arXiv subjects

S. Kraemer

Publications and source records attributed to S. Kraemer.

At least 19 recordsLinked to original sources

arXiv2026

Exploring $\alpha$- and $\beta$-decay-induced quenching of the $^{229}$Th nuclear-clock isomer in solid-state hosts

The radiative decay dynamics of an ensemble of $^{229\mathrm{m}}$Th nuclei embedded in CaF$_2$ and MgF$_2$ is investigated. The isomer is populated through $\beta$ decay of $^{229}$Ac following ion implantation, and its radiative decay is detected using vacuum-ultraviolet spectroscopy and measured as a function of time. This allows to identify and quantify the quenching of the radiative-decay signal induced by $\alpha$ or $\beta$ radiation. The quenching probability density is determined in different CaF$_2$ crystals and in a MgF$_2$ crystal, revealing differences up to two orders of magnitude between the investigated samples and a strong dependence on the host material and defect densities. The results support a microscopic mechanism mediated by charge carriers in which electronic excitations created by the decay radiation are captured near Th defects, thereby favoring non-radiative decay channels.

nucl-ex↗

arXiv2026

Supermassive Black Hole Winds in X-rays: SUBWAYS V. Properties of hot coronae in quasars at intermediate redshift

We present the X-ray analysis of coronal properties in a statistically representative sample of 23 mostly radio-quiet AGN from the SUBWAYS campaign (SUpermassive Black holes Winds in XrAYs), focusing on quasars at redshifts $0.1 < z < 0.4 $ and bolometric luminosities $2 \times 10^{44} <L_{bol}(erg/s) < 2 \times 10^{46}$. The main aim of this work is to investigate the properties of the hot corona through the study of the hard X-ray band emission, including a proper treatment of the soft X-ray band. High-quality X-ray spectra from XMM-Newton, complemented by NuSTAR data extending up to 30-40 keV in the rest frame, are available for this sample. The soft X-ray band (0.3-2 keV) spectrum is best fitted by a warm corona model with a median temperature of 0.40 keV, and an optical depth in the range $\tau$=20 - 40, consistent with previous results on lower luminosity sources. The hard X-ray band is well described using a hot corona model, with a median high-energy cut-off of 87 keV, at the lower end of the distribution of typical values found in Seyfert galaxies (100 - 200 keV). The derived median value of the optical depth ($\tau$ = 1 - 5) suggests the presence of a moderately optically thick corona. Combining the SUBWAYS results with literature samples at low and high redshift, we assemble the largest sample to date of AGN with E$_{cut}$ and accretion parameter measurements, finding a significant anticorrelation of E$_{cut}$ with both $\lambda_{Edd}$ and $L_{bol}$ with the median E$_{cut}$ decreasing from 250 - 300 keV at low accretion rates and luminosities to 90 - 100 keV at high accretion rates and luminosities - consistent with enhanced coronal cooling, possibly driven by pair-production. These results favor cooler, optically thicker coronae in luminous AGN compared to those in lower-luminosity Seyfert galaxies.

astro-ph.HE↗

arXiv2026

Hot, Photoionized X-ray Gas in Two Luminous Type 2 Quasars: Chandra-HST Evidence for a Wind-Driven Sequence

We present new Chandra/ACIS-S imaging spectroscopy of two luminous type 2 quasars, FIRST J120041.4+314745 ($z$=0.116) and 2MASX J13003807+5454367 ($z$=0.088), and compare their X-ray emission with Hubble Space Telescope [O III]$λ$5007 morphologies and kinematics. Both systems show kiloparsec-scale soft X-ray emission. In FIRST J120041, the X-ray morphology is clumpy and closely follows the [O III] structures, with surface-brightness peaks co-spatial with the highest [O III] velocities (600-750 km s$^{-1}$) and broadest line widths ($\sim$1700 km s$^{-1}$). In 2MASX J130038, the X-ray emission is centrally concentrated and weakly correlated with rotational [O III] kinematics. Spectral modeling indicates that photoionization dominates the soft X-rays in both quasars. The inferred hot-gas reservoirs are substantial, $M_{\rm x-ray}\sim4.5\times10^{8}M_\odot$ (FIRST J120041) and $M_{\rm x-ray}\sim1.8\times10^{8}M_\odot$ (2MASX J130038), exceeding the outflowing [O III] masses by factors of $\sim$4 and $\sim$16. In 2MASX J130038, we identify a tentative blueshifted Fe XXVI Ly$α$ line at $E_{\rm rest}=7.14\pm0.06$ keV ($v\sim7600$ km s$^{-1}$), consistent with a hot wind confined to the inner few hundred parsecs. Combining these results with a broader sample of twelve type 2 quasars, we argue that luminous quasars evolve along a continuous feedback sequence regulated by progressive clearing of circumnuclear gas. As AGN radiation and winds pierce the surrounding medium, systems transition from heavily enshrouded, compact configurations to phases where the X-ray and [O III] components strongly couple and, eventually, to energetically dominant outflows. FIRST J120041 and 2MASX J130038 represent two points along this sequence, tracing the emergence and growth of hot winds as primary drivers of quasar-scale feedback.

astro-ph.GA↗

arXiv2025

Mapping the Excitation Mechanisms in the LINER I Active Galactic Nucleus NGC 5005: Positive Feedback and a Thin LINER Cocoon

We present a spatially resolved Baldwin-Phillips-Terlevich analysis of the narrow-line region (NLR) in the low-ionization nuclear emission-line region (LINER) I galaxy NGC 5005 using Hubble Space Telescope narrowband imaging of [O III]$λ$5007, H$β$, H$α$, and [S II]$λλ$6717,6731. With a resolution of ${\lesssim}$0.1 (${\lesssim}$10 pc at z = 0.003), we dissect the NLR into H II (star-forming), Seyfert, and LINERs across spatial scales extending up to r$\sim$8 kpc from the nucleus. Our results reveal a compact nuclear region exhibiting Seyfert-like emission, consistent with photoionization by a low-luminosity active galactic nucleus (AGN). Surrounding this Seyfert-like nucleus is a thin ($\sim$20 pc thick) higher-excitation LINER-like cocoon, likely arising from shock-excited gas in the interstellar medium (ISM). Beyond this cocoon, a centrally localized extended (r$\sim$1 kpc) LINER-like region surrounds the Seyfert-like nucleus and cocoon, likely ionized by the AGN, while a more extended (r${\gtrsim}$2 kpc) LINER-like zone may be ionized by a combination of post-AGB stars and shocks from gas inflows. We also detect H II-like regions at both small and large scales. In the inner 500 pc, these regions may be triggered by jet-ISM interactions, potentially inducing localized star formation. At r$\sim$4 kpc, we identify an outer H II-like region tracing a large-scale star-forming ring, where ionization is dominated by young stars.

astro-ph.GA↗

arXiv2024

Radiative Decay of the $^{229m}$Th Nuclear Clock Isomer in Different Host Materials

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the $^{229m}$Th nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of $^{229m}$Th embedded are determined for single crystalline CaF$_2$, MgF$_2$, LiSrAlF$_6$, AlN, and amorphous SiO$_2$. For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in LiSrAlF$_6$ and CaF$_2$, reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation.

nucl-ex↗

arXiv2024

Supermassive Black Hole Winds in X-rays -- SUBWAYS. III. A population study on ultra-fast outflows

The detection of blue-shifted absorption lines likely associated with ionized Iron K-shell transitions in the X-ray spectra of many Active Galactic Nuclei (AGN) suggests the presence of a highly ionized gas outflowing with mildly relativistic velocities (0.03c-0.6c), named Ultra-Fast Outflow (UFO). Within the SUBWAYS project we characterized these winds starting from a sample of 22 radio-quiet quasars at 0.1 < z < 0.4, and compared the results with similar studies in the literature on samples of 42 local radio-quiet Seyfert galaxies and 14 high redshift radio-quiet quasars. The scope of our work is a statistical study of UFO parameters and incidence, considering key physical properties of the sources, e.g. supermassive black hole (SMBH) mass, bolometric luminosity, accretion rates and Spectral Energy Distribution, with the aim of gaining new insights into the UFO launching mechanisms. We find indications that highly luminous AGN with steeper X-ray/UV ratio, are more likely to host UFO. The presence of UFO is not significantly related to any other AGN property in our sample. These findings suggest that the UFO phenomenon may be transient. Focusing on AGN with UFO, other important results are: (1) faster UFO have larger ionization parameters and column densities; (2) X-ray radiation plays a more crucial role in driving highly ionized winds compared to UV; (3) the correlation between outflow velocity and luminosity is significantly flatter than what expected for radiatively driven winds; (4) more massive BH experience higher wind mass-losses, suppressing accretion of matter onto the BH; (5) the UFO launching radius is positively correlated with the Eddington ratio. Furthermore, our analysis suggest the involvement of multiple launching mechanisms, including radiation pressure and magneto-hydrodynamic processes, rather than pointing to a single, universally applicable mechanism.

astro-ph.GA↗

arXiv2022

Supermassive Black Hole Winds in X-rays -- SUBWAYS. I. Ultra-fast outflows in QSOs beyond the local Universe

We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$α$, Fe\,\textsc{xxvi}\,Ly$α$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations.

astro-ph.HE↗

arXiv2022

Tunneling spectroscopy of few-monolayer NbSe$_2$ in high magnetic field: Ising protection and triplet superconductivity

In conventional Bardeen-Cooper-Scrieffer (BCS) superconductors, Cooper pairs of electrons of opposite spin (i.e. singlet structure) form the ground state. Equal spin triplet pairs (ESTPs), as in superfluid $^3$He, are of great interest for superconducting spintronics and topological superconductivity, yet remain elusive. Recently, odd-parity ESTPs were predicted to arise in (few-)monolayer superconducting NbSe$_2$, from the non-colinearity between the out-of-plane Ising spin-orbit field (due to the lack of inversion symmetry in monolayer NbSe$_2$) and an applied in-plane magnetic field. These ESTPs couple to the singlet order parameter at finite field. Using van der Waals tunnel junctions, we perform spectroscopy of superconducting NbSe$_2$ flakes, of 2--25 monolayer thickness, measuring the quasiparticle density of states (DOS) as a function of applied in-plane magnetic field up to 33T. In flakes $\lesssim$ 15 monolayers thick the DOS has a single superconducting gap. In these thin samples, the magnetic field acts primarily on the spin (vs orbital) degree of freedom of the electrons, and superconductivity is further protected by the Ising field. The superconducting energy gap, extracted from our tunnelling spectra, decreases as a function of the applied magnetic field. However, in bilayer NbSe$_2$, close to the critical field (up to 30T, much larger than the Pauli limit), superconductivity appears to be more robust than expected from Ising protection alone. Our data can be explained by the above-mentioned ESTPs.

cond-mat.supr-con↗

arXiv2020

The Heidelberg compact electron beam ion traps

Electron beam ion traps (EBIT) are ideal tools for both production and study of highly charged ions (HCI). In order to reduce their construction, maintenance, and operation costs we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar$^{16+}$ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e. g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe$^{24+}$, achieving an electron-energy resolving power of $E/ΔE > 1500$ at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating resonant photoexcitation of highly charged oxygen.

physics.atom-ph↗

arXiv2019

An alternative approach to populate and study the $^{229}$Th nuclear clock isomer

A new approach to observe the radiative decay of the $^{229}$Th nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock, a nuclear laser and the search for time variations of the fundamental constants. The isomer's $γ$ decay towards the ground state will be studied with a high-resolution VUV spectrometer after its production by the $β$ decay of $^{229}$Ac. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used $^{233}$U $α$-decay recoil source. In this paper, a feasibility analysis of this new concept, and an experimental investigation of its key ingredients, using a pure $^{229}$Ac ion beam produced at the ISOLDE radioactive beam facility, is reported.

nucl-ex↗

arXiv2019

Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39

We present the first spatially resolved analysis of rest-frame optical and UV imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGN. This unique opportunity - combining gravitational lensing, AO guiding, redshift, and AGN activity - allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon. By analyzing the spatial extent and morphology of the Ly-alpha and dust-corrected H-alpha emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.

astro-ph.GA↗

arXiv2016

On the limits to mobility in InAs quantum wells with nearly lattice-matched barriers

The growth and the density dependence of the low temperature mobility of a series of two-dimensional electron systems confined to un-intentionally doped, low extended defect density InAs quantum wells with Al$_{1-x}$Ga$_{x}$Sb barriers are reported. The electron mobility limiting scattering mechanisms were determined by utilizing dual-gated devices to study the dependence of mobility on carrier density and electric field independently. Analysis of the possible scattering mechanisms indicate the mobility was limited primarily by rough interfaces in narrow quantum wells and a combination of alloy disorder and interface roughness in wide wells at high carrier density within the first occupied electronic sub-band. At low carrier density the functional dependence of the mobility on carrier density provided evidence of coulombic scattering from charged defects. A gate-tuned electron mobility exceeding 750,000 cm$^{2}$/Vs was achieved at a sample temperature of 2 K.

cond-mat.mtrl-sci↗

arXiv2015

Two-dimensional epitaxial superconductor-semiconductor heterostructures: A platform for topological superconducting networks

Progress in the emergent field of topological superconductivity relies on synthesis of new material combinations, combining superconductivity, low density, and spin-orbit coupling (SOC). For example, theory [1-4] indicates that the interface between a one-dimensional (1D) semiconductor (Sm) with strong SOC and a superconductor (S) hosts Majorana modes with nontrivial topological properties [5-8]. Recently, epitaxial growth of Al on InAs nanowires was shown to yield a high quality S-Sm system with uniformly transparent interfaces [9] and a hard induced gap, indicted by strongly suppressed sub gap tunneling conductance [10]. Here we report the realization of a two-dimensional (2D) InAs/InGaAs heterostructure with epitaxial Al, yielding a planar S-Sm system with structural and transport characteristics as good as the epitaxial wires. The realization of 2D epitaxial S-Sm systems represent a significant advance over wires, allowing extended networks via top-down processing. Among numerous potential applications, this new material system can serve as a platform for complex networks of topological superconductors with gate-controlled Majorana zero modes [1-4]. We demonstrate gateable Josephson junctions and a highly transparent 2D S-Sm interface based on the product of excess current and normal state resistance.

cond-mat.mes-hall↗

arXiv2010

Mid-Infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. Emission-Line Diagnostics

We compare mid-infrared emission-line properties, from high-resolution Spitzer spectra of a hard X-ray (14 -- 195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 micron, [Ne II] 12.81 micron, [Ne III] 15.56 micron and [Ne V] 14.32/24.32 micron, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the mid-infrared correlations and BAT fluxes and luminosities suggests that the emission lines primarily arise in gas ionized by the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with those from published studies of ULIRGs, PG QSOs, star-forming galaxies and LINERs. We find that the BAT AGN sample fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line ratios are lower in sources that have been previously classified in the mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that, in our X-ray selected sample, the AGN represents the main contribution to the observed line emission. These ratios represent a new emission line diagnostic for distinguishing between AGN and star forming galaxies.

astro-ph.CO↗

arXiv2009

Edge-on disk around the T Tauri star [MR81] Halpha 17 NE in CrA

Using the speckle camera SHARP at the 3.5m ESO NTT, Köhler and collaborators found an object ~3.5 mag fainter in K only 1.3" north-east of the T Tauri star [MR81] Ha 17 in the Corona Australis (CrA) star-forming region, which could be either a brown dwarf or a T Tauri star with an edge-on disk. We attempt to study this faint object in detail. We acquired deep VLT NACO near-infrared images at three epochs to determine, whether [MR81] Ha 17 and the nearby faint object are co-moving and to measure the infrared colors of both objects. We obtained optical and infrared spectra of both objects with the VLT using FORS and ISAAC, respectively, to determine spectral types and temperatures as well as ages and masses. The T Tauri star [MR81] Ha 17 and the faint nearby object have a projected separation of 1369.58 mas, i.e. 178 AU at 130 pc. They share the same proper motion (~5 sigma), so that they most certainly form a bound binary pair. The apparently fainter component [MR81] Ha 17 NE has a spectral type of M2e, while the apparently brighter component [MR81] Ha 17 SW, the previously known T Tauri star, has a spectral type of M4-5e. We can identify a nearly edge-on disk around [MR81] Ha 17 NE by visual inspection, which has a diameter of at least 30 to 50 AU. We are able to detect strong emission lines in [MR81] Ha 17 NE, which are almost certainly due to ongoing accretion. The NE object is detectable only by means of its scattered light. If both objects are coeval (2-3 Myr) and located at the same distance (~130 pc as CrA), then the apparently fainter [MR81] Ha 17 NE is more massive (primary) component with a nearly edge-on disk and the apparently brighter component [MR81] Ha 17 SW is less massive (com- panion). Both are low-mass T Tauri stars with masses of ~0.5 and 0.23 \pm 0.05 solar masses, respectively.

astro-ph.SR↗

arXiv2006

Magnetotransport of lanthanum doped RuSr2GdCu2O8 - the role of gadolinium

Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO2 planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K for low applied magnetic field and the gadolinium sublattice antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a complicated temperature dependence due to the combination of the two magnetic orderings and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO2 layers while the gadolinium magnetism influences the conductivity in the CuO2 layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic when gadolinium orders antiferromagnetically.

cond-mat.supr-con↗

arXiv2005

Evidence for Gravitational Infall of Matter onto the Super-Massive Black Hole in the quasar PG 1211+143?

We report the detection of redshifted iron K-alpha absorption lines in the Chandra LETG spectrum of the narrow-line quasar, PG 1211+143. The absorption lines are observed at 4.22 keV and 4.93 keV in the quasar spectrum, corresponding to 4.56 keV and 5.33 keV in the rest frame of PG 1211+143. From Monte Carlo simulations, the chance probability of both lines being false detections is low at 1.36e-04. Highly redshifted ionized iron K-alpha (Fe XXV or Fe XXVI) is the most plausible identification for the lines at their observed energies. If identified with H-like iron K-alpha at 6.97 keV, then the relativistic velocity shifts required are 0.40c and 0.26c. The extreme velocities can be explained by pure gravitational redshift if the matter exists in a stable orbit within 6 gravitational radii of the black hole. This would require a Kerr metric for the black hole. Alternatively the absorption may be the result of matter infalling directly onto the black hole, with a maximum observed velocity of 0.38c at 6Rg in the Schwarzschild metric. This matter may originate in a failed outflow or jet, which does not escape the gravitational potential of the black hole.

astro-ph↗

arXiv2001

The X-ray Emission from the Nucleus of the Dwarf Elliptical Galaxy NGC 3226

We present the first high resolution X-ray image of the dwarf elliptical galaxy NGC 3226. The data were obtained during an observation of the nearby Seyfert Galaxy NGC 3227 using the Chandra X-ray Observatory. We detect a point X-ray source spatially consistent with the optical nucleus of NGC 3226 and a recently-detected, compact, flat-spectrum, radio source. The X-ray spectrum can be measured up to ~10 keV and is consistent with a power law with a photon index 1.7 <~ Gamma <~ 2.2, or thermal bremmstrahlung emission with 4 <~ kT <~ 10 keV. In both cases the luminosity in the 2--10 keV band ~10^{40} h_{75}^{-1} erg/s. We find marginal evidence that the nucleus varies within the observation. These characteristics support evidence from other wavebands that NGC 3226 harbors a low-luminosity, active nucleus. We also comment on two previously-unknown, fainter X-ray sources <~ 15 arcsec from the nucleus of NGC 3226. Their proximity to the nucleus (with projected distances <~ 1.3/h_{75} kpc) suggests both are within NGC 3226, and thus have luminosities (~few x 10^{38} -- few x 10^{39} erg/s) consistent with black-hole binary systems.

astro-ph↗