We present Neutron Star Interior Composition Explorer X-ray and Arcminute Microkelvin Imager Large Array radio observations of a rapid hard-to-soft state transition in the black hole X-ray transient ...MAXI J1820+070. During the transition from the hard state to the soft state a switch between two particular types of quasiperiodic oscillations (QPOs) was seen in the X-ray power density spectra, from type-C to type-B, along with a drop in the strength of the broadband X-ray variability and a brief flare in the 7-12 keV band. Soon after this switch (∼2-2.5 hr) a strong radio flare was observed that corresponded to the launch of superluminal ejecta. Although hints of a connection between QPO transitions and radio flares have been seen in other black hole X-ray transients, our observations constitute the strongest observational evidence to date for a link between the appearance of type-B QPOs and the launch of discrete jet ejections.
The central engines of active galactic nuclei (AGNs) are powered by accreting supermassive black holes, and while AGNs are known to play an important role in galaxy evolution, the key physical ...processes occur on scales that are too small to be resolved spatially (aside from a few exceptional cases). Reverberation mapping is a powerful technique that overcomes this limitation by using echoes of light to determine the geometry and kinematics of the central regions. Variable ionizing radiation from close to the black hole drives correlated variability in surrounding gas/dust but with a time delay due to the light travel time between the regions, allowing reverberation mapping to effectively replace spatial resolution with time resolution. Reverberation mapping is used to measure black hole masses and to probe the innermost X-ray emitting region, the UV/optical accretion disk, the broad emission line region, and the dusty torus. In this article, we provide an overview of the technique and its varied applications.
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Observational astronomy; Extragalactic astrophysics; Astrophysics methods
Stellar tidal disruption events (TDEs) are typically discovered by transient emission due to accretion or shocks of the stellar debris. Yet this luminous flare can be reprocessed by gas or dust that ...inhabits a galactic nucleus, resulting in multiple reverberation signals. Nuclear dust heated by the TDE will lead to an echo at infrared wavelengths (1-10 μm) and transient coronal lines in optical spectra of TDEs trace reverberation by gas that orbits the black hole. Both of these signal have been detected, here we review this rapidly developing field. We also review the results that have been extracted from TDEs with high-quality X-ray light curves: quasi periodic oscillations (QPOs), reverberation lags of fluorescence lines, and cross-correlations with emission at other wavelengths. The observational techniques that are covered in this review probe the emission from TDEs over a wide range of scales: from
∼
1
light year to the innermost parts of the newly formed accretion disk. They provide insights into important properties of TDEs such as their bolometric output and the geometry of the accretion flow. While reverberation signals are not detected for every TDE, we anticipate they will become more commonplace when the next generation of X-ray and infrared instruments become operational.
We present Zwicky Transient Facility (ZTF) observations of the tidal disruption flare AT2018zr/PS18kh reported by Holoien et al. and detected during ZTF commissioning. The ZTF light curve of the ...tidal disruption event (TDE) samples the rise-to-peak exceptionally well, with 50 days of g- and r-band detections before the time of maximum light. We also present our multi-wavelength follow-up observations, including the detection of a thermal (kT 100 eV) X-ray source that is two orders of magnitude fainter than the contemporaneous optical/UV blackbody luminosity, and a stringent upper limit to the radio emission. We use observations of 128 known active galactic nuclei (AGNs) to assess the quality of the ZTF astrometry, finding a median host-flare distance of 0 2 for genuine nuclear flares. Using ZTF observations of variability from known AGNs and supernovae we show how these sources can be separated from TDEs. A combination of light-curve shape, color, and location in the host galaxy can be used to select a clean TDE sample from multi-band optical surveys such as ZTF or the Large Synoptic Survey Telescope.
Abstract
We analyze five epochs of Neutron star Interior Composition Explorer (NICER) data of the black hole X-ray binary MAXI J1820+070 during the bright hard-to-soft state transition in its 2018 ...outburst with both reflection spectroscopy and Fourier-resolved timing analysis. We confirm the previous discovery of reverberation lags in the hard state, and find that the frequency range where the (soft) reverberation lag dominates decreases with the reverberation lag amplitude increasing during the transition, suggesting an increasing X-ray emitting region, possibly due to an expanding corona. By jointly fitting the lag-energy spectra in a number of broad frequency ranges with the reverberation model
reltrans
, we find the increase in reverberation lag is best described by an increase in the X-ray coronal height. This result, along with the finding that the corona contracts in the hard state, suggests a close relationship between spatial extent of the X-ray corona and the radio jet. We find the corona expansion (as probed by reverberation) precedes a radio flare by ∼5 days, which may suggest that the hard-to-soft transition is marked by the corona expanding vertically and launching a jet knot that propagates along the jet stream at relativistic velocities.
Abstract
We perform the first systematic search of all NICER archival observations of black hole (and candidate) low-mass X-ray binaries for signatures of reverberation. Reverberation lags result ...from the light travel time difference between the direct coronal emission and the reflected disk component, and therefore their properties are a useful probe of the disk-corona geometry. We detect new signatures of reverberation lags in eight sources, increasing the total sample from three to 11, and study the evolution of reverberation lag properties as the sources evolve in outbursts. We find that in all of the nine sources with more than one reverberation lag detection, the reverberation lags become longer and dominate at lower Fourier frequencies during the hard-to-soft state transition. This result shows that the evolution in reverberation lags is a global property of the state transitions of black hole low-mass X-ray binaries, which is valuable in constraining models of such state transitions. The reverberation lag evolution suggests that the corona is the base of a jet that vertically expands and/or gets ejected during state transition. We also discover that in the hard state, the reverberation lags get shorter, just as the quasiperiodic oscillations (QPOs) move to higher frequencies, but then in the state transition, while the QPOs continue to higher frequencies, the lags get longer. We discuss the implications of the coronal geometry and physical models of QPOs in light of this new finding.
Abstract
UV and optical continuum reverberation mapping is a powerful tool for probing the accretion disk and inner broad-line region. However, recent reverberation mapping campaigns in the X-ray, ...UV, and optical have found lags consistently longer than those expected from the standard disk reprocessing picture. The largest discrepancy to date was recently reported in Mrk 335, where UV/optical lags are up to 12 times longer than expected. Here, we perform a frequency-resolved time lag analysis of Mrk 335, using Gaussian processes to account for irregular sampling. For the first time, we compare the Fourier frequency-resolved lags directly to those computed using the popular interpolated cross-correlation function method applied to both the original and detrended light curves. We show that the anticipated disk reverberation lags are recovered by the Fourier lags when zeroing in on the short-timescale variability. This suggests that a separate variability component is present on long timescales. If this separate component is modeled as reverberation from another region beyond the accretion disk, we constrain a size scale of roughly 15 lt-days from the central black hole. This is consistent with the size of the broad-line region inferred from H
β
reverberation lags. We also find tentative evidence for a soft X-ray lag, which we propose may be due to light travel time delays between the hard X-ray corona and distant photoionized gas that dominates the soft X-ray spectrum below 2 keV.
We present a study of the relationship between black hole accretion rate (BHAR) and star formation rate (SFR) in a sample of giant elliptical galaxies. These galaxies, which live at the centers of ...galaxy groups and clusters, have star formation and black hole activity that is primarily fueled by gas condensing out of the hot intracluster medium. For a sample of 46 galaxies spanning five orders of magnitude in BHAR and SFR, we find a mean ratio of , independent of the methodology used to constrain both SFR and BHAR. This ratio is significantly higher than most previously published values for field galaxies. We investigate whether these high BHAR/SFR ratios are driven by high BHAR, low SFR, or a different accretion efficiency in radio galaxies. The data suggest that the high BHAR/SFR ratios are primarily driven by boosted black hole accretion in spheroidal galaxies compared to their disk counterparts. We propose that the angular momentum of the cool gas is the primary driver in suppressing BHAR in lower-mass galaxies, with massive galaxies accreting gas that has condensed out of the hot phase on nearly radial trajectories. Additionally, we demonstrate that the relationship between specific BHAR and SFR (sBHAR and sSFR) has much less scatter over six orders of magnitude in both parameters, due to competing dependence on morphology between the MBH-M* and BHAR-SFR relations. In general, active galaxies selected by typical techniques have sBHAR/sSFR ∼ 10, while galactic nuclei with no clear AGN signatures have sBHAR/sSFR ∼ 1, consistent with a universal MBH-Mspheroid relation.
ABSTRACT
NGC 1275 is the brightest cluster galaxy (BCG) in the Perseus cluster and hosts the active galactic nucleus (AGN) that is heating the central 100 kpc of the intracluster medium atmosphere ...via a regulated feedback loop. Here, we use a deep (490 ks) Cycle-19 Chandra High-Energy Transmission Grating (HETG) observation of NGC 1275 to study the anatomy of this AGN. The X-ray continuum is adequately described by an unabsorbed power law with photon index Γ ≈ 1.9, creating strong tension with the detected column of molecular gas seen via HCN and HCO+ line absorption against the parsec-scale core/jet. This tension is resolved if we permit a composite X-ray source; allowing a column of $N_\mathrm{ H}\sim 8\times 10^{22}\hbox{${\rm \, cm}^{-2}\, $}$ to cover ∼15 per cent of the X-ray emitter does produce a significant improvement in the statistical quality of the spectral fit. We suggest that the dominant unabsorbed component corresponds to the accretion disc corona, and the sub-dominant X-ray component is the jet working surface and/or jet cocoon that is expanding into clumpy molecular gas. We suggest that this may be a common occurrence in BCG-AGN. We conduct a search for photoionized absorbers/winds and fail to detect such a component, ruling out columns and ionization parameters often seen in many other Seyfert galaxies. We detect the 6.4 keV iron-K α fluorescence line seen previously by XMM–Newton and Hitomi. We describe an analysis methodology that combines dispersive HETG spectra, non-dispersive microcalorimeter spectra, and sensitive XMM–Newton/EPIC spectra in order to constrain (sub)arcsec-scale extensions of the iron-K α emission region.
Abstract
Accreting black holes commonly exhibit hard X-ray emission, originating from a region of hot plasma near the central engine referred to as the corona. The origin and geometry of the corona ...are poorly understood, and models invoking either inflowing or outflowing material (or both) can successfully explain only parts of the observed phenomenology. In particular, recent works indicate that the time-averaged and variability property might originate in different regions of the corona. In this paper we present a model designed to move beyond the lamppost paradigm, with the goal of accounting for the vertical extent of the corona. In particular, we highlight the impact of including self-consistently a second lamppost, mimicking, for example, an extended jet base. We fully include the effect that the second source has on the time-dependent disk ionization, reflection spectrum, and reverberation lags. We also present an application of this new model to NICER observations of the X-ray binary MAXI J1820+070 near its hard-to-soft state transition. We demonstrate that in these observations, a vertically extended corona can capture both spectral and timing properties, while a single-lamppost model can not. In this scenario, the illumination responsible for the time-averaged spectrum originates close to the black hole, while the variability is likely associated with the ballistic jet.
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