exposures of known Black Hole Low-Mass X-ray Binary candidates. Our results agree with previous studies, with wind detections exclusively found in dipping, high-inclined sources, and almost exclusively in bright ($L_{X}>0.01L_{Edd}$) soft ($HR<0.8$) states, with blueshift values generally restricted to few 100 km s$^{-1}$. The line parameters indicate similar properties between objects and outbursts of single sources, and despite more than 20 years of data, very few sources have the HID sampling necessary to properly study the evolution of the wind during single outbursts. We provide an online tool with details of the wind signatures and outburst evolution data for all sources in the sample

The current state of disk wind observations in BHLMXBs through X-ray absorption lines in the iron band

International audienceThe presence of blueshifted absorption lines in the X-ray spectra of Black Hole Low Mass X-ray Binaries is the telltale of massive outflows called winds. These signatures are found almost exclusively in soft states of high-inclined systems, hinting at equatorial ejections originating from the accretion disk and deeply intertwined with the evolution of the outburst patterns displayed by these systems. In the wake of the launch of the new generation of X-ray spectrometers, studies of wind signatures remain mostly restricted to single sources and outbursts, with some of the recent detections departing from the commonly expected behaviors. We thus give an update to the current state of iron band absorption lines detections, through the analysis of all publicly available XMM-$Newton$-PN and $Chandra$-HETG exposures of known Black Hole Low-Mass X-ray Binary candidates. Our results agree with previous studies, with wind detections exclusively found in dipping, high-inclined sources, and almost exclusively in bright ($L_{X}>0.01L_{Edd}$) soft ($HR<0.8$) states, with blueshift values generally restricted to few 100 km s$^{-1}$. The line parameters indicate similar properties between objects and outbursts of single sources, and despite more than 20 years of data, very few sources have the HID sampling necessary to properly study the evolution of the wind during single outbursts. We provide an online tool with details of the wind signatures and outburst evolution data for all sources in the sample

Supermassive black hole winds in X-rays: SUBWAYS: II. HST UV spectroscopy of winds at intermediate redshifts

High Energy Astrophysic