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Register a new userMeasuring the Obscuring Column of a Disk Megamaser AGN in a Nearby Merger
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Active Galactic Nuclei (AGNs) hosting disk water megamasers are well known to be obscured by large amounts of gas, likely due to the presence along the line of sight of an almost edge-on disky structure orbiting the supermassive black hole. Correcting for the high obscuration is crucial to infer parameters intrinsic to the source, like its luminosity. We present a broadband X-ray spectral analysis of a water megamaser AGN in an early merger (NGC 5765B), combining Chandra and NuSTAR data. NGC 5765B is highly Compton-thick and reflection-dominated, following the general trend among disk megamasers. Combining the exquisite black hole mass from masers with our X-ray spectroscopy, the Eddington ratio of the megamaser is estimated to be in the $2-14%$ range, and its robustness is confirmed through SED fitting.
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Aims. Study the connection between the masing disk and obscuring torus in Seyfert 2 galaxies. Methods. We present a uniform X-ray spectral analysis of the high energy properties of 14 nearby megamaser Active Galactic Nuclei observed by NuSTAR. We use a simple analytical model to localize the maser disk and understand its connection with the torus by combining NuSTAR spectral parameters with available physical quantities from VLBI mapping. Results. Most of the sources analyzed are heavily obscured, showing a column density in excess of $sim 10^{23}$ cm$^{-2}$. In particular, $79%$ are Compton-thick ($N_{rm H} > 1.5 times 10^{24}$ cm$^{-2}$). Using column densities measured by NuSTAR, with the assumption that the torus is the extension of the maser disk, and further assuming a reasonable density profile, the torus dimensions can be predicted. They are found to be consistent with mid-IR interferometry parsec-scale observations of Circinus and NGC 1068. In this picture, the maser disk is intimately connected to the inner part of the torus. It is probably made of a large number of molecular clouds connecting the torus and the outer part of the accretion disk, giving rise to a thin disk rotating in most cases in Keplerian or sub-Keplerian motion. This toy model explains the established close connection between water megamaser emission and nuclear obscuration as a geometric effect.
We present NuSTAR and Swift observations of the neutron star Aquila X-1 during the peak of its July 2014 outburst. The spectrum is soft with strong evidence for a broad Fe Kalpha line. Modeled with a relativistically broadened reflection model, we find that the inner disk is truncated with an inner radius of 15+/-3 R_G. The disk is likely truncated by either the boundary layer and/or a magnetic field. Associating the truncated inner disk with pressure from a magnetic field gives an upper limit of B<5+/-2x10^8G. Although the radius is truncated far from the stellar surface, material is still reaching the neutron star surface as evidenced by the X-ray burst present in the t NuSTAR observation.
We compile a blue AGN sample from SDSS and investigate the ratio of hard X-ray to bolometric luminosity in dependence on Eddington ratio and black hole mass. Our sample comprises 240 radio-quiet Seyfert 1 galaxies and QSOs. We find that the fraction of hard X-ray luminosity (log$(L_{rm 2-10 kev}/L_{rm bol})$) decreases with the increase of Eddington ratio. We also find that the fraction of hard X-ray luminosity is independent on the black hole mass for the radio-quiet AGNs. The relation of log$(L_{rm 2-10 kev}/L_{rm bol})$ decreasing with increasing Eddington ratio indicates that X-ray bolometric correction is not a constant, from a larger sample supporting the results of Vasudevan & Fabian (2007). We interpret our results by the disk corona evaporation/condensation model (Meyer et al. cite{me200}; Liu et al. 2002a; Liu et al. 2007). In the frame of this model, the Compton cooling becomes efficient in cooling of the corona at high accretion rate (in units of Eddington rate), leading to condensation of corona gas to the disk. Consequently, the relative strength of corona to the disk becomes weaker at higher Eddington ratio. Therefore, the fraction of hard X-ray emission to disk emission and hence to the bolometric emission is smaller at higher Eddington ratio. The independence of the fraction of hard X-ray luminosity on the mass of the black hole can also be explained by the disk corona model since the corona structure and luminosity (in units of Eddington luminosity) are independent on the mass of black holes.
We present the time-resolved spectral analysis of the XMM-Newton data of NGC 1365, collected during one XMM-Newton observation, which caught this changing-look AGN in a high flux state characterized also by a low column density ($N_{mathrm{H}}sim 10^{22}$ cm $^{-2}$) of the X-ray absorber. During this observation the low energy photoelectric cut-off is at about $sim 1$ keV and the primary continuum can be investigated with the XMM-Newton-RGS data, which show strong spectral variability that can be explained as a variable low $N_{mathrm{H}}$, which decreased from $N_{mathrm{H}} sim10^{23}$ cm $^{-2}$ to $10^{22}$ cm $^{-2}$ in a 100 ks time-scale. The spectral analysis of the last segment of the observation revealed the presence of several absorption features that can be associated with an ionized (log $xi sim 2$ erg cm s$^{-1}$) outflowing wind ($v_{mathrm{out}} sim 2000$ km s$^{-1}$). We detected for the first time a possible P-Cygni profile of the Mg,textsc{xii} Ly$alpha$ line associated with this mildly ionized absorber indicative of a wide angle outflowing wind. We suggest that this wind is a low ionization zone of the highly ionized wind present in NGC 1365, which is responsible for the iron K absorption lines and is located within the variable X-ray absorber. At the end of the observation, we detected a strong absorption line at $Esim 0.76$ keV most likely associated with a lower ionization zone of the absorber (log $xi sim 0.2$ erg cm s$^{-1}$, $N_{mathrm{H}} sim 10^{22}$ cm $^{-2}$), which suggests that the variable absorber in NGC 1365 could be a low ionization zone of the disk wind.
Accretion disks around supermassive black holes (SMBH) are promising sites for stellar mass black hole (BH) mergers due to mass segregation and merger acceleration by disk gas torques. Here we show that a GW-kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If $R_{H}geq H$, the disk height, an off-center UV flare at $a_{rm BH} sim 10^{3}r_{g}$ emerges within $t_{rm UV} sim rm{O}(2 {rm days})(a_{rm BH}/10^{3}r_{g})(M_{rm SMBH}/10^{8}M_{odot})(v_{rm kick}/10^{2}rm{km/s})$ post-merger and lasts O$(R_{H}/v_{rm kick}) sim rm{O}(5 t_{rm UV}$). The flare emerges with luminosity O($10^{42}{rm erg/s})(t_{rm UV}/2{rm days})^{-1}(M_{rm Hill}/1M_{odot})(v_{rm kick}/10^{2}{rm km/s})^{2}$. AGN optical/UV photometry alters and asymmetric broad emission line profiles can develop after weeks. If $R_{H}<H$, detectability depends on disk optical depth. Follow-up by large optical sky surveys is optimized for small GW error volumes and for LIGO/Virgo triggers $>50M_{odot}$.
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