Black Hole X-ray Nova Research Articles

I-band photometry of the quiescent black hole X-ray nova GROJ0422 + 32 = V518 Per: modelling of the orbital light curve and estimation of the black hole mass

ABSTRACT We present new photometric observations of the X-ray nova GRO J0422 + 32 (V518 Per) carried out in the I$_c$ band over 14 nights in 2020–2023. We had to revise the orbital period of the system, the new value $P_{\rm orb}=5^{\rm h}04^{\rm m}35{_{.}^{\rm s}}50 \pm 0{_{.}^{\rm s}}04$ is about one minute shorter than the period by Webb et al. but close to the result reported earlier by Filippenko, Matheson & Ho. The obtained folded light curve has a regular shape with a clear ellipticity effect and signatures of a slight heating effect. The simulations of this light curve in terms of the model of an interacting binary system allowed us to estimate the orbital inclination $i = 33^\circ {\small --} 49^\circ$ of the system and derive masses of the black hole $M_x=(6.5\pm 2.9)\,\mathrm{M}_\odot$ and companion star $M_v=(0.47\pm 0.21)\,\mathrm{M}_\odot$. This range of the black hole masses overlaps with the known gap of (2–5) M$_\odot$ in the distribution of compact objects masses but mostly it lies above the upper boundary of this gap. To obtain more precise estimates one needs to know the degree of heating of the donor star, so synchronous X-ray/optical observations of this system are desirable.

Optical, J and K light curves of XTE J1118+480 = KV UMa: the mass of the black hole and the spectrum of the non-stellar component

ABSTRACT Optical, J and K photometric observations of the KV UMa black hole X-ray nova in its quiescent state obtained in 2017–2018 are presented. A significant flickering within light curves was not detected, although the average brightness of the system faded by ≈0.1m over 350 d. Changes in the average brightness were not accompanied with an increase or decrease in the flickering. From the modelling of five light curves the inclination of the KV UMa orbit and the black hole mass were obtained: i = 74 ± 4°, $M_\mathrm{BH}=(7.06\rm {-}7.24)\, \mathrm{M}_{\odot }$, depending on the mass ratio used. The non-stellar component of the spectrum in the range λ = 6400–22 000 Å can be fitted by a power law Fλ ∼ λα, α ≈ −1.8. The accretion disc orientation angle changed from one epoch to another. The model with spots on the star was inadequate. Evolutionary calculations using the scenario machine code were performed for low-mass X-ray binaries, with a recently discovered anomalously rapid decrease of the orbital period taken into account. We show that the observed decrease can be consistent with the magnetic stellar wind of the optical companion, whose magnetic field was increased during the common-envelope stage. Several constraints on evolutionary scenario parameters were developed.

Optical andJ, K-photometry of the quiescent black hole X-ray nova A0620−00 in the passive and active states

Photometric observations of the low-mass X-ray binary system A0620-00=V616 Mon are performed in the optical (unfiltered light, lambda_eff~6400A) and the near-infrared J and K-bands. The mean system flux, the orbital light curve shape and the flickering amplitude dependences on wavelength are examined for two activity stages of the system remaining in quiescence. In 2015-16 A0620-00 was in passive stage (as by Cantrell et al., 2008) exhibiting the regular orbital light curves and low flickering. In less than 230 days in 2016-17 the system switched into active stage: the brightness increased by ~0.2-0.3 mag, the orbital light curve changed while the flickering amplitude increased more than twice. The object regular orbital light curves were fitted by models with "cold" spots on the optical star surface and without those. These models reproduce the observed orbital light curves both in passive and in active stages. The dependence of the mean square flickering amplitude (in fluxes, extinction corrected) on wavelength is computed in the lambda 6400-22000AA range. In active stage, the observed flickering amplitude decreases over the whole studied range and may be represented as Delta F_fl~lambda^{-2} which corresponds to the free-free emission of optically thin high-temperature plasma. In passive stage, flickering obeys Delta F_fl~lambda^{-4} law in the range 6400-12500AA that corresponds to the thermal radiation of optically thick high-temperature plasma. At longer wavelengths the flickering amplitude dependence is flat which may imply existence of a synchrotron component of the relativistic jets emission. These flickering features let us propose that the flickering mechanism includes at least two components: thermal and, apparently, synchrotron, that agrees with the recent discovery of the variable linear polarization of the IR system emission (Russell et al., 2016).

Characterizing black hole variability with nonlinear methods: the case of the X-ray Nova 4U 1543–47

We investigate the possible nonlinear variability properties of the black hole X-ray nova 4U1543-47 to complement the temporal studies based on linear techniques, and to search for signs of nonlinearity in Galactic black hole (GBH) light curves. First, we apply the weighted scaling index method (WSIM) to characterize the X-ray variability properties of 4U1543-47 in different spectral states during the 2002 outburst. Second, we use surrogate data to investigate whether the variability is nonlinear in any of the different spectral states. The main findings can be summarized as follows. The mean weighted scaling index appears to be able to parametrize uniquely the temporal variability properties of this GBH: the 3 different spectral states of the 2002 outburst of 4U1543-47 are characterized by different and well constrained values. The search for nonlinearity reveals that the variability is linear in all light curves with the notable exception of the very high state. Our results imply that we can use the WSIM to assign a single number, namely the mean weighted scaling index, to a light curve, and in this way discriminate among the different spectral states of a source. The detection of nonlinearity in the VHS, that is characterized by the presence of most prominent QPOs, suggests that intrinsically linear models which have been proposed to account for the low frequency QPOs in GBHs may be ruled out (abridged).

The Spectrum of the Black Hole X‐Ray Nova V404 Cygni in Quiescence as Measured byXMM‐Newton

We present XMM observations of the black hole X-ray nova V404 Cygni in quiescence. Its quiescent spectrum can be best fitted by a simple power-law with slope 2. The spectra are consistent with that expected for the advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in luminosity compared to the previous observation of Chandra. We see variability of a factor of 4 during the observation. We find no evidence for the presence of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and 110 eV respectively. The limit on the fluorescent emission is improved by a factor of 15 over the previous estimate, and the restriction on H-like/He-like emission is lower than predicted from models by a factor of roughly 2.

Resonant Oscillations of Accretion Flow and Khz QPOS

High-frequency quasi-periodic variations (HF QPOs) in the X-ray light curves of black hole X-ray novae can be understood as oscillations of the accretion disk in a nonlinear 3:2 resonance. An m = 0 vertical oscillation near a black hole modulates the X-ray emission through gravitational lensing (light-bending) at the source. Certain oscillations of the accretion disk will also modulate the mass accretion rate, and in neutron-star systems this would lead to nearly periodic variations in brightness of the luminous boundary layer on the stellar surface — the amplitude of the neutron-star HF QPOs would be thus increased relative to the black hole systems.

EXITE2 Observation of the SIGMA Source GRS 1227+025

We report the second-generation Energetic X-Ray Imaging Telescope Experiment (EXITE2) hard X-ray imaging of the sky around 3C 273. A hr observation on 1997 May 8 shows a ~260 mcrab source detected at ~4 σ in each of two bands (50-70 and 70-93 keV) and located ~30' from 3C 273 and consistent in position with the Granat SIGMA source GRS 1227+025. The EXITE2 spectrum is consistent with a power law with photon index 3 and large low-energy absorption, as indicated by the SIGMA results. No source was detected in more sensitive follow-up EXITE2 observations in 2000 and 2001 with 3 σ upper limits of 190 and 65 mcrab, respectively. Comparison with the flux detected by SIGMA shows the source to be highly variable, suggesting it may be nonthermal and beamed and thus the first example of a type 2 (absorbed) blazar. Alternatively, it might be an unprecedented very highly absorbed binary system undergoing accretion-disk instability outbursts, possibly either a magnetic cataclysmic variable or a black hole X-ray nova.

High-energy observations of the state transition of the X-ray nova and black hole candidate XTE J1720-318

We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL, XMM-Newton and RXTE. The source, which underwent an X-ray outburst in 2003 January, was observed in February in a spectral state dominated by a soft component with a weak high-energy tail. The XMM-Newton data provided a high column density Nh of 1.2*e22 cm^{-2} which suggests that the source lies at the Galactic Centre distance. The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail, typical of a black-hole binary in the so-called High/Soft State. We then followed the evolution of the source outburst over several months using the INTEGRAL Galactic Centre survey observations. The source became active again at the end of March: it showed a clear transition towards a much harder state, and then decayed to a quiescent state after April. In the hard state, the source was detected up to 200 keV with a power law index of 1.9 and a peak luminosity of 7*e36 erg s^{-1} in the 20-200 keV band, for an assumed distance of 8 kpc. We conclude that XTE J1720-318 is indeed a new member of the black hole X-ray novae class which populate our galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries.

A Synoptic X‐Ray Study of M31 with theChandraHigh Resolution Camera

We have obtained 17 epochs of Chandra High Resolution Camera (HRC) snapshot images, each covering most of the M31 disk. The data cover a total baseline of ~2.5 yr and contain a mean effective exposure of 17 ks. We have measured the mean fluxes and long-term light curves for 166 objects detected in these data. At least 25% of the sources show significant variability. The cumulative luminosity function (CLF) of the disk sources is well fitted by a power law with a slope comparable to those observed in typical elliptical galaxies. The CLF of the bulge is a broken power law similar to measurements made by previous surveys. We note several sources in the southwestern disk with LX > 1037 ergs s-1. We cross-correlate all of our sources with published optical and radio catalogs, as well as new optical data, finding counterpart candidates for 55 sources. In addition, 17 sources are likely X-ray transients. We analyze follow-up Hubble Space Telescope (HST) WFPC2 data of two X-ray transients, finding F336W (U-band equivalent) counterparts. In both cases, the counterparts are variable. In one case, the optical counterpart is transient with F336W = 22.3 ± 0.1 mag. The X-ray and optical properties of this object are consistent with a ~10 M☉ black hole X-ray nova with an orbital period of 23 days. In the other case, the optical counterpart varies between F336W = 20.82 ± 0.06 and 21.11 ± 0.02 mag. Ground-based and HST observations show that this object is bright (V = 18.8 ± 0.1) and slightly extended. Finally, the frequency of bright X-ray transients in the M31 bulge suggests that the ratio of neutron star to black hole primaries in low-mass X-ray binaries (NS/BH) is ~1.

The optical and X-ray flickering of XTE J1118+480

Abstract We study the complex correlations between optical and X-ray variability in the black hole X-ray nova XTE J1118+480. We find that the optical and X-ray fluctuations of very different shapes, amplitudes and time-scales are correlated in a similar mode where the optical light curve is seemingly related to the time derivative of the X-rays.

The optical and X-ray flickering of XTE J1118+480

We use both time-domain and Fourier techniques to study the correlated optical/X-rays variability in the black hole X-ray nova XTE J1118+480. Its X-ray timing properties such as the shape of the X-ray power spectrum and cross-correlation functions (CCFs) between X-ray energy bands, the slight decrease of rms variability from 30% in the 2-5.9 ke V to 19% in the 15.5-44.4 ke V band, as well as the X-ray hardness/flux anti-correlation are very similar to what is found in other black hole binaries in the hard state. The optical/X-ray CCF is virtually independent of the X-ray energies. The optical flux appears to be correlated not only with the X-ray flux but also with the X-ray spectral variability. Both the coherence function and the lags between optical and the X-rays are Fourier frequency dependent. The optical/X-ray coherence function reaches its maximum (∼0.3) in the 0.1-1 Hz range and the time-lags decrease with frequency approximatively like f - 0 . 8 . The correlation between X-ray and optical light curves appears to have time-scale-invariant properties. The X-ray/optical CCF maintains a similar but resealed shape on time-scales ranging at least from 0.1 s to few 10 s. Using the event superposition method we show that the correlation is not triggered by a single type of event (dip or flare) in the light curves Instead, optical and X-ray fluctuations of very different shapes, amplitudes and time-scales are correlated in a similar mode where the optical light curve is seemingly related to the time derivative of the X-rays.

Resolved Jets and Long‐Period Black Hole X‐Ray Novae

In this brief note we point out that the four spatially resolved relativistic jets among the 14 dynamically confirmed black hole X-ray novae are all in systems with long orbital periods. Many shorter period systems show transient radio outbursts that are attributed to jets, but these jets have not been spatially resolved. Super-Eddington accretion has been suggested as a requirement for jet formation and may be consistent with our compilation of luminosities, but some super-Eddington outbursts did not form spatially resolved jets. We speculate that some as yet unknown process (or combination of processes) favors formation of substantially larger jets in long-period systems. Two short-period systems show evidence of being extended, but have not been resolved into multiple components, as the long-period systems have.

The X‐Ray Spectra of Black Hole X‐Ray Novae in Quiescence as Measured byChandra

We present Chandra observations of black hole X-ray novae V404 Cyg, A0620-00, GRO J1655-40 and XTE J1550-564 in quiescence. Their quiescent spectra can be well fitted by a power-law model with slope $\alpha \sim 2$. While a coronal (Raymond-Smith) model is also a statistically acceptable representation of the spectra, the best fit temperatures of these models is $\sim 5$ times higher than that seen in active stellar coronae. These four spectra of quiescent X-ray novae are all consistent with that expected for accretion via an advection-dominated accretion flow (ADAF) and inconsistent with that expected from a stellar corona. This evidence for continued accretion in quiescence further strengthens the case for the existence of event horizons in black holes. Both A0620-00 and GRO J1655-40 were fainter than in previous observations, while V404 Cyg was more luminous and varied by a factor of 2 in a few ksec. A reanalysis of the X-ray data for XTE J1550-564 shows that (like V404 Cyg and A0620-00) its luminosity exceeds the maximum prediction of the coronal model by a large factor. The 0.3-7 keV luminosity of the four sources studied ranges from $\sim 10^{30}-10^{33}$ erg/s.

Optical Observations of XTE J1118 + 480 during the 2000 Outburst

Abstract We report on photometric and spectroscopic observations of a possible halo black-hole X-ray nova, XTE J1118$ +$480 ($ =$ KV UMa) during outburst. Our photometric monitoring during the main outburst revealed that the optical maximum as well as the onset of the outburst precede those in the X-ray region. This indicates that the event was an “outside-in” type outburst and that its optical flux was dominated by viscous heating, itself, and not the effect of X-ray irradiation. Based on these results, we suggest an outburst scenario analogous to superoutbursts in SU UMa-type dwarf novae. This scenario predicts a superhump phenomenon, which we indeed detected throughout the outburst. We determined its period to be $ 0.170529\pm 0.000006 \,\mathrm{d}$, which is slightly longer than the orbital periods suggested from spectroscopic observations. We have furthermore revealed the first evidence of a continuous period decreasing in X-ray novae. The most prominent feature in our optical spectrum is a double-peak He II 4686Å emission line having an asymmetric profile with an outstanding blue side peak. Using a Doppler mapping method, we found that the He II emission originates from the accretion disk, which particularly concentrates on the hot spot. The time that the blue peak becomes strongest corresponds to a superhump peak. This implies that we see an elongated side of an eccentric disk at that time and, hence, it may cause an asymmetric emission profile. Substituting the observed fractional superhump excess for a theoretically expected relation between it and the mass ratio, we estimate that the black-hole mass is larger than $9.5 \,{{{M}_{\odot}}}$. XTE J1118$ +$480 thus has a large mass of a compact object compared with the typical black-hole X-ray novae.

A high-velocity black hole on a Galactic-halo orbit in the solar neighbourhood

Only a few of the dozen or so known stellar-mass black holes have been observed away from the plane of the Galaxy. Those few could have been ejected from the plane as a result of a 'kick' received during a supernova explosion, or they could be remnants of the population of massive stars formed in the early stages of evolution of the Galaxy. Determining their orbital motion should help to distinguish between these options. Here we report the transverse motion (in the plane of the sky) for the black-hole X-ray nova XTE J1118+480 (refs 2, 3, 4, 5), from which we derive a large space velocity. This X-ray binary system has an eccentric orbit around the Galactic Centre, like most objects in the halo of the Galaxy, such as ancient stars and globular clusters. The properties of the system suggest that its age is comparable to or greater than the age of the Galactic disk. Only an extraordinary 'kick' from a supernova could have launched the black hole into an orbit like this from a birthplace in the disk of the Galaxy.

Characterizing the Quasi‐periodic Oscillation Behavior of the X‐Ray Nova XTE J1550−564

For all 209 Rossi X-Ray Timing Explorer observations of the X-ray nova XTE J1550-564 during its major outburst of 1998-1999, we have analyzed the X-ray power spectra, phase lags, and coherence functions. These observations constitute one of the richest and most complete data sets obtained for any black hole X-ray nova. The phase lags and coherence measures of low-frequency quasi-periodic oscillations (QPOs; ν 100 Hz). In general, the amplitude of low-frequency QPOs decreases when high-frequency oscillations appear, and when both low-frequency and high-frequency QPOs are present, their Q-values (ν/FWHM) are anticorrelated. We speculate that this opposition between low-frequency and high-frequency QPOs arises from competing structures in a perturbed accretion disk. However, we find that the frequencies of slow and fast QPOs are not correlated. In addition, we encounter systematic problems in attempting to reliably compare the QPO frequencies with broad features in the power continuum, since there are a variable number of features or spectral breaks in the power spectra. These results cast some doubt on the reported global relationship between QPOs from neutron stars and those from black hole systems.

New Evidence for Black Hole Event Horizons from [ITAL]Chandra[/ITAL

Previously we claimed that black hole X-ray novae (BHXNs) in quiescence are much less luminous than equivalent neutron star X-ray novae (NSXNs). This claim was based on the quiescent detection of a single short-period BHXN (A0620-00, Porb = 7.8 hr) and two longer period BHXNs (GRO J1655-40, Porb = 62.9 hr; V404 Cygni, Porb = 155.3 hr), along with sensitive upper limits. Here we announce the detection of two more short-period BHXNs (GRO J0422+32, Porb = 5.1 hr; GS 2000+25, Porb = 8.3 hr), an upper limit for a third that is improved by 2 orders of magnitude (4U 1543-47, Porb = 27.0 hr), and a new, much lower quiescent measurement of GRO J1655-40. Taken together, these new Chandra Advanced CCD Imaging Spectrometer measurements confirm that the quiescent X-ray luminosities of BHXNs are significantly lower than those of NSXNs. We argue that this provides strong evidence for the existence of event horizons in BHXNs.

A Black Hole Greater Than 6 [ITAL]M[/ITAL][TINF]⊙[/TINF] in the X-Ray Nova XTE J1118+480

Observations of the quiescent X-ray nova XTE J1118+480 with the new 6.5 m Multiple Mirror Telescope have revealed that the velocity amplitude of the dwarf secondary is 698 ± 14 km s-1 and the orbital period of the system is 0.17013 ± 0.00010 days. The implied value of the mass function, f(M) = 6.00 ± 0.36 M☉, provides a hard lower limit on the mass of the compact primary that greatly exceeds the maximum allowed mass of a neutron star (~3 M☉). Thus, we conclude that the compact primary is a black hole. Among the 11 dynamically established black hole X-ray novae, the large mass function of XTE J1118+480 is rivaled only by that of V404 Cyg. We estimate that the secondary supplies 34% ± 8% of the total light at 5900 A and that its spectral type is in the range from K5 V to M1 V. A double-humped I-band light curve is probably due to ellipsoidal modulation, although this interpretation is not entirely secure because of an unusual 12 minute offset between the spectroscopic and photometric ephemerides. Assuming that the light curve is ellipsoidal, we present a provisional analysis that indicates that the inclination of the system is high and the mass of the black hole is correspondingly modest (M1 10 M☉). The broad Balmer emission lines (FWHM = 2300-2900 km s-1) also suggest a high inclination. For the range of spectral types given above, we estimate a distance of 1.8 ± 0.6 kpc.

CompleteRXTESpectral Observations of the Black Hole X‐Ray Nova XTE J1550−564

We report on the X-ray spectral behavior of XTE J1550(564 during its 1998¨1999 outburst. XTE J1550(564 is an exceptionally bright X-ray nova and is also the third Galactic black hole candi- date known to exhibit quasi-periodic X-ray oscillations above 50 Hz. Our study is based on 209 pointed observations using the PCA and HEXTE instruments on board the Rossi X-Ray T iming Explorer (RXT E) spanning 250 days and covering the entire double-peaked eruption that occurred from 1998 September until 1999 May. The spectra are —tted to a model including multicolor blackbody disk and power-law components. The spectra from the —rst half of the outburst are dominated by the power-law component, whereas the spectra from the second half are dominated by the disk component. The source is observed in the very high and high/soft outburst states of black hole X-ray novae. During the very high state, when the power-law component dominated the spectrum, the inner disk radius is observed to vary by more than an order of magnitude; the radius decreased by a factor of 16 in one day during a 6.8 crab —are. If the larger of these observed radii is taken to be the last stable orbit, then the smaller observed radius would imply that the inner edge of the disk is inside the event horizon! However, we conclude that the apparent variations of the inner disk radius observed during periods of increased power-law emission are probably caused by the failure of the multicolor disk/power-law model; the actual physical radius of the inner disk may remain fairly constant. This interpretation is supported by the fact that the observed inner disk radius remains approximately constant over 120 days in the high state, when the power-law component is weak, even though the disk —ux and total —ux vary by an order of magnitude. The mass of the black hole inferred by equating the approximately constant inner disk radius observed in the high/soft state with the last stable orbit for a Schwarzschild black hole is M BH 7.4 kpc)(cos i)~1@2. M _ (D/6 Subject headings: black hole physicsstars: individual (XTE J1550(564) ¨ X-rays: stars On-line material: machine-readable tables

RXTE observations of Galactic microquasar XTE J1748-288 during its 1998 outburst

We present an analysis of the RXTE observations of the recently discovered Galactic microquasar XTE J1748-288 during its 1998 outburst. General spectral and temporal properties of the source and their evolution were very typical for the Galactic black hole candidates (BHC) and, in particular, black hole X-ray novae. The spectral evolution of the source during the outburst can be considered a sequence of qualitatively distinct states. During the first observations, corresponding to a maximum of the X-ray flux, the spectrum of the source consisted of a dominating hard power-law component and a soft thermal component, which can be described by a model for the multicolour-disc emission. The hard component contributed ≥80 per cent to the X-ray luminosity in the 3–25 keV energy band. Overall the two-component spectral shape is an attribute of the very high state observed previously in BHC, but the domination of the hard component is unusual. Later on, as the X-ray source faded, its energy spectrum qualitatively changed, showing high and then low states, both typical for black hole binaries. As the energy spectrum changed, the fast variability also evolved dramatically. Initially the power-density spectrum was formed by a dominating band-limited noise component, quasi periodical oscillation features at 20–30 Hz and at |0.5 Hz, and a very low-frequency noise component. After a significant decrease of the contribution of the hard spectral component, the amplitude of the fractional variability decreased by an order of magnitude and the power-density spectrum adopted a power-law shape with a broad quasi periodical oscillation peak around 0.03 Hz. When the system switched to the low state, the power-density spectrum shape changed again and the quasi periodical oscillations have not been detected since. When the source was observed in the very high state, a clear correlation between quasi periodical oscillation parameters and X-ray flux was seen. Such a correlation gives an insight into our understanding of the accretion process in X-ray black hole binaries.