Search

We examine lengthy radio light curves of the flat spectrum radio galaxy 3C 454.3 for possible quasi-periodic oscillations (QPOs). The data used in this work were collected at five radio frequencies, 4.8, 8.0, 14.5, 22.0, and 37.0 GHz between 1979--2013 as observed at the University of Michigan Radio Astronomical Observatory, Crimean Astrophysical Observatory, and Aalto University Mets{\"a}hovi Radio Observatory. We employ generalized Lomb-Scargle periodogram and weighted wavelet transform analyses to search for periodicities in these light curves. We confirm a QPO period of $\sim$ 2000 day to be at least 4$\sigma$ significant using both methods at all five radio frequencies between 1979 and 2007, after which a strong flare changed the character of the light curve. We also find a $\sim$~600 day period which is at least 4$\sigma$ significant, but only in the 22.0 and 37.0 GHz light curves. We briefly discuss physical mechanisms capable of producing such variations., Comment: 19 pages, 11 figures, Published in the Astrophysical Journal

MoonLITE (Lunar InTerferometry Explorer) is an Astrophysics Pioneers proposal to develop, build, fly, and operate the first separated-aperture optical interferometer in space, delivering sub-mas science results. MoonLITE will leverage the Pioneers opportunity for utilizing NASA's Commercial Lunar Payload Services (CLPS) to deliver an optical interferometer to the lunar surface, enabling unprecedented discovery power by combining high spatial resolution from optical interferometry with deep sensitivity from the stability of the lunar surface. Following landing, the CLPS-provided rover will deploy the pre-loaded MoonLITE outboard optical telescope 100 meters from the lander's inboard telescope, establishing a two-element interferometric observatory with a single deployment. MoonLITE will observe targets as faint as 17th magnitude in the visible, exceeding ground-based interferometric sensitivity by many magnitudes, and surpassing space-based optical systems resolution by a factor of 50 times. The capabilities of MoonLITE open a unique discovery space that includes direct size measurements of the smallest, coolest stars and substellar brown dwarfs; searches for close-in stellar companions orbiting exoplanet-hosting stars that could confound our understanding and characterization of the frequency of Earth-like planets; direct size measurements of young stellar objects and characterization of the terrestrial planet-forming regions of these young stars; measurements of the inner regions and binary fraction of active galactic nuclei; and a probe of the very nature of spacetime foam itself. A portion of the observing time will also be made available to the broader community via a guest observer program. MoonLITE takes advantage of the CLPS opportunity and delivers an unprecedented combination of sensitivity and angular resolution at the remarkably affordable cost point of Pioneers., Comment: 13 pages, 8 figures, SPIE Astronomical Telescopes + Instrumentation 2024

Optical timing with rapid, seconds-to-minutes cadences with high photometric precision and gap-free long baselines is necessary for an unambiguous physical picture of accretion phenomena, and is only possible from space. Exoplanet-hunting missions like Kepler and TESS have offered an outstanding new window into detailed jet and accretion physics, but have been severely hampered by incomplete calibration and systematics treatments and, most especially, a monochromatic single wide bandpass. Advances made using Kepler and TESS survey data, when considered alongside detailed, expensive multi-color experiments done from the ground, reveal the enormous potential of a space-based multi-color optical timing mission with a high energy focus., Comment: 5 pages, no figures. Published in Frontiers in Astronomy and Space Sciences

We present a study of high-cadence, high-precision, optical light curves from the TESS satellite of 67 blazars in the southern sky. We provide descriptive flux statistics, power spectral density model parameters, and characteristic variability timescales. We find that only 15 BL Lacertae objects (BLLs) and 18 Flat Spectrum Radio Quasars (FSRQs) from the initial 26 and 41, respectively exhibit statistically-significant variability. We employ an adapted Power Spectral Response method to test the goodness of fit for the power spectral density function (PSD) to 3 power-law variant models. From our best-fitting description of the PSD, we extract the high-frequency power-spectral slopes and, if present, determine the significant bend or break in the model to identify characteristic timescales. We find no significant difference in the excess variance or rms-scatter between blazar subpopulations. We identify a linear rms-flux relation in ~69% of our sample, in which ~20% show a strong correlation. We find that both subpopulations of blazars show power spectral slope of $\alpha$~2 in which a broken power-law best fits 5 BLL & 6 FSRQ and a bending power-law best fits 1 BLL & 5 FSRQ. The shortest timescales of variability in each light curve range widely from minutes to weeks. Additionally, the objects' characteristic timescales range from ~0.8-8 days, consistent with the optical variability originating in the jet.

In a previous paper, we reported evidence for quasi-periodicities in the \textsl{TESS} light curves of BL Lacerate and two other blazars found serendipitously in the SDSS AGN catalog. In this work, we find tentative evidence for quasi-periodic features in the \textsl{TESS} observations of five sources in the fourth catalog of the Fermi--LAT (4FGL) sources: J090453.4$-$573503, J2345$-$1555, B0422+004, J002159.2$-$514028, and B0537$-$441. We analysed the \textsl{TESS} light curves of these blazars that we extracted using a customized approach. The quasi-periodic oscillations (QPOs) are searched for using two timing analysis techniques: generalized Lomb-Scargle periodogram and weighted wavelet Z-transform. Their apparent periods lie in the range of 2.8--6.5 days and have at least 3$\sigma$ significance in both of these methods. QPOs at such timescales can originate from the kink instability model which relates the quasi-periodic feature with the growth of kinks in the magnetized relativistic jets. We performed MCMC simulations to obtain the posterior distribution of parameters associated with this model and found the kink period consistent with previous studies., Comment: 12 pages, 4 figures. Accepted for publication in MNRAS main journal

We report the time series analysis of TESS light curves of three blazars, BL Lacertae, 1RXS J111741.0+254858, and 1RXS J004519.6+212735, obtained using a customized approach for extracting AGN light curves. We find tentative evidence for quasi-periodic oscillations (QPOs) in these light curves that range from 2 to 6 days. Two methods of analysis are used for assessing their significance: generalized Lomb-Scargle periodograms and weighted wavelet Z-transforms. The different approaches of these methods together ensure a robust measurement of the significance of the claimed periodicities. We can attribute the apparent QPOs to the kink instability model which postulates that the observed QPOs are related to the temporal growth of kinks in the magnetized relativistic jet. We confirm the application of this model to BL Lacertae and extend the kink instability model to the other two BL Lac objects., Comment: Accepted for publication in MNRAS

The sampling strategy of the Transiting Exoplanet Survey Satellite (TESS) make TESS light curves extremely valuable to investigate high cadence optical variability of AGN. However, because the TESS instrument was primarily designed for exoplanet science, the use of the satellite for other applications requires careful treatment of the data. In this paper we introduce Quaver, a new software tool designed specifically to extract TESS light curves of extended and faint sources presenting stochastic variability. We then use this new tool to extract light curves of the nearby radio-loud AGN Pictor A, and perform a temporal and power spectral analysis of its high cadence optical variability. The obtained light curves are well fit with a damped random walk (DRW) model, exhibiting both stochastic AGN variations and flaring behavior. The DRW characteristic timescales $\tau_{\rm DRW} \sim 3-6$ days during more quiet periods, and $\tau_{\rm DRW} \sim 0.8$ days for periods with strong flares, even when the flares themselves are masked from the DRW fit. The observed timescales are consistent with the dynamical, orbital and thermal timescales expected for the low black hole mass of Pictor A., Comment: 28 pages, 24 figures, 1 table. Accepted for publication in the Astrophysical Journal

We investigate K2BS5, an optical transient that we identified in Campaign 13 of the Kepler/K2 archives by the "K2 Background Survey", and classify it as a new SU UMa-type dwarf nova. Using the light curve generated from Kepler's long-cadence observation mode, we analyze the dwarf nova during quiescence and superoutburst. Following 20 days of quiescence at the start of the observation, the system entered a superoutburst lasting 12 days, after which it experienced at least one rebrightening. K2BS5 clearly meets the criteria for an SU UMa star, but at the peak of the superoutburst, it also shows double-wave oscillations consistent with the spectroscopic orbital period, a phenomenon that closely resembles early superhumps in WZ Sge stars. While we do not classify K2BS5 as a WZ Sge system, we discuss how this phenomenon could complicate efforts to use the suspected detection of early superhumps to distinguish SU UMa-type dwarf novae from the recently recognized class of long-orbital-period WZ Sge systems., Comment: 11 pages, 7 figures. Accepted for publication in the Astronomical Journal

We present a catalog of the millimeter-wave (mm-wave) continuum properties of 98 nearby ($z <$ 0.05) active galactic nuclei (AGNs) selected from the 70-month Swift/BAT hard X-ray catalog that have precisely determined X-ray spectral properties and subarcsec-resolution ALMA Band-6 (211--275 GHz) observations as of 2021 April. Due to the hard-X-ray ($>$ 10 keV) selection, the sample is nearly unbiased for obscured systems at least up to Compton-thick-level obscuration, and provides the largest number of AGNs with high physical resolution mm-wave data ($\lesssim$ 100--200 pc). Our catalog reports emission peak coordinates, spectral indices, and peak fluxes and luminosities at 1.3 mm (230 GHz). Additionally, high-resolution mm-wave images are provided. Using the images and creating radial surface brightness profiles of mm-wave emission, we identify emission extending from the central source and isolated blob-like emission. Flags indicating the presence of these emission features are tabulated. Among 90 AGNs with significant detections of nuclear emission, 37 AGNs ($\approx$ 41%) appear to have both or one of extended or blob-like components. We, in particular, investigate AGNs that show well-resolved mm-wave components and find that these seem to have a variety of origins (i.e., a jet, radio lobes, a secondary AGN, stellar clusters, a narrow line region, galaxy disk, active star-formation regions, and AGN-driven outflows), and some components have currently unclear origins., Comment: 49 pages, 7 figures, 3 tables, accepted for publication in ApJS

The ultra-luminous X-ray source CXO~J133815.6+043255 is a strong candidate for a bona-fide intermediate mass black hole, residing in the outskirts of NGC~5252. We present 22~GHz radio observations of this source obtained serendipitously in an ongoing high-frequency imaging survey of radio-quiet Active Galactic Nuclei (AGN), and use this new data point to construct the broad-band radio spectral energy distribution (SED). We find that the SED exhibits a spectral slope of $\alpha=-0.66\pm0.02$, consistent with a steep spectrum from optically-thin synchrotron emission from an unresolved jet. We also find that the $L_R / L_X$ ratio is approximately $10^{-3}$, inconsistent with radio-quiet AGN and many ULXs but consistent with low-luminosity AGN (LLAGN) and radio-loud quasars. Together, these observations support the conclusion that CXO~J133815.6+043255 is an intermediate-mass black hole producing a low-mass analog of radio jets seen in classical quasars., Comment: 8 pages, 3 figures, accepted for publication in the Astrophysical Journal

To understand the origin of nuclear ($\lesssim$ 100 pc) millimeter-wave (mm-wave) continuum emission in active galactic nuclei (AGNs), we systematically analyzed sub-arcsec resolution Band-6 (211-275 GHz) ALMA data of 98 nearby AGNs ($z <$ 0.05) from the 70-month Swift/BAT catalog. The sample, almost unbiased for obscured systems, provides the largest number of AGNs to date with high mm-wave spatial resolution sampling ($\sim$ 1-200 pc), and spans broad ranges of 14-150 keV luminosity {$40 < \log[L_{\rm 14-150}/({\rm erg\,s^{-1}})] < 45$}, black hole mass [$5 < \log(M_{\rm BH}/M_\odot) < 10$], and Eddington ratio ($-4 < \log \lambda_{\rm Edd} < 2$). We find a significant correlation between 1.3 mm (230 GHz) and 14-150 keV luminosities. Its scatter is $\approx$ 0.36 dex, and the mm-wave emission may serve as a good proxy of the AGN luminosity, free of dust extinction up to $N_{\rm H} \sim 10^{26}$ cm$^{-2}$. While the mm-wave emission could be self-absorbed synchrotron radiation around the X-ray corona according to past works, we also discuss different possible origins of the mm-wave emission; AGN-related dust emission, outflow-driven shocks, and a small-scale ($<$ 200 pc) jet. The dust emission is unlikely to be dominant, as the mm-wave slope is generally flatter than expected. Also, due to no increase in the mm-wave luminosity with the Eddington ratio, a radiation-driven outflow model is possibly not the common mechanism. Furthermore, we find independence of the mm-wave luminosity on indicators of the inclination angle from the polar axis of the nuclear structure, which is inconsistent with a jet model whose luminosity depends only on the angle., Comment: 44 pages, 35 figures, 3 tables, accepted for publication in ApJ; modified format, added supplementary figure (Fig. 32)

We present a spectroscopic and imaging study of an abnormal active galactic nucleus (AGN), 2MASX J00423991+3017515. This AGN is newly identified in the hard X-rays by the Swift BAT All-Sky survey and found in an edge-on disk galaxy interacting with a nearby companion. Here, we analyze the first optical spectra obtained for this system (taken in 2011 and 2016), high-resolution imaging taken with the Hubble Space Telescope and Chandra X-ray Observatory, and 1" imaging with the Very Large Array. Two unique properties are revealed: the peaks of the broad Balmer emission lines (associated with gas orbiting very near the supermassive black hole) are blue shifted from the corresponding narrow line emission and host galaxy absorption by 1540 km/s, and the AGN is spatially displaced from the apparent center of its host galaxy by 3.8 kpc. We explore several scenarios to explain these features, along with other anomalies, and propose that 2MASX J00423991+3017515 may be an AGN with an unusually strong wind residing in a uniquely configured major merger, or that it is an AGN recoiling from either a gravitational "slingshot" in a three-body interaction or from a kick due to the asymmetric emission of gravitational waves following the coalescence of two progenitor supermassive black holes., Comment: 17 pages, 10 figures, 4 tables, accepted for publication in MNRAS

The TESS exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long Gamma-Ray Burst (GRB) detected by Swift-BAT but without prompt XRT or UVOT follow-up due to proximity to the moon. The afterglow has a late peak at least 1000 seconds after the BAT trigger, with a brightest-detected TESS datapoint at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of rising light curve. Using ground-based photometry, we estimate a photometric redshift of $z_\mathrm{phot} = 3.29\pm{0.40}$. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor $\Gamma_\mathrm{BL}$ range from $90-133$. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of $R=15.1$ mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect $\sim1$ GRB afterglow per year above its magnitude limit., Comment: 10 pages, 7 figures. Accepted for publication in the Astrophysical Journal

The $\textit{Kepler}$ satellite potentially provides the highest precision photometry of active galactic nuclei (AGN) available to investigate short-timescale optical variability. We targeted quasars from the Sloan Digital Sky Survey that lie in the fields of view of the $\textit{Kepler/K2}$ campaigns. Based on those observations, we report the discovery and properties of a previously unidentified instrumental signature in K2. Systematic errors in K2, beyond those due to the motion of the detector, plague our AGN and other faint-target, guest-observer science proposals. Weakly illuminated pixels are dominated by low frequency trends that are both non-astrophysical and correlated from object to object. A critical clue to understanding this instrumental noise is that different targets observed in the same channels of Campaign 8 (rear facing) and Campaign 16 (forward facing) had nearly identical light curves after time reversal of one of the campaigns. This observation strongly suggests that the underlying problem relates to the relative Sun-spacecraft-field orientation, which was approximately the same on day 1 of Campaign 8 as the last day of Campaign 16. Furthermore, we measure that the instrumental signature lags in time as a function of radius from the center of the detector, crossing channel boundaries. Systematics documented in this investigation are unlikely to be due to Moir\'{e} noise, rolling band, or pointing jitter. Instead this work strongly suggests temperature-dependent focus changes that are further subject to channel variations. Further characterization of this signature is crucial for rehabilitating K2 data for use in investigations of AGN light curves., Comment: 21 pages, 16 figures

The NASA LISA Study Team was tasked to study how NASA might support US scientists to participate and maximize the science return from the Laser Interferometer Space Antenna (LISA) mission. LISA is gravitational wave observatory led by ESA with NASA as a junior partner, and is scheduled to launch in 2034. Among our findings: LISA science productivity is greatly enhanced by a full-featured US science center and an open access data model. As other major missions have demonstrated, a science center acts as both a locus and an amplifier of research innovation, data analysis, user support, user training and user interaction. In its most basic function, a US Science Center could facilitate entry into LISA science by hosting a Data Processing Center and a portal for the US community to access LISA data products. However, an enhanced LISA Science Center could: support one of the parallel independent processing pipelines required for data product validation; stimulate the high level of research on data analysis that LISA demands; support users unfamiliar with a novel observatory; facilitate astrophysics and fundamental research; provide an interface into the subtleties of the instrument to validate extraordinary discoveries; train new users; and expand the research community through guest investigator, postdoc and student programs. Establishing a US LISA Science Center well before launch can have a beneficial impact on the participation of the broader astronomical community by providing training, hosting topical workshops, disseminating mock catalogs, software pipelines, and documentation. Past experience indicates that successful science centers are established several years before launch; this early adoption model may be especially relevant for a pioneering mission like LISA., Comment: 93 pages with a lovely cover page thanks to Bernard Kelly and Elizabeth Ferrara

We compile observations of high-frequency quasi-periodic oscillations (QPOs) around black holes, both stellar and supermassive, and compare their positions in the parameter space of black hole mass, spin, and oscillation frequency. We find that supermassive black holes occupy a separate region of parameter space than stellar, and further, that QPOs seen around tidal disruption events rather than Seyfert-type AGN occupy an entirely different space. We then compare these results to the orbital resonance, diskoseismic, warped disk, and disk-jet coupling theoretical models for the origin of high-frequency QPOs. We find that while oscillations around stellar mass black holes are generally consistent with the above models, supermassive black holes are decidedly not. Oscillations seen in tidal disruption events are consistent with oscillations near the frequency of the innermost stable circular orbit (ISCO), while QPOs in AGN are not accounted for by any of the physical models in consideration. This indicates that despite the scale invariance of accretion processes implied by a decades-wide correlation between QPO frequency and black hole mass, any theory of high frequency QPOs must relate the frequency to more than just the mass and spin., Comment: 9 pages, 3 figures, 2 tables. Accepted for publication in the Astrophysical Journal

We conducted 22~GHz 1" JVLA imaging of 100 radio-quiet X-ray selected AGN from the Swift-BAT survey. We find AGN-driven kiloparsec-scale radio structures inconsistent with pure star formation in 11 AGN. The host galaxies of these AGN lie significantly below the star-forming main sequence, indicating suppressed star formation. While these radio structures tend to be physically small compared to the host galaxy, the global star formation rate of the host is affected. We evaluate the energetics of the radio structures interpreted first as immature radio jets, and then as consequences of an AGN-driven radiative outflow, and compare them to two criteria for successful feedback: the ability to remove the CO-derived molecular gas mass from the galaxy gravitational potential and the kinetic energy transfer to molecular clouds leading to $v_\mathrm{cloud} > \sigma_*$. In most cases, the jet interpretation is insufficient to provide the energy necessary to cause the star formation suppression. Conversely, the wind interpretation provides ample energy in all but one case. We conclude that it is more likely that the observed suppression of star formation in the global host galaxy is due to ISM interactions of a radiative outflow, rather than a small-scale radio jet., Comment: 15 pages, 3 figures, 2 tables. Accepted for publication in the Astrophysical Journal

We have conducted 22 GHz radio imaging at 1" resolution of 100 low-redshift AGN selected at 14-195 keV by the Swift-BAT. We find a radio core detection fraction of 96%, much higher than lower-frequency radio surveys. Of the 96 radio-detected AGN, 55 have compact morphologies, 30 have morphologies consistent with nuclear star formation, and 11 have sub-kpc to kpc-scale jets. We find that the total radio power does not distinguish between nuclear star formation and jets as the origin of the radio emission. For 87 objects, we use optical spectroscopy to test whether AGN physical parameters are distinct between radio morphological types. We find that X-ray luminosities tend to be higher if the 22 GHz morphology is jet-like, but find no significant difference in other physical parameters. We find that the relationship between the X-ray and core radio luminosities is consistent with the $L_R/L_X \sim 10^{-5}$ of coronally active stars. We further find that the canonical fundamental planes of black hole activity systematically over-predict our radio luminosities, particularly for objects with star formation morphologies., Comment: 22 pages, 10 figures, 2 tables. Accepted for publication in MNRAS

Theory predicts that a supermassive black hole binary (SMBHB) could be observed as a luminous active galactic nucleus (AGN) that periodically varies on the order of its orbital timescale. In X-rays, periodic variations could be caused by mechanisms including relativistic Doppler boosting and shocks. Here we present the first systematic search for periodic AGNs using $941$ hard X-ray light curves (14-195 keV) from the first 105 months of the Swift Burst Alert Telescope (BAT) survey (2004-2013). We do not find evidence for periodic AGNs in Swift-BAT, including the previously reported SMBHB candidate MCG+11$-$11$-$032. We find that the null detection is consistent with the combination of the upper-limit binary population in AGNs in our adopted model, their expected periodic variability amplitudes, and the BAT survey characteristics. We have also investigated the detectability of SMBHBs against normal AGN X-ray variability in the context of the eROSITA survey. Under our assumptions of a binary population and the periodic signals they produce which have long periods of hundreds of days, up to $13$% true periodic binaries can be robustly distinguished from normal variable AGNs with the ideal uniform sampling. However, we demonstrate that realistic eROSITA sampling is likely to be insensitive to long-period binaries because longer observing gaps reduce their detectability. In contrast, large observing gaps do not diminish the prospect of detecting binaries of short, few-day periods, as 19% can be successfully recovered, the vast majority of which can be identified by the first half of the survey., Comment: 17 pages, including 8 figures and 4 tables. Accepted for publication in ApJ

We present optical SuperNova Integral Field Spectrograph (SNIFS) integral field spectroscopy, Hubble Space Telescope optical imaging, Chandra X-ray imaging, and Very Large Array radio interferometry of the merging galaxy 2MASX J04234080+0408017, which hosts a Seyfert 2 active galactic nucleus (AGN) at z = 0.046. Our observations reveal that radiatively driven, ionized gas outflows are successful to distances > 10 kpc due to the low mass of the host system, encompassing the entirety of the observed optical emission. We also find that at large radii, where observed velocities cannot be reproduced by radiative driving models, high velocity kinematics are likely due to mechanical driving from AGN winds impacting high density host material. This impacting deposits sufficient energy to shock the host material, producing thermal X-ray emission and cosmic rays, which in turn promote the formation of in situ radio structure in a pseudo-jet morphology along the high density lanes., Comment: Accepted for publication in ApJ. 20 pages, 20 figures

We examine the light curves of two quasars, motivated by recent suggestions that a supermassive black hole binary (SMBHB) can exhibit sharp lensing spikes. We model the variability of each light curve as due to a combination of two relativistic effects: the orbital relativistic Doppler boost and gravitational binary self-lensing. In order to model each system we extend previous Doppler plus self-lensing models to include eccentricity. The first quasar is identified in optical data as a binary candidate with a 20-yr period (Ark 120), and shows a prominent spike. For this source, we rule out the lensing hypothesis and disfavor the Doppler-boost hypothesis due to discrepancies in the measured vs. recovered values of the binary mass and optical spectral slope. The second source, which we nickname Spikey, is the rare case of an active galactic nucleus (AGN) identified in Kepler's high-quality, high-cadence photometric data. For this source, we find a model, consisting of a combination of a Doppler modulation and a narrow symmetric lensing spike, consistent with an eccentric SMBHB with a total mass of approximately 30 million solar masses, rest-frame orbital period T=418 days, eccentricity e=0.5, and seen at an inclination of 8 degrees from edge-on. This interpretation can be tested by monitoring Spikey for periodic behavior and recurring flares in the next few years. In preparation for such monitoring we present the first X-ray observations of this object taken by the Neil Gehrels Swift observatory., Comment: Accepted to MNRAS

We have performed a very long baseline interferometry (VLBI) survey of local (z < 0.05) ultra hard X-ray (14-195 keV) selected active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) using KVN, KaVA, and VLBA. We first executed fringe surveys of 142 BAT-detected AGN at 15 or 22 GHz. Based on the fringe surveys and archival data, we find 10/279 nearby AGN (~4%) VLBI have 22 GHz flux above 30 mJy. This implies that the X-ray AGN with a bright nuclear jet are not common. Among these 10 radio-bright AGN, we obtained 22 GHz VLBI imaging data of our own for four targets and reprocessed archival data for six targets. We find that, although our 10 AGN observed with VLBI span a wide range of pc-scale morphological types, they lie on a tight linear relation between accretion luminosity and nuclear jet luminosity. Our result suggests that a powerful nuclear radio jet correlates with the accretion disc luminosity. We also probed the fundamental plane of black hole activity at VLBI scales (e.g., few milli-arcsecond). The jet luminosity and size distribution among our sample roughly fit into the proposed AGN evolutionary scenario, finding powerful jets after the blow-out phase based on the Eddington ratio (\lambda_{Edd})-hydrogen column density (N_{H}) relation. In addition, we find some hints of gas inflow or galaxy-galaxy merger in the majority of our sample. This implies that gas supply via tidal interactions in galactic scale may help the central AGN to launch a powerful parsec-scale jet., Comment: 11+2 pages, 6 figures, Accepted for publication in MNRAS, Comments are welcome

In response to the need for the Astro2020 Decadal Survey to explicitly engage early career astronomers, the National Academies of Sciences, Engineering, and Medicine hosted the Early Career Astronomer and Astrophysicist Focus Session (ECFS) on October 8-9, 2018 under the auspices of Committee of Astronomy and Astrophysics. The meeting was attended by fifty six pre-tenure faculty, research scientists, postdoctoral scholars, and senior graduate students, as well as eight former decadal survey committee members, who acted as facilitators. The event was designed to educate early career astronomers about the decadal survey process, to solicit their feedback on the role that early career astronomers should play in Astro2020, and to provide a forum for the discussion of a wide range of topics regarding the astrophysics career path. This white paper presents highlights and themes that emerged during two days of discussion. In Section 1, we discuss concerns that emerged regarding the coming decade and the astrophysics career path, as well as specific recommendations from participants regarding how to address them. We have organized these concerns and suggestions into five broad themes. These include (sequentially): (1) adequately training astronomers in the statistical and computational techniques necessary in an era of "big data", (2) responses to the growth of collaborations and telescopes, (3) concerns about the adequacy of graduate and postdoctoral training, (4) the need for improvements in equity and inclusion in astronomy, and (5) smoothing and facilitating transitions between early career stages. Section 2 is focused on ideas regarding the decadal survey itself, including: incorporating early career voices, ensuring diverse input from a variety of stakeholders, and successfully and broadly disseminating the results of the survey., Comment: 9 pages; Astro2020 APC White Paper: State of the Profession Consideration

The photometric precision, monitoring baselines, and rapid, even sampling rates required by modern satellites designed for detecting the signal of transiting exoplanets are ideally suited to a large number of applications in high-energy astrophysics. I will exemplify this by discussing the results for active galactic nuclei from Kepler and summarizing other high-energy results from Kepler/K2. These precision instruments are currently underutilized for high-energy applications despite their great potential, due in part to complex systematics affecting the data. I will summarize these effects and mitigation approaches, and conclude by discussing how the recently launched Transiting Exoplanet Survey Satellite mission will differ from Kepler/K2 in ways significant to the high-energy community., Comment: Accepted for publication in Astronomische Nachrichten. Conference Proceedings from "Time-Domain Astronomy: A High Energy View", June 13-15 2018, ESAC, Madrid, Spain

We present the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probe-class mission concept selected for study by NASA. It combines huge collecting area, high throughput, broad energy coverage, and excellent spectral and temporal resolution in a single facility. STROBE-X offers an enormous increase in sensitivity for X-ray spectral timing, extending these techniques to extragalactic targets for the first time. It is also an agile mission capable of rapid response to transient events, making it an essential X-ray partner facility in the era of time-domain, multi-wavelength, and multi-messenger astronomy. Optimized for study of the most extreme conditions found in the Universe, its key science objectives include: (1) Robustly measuring mass and spin and mapping inner accretion flows across the black hole mass spectrum, from compact stars to intermediate-mass objects to active galactic nuclei. (2) Mapping out the full mass-radius relation of neutron stars using an ensemble of nearly two dozen rotation-powered pulsars and accreting neutron stars, and hence measuring the equation of state for ultradense matter over a much wider range of densities than explored by NICER. (3) Identifying and studying X-ray counterparts (in the post-Swift era) for multiwavelength and multi-messenger transients in the dynamic sky through cross-correlation with gravitational wave interferometers, neutrino observatories, and high-cadence time-domain surveys in other electromagnetic bands. (4) Continuously surveying the dynamic X-ray sky with a large duty cycle and high time resolution to characterize the behavior of X-ray sources over an unprecedentedly vast range of time scales. STROBE-X's formidable capabilities will also enable a broad portfolio of additional science., Comment: 50 pages, Probe class mission concept study report submitted to NASA for Astro2020 Decadal Survey

We report evidence for a quasi-periodic oscillation (QPO) in the optical light curve of KIC 9650712, a narrow-line Seyfert 1 galaxy in the original Kepler field. After the development and application of a pipeline for Kepler data specific to active galactic nuclei (AGN), one of our sample of 21 AGN selected by infrared photometry and X-ray flux demonstrates a peak in the power spectrum at log $\nu$ = -6.58 Hz, corresponding to a temporal period of t=44 days. We note that although the power spectrum is well-fit by a model consisting of a Lorentzian and a single power law, alternative continuum models cannot be ruled out. From optical spectroscopy, we measure the black hole mass of this AGN as log $M_{\mathrm{BH}} / M_\odot$ = 8.17. We find that this frequency lies along a correlation between low-frequency QPOs and black hole mass from stellar and intermediate mass black holes to AGN, similar to the known correlation in high-frequency QPOs., Comment: 6 pages, 4 figures, Accepted for Publication in ApJ Letters

We present a comprehensive analysis of 21 light curves of Type 1 AGN from the Kepler spacecraft. First, we describe the necessity and development of a customized pipeline for treating Kepler data of stochastically variable sources like AGN. We then present the light curves, power spectral density functions (PSDs), and flux histograms. The light curves display an astonishing variety of behaviors, many of which would not be detected in ground-based studies, including switching between distinct flux levels. Six objects exhibit PSD flattening at characteristic timescales which roughly correlate with black hole mass. These timescales are consistent with orbital timescales or freefall accretion timescales. We check for correlations of variability and high-frequency PSD slope with accretion rate, black hole mass, redshift and luminosity. We find that bolometric luminosity is anticorrelated with both variability and steepness of the PSD slope. We do not find evidence of the linear rms-flux relationships or lognormal flux distributions found in X-ray AGN light curves, indicating that reprocessing is not a significant contributor to optical variability at the 0.1-10% level., Comment: 39 pages including 2 appendices. Accepted for Publication in the Astrophysical Journal, with higher resolution figures

We have conducted 22 GHz 1" JVLA imaging of 70 radio-quiet AGN from the Swift-BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission to that predicted from previous Herschel observations using the canonical FIR-radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics in the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGN, and find general consistency with both models. However, we find that the $L_{\mathrm{R}} / L_{\mathrm{X}}$ relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGN. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence of star formation, and conclude that those AGN that fall below the main sequence, as X-ray selected AGN have been found to do, have core-dominated or jet-like 22 GHz morphologies., Comment: 17 pages, 9 figures, accepted for publication in the Astrophysical Journal

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type FK, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, that is evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a process believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short-lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity., Comment: 34 pages, Accepted in ApJ

We introduce the first phase of the Kepler-Swift Active Galaxies and Stars survey (KSwAGS), a simultaneous X-ray and UV survey of ~6 square degrees of the Kepler field using the Swift XRT and UVOT. We detect 93 unique X-ray sources with S/N>3 with the XRT, of which 60 have observed UV counterparts. We use the Kepler Input Catalog (KIC) to obtain the optical counterparts of these sources, and construct the X-ray to optical flux ratio as a first approximation of the classification of the source. The survey produces a mixture of stellar sources, extragalactic sources, and sources which we are not able to classify with certainty. We have obtained optical spectra for thirty of these targets, and are conducting an ongoing observing campaign to fully identify the sample. For sources classified as stellar or AGN with certainty, we construct SEDs using the 2MASS, UBV and GALEX data supplied for their optical counterparts by the KIC, and show that the SEDs differ qualitatively between the source types, and so can offer a method of classification in absence of a spectrum. Future papers in this series will analyze the timing properties of the stars and AGN in our sample separately. Our survey provides the first X-ray and UV data for a number of known variable stellar sources, as well as a large number of new X-ray detections in this well-studied portion of the sky. The KSwAGS survey is currently ongoing in the K2 ecliptic plane fields., Comment: Accepted for publication in the Astronomical Journal. 19 pages, 8 figures, 3 tables

We present near-infrared (NIR) spectra of four optically-elusive AGN and four X- ray bright, optically normal galaxies (XBONGs) from the Swift-BAT survey. With archival observations from SDSS, 2MASS, Spitzer and WISE, we test a number of AGN indicators in the NIR and MIR; namely, NIR emission line diagnostic ratios, the presence of coronal high-ionization lines, and infrared photometry. Of our eight hard X-ray selected AGN, we find that optical normalcy has a variety of causes from object to object, and no one explanation applies. Our objects have normal Eddington ratios, and so are unlikely to host radiatively-inefficient accretion flows (RIAFs). It is unlikely that star formation in the host or starlight dilution is contributing to their failure of optical diagnostics, except perhaps in two cases. The NIR continua are well-fit by two blackbodies: one at the stellar temperature, and a hot dust component near the dust sublimation temperature. XBONGs are more likely to have significant hot dust components, while these components are small relative to starlight in the optically-elusive AGN. Some of our sample have NIR line ratios typical of AGN, but NIR diagnostics are unsuccessful in distinguishing HII regions from AGN in general. In one object, we discover a hidden broad line region in the NIR. These results have strong relevance to the origin of optically normal AGN in deep X-ray surveys., Comment: 38 pages including 3 tables and 11 figures, Accepted for publication in ApJ

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m telescope from February to November of 2012, and obtained complementary V-band images from five other ground-based telescopes. We measured the H-beta light curve lag with respect to the V-band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53 (+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s. Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei.

AGN with double-peaked narrow lines (DPAGN) may be caused by kiloparsec scale binary AGN, bipolar outflows, or rotating gaseous disks. We examine the class of DPAGN in which the two narrow line components have closely similar intensity as being especially likely to involve disks or jets. Two spectroscopic indicators support this likelihood. For DPAGN from Smith et al. (2010), the "equal-peaked" objects (EPAGN) have [Ne V]/[O III] ratios lower than for a control sample of non-double peaked AGN. This is unexpected for a pair of normal AGN in a galactic merger, but may be consistent with [O III] emission from a rotating ring with relatively little gas at small radii. Also, [O III]/H-beta ratios of the redshifted and blueshifted systems in the EPAGN are more similar to each other than in a control sample, suggestive of a single ionizing source and inconsistent with the binary interpretation., Comment: 7 pages, 2 figures. Published in ApJ, after substantial revision

We introduce the first phase of the Kepler-Swift Active Galaxies and Stars survey (KSwAGS), a simultaneous X-ray and UV survey of approximately 6 square degrees of the Kepler field using the Swift XRT and UVOT. We detect 93 unique X-ray sources with S/N greater or equal to 3 with the XRT, of which 60 have UV counterparts. We use the Kepler Input Catalog (KIC) to obtain the optical counterparts of these sources, and construct the fX / fV ratio as a first approximation of the classification of the source. The survey produces a mixture of stellar sources, extragalactic sources, and sources which we are not able to classify with certainty. We have obtained optical spectra for thirty of these targets, and are conducting an ongoing observing campaign to fully identify the sample. For sources classified as stellar or AGN with certainty, we construct SEDs using the 2MASS, UBV and GALEX data supplied for their optical counterparts by the KIC, and show that the SEDs differ qualitatively between the source types, and so can offer a method of classification in absence of a spectrum. Future papers in this series will analyze the timing properties of the stars and AGN in our sample separately. Our survey provides the first X-ray and UV data for a number of known variable stellar sources, as well as a large number of new X-ray detections in this well-studied portion of the sky. The KSwAGS survey is currently ongoing in the K2 ecliptic plane fields.