X-ray Astronomy from the Lunar Surface

Motivated by efforts to return humanity to the Moon, three cases are reviewed for X-ray astronomy from the lunar surface: (1) Facilitation of ambitious engineering designs including high throughput telescopes, long focal length optics and X-ray interferometery; (2) Occultation studies and the gain they enable in astrometric precision; (3) Multimessenger time-domain coordinated observations. The potential benefits of, and challenges presented by, operating from the Moon are discussed. Some of these cases have relatively low mass budgets and could be conducted as early pathfinders, while others are more ambitious and will likely need to await improvements in technology or well-developed lunar bases.Comment: Invited peer-reviewed article (author version) for a theme issue of Phil. Trans. R. Soc. A on 'Astronomy from the Moon: the next decades (Part 2)' eds. I. Crawford, M. Elvis, J. Silk and J. Zarnecki. Comments/collaboration welcom

NuSTAR catches the unveiling nucleus of NGC 1068

We present a NuSTAR and XMM–Newton monitoring campaign in 2014/2015 of the Compton-thick Seyfert 2 galaxy, NGC 1068. During the 2014 August observation, we detect with NuSTAR a flux excess above 20 keV (32 ± 6?per?cent) with respect to the 2012 December observation and to a later observation performed in 2015 February. We do not detect any spectral variation below 10 keV in the XMM–Newton data. The transient excess can be explained by a temporary decrease of the column density of the obscuring material along the line of sight (from NH ? 1025 cm?2 to NH = 6.7 ± 1.0 × 1024 cm?2), which allows us for the first time to unveil the direct nuclear radiation of the buried active galactic nucleus in NGC 1068 and to infer an intrinsic 2–10 keV luminosity LX=7+7?4×1043 erg s?

The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kalpha line emission in Type 1 AGN

The Fe Kalpha emission line is the most ubiquitous feature in the X-ray spectra of active galactic nuclei (AGN), but the origin of its narrow core remains uncertain. Here, we investigate the connection between the sizes of the Fe core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGN. The observed Fe K emission radii (R_fe) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (R_dust) are measured either from optical/near-infrared reverberation time lags or from resolved near-infrared interferometric data. This direct comparison shows, on an object-by-object basis, that the dust sublimation radius forms an outer envelope to the bulk of the Fe K emission. R_fe matches R_dust well in the AGN with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, R_fe is similar to, or smaller than the radius of the optical broad line region. These facts place important constraints on the torus geometries for our sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. We also test for luminosity scalings of R_fe, finding that Eddington ratio is not a prime driver in determining the line location in our sample. We discuss in detail potential caveats due to data analysis and instrumental limitations, simplistic line modeling, uncertain black hole masses, as well as sample selection, showing that none of these is likely to bias our core result. The calorimeter on board Astro-H will soon vastly increase the parameter space over which line measurements can be made, overcoming many of these limitations.Comment: ApJ in press. Community comments greatly appreciated. 13 pages, 4 figures and 2 tables including an appendi

WISE view of Narrow-Line Seyfert 1 galaxies: mid-infrared color and variability

We present the color and flux variability analysis at 3.4 {\mu}m (W1-band) and 4.6 {\mu}m (W 2-band) of 492 narrow-line Seyfert 1 (NLSy1) galaxies using archival data from the Wide-field Infrared Survey Explorer (WISE). In the WISE color-color, (W1 - W2) versus (W2 - W3) diagram, ~58% of the NLSy1 galaxies of our sample lie in the region occupied by the blazar category of active galactic nuclei (AGN). The mean W1 - W2 color of candidate variable NLSy1 galaxies is $0.99 \pm 0.18$ mag. The average amplitude of variability is $0.11 \pm 0.07$ mag in long-term (multi-year) with no difference in variability between W1 and W2-bands. The W1 - W2 color of NLSy1 galaxies is anti-correlated with the relative strength of [O III] to H{\beta}, strongly correlated with continuum luminosity, black hole mass, and Eddington ratio. The long-term amplitude of variability shows weak anti-correlation with the Fe II strength, continuum luminosity and Eddington ratio. A positive correlation between color as well as the amplitude of variability with the radio power at 1.4 GHz was found for the radio-detected NLSy1 galaxies. This suggests non-thermal synchrotron contribution to the mid-infrared color and flux variability in radio-detected NLSy1 galaxies.Comment: 10 pages; Accepted for publication in MNRA

CorrSim: A Multiwavelength Timing Observation Simulator

Studying the rapid variability of many astronomical objects is key to understanding the underlying processes at play. However, a combination of limited telescope availability, viewing constraints, and the unpredictable nature of many sources mean that obtaining data well-suited to this task can be tricky, especially when it comes to simultaneous multiwavelength observations. Researchers can often find themselves tuning observational parameters in real-time, or may realise later that their observation did not achieve their goals. Here, we present CorrSim, a program to aid planning of multiwavelength coordinated observations. CorrSim takes a model of a system (i.e. Power Spectra, Coherence, and Lags), and returns a simulated multiwavelength observation, including effects of noise, telescope parameters, and finite sampling. The goals of this are: (i) To simulate a potential observation (to inform decisions about its feasibility); (ii) To investigate how different Fourier models affect a system's variability (e.g. how altering the frequency-dependent lags between bands can affect data products like cross-correlation functions); and (iii) To simulate existing data and investigate its trustworthiness. We outline the methodology behind CorrSim, show how a variety of parameters (e.g. noise sources, observation length, and telescope choice) can affect data, and present examples of the software in action.Comment: 20 pages + Supplementary Materia

Spectroscopy along Multiple, Lensed Sightlines through Outflowing Winds in the Quasar SDSS J1029+2623

We study the origin of absorption features on the blue side of the C IV broad emission line of the large-separation lensed quasar SDSS J1029+2623 at z_em ~ 2.197. The quasar images, produced by a foreground cluster of galaxies, have a maximum separation angle of ~ 22".5. The large angular separation suggests that the sight-lines to the quasar central source can go through different regions of outflowing winds from the accretion disk of the quasar, providing a unique opportunity to study the structure of outflows from the accretion disk, a key ingredient for the evolution of quasars as well as for galaxy formation and evolution. Based on medium- and high-resolution spectroscopy of the two brightest images conducted at the Subaru telescope, we find that each image has different intrinsic levels of absorptions, which can be attributed either to variability of absorption features over the time delay between the lensed images, ~ 774 days, or to the fine structure of quasar outflows probed by the multiple sight-lines toward the quasar. While both these scenarios are consistent with the current data, we argue that they can be distinguished with additional spectroscopic monitoring observations.Comment: 17 pages, including 7 figures; accepted for publication in the Astronomical Journa