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'Bare' active galactic nuclei (AGN) are a subclass of Type 1 AGN that show little or no intrinsic absorption. They offer an unobscured view of the central regions of the AGN and therefore serve as ideal targets to study the relativistic reflection features originating from the innermost regions of the accretion disc. We present a detailed broadband spectral analysis ($0.3 - 70$ keV) of one of the most luminous bare AGN in the local universe, RBS 1124 ($z= 0.208$) using a new, co-ordinated high signal-to-noise observation obtained by $\textit{XMM-Newton}$ and $\textit{NuSTAR}$. The source exhibits a power-law continuum with $\Gamma \sim$ 1.8 along with a soft excess below 2 keV, a weak neutral iron line and curvature at high energies ($\sim 30$ keV). The broadband spectrum, including the soft excess and the high-energy continuum, is well fit by the relativistic reflection model when the accretion disc is allowed to have densities of log$(n_{\rm e}$/cm$^{-3}$) $\gtrsim 19.2$. Our analysis therefore suggests that when high-density effects are considered, relativistic reflection remains a viable explanation for the soft excess., Comment: 14 pages, 9 figures, accepted for publication in MNRAS

Tidal disruption events (TDEs) can potentially probe low-mass black holes in host galaxies that might not adhere to bulge or stellar-dispersion relationships. At least initially, TDEs can also reveal super-Eddington accretion. X-ray spectroscopy can potentially constrain black hole masses, and reveal ionized outflows associated with super-Eddington accretion. Our analysis of XMM-Newton X-ray observations of the TDE AT2021ehb, around 300 days post-disruption, reveals a soft spectrum and can be fit with a combination of multi-color disk blackbody and power-law components. Using two independent disk models with properties suited to TDEs, we estimate a black hole mass at $M \simeq 10^{5.5}~M_{\odot}$, indicating AT2021ehb may expose the elusive low-mass end of the nuclear black hole population. These models offer simple yet robust characterization; more complicated models are not required, but provide important context and caveats in the limit of moderately sensitive data. If disk reflection is included, the disk flux is lower and inferred black hole masses are $\sim$ 0.35 dex higher. Simple wind formulations imply an extremely fast $v_{\mathrm{out}} = -0.2~c$ outflow and obviate a disk continuum component. Assuming a unity filling factor, such a wind implies an instantaneous mass outflow rate of $\dot{M} \simeq 5~M_{\odot}~{\rm yr}^{-1}$. Such a high rate suggests that the filling factor for the Ultra Fast Outflow (UFO) must be extremely low, and/or the UFO phase is ephemeral. We discuss the strengths and limitations of our analysis and avenues for future observations of TDEs., Comment: 19 pages, 4 figures

Markarian 817 is a bright and variable Seyfert-1.2 active galactic nucleus (AGN). X-ray monitoring of Mrk 817 with the Neil Gehrels Swift Observatory in 2022 revealed that the source flux had declined to a lower level than recorded at any prior point in the then-19-year mission. We present an analysis of deep XMM-Newton and NuSTAR observations obtained in this low flux state. The spectra reveal a complex X-ray wind consisting of neutral and ionized absorption zones. Three separate velocity components are detected as part of a structured ultra-fast outflow (UFO), with v/c = 0.043 (+0.007,-0.003), v/c = 0.079 (+0.003,-0.0008), and v/c = 0.074 (+0.004,-0.005). These projected velocities suggest that the wind likely arises at radii that are much smaller than the optical broad line region (BLR). In order for each component of the outflow to contribute significant feedback, the volume filling factors must be greater than f ~ 0.009, f ~ 0.003, and f ~ 0.3, respectively. For plausible, data-driven volume filling factors, these limits are passed, and the total outflow likely delivers the fierce feedback required to reshape its host environment, despite a modest radiative Eddington fraction of lambda ~ 0.008-0.016 (this range reflects plausible masses). UFOs are often detected at or above the Eddington limit; this result signals that black hole accretion has the potential to shape host galaxies even at modest Eddington fractions, and over a larger fraction of a typical AGN lifetime. We discuss our findings in terms of models for disk winds and black hole feedback in this and other AGN., Comment: Accepted for publication in ApJL

The Advanced X-ray Imaging Satellite (AXIS) promises revolutionary science in the X-ray and multi-messenger time domain. AXIS will leverage excellent spatial resolution (<1.5 arcsec), sensitivity (80x that of Swift), and a large collecting area (5-10x that of Chandra) across a 24-arcmin diameter field of view to discover and characterize a wide range of X-ray transients from supernova-shock breakouts to tidal disruption events to highly variable supermassive black holes. The observatory's ability to localize and monitor faint X-ray sources opens up new opportunities to hunt for counterparts to distant binary neutron star mergers, fast radio bursts, and exotic phenomena like fast X-ray transients. AXIS will offer a response time of <2 hours to community alerts, enabling studies of gravitational wave sources, high-energy neutrino emitters, X-ray binaries, magnetars, and other targets of opportunity. This white paper highlights some of the discovery science that will be driven by AXIS in this burgeoning field of time domain and multi-messenger astrophysics., Comment: This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at http://axis.astro.umd.edu

The variability of blazars in the X-ray and optical regions informs both the physics of their emitting region and places demands on the observer if a program requires that the object be bright or faint. The extensive simultaneous X-ray and optical observation by Swift provides the best insight into the variable nature of these objects. This program uses \textit{Swift} data for 19 X-ray-bright blazars, generally at $z > 0.1$, to determine their variability properties. The analysis is based on structure functions and provides insight into the nature of the variability and how it depends on time, luminosity, and redshift. We also consider strategies for observing blazars at or above average brightness, given a time delay between planning an observation and obtaining the data. This is critical to observations with orbiting X-ray telescopes, current or future. The variability in the soft X-ray band is typically three to eight times larger than at UV-optical wavelengths, at fixed time differences (i.e., 30 or 100 days). There is almost no difference in the amplitude of variation (X-ray or UV-optical) as a function of redshift (time delay of 30 days) and a modest positive correlation with luminosity. In the X-ray band, blazars that become brighter than normal typically remain bright for at least 2-3 months, although with significant flickering. One can avoid observing objects that are significantly below the average X-ray flux by scheduling the observation when the $F_X > 0.9 F_{X,avg}$, which requires monitoring observations near the time of the scheduling activity., Comment: 24 pages, 10 figures

The optical light curves of quiescent black hole low-mass X-ray binaries often exhibit significant non-ellipsoidal variabilities, showing the photospheric radiation of the companion star is veiled by other source of optical emission. Assessing this "veiling" effect is critical to the black hole mass measurement. Here in this work, we carry out a strictly simultaneous spectroscopic and photometric campaign on the prototype of black hole low-mass X-ray binary A0620-00. We find that for each observation epoch, the extra optical flux beyond a pure ellipsoidal modulation is positively correlated with the fraction of veiling emission, indicating the accretion disk contributes most of the non-ellipsoidal variations. Meanwhile, we also obtain a K2V spectral classification of the companion, as well as the measurements of the companion's rotational velocity $v \sin i = 83.8\pm1.9$ km s$^{-1}$ and the mass ratio between the companion and the black hole $q=0.063\pm0.004$., Comment: Accepted for publication in ApJ

NuSTAR observed the black hole candidate XTE J1908$+$094 during its 2013 and 2019 outbursts. We use relativistic reflection to measure the spin of the black hole through 19 different assumptions of relxill flavors and parameter combinations. The most favored model in terms of Deviance Information Criterion (DIC) measures the spin of the black hole to be $a = 0.55^{+0.29}_{-0.45}$, and an inclination of $\theta=27^{+2}_{-3}$ degrees ($1\sigma$ statistical errors). We look at the effects of coronal geometry assumptions and density of the accretion disk on the spin prediction. All 19 tested models provide consistent spin estimates. We discuss the evolution of spin measurement techniques using relativistic reflection in X-ray binaries and discuss the implications of this spin measurement in reconciling the distributions of stellar mass black hole spin measurements made through X-ray and gravitational wave observations., Comment: 16 pages, 7 figures, 3 tables. Accepted for publication in ApJ

The black hole candidate EXO 1846-031 underwent an outburst in 2019, after at least 25 years in quiescence. We observed the system using \textit{NuSTAR} on August 3rd, 2019. The 3--79 keV spectrum shows strong relativistic reflection features. Our baseline model gives a nearly maximal black hole spin value of $a=0.997_{-0.002}^{+0.001}$ ($1\sigma$ statistical errors). This high value nominally excludes the possibility of the central engine harboring a neutron star. Using several models, we test the robustness of our measurement to assumptions about the density of the accretion disk, the nature of the corona, the choice of disk continuum model, and addition of reflection from the outer regions of the accretion disk. All tested models agree on a very high black hole spin value and a high value for the inclination of the inner accretion disk of $\theta\approx73^\circ$. We discuss the implications of this spin measurement in the population of stellar mass black holes with known spins, including LIGO events., Comment: 13 pages, 5 figures, 1 table. Published in ApJ

We present the first results from BAYMAX (Bayesian AnalYsis of Multiple AGN in X-rays), a tool that uses a Bayesian framework to quantitatively evaluate whether a given Chandra observation is more likely a single or dual point source. Although the most robust method of determining the presence of dual AGNs is to use X-ray observations, only sources that are widely separated relative to the instrument PSF are easy to identify. It becomes increasingly difficult to distinguish dual AGNs from single AGNs when the separation is on the order of Chandra's angular resolution (<1''). Using likelihood models for single and dual point sources, BAYMAX quantitatively evaluates the likelihood of an AGN for a given source. Specifically, we present results from BAYMAX analyzing the lowest-mass dual AGN candidate to date, SDSS J0914+0853, where archival Chandra data shows a possible secondary AGN ~0.3'' from the primary. Analyzing a new 50 ks Chandra observation, results from BAYMAX shows that SDSS J0914+0853 is most likely a single AGN with a Bayes factor of 13.5 in favor of a single point source model. Further, posterior distributions from the dual point source model are consistent with emission from a single AGN. We find the probability of SDSS J0914+0853 being a dual AGN system with a flux ratio f>0.3 and separation r>0.3'' to be very low. Overall, BAYMAX will be an important tool for correctly classifying candidate dual AGNs in the literature, and studying the dual AGN population where past spatial resolution limits have prevented systematic analyses., Comment: 16 pages, 5 figures, accepted to ApJ

We present the results of ellipsoidal light curve modeling of the low mass X-ray binary Cen X-4 in order to constrain the inclination of the system and mass of the neutron star. Near-IR photometric monitoring was performed in May 2008 over a period of three nights at Magellan using PANIC. We obtain J, H and K lightcurves of Cen X-4 using differential photometry. An ellipsoidal modeling code was used to fit the phase folded light curves. The lightcurve fit which makes the least assumptions about the properties of the binary system yields an inclination of 34.9 (+4.9, -3.6) degrees, which is consistent with previous determinations of the system's inclination but with improved statistical uncertainties. When combined with the mass function and mass ratio, this inclination yields a neutron star mass of 1.51 (+0.40, -0.55) M_sun. This model allows accretion disk parameters to be free in the fitting process. Fits that do not allow for an accretion disk component in the near-IR flux gives a systematically lower inclination between approximately 33 and 34 degrees, leading to a higher mass neutron star between approximately 1.7 M_sun and 1.8 M_sun. We discuss the implications of other assumptions made during the modeling process as well as numerous free parameters and their effects on the resulting inclination., Comment: 7 pages, 4 figures, 2 tables, accepted for publication in MNRAS

We present results of multiband optical photometry of the black hole X-ray binary system V404 Cygni obtained using Wheaton College Observatory's 0.3m telescope, along with strictly simultaneous INTEGRAL and Swift observations during 2015 June 25.15--26.33 UT, and 2015 June 27.10--27.34 UT. These observations were made during the 2015 June outburst of the source when it was going through an epoch of violent activity in all wavelengths ranging from radio to $\gamma$-rays. The multiwavelength variability timescale favors a compact emission region, most likely originating in a jet outflow, for both observing epochs presented in this work. The simultaneous INTEGRAL/Imager on Board the Integral Satellite (IBIS) 20--40 keV light curve obtained during the June 27 observing run correlates very strongly with the optical light curve, with no detectable delay between the optical bands as well as between the optical and hard X-rays. The average slope of the dereddened spectral energy distribution was roughly flat between the $I_C$- and $V$-bands during the June 27 run, even though the optical and X-ray flux varied by $>$25$\times$ during the run, ruling out an irradiation origin for the optical and suggesting that the optically thick to optically thin jet synchrotron break during the observations was at a frequency larger than that of $V$-band, which is quite extreme for X-ray binaries. These observations suggest that the optical emission originated very close to the base of the jet. A strong H$\alpha$ emission line, probably originating in a quasi-spherical nebula around the source, also contributes significantly in the $R_C$-band. Our data, in conjunction with contemporaneous data at other wavelengths presented by other groups, strongly suggest that the jet-base was extremely compact and energetic during this phase of the outburst., Comment: 15 pages, 2 tables, 5 figures. Accepted for publication in ApJ

Observational constraints of relativistic jets from black holes has largely come from the most powerful and extended jets\cite{Jorstad05,Asada14}, leaving the nature of the low luminosity jets a mystery\cite{Falcke04}. M81* is one of the nearest low-luminosity jets, which underwent an extremely large radio flare in 2011, allowing us to study compact core emission with unprecedented sensitivity and linear resolution. Utilizing a multi-wavelength campaign, we were able to track the flare as it re-brightened and became optically thick. Simultaneous X-ray observations indicated the radio re-brightening was preceded by a low energy X-ray flare at least $t_{\rm delay}>12\ {\rm days}$ prior. Associating the time delay between the two bands as the cooling time in a synchrotron flare\cite{Urry97,Bai03}, we find the magnetic field strength was $1.9

We present optical spectroscopy, ultraviolet to infrared imaging and X-ray observations of the intermediate luminosity optical transient (ILOT) SN 2010da in NGC 300 (d=1.86 Mpc) spanning from -6 to +6 years relative to the time of outburst in 2010. Based on the light curve and multi-epoch SEDs of SN 2010da, we conclude that the progenitor of SN 2010da is a ~10-12 Msol yellow supergiant possibly transitioning into a blue loop phase. During outburst, SN 2010da had a peak absolute magnitude of M<-10.4 mag, dimmer than other ILOTs and supernova impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca II emission lines in our high-resolution spectra, which indicate a dusty and complex circumstellar environment. Since the 2010 eruption, the star has brightened by a factor of ~5 and remains highly variable in the optical. Furthermore, we detect SN 2010da in archival Swift and Chandra observations as an ultraluminous X-ray source (L~6x10^{39} erg/s). We additionally attribute He II 4686 Angstrom and coronal Fe emission lines in addition to a steady X-ray luminosity of ~10^{37} erg/s to the presence of a compact companion., Comment: published; updated citations and other minor edits

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/UV flares in galactic centers. Prior studies based on modeling decaying flux trends have been able to estimate broad properties, such as the mass accretion rate. Here we report the detection of flows of highly ionized X-ray gas in high-resolution X-ray spectra of a nearby tidal disruption event. Variability within the absorption-dominated spectra indicates that the gas is relatively close to the black hole. Narrow line widths 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 kilometers per second are observed, significantly 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 apocenter of an elliptical orbit. Flows of this sort are predicted by fundamental analytical theory and more recent numerical simulations., Comment: Published in the Oct 22 2015 issue of Nature

As one of the best-characterized stellar-mass black holes, with good measurements of its mass, distance and inclination, V404 Cyg is the ideal candidate to study Eddington-limited accretion episodes. After a long quiescent period, V404 Cyg underwent a new outburst in June 2015. We obtained two Chandra HETG exposures of 20 ksec and 25 ksec. Many strong emission lines are observed; the ratio of Si He-like triplet lines gives an estimate for the formation region distance of $4\times10^{11}$ cm, while the higher ionization Fe XXV He-like triplet gives an estimate of $7\times10^9$ cm. A narrow Fe K$\alpha$ line is detected with an equivalent width greater than 1 keV in many epochs, signaling that we do not directly observe the central engine. Obscuration of the central engine and strong narrow emission lines signal that the outer disk may be illuminated, and its structure may help to drive the strong variability observed in V404 Cyg. In the highest flux phases, strong P-Cygni profiles consistent with a strong disk wind are observed. The kinetic power of this wind may be extremely high., Comment: Submitted to ApJ Letters, 8 pages, 4 figures, 1 Table

We present a spectroscopic analysis of the black hole binary Nova Muscae 1991 in quiescence using data obtained in 2009 with MagE on the Magellan Clay telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las Campanas Observatory. Emission from the disc is observed in H alpha, H beta and Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all three emission lines. The existence of this spot establishes ongoing mass transfer from the donor star in 2009-2010 and, given its absence in the 1993-1995 observations, demonstrates the presence of a variable hotspot in the system. We find the radial distance to the hotspot from the black hole to be consistent with the circularization radius. Our tomograms are suggestive of stream-disc overflow in the system. We also detect possible Ca II (8662 A) absorption from the donor star., Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRAS

We present a dynamical study of the Galactic black hole binary system Nova Muscae 1991 (GS/GRS 1124-683). We utilize 72 high resolution Magellan Echellette (MagE) spectra and 72 strictly simultaneous V-band photometric observations; the simultaneity is a unique and crucial feature of this dynamical study. The data were taken on two consecutive nights and cover the full 10.4-hour orbital cycle. The radial velocities of the secondary star are determined by cross-correlating the object spectra with the best-match template spectrum obtained using the same instrument configuration. Based on our independent analysis of five orders of the echellette spectrum, the semi-amplitude of the radial velocity of the secondary is measured to be K_2 = 406.8+/-2.7 km/s, which is consistent with previous work, while the uncertainty is reduced by a factor of 3. The corresponding mass function is f(M) = 3.02+/-0.06 M_\odot. We have also obtained an accurate measurement of the rotational broadening of the stellar absorption lines (v sin i = 85.0+/-2.6 km/s) and hence the mass ratio of the system q = 0.079+/-0.007. Finally, we have measured the spectrum of the non-stellar component of emission that veils the spectrum of the secondary. In a future paper, we will use our veiling-corrected spectrum of the secondary and accurate values of K_2 and q to model multi-color light curves and determine the systemic inclination and the mass of the black hole., Comment: ApJ accepted version; minor revision; added a subsection about systematic uncertainties

Observations over the past 20 years have revealed a strong relationship between the properties of the supermassive black hole (SMBH) lying at the center of a galaxy and the host galaxy itself. The magnitude of the spin of the black hole will play a key role in determining the nature of this relationship. To date, direct estimates of black hole spin have been restricted to the local Universe. Herein, we present the results of an analysis of $\sim$ 0.5 Ms of archival Chandra observations of the gravitationally lensed quasar Q 2237+305 (aka the "Einstein-cross"), lying at a redshift of z = 1.695. The boost in flux provided by the gravitational lens allows constraints to be placed on the spin of a black hole at such high redshift for the first time. Utilizing state of the art relativistic disk reflection models, the black hole is found to have a spin of $a_* = 0.74^{+0.06}_{-0.03}$ at the 90% confidence level. Placing a lower limit on the spin, we find $a_* \geq 0.65$ (4$\sigma$). The high value of the spin for the $\rm \sim 10^9~M_{\odot}$ black hole in Q 2237+305 lends further support to the coherent accretion scenario for black hole growth. This is the most distant black hole for which the spin has been directly constrained to date., Comment: 5 pages, 3 figures, 1 table, formatted using emulateapj.cls. Accepted for publication in ApJL

The quiescent state is the dominant accretion mode for black holes on all mass scales. Our knowledge of the X-ray spectrum is limited due to the characteristic low luminosity in this state. Herein, we present an analysis of the sample of dynamically-confirmed stellar-mass black holes observed in quiescence in the \textit{Chandra/XMM-Newton/Suzaku} era resulting in a sample of 8 black holes with $\sim$ 570 ks of observations. In contrast to the majority of AGN where observations are limited by contamination from diffuse gas, the stellar-mass systems allow for a clean study of the X-ray spectrum resulting from the accretion flow alone. The data are characterized using simple models. We find a model consisting of a power-law or thermal bremsstrahlung to both provide excellent descriptions of the data, where we measure $\rm \Gamma = 2.06 \pm 0.03$ and $\rm kT = 5.03^{+0.33}_{-0.31} keV$ respectively in the 0.3 -- 10 keV bandpass, at a median luminosity of $\rm L_x \sim 5.5\times10^{-7} L_{Edd}$. This result in discussed in the context of our understanding of the accretion flow onto stellar and supermassive black holes at low luminosities., Comment: 12 pages, 5 figures, 2 tables, MNRAS accepted

The co-evolution of a supermassive black hole with its host galaxy through cosmic time is encoded in its spin. At $z>2$, supermassive black holes are thought to grow mostly by merger-driven accretion leading to high spin. However, it is unknown whether below $z\sim1$ these black holes continue to grow via coherent accretion or in a chaotic manner, though clear differences are predicted in their spin evolution. An established method to measure the spin of black holes is via the study of relativistic reflection features from the inner accretion disk. Owing to their greater distances, there has hitherto been no significant detection of relativistic reflection features in a moderate-redshift quasar. Here, we use archival data together with a new, deep observation of a gravitationally-lensed quasar at $z=0.658$ to rigorously detect and study reflection in this moderate-redshift quasar. The level of relativistic distortion present in this reflection spectrum enables us to constrain the emission to originate within $\lesssim3$ gravitational radii from the black hole, implying a spin parameter $a=0.87^{+0.08}_{-0.15} $ at the $3\sigma$ level of confidence and $a>0.66$ at the $5\sigma$ level. The high spin found here is indicative of growth via coherent accretion for this black hole, and suggests that black hole growth between $0.5\lesssim z \lesssim 1$ occurs principally by coherent rather than chaotic accretion episodes., Comment: 42 pages, 11 figures, 2 tables, Nature 507, 207 (13 March 2014)

Simultaneous observations of X-rays and radio luminosities have been well studied in accreting stellar-mass black holes. These observations are performed in order to understand how mass accretion rates and jetted outflows are linked in these individual systems. Such contemporaneous studies in supermassive black holes (SMBH) are harder to perform, as viscous times scale linearly with mass. However, as NGC 4395 is the lowest known mass Seyfert galaxy, we have used it to examine the simultaneous X-ray (Swift) and radio (VLA) correlation in a SMBH in a reasonably timed observing campaign. We find that the intrinsic X-ray variability is stronger than the radio variability, and that the fluxes are only weakly or tentatively coupled, similar to prior results obtained in NGC 4051. If the corona and the base of the jet are one and the same, this may suggest that the corona in radio-quiet AGN filters disk variations, only transferring the strongest and/or most sustained variations into the jet. Further, when both NGC 4395 and NGC 4051 are placed on the stellar-mass L_X-L_R plane, they appear to reside on the steeper L_X-L_R track. This suggests that SMBHs also follow two distinct tracks just as stellar-mass black holes do, and supports the idea that the same physical disk-jet mechanisms are at play across the mass scale., Comment: 9 pages, 10 figures, Accepted to ApJ Letters

We present new results of uniform spectral analysis of Swift/XRT observations of the X-ray binary system 4U 1957+11. This includes 26 observations of the source made between MJD 54282$-$55890 (2007 July 01 $-$ 2011 November 25). All 26 spectra are predominantly thermal, and can be modeled well with emission from an accretion disk around a black hole. We analyze all 26 spectra jointly using traditional chi-squared fitting as well as Markov Chain Monte Carlo simulations. The results from both methods agree, and constrains on model parameters like inclination, column density, and black hole spin. These results indicate that the X-ray emitting inner accretion disk is inclined to our line-of-sight by $77.6^{+1.5}_{-2.2}$ degrees. Additionally, the other constraints we obtain on parameters like the column density and black hole spin are consistent with previous X-ray observations. Distances less than 5 kpc are unlikely and not only ruled out based on our analysis but also from other independent observations. Based on model-derived bolometric luminosities, we require the source distance to be >10 kpc if the black hole's mass is >10 M$_{Sun}$. If the hole's mass is <10 M$_{Sun}$, then the distance could be in the range of 5$-$10 kpc., Comment: Accepted for publication in ApJ. Uses emulateapj style. 14 pages, 11 figures, 3 tables

We report on a Suzaku observation of the newly discovered X-ray binary MAXI J1836-194. The source is found to be in the hard/intermediate spectral state and displays a clear and strong relativistically broadened iron emission line. We fit the spectra with a variety of phenomenological, as well as physically motivated disk reflection models, and find that the breadth and strength of the iron line is always characteristic of emission within a few gravitational radii around a black hole. This result is independent of the continuum used and strongly points toward the central object in MAXI J1836-194 being a stellar mass black hole rotating with a spin of $a=0.88\pm0.03$ (90% confidence). We discuss this result in the context of spectral state definitions, physical changes (or lack thereof) in the accretion disk and on the potential importance of the accretion disk corona in state transitions., Comment: 11 pages, 9 Figures, Accepted for publication in ApJ

We report the discovery of a strong emission line near 24.8 angstrom (0.5 keV) in the newly discovered X-ray binary system MAXI J0556-332 with the reflection grating spectrometer onboard the XMM-Newton observatory. The X-ray light curve morphology during these observations is complex and shows occasional dipping behavior. Here we present time- and rate-selected spectra from the RGS and show that this strong emission line is unambiguously present in all the XMM observations. The measured line center is consistent with the Ly-alpha transition of N VII in the rest frame. While the spectra contain imprints of absorption lines and edges, there appear to be no other significantly prominent narrow line due to the source itself, thus making the identification of the 24.8 angstrom line uncertain. We discuss possible physical scenarios, including a gravitationally redshifted O VIII Ly-alpha line originating at the surface of a neutron star or an unusual donor with an extremely high N/O abundance (>57) relative to solar, that may have produced this comparatively strong emission line., Comment: Accepted for publication in ApJ Letters. Uses aastex.cls, 4 figures, 2 tables, 15 pages

We report on the results of a simultaneous monitoring campaign employing eight Chandra X-ray (0.5-10 keV) and six VLA/EVLA (8.4 GHz) radio observations of NGC 4051 over seven months. Evidence for compact jets is observed in the 8.4 GHz radio band; This builds on mounting evidence that jet production may be prevalent even in radio-quiet Seyferts. Assuming comparatively negligible local diffuse emission in the nucleus, the results also demonstrate an inverse correlation of L_radio proportional to L_X-ray ^(-0.72+/-0.04) . Current research linking the mass of supermassive black holes and stellar-mass black holes in the "low/hard" state to X-ray luminosities and radio luminosities suggest a "fundamental plane of accretion onto black holes" that has a positive correlation of L_radio proportional to L_X-ray^(0.67+/-0.12) . Our simultaneous results differ from this relation by more than 11 sigma, indicating that a separate mode of accretion and ejection may operate in this system. A review of the literature shows that the inverse correlation seen in NGC 4051 is seen in three other black hole systems, all of which accrete at near 10% of their Eddington luminosity, perhaps suggesting a distinct mode of disk-jet coupling at high Eddington fractions. We discuss our results in the context of disk and jets in black holes and accretion across the black hole mass scale., Comment: 12 pages, 9 figures

We present Chandra HETGS spectroscopy of the Be/X-ray binary 1A 0535+262 obtained during the 2009/2010 giant outburst. These are the first CCD grating spectra of this type of system during a giant outburst. Our spectra reveal a number of lines including a narrow Fe K_alpha emission line with a FWHM of ~ 5000 km s^-1. For the first time, we detect the presence of a highly ionized outflow in a Be/X-ray binary. Assuming that the line is He-like Fe XXV, fits with a simple Gaussian imply an outflow velocity of ~ 1500 km s^-1. However, self-consistent photoionization modeling with XSTAR suggests that Fe XXIII-XXIV must also contribute. In this case, an outflow velocity of ~ 3000 km s^-1 is implied. These results are discussed in the context of the accretion flow in Be-star, neutron star, and black hole X-ray binaries., Comment: 7 pages, 4 figures, formatted using emulateapj.cls. Accepted for publication in ApJ

The most widely used means of measuring the mass of black holes in Galactic binaries - specifically the X-ray novae - involves both radial velocity measurements of the secondary star, and photometric measurements of its ellipsoidal variability. The latter is important in constraining the inclination and mass ratio, and requires as direct a measure of the flux of the secondary as possible. Up to now, such measurements have been preferentially carried out in the NIR (1 -- 2.5$\mu m$), where the flux from the cooler secondary is expected to dominate over that from the accretion disc. However, here we present evidence of a significant non-stellar contribution to the NIR flux in many of those quiescent X-ray novae that are thought to contain a black hole primary. We discuss origins of this excess and the effect of such contamination on Galactic black hole mass measurements., Comment: 9 pages, 4 figures, 2 tables, accepted for publication in MNRAS

We present Keck K-band photometry and low-resolution H & K-band spectroscopy of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent state. No clear ellipsoidal modulation is present in the light curve, which is instead dominated by a strong flickering component. In the K-band we observe strong Br_gamma emission, with an equivalent width of 38 +/- 5 Angstroms. From this we conclude that the accretion disc is the most likely source of the observed photometric contamination, and that previous infrared-based attempts to constrain the mass of the putative black hole in this system are prone to considerable uncertainty. We finally proceed to show how it is possible to place meaningful constraints on some of the binary parameters of this system, even in the presence of a relatively high level of contamination from the disc., Comment: 7 pages, 6 figures & 1 table. Accepted for publication in MNRAS

We present X-ray and radio observations of the new Galactic supernova remnant (SNR) G306.3−0.9, recently discovered by Swift. Chandra imaging reveals a complex morphology, dominated by a bright shock. The X-ray spectrum is broadly consistent with a young SNR in the Sedov phase, implying an age of 2500 yr for a distance of 8 kpc, plausibly identifying this as one of the 20 youngest Galactic SNRs. Australia Telescope Compact Array imaging reveals a prominent ridge of radio emission that correlates with the X-ray emission. We find a flux density of ∼160 mJy at 1 GHz, which is the lowest radio flux recorded for a Galactic SNR to date. The remnant is also detected at 24μm, indicating the presence of irradiated warm dust. The data reveal no compelling evidence for the presence of a compact stellar remnant.