19 research outputs found
Characterisation of a candidate dual AGN
We present Chandra and optical observations of a candidate dual AGN
discovered serendipitously while searching for recoiling black holes via a
cross-correlation between the serendipitous XMM source catalog (2XMMi) and
SDSS-DR7 galaxies with a separation no larger than ten times the sum of their
Petrosian radii. The system has a stellar mass ratio M/M. One of the galaxies (Source 1) shows clear evidence for AGN activity in
the form of hard X-ray emission and optical emission-line diagnostics typical
of AGN ionisation. The nucleus of the other galaxy (Source 2) has a soft X-ray
spectrum, bluer colours, and optical emission line ratios dominated by stellar
photoionisation with a "composite" signature, which might indicate the presence
of a weak AGN. When plotted on a diagram with X-ray luminosity vs [OIII]
luminosity both nuclei fall within the locus defined by local Seyfert galaxies.
From the optical spectrum we estimate the electron densities finding n e cm and n e cm. From a 2D
decomposition of the surface brightness distribution we infer that both
galaxies host rotationally supported bulges (Sersic index ). While the
active nature of Source 1 can be established with confidence, whether the
nucleus of Source 2 is active remains a matter of debate. Evidence that a faint
AGN might reside in its nucleus is, however, tantalising.Comment: 16 pages, 9 figures. Accepted for publication on MNRAS. Comments
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Ask The Machine: Systematic detection of wind-type outflows in low-mass X-ray binaries
The systematic discovery of outflows in the optical spectra of low-mass X-ray
binaries opened a new avenue for the study of the outburst evolution in these
extreme systems. However, the efficient detection of such features in a
continuously growing database requires the development of new analysis
techniques with a particular focus on scalability, adaptability, and
automatization. In this pilot study, we explore the use of machine learning
algorithms to perform the identification of outflows in spectral line profiles
observed in the optical range. We train and test the classifier on a simulated
database, constructed through a combination of disc emission line profiles and
outflow signatures, emulating typical observations of low-mass X-ray binaries.
The final, trained classifier is applied to two sets of spectra taken during
two bright outbursts that were particularly well covered, those of V404 Cyg
(2015) and MAXI J1820+070 (2018). The resulting classification gained by this
novel approach is overall consistent with that obtained through traditional
techniques, while it simultaneously provides a number of key advantages over
the latter, including the access to low velocity outflows. This study sets the
foundations for future studies on large samples of spectra from low-mass X-ray
binaries and other compact binaries.Comment: Accepted for publication in MNRAS. 13 pages, 6 figure
Characterization of a candidate dual AGN
We present Chandra and optical observations of a candidate dual active galactic nucleus (AGN) discovered serendipitously while searching for recoiling black holes via a cross-correlation between the serendipitous XMM source catalogue (2XMMi) and SDSS-DR7 galaxies with a separation no larger than 10 times the sum of their Petrosian radii. The system has a stellar mass ratio M_1/M_2 â 0.7. One of the galaxies (Source 1) shows clear evidence for AGN activity in the form of hard X-ray emission and optical emission-line diagnostics typical of AGN ionization. The nucleus of the other galaxy (Source 2) has a soft X-ray spectrum, bluer colours, and optical emission-line ratios dominated by stellar photoionization with a âcompositeâ signature, which might indicate the presence of a weak AGN. When plotted on a diagram with X-ray luminosity versus [OIII] luminosity, both nuclei fall within the locus defined by local Seyfert galaxies. From the optical spectrum, we estimate the electron densities finding n_1 < 27 eââcm^(â3) and n_2 â 200 eââcm^(â3). From a 2D decomposition of the surface brightness distribution, we infer that both galaxies host rotationally supported bulges (SĂ©rsic index <1). While the active nature of Source 1 can be established with confidence, whether the nucleus of Source 2 is active remains a matter of debate. Evidence that a faint AGN might reside in its nucleus is, however, tantalizing
Unveiling optical signatures of outflows in accreting white dwarfs
Accreting white dwarfs are known to show signatures of wind-type outflows in
the ultraviolet. At optical wavelengths, however, wind detections have only
been reported for a few sources. We present GTC-10.4m 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. We focused the analysis on four emission lines:
H and He I 5876, 6678, 7065. Line profiles
are complex and variable on short (minutes) and long (days to weeks) time
scales, with transient absorption and emission components. Among them, we
detect strong blue-shifted absorptions at km s. 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 case 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 be also 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.Comment: Accepted for publication in A&
Optical and near-infrared spectroscopy of the black hole transient 4U 1543-47 during its 2021 ultra-luminous state
We present simultaneous optical and near-infrared spectra obtained during the
2021 outburst of the black hole transient 4U 1543-47. The X-ray
hardness-intensity diagram and the comparison with similar systems reveal a
luminous outburst, probably reaching the Eddington luminosity, as well as a
long-lasting excursion to the so-called ultra-luminous state. VLT/X-shooter
spectra were taken in two epochs 14 days apart during the early and brightest
part of the outburst, while the source was in this ultra-luminous accretion
state. The data show strong H and HeI emission lines, as well as
high-excitation HeII and OIII transitions. Most lines are single-peaked in both
spectra, except for the OIII lines that exhibit evident double-peaked profiles
during the second epoch. The Balmer lines are embedded in broad absorption
wings that we believe are mainly produced by the contribution of the A2V donor
to the optical flux, which we estimate to be in the range of 11 to 14 per cent
in the band during our observations. Although no conspicuous outflow
features are found, we observe some wind-related line profiles, particularly in
the near-infrared. Such lines include broad emission line wings and skewed red
profiles, suggesting the presence of a cold (i.e. low ionisation) outflow with
similar observational properties to those found in other low-inclination black
hole transients.Comment: Accepted for publication in A&
Discovery of optical outflows and inflows in the black hole candidate GRS 1716-249
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
characterised by P-Cyg (as well as flat-top and asymmetric) profiles in the
H, H and He II (4686) emission lines, implying the
presence of an accretion disc wind, which is likely hot and dense. The wind's
terminal velocity (2000 km s) 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. 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.Comment: Published in MNRAS main journa
Sub-second infrared variability from the archetypal accreting neutron star 4U 1728â34
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 â 2 h of simultaneous observations of 4U 1728â34 using HAWK-I@VLT, XMMâ 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 â 30â40 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 â 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 1728â34 must have an orbital period longer than 3 h and an inclination higher than 8âŠ
Discovery of optical and infrared accretion disc wind signatures in the black hole candidate MAXI J1348â630
MAXI J1348â630 is a low mass X-ray binary discovered in 2019 during a bright outburst. During this event, the system experienced both hard and soft states following the standard evolution. We present multi-epoch optical and near-infrared spectroscopy obtained with X-shooter at the Very Large Telescope. Our dataset includes spectra taken during the brightest phases of the outburst as well as the decay towards quiescence. We study the evolution of the main emission lines, paying special attention to the presence of features commonly associated with accretion disc winds, such as blueshifted absorptions, broad emission line wings and flat-top profiles. We find broad emission line wings in Hα during the hard-to-soft transition and blueshifted absorption troughs at âŒâ
ââ
500 km sâ1 in HÎČ, HeâŻIâ5876, Hα and PaÎČ during the bright soft-intermediate state. In addition, flat-top profiles are seen throughout the outburst. We interpret these observables as signatures of a cold (i.e., optical-to-infrared) accretion disc wind present in the system. We discuss the properties of the wind and compare them with those seen in other X-ray transients. In particular, the wind velocity that we observe is low when compared to those of other systems, which might be a direct consequence of the relatively low binary inclination, as suggested by several observables. This study strengthens the hypothesis that cold winds are a common feature in low mass X-ray binaries and that they can also be detected in low inclination objects via high-quality optical and infrared spectroscopy
Discovery of optical and infrared accretion disc wind signatures in the black hole candidate MAXI J1348-630
MAXI J1348-630 is a low mass X-ray binary discovered in 2019 during a bright outburst. During this event, the system experienced both hard and soft states following the standard evolution. We present multi-epoch optical and near-infrared spectroscopy obtained with X-shooter at the Very Large Telescope. Our dataset includes spectra taken during the brightest phases of the outburst as well as the decay towards quiescence. We study the evolution of the main emission lines, paying special attention to the presence of features commonly associated with accretion disc winds, such as blueshifted absorptions, broad emission line wings and flat-top profiles. We find broad emission line wings in Ha during the hard-to-soft transition and blueshifted absorption troughs at similar to-500 km s(-1 )in H beta, He1-5876, H alpha and Pa beta during the bright soft-intermediate state. In addition, flat-top profiles are seen throughout the outburst. We interpret these observables as signatures of a cold (i.e., optical-to-infrared) accretion disc wind present in the system. We discuss the properties of the wind and compare them with those seen in other X-ray transients. In particular, the wind velocity that we observe is low when compared to those of other systems, which might be a direct consequence of the relatively low binary inclination, as suggested by several observables. This study strengthens the hypothesis that cold winds are a common feature in low mass X-ray binaries and that they can also be detected in low inclination objects via high-quality optical and infrared spectroscopy