W. Peter Maksym

Flows of X-ray gas reveal the disruption of a star by a massive black hole

Tidal forces close to massive black holes can violently disrupt stars that make a close approach. These extreme events are discovered via bright X-ray and optical/ultraviolet flares in galactic centres. Prior studies based on modelling decaying flux trends have been able to estimate broad properties, such as the mass accretion rate. Here we report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 043234. Variability within the absorption-dominated spectra indicates that the gas is relatively close to the black hole. Narrow linewidths indicate that the gas does not stretch over a large range of radii, giving a low volume filling factor. Modest outflow speeds of a few hundred kilometres per second are observed; these are below the escape speed from the radius set by variability. The gas flow is consistent with a rotating wind from the inner, super-Eddington region of a nascent accretion disk, or with a filament of disrupted stellar gas near to the apocentre of an elliptical orbit. Flows of this sort are predicted by fundamental analytical theory and more recent numerical simulations.

HST IMAGING OF FADING AGN CANDIDATES. I. HOST-GALAXY PROPERTIES AND ORIGIN OF THE EXTENDED GAS*

We present narrow- and medium-band HST imaging, with additional supporting ground-based data, for 8 galaxies identified as hosting fading AGN. These have AGN-ionized gas projected >10 kpc from the nucleus, and significant shortfall of ionizing radiation between the distant gas and the AGN, indicating fading AGN on ~50,000-year timescales. Every system shows evidence of ongoing or past interactions; a similar sample of obscured AGN with extended ionized clouds shares this incidence of disturbances. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material ~1.5 Gyr after initial arrival. The gas has lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. In contrast to clouds near radio-loud AGN, these are dominated by rotation, in some cases in warped disks. Outflows are important only in localized regions near some of the AGN. In UGC 7342 and UGC 11185, luminous star clusters are seen within projected ionization cones, potentially triggered by outflows. As in the discovery example Hannys Voorwerp/IC 2497, some clouds lack a strong correlation between H-alpha surface brightness and ionization parameter, indicating unresolved fine structure. Together with thin coherent filaments spanning several kpc, persistence of these structures over their orbital lifetimes may require a role for magnetic confinement. (Abridged)

Fading AGN Candidates: AGN Histories and Outflow Signatures

We consider the energy budgets and radiative history of eight fading AGN, identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on ≈ 50, 000-year timescales. We explore the use of minimum ionizing luminosity Qion derived from photoionization balance in the brightest pixels in Hα at each projected radius. Tests using presumably constant Palomar-Green (PG) QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGN, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Qion values is roughly constant for a given object and therefore does not prevent such derivation. The AGN in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈ 2 × 10 years before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 years. In the limit of largely obscured AGN, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from from infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGN, to simulations of AGN accretion; the strongest variations on these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission, morphologically suggestive of outflow, are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows < 300 km s−1, largely associated with very diffuse emission, and possibly entraining gas in one of the clouds seen in HST images. Only in the Teacup AGN do we see outflow signatures of order 1000 km s−1. In contrast to the extended emission regions around many radio-loud AGN, the clouds around these fading AGN consist largely of tidal debris being externally illuminated but not displaced by AGN outflows. Subject headings: galaxies: active — galaxies: individual (NGC 5792, NGC 5252, UGC 7342, UGC 11185, Mkn 1498) — galaxies: Seyfert — galaxies: interacting 1Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 2wkeel@ua.edu, Twitter: @NGC3314 3Astrophysics, Oxford University; and Adler Planetarium, 1300 S. Lakeshore Drive, Chicago, IL 60605 4Current address: Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 5Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407 6Department of Astronomy, New Mexico State University, P. O. Box 30001, MSC 4500, Las Cruces, New Mexico 1 ar X iv :1 61 2. 06 00 6v 1 [ as tr oph .G A ] 1 8 D ec 2 01 6

RBS 1032: A TIDAL DISRUPTION EVENT IN ANOTHER DWARF GALAXY?

RBS 1032 is a supersoft (

Extended X-ray emission in the IC 2497 – Hanny's Voorwerp system: energy injection in the gas around a fading AGN

\Gamma\sim5

A likely decade-long sustained tidal disruption event

), luminous (

Mapping Seyfert and LINER Excitation Modes in the Inner kpc of NGC 3393

\sim10^{43}

Ultraluminous X-ray bursts in two ultracompact companions to nearby elliptical galaxies

erg/s) ROSAT PSPC source which has been associated with an inactive dwarf galaxy at

The Cheshire Cat Gravitational Lens: The Formation of a Massive Fossil Group

z=0.026

Mapping Excitation in the Inner Regions of the Planetary Nebula NGC 5189 Using HST WFC3 Imaging

, SDSS J114726.69+494257.8. We have analyzed an XMM-Newton observation which confirms that RBS 1032 is indeed associated with the dwarf galaxy. Moreover, RBS 1032 has undergone a factor of