The black hole transient MAXI J1820+070 displayed optical P Cyg profiles and other wind-related emission line features during the hard state of its discovery outburst. We present near-infrared (NIR) ...spectroscopy covering the different accretion states of the system during this event. Our eight-epoch data set (VLT/X-shooter) reveals strong variability in the properties of the NIR emission lines. This includes absorption troughs and extended emission line wings with kinetic properties that are remarkably similar to those inferred from the wind signatures observed in optical emission lines, indicating that they most likely trace the same accretion disc wind. Unlike the optical features, these NIR signatures are not exclusive of the hard state, as they are also witnessed across the soft state with similar observational properties. This supports the presence of a relatively steady outflow during the entire outburst of the system, and it represents the first detection of an accretion disc wind in a black hole soft state at energies other than X-rays. We discuss the visibility of the wind as a function of the spectral band and the potential of NIR spectroscopy for wind studies, in particular during luminous accretion phases.
We report on a detailed optical spectroscopic follow-up of the black hole (BH) transient MAXI J1820+070 (ASASSN-18ey). The observations cover the main part of the X-ray binary outburst, when the ...source alternated between hard and soft states following the classical pattern widely seen in other systems. We focus the analysis on the He i emission lines at 5876 and 6678 , as well as on H . We detect clear accretion disk wind features (P-Cyg profiles and broad emission line wings) in the hard state, both during outburst rise and decay. These are not witnessed during the several months long soft state. However, our data suggest that the visibility of the outflow might be significantly affected by the ionization state of the accretion disk. The terminal velocity of the wind is above ∼1200 km s−1, which is similar to outflow velocities derived from (hard-state) optical winds and (soft-state) X-ray winds in other systems. The wind signatures, in particular the P-Cyg profiles, are very shallow, and their detection has only been possible thanks to a combination of source brightness and intense monitoring at very high signal-to-noise. This study indicates that cold, optical winds are most likely a common feature of BH accretion, and therefore, that wind-like outflows are a general mechanism of mass and angular momentum removal operating throughout the entire X-ray binary outburst.
ABSTRACT
We present a new method to derive binary inclinations in quiescent black hole (BH) X-ray transients (XRTs), based on the depth of the trough (T) from double-peaked H α emission profiles ...arising in accretion discs. We find that the inclination angle (i) is linearly correlated with T in phase-averaged spectra with sufficient orbital coverage (≳50 per cent) and spectral resolution, following i(deg) = 93.5 × T + 23.7. The correlation is caused by a combination of line opacity and local broadening, where a leading (excess broadening) component scales with the deprojected velocity of the outer disc. Interestingly, such scaling allows to estimate the fundamental ratio M1/Porb by simply resolving the intrinsic width of the double-peak profile. We apply the T–i correlation to derive binary inclinations for GRO J0422+32 and Swift J1357−0933, two BH XRTs where strong flickering activity has hindered determining their values through ellipsoidal fits to photometric light curves. Remarkably, the inclination derived for GRO J0422+32 (i = 55.6 ± 4.1○) implies a BH mass of $2.7^{+0.7}_{-0.5}$ M⊙ thus placing it within the gap that separates BHs from neutron stars. This result proves that low-mass BHs exist in nature and strongly suggests that the so-called ‘mass gap’ is mainly produced by low number statistics and possibly observational biases. On the other hand, we find that Swift J1357−0933 contains a $10.9^{+1.7}_{-1.6}$ M⊙ BH, seen nearly edge on ($i=87.4^{+2.6}_{-5.6}$ deg). Such extreme inclination, however, should be treated with caution since it relies on extrapolating the T–i correlation beyond i ≳ 75○, where it has not yet been tested.
Abstract
We present 12 epochs of optical spectroscopy taken across the discovery outburst of the black hole (BH) candidate MAXI J1803−298 with the Gran Telescopio Canarias and Very Large Telescope. ...The source followed a standard outburst evolution with hard and soft states. The system displays a triangular shape in the hardness intensity diagram, consistent with that seen in high-inclination BH transients and the previously reported detection of X-ray dips. The two epochs observed during the initial hard state exhibited asymmetric emission-line profiles, including a P-Cygni profile simultaneously detected in H
α
and He
i
6678, which indicates the presence of an optical wind in the system. The remaining spectra, obtained during the transition to the soft state and the subsequent decay, are instead characterized by narrower, double-peaked emission lines embedded into broad absorption components. One epoch (intermediate state) also includes near-infrared (NIR) coverage, revealing complex line profiles in the Paschen and Bracket series, which suggests that the outflow is still present during the outburst decay through the soft state. The growing list of low-mass X-ray binaries with optical and NIR outflow signatures indicates that these are common features. Furthermore, the lowest luminosity spectrum exhibits an H
α
FWHM of 1570 ± 100 km s
−1
. This, together with previous constraints on the binary parameters, allows us to favor a compact object mass of ∼3–10
M
⊙
, further supporting its BH nature.
ABSTRACT
We present optical spectroscopy obtained with the GTC, VLT, and SALT telescopes during the decline of the 2016–2017 outburst of the black hole candidate GRS 1716−249 (Nova Oph 1993). Our ...18-epoch data set spans 6 months and reveals that the observational properties of the main emission lines are very variable, even on time-scales of a few hours. Several epochs are characterized by P-Cyg (as well as flat-top and asymmetric) profiles in the Hα, Hβ, and He ii (λ4686) emission lines, implying the presence of an accretion disc wind, which is likely hot and dense. The wind’s terminal velocity (∼2000 km s−1) is similar to that observed in other black hole X-ray transients. These lines also show transient and sharp red-shifted absorptions, taking the form of inverted P-Cyg profiles. We argue that these profiles can be explained by the presence of infalling material at ∼1300 km s−1. We propose a failed wind scenario to explain this inflow and discuss other alternatives, such as obscuration produced by an accretion-related structure (e.g. the gas stream) in a high inclination system.
Accreting white dwarfs are known to show signatures of wind-type outflows in the ultraviolet. However, at optical wavelengths, wind detections have only been reported for a few sources. We present ...GTC-10.4 m optical spectroscopy of four accreting white dwarfs (BZ Cam, V751 Cyg, MV Lyr, and V425 Cas) observed during luminous epochs, when their optical emission is expected to be dominated by the accretion disc. Our analysis focuses on four emission lines: H
α
and He
I
λ
5876,
λ
6678, and
λ
7065. Line profiles are complex and variable on short (minutes) and long (days to weeks) timescales, with transient absorption and emission components. Among them, we detect strong blueshifted absorptions at ≳1000 km s
−1
. These high-velocity components, present only in the blue wing of the emission lines, are observed in all four sources and could be associated with accretion disc winds. For MV Lyr and V425 Cas, these would represent the first detection of optical outflows in these objects, while in the cases of BZ Cam and V751 Cyg, the presence of outflows has been previously reported. This study suggests that, in addition to ultraviolet winds, optical outflows might also be common in accreting white dwarfs. We discuss the observational properties of these winds and their possible similarity to those detected in accreting black holes and neutrons stars.
Swift J1357.2-0933 is a black hole transient that is of particular interest due to the optical recurrent dips found during its first two outbursts (in 2011 and 2017), which lack an obvious X-ray ...equivalent. We present a study based on fast optical photometry during its two most recent outbursts, in 2019 and 2021. Our observations reveal that the optical dips were present in every observed outburst of the source, although they were shallower and showed longer recurrence periods in the two most recent and fainter events. We performed a global study of the dips properties in the four outbursts and found that they do not follow a common temporal evolution. In addition, we discovered a correlation with the X-ray and optical fluxes, with the dips being more profound and showing shorter recurrence periods for brighter stages. This trend seems to extend even to the faintest, quiescent states of the source. We discuss these results in the context of the possible connection between optical dips and outflows found in previous works.
ABSTRACT
We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed $\approx 2\,$ h of ...simultaneous observations of 4U 1728−34 using HAWK-I@VLT, XMM–Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of $\approx 30 \!-\! 40\,$ ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of $\approx 7.2\,$ s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728−34 must have an orbital period longer than $3\,$ h and an inclination higher than 8○.
ABSTRACT
We present a dynamical study of the eclipsing intermediate polar XY Ari based on time-resolved near-infrared spectroscopy obtained with the EMIR spectrograph on the 10.4-m Gran Telescopio ...Canarias. Using main sequence template spectra taken with the same instrument setup as the target spectra, we measure a radial velocity amplitude of the late K- type donor star K2 = 256 ± 2 km s−1. We also obtain the rotational broadening of its photospheric lines vrot sin i = 141 ± 3 km s−1. From these and the eclipse geometry, we derive a donor-to-white dwarf mass ratio q = M2/M1 = 0.62 ± 0.02, an orbital inclination i = 80.8° ± 0.5° and dynamical masses $M_{1} = 1.21 \pm 0.04 \, \mathrm{M}_{\odot }$ and $M_2 = 0.75 \pm 0.04 \, \mathrm{M}_{\odot }$ (1σ). This result places the white dwarf in XY Ari as one of the three most massive known in a cataclysmic variable. Comparison with white dwarf mass estimates from X-ray spectral studies could indicate the necessity of an improvement of the X-ray models and/or analysis techniques, as a number of X-ray white dwarf masses are in disagreement with the dynamical mass value.
We present the discovery of an optical accretion disk wind in the X-ray transient Swift J1858.6-0814. Our 90-spectrum data set, taken with the 10.4 m Gran Telescopio Canarias telescope over eight ...different epochs and across five months, reveals the presence of conspicuous P-Cyg profiles in He i at 5876 and H . These features are detected throughout the entire campaign, albeit their intensity and main observational properties are observed to vary on timescales as short as 5 minutes. In particular, we observe significant variations in the wind velocity, between a few hundreds and ∼2400 . In agreement with previous reports, our observations are characterized by the presence of frequent flares, although the relation between the continuum flux variability and the presence/absence of wind features is not evident. The reported high activity of the system at radio waves indicates that the optical wind of Swift J1858.6-0814 is contemporaneous with the radio jet, as is the case for the handful of X-ray binary transients that have shown so far optical P-Cyg profiles. Finally, we compare our results with those of other sources showing optical accretion disk winds, with emphasis on V404 Cyg and V4641 Sgr, since they also display strong and variable optical wind features as well as similar flaring behavior.
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