46 research outputs found
Agujeros Negros de Masas Estelares en la Galaxia
Resumen: En esta contribuciĂłn se presenta un catĂĄlogo de candidatos a agujeros negros de masas estelares, principalmente en nuestra Galaxia, que representa la mayor base de datos disponible en la literatura al presente. Los candidatos confirmados, todos ellos pertenecientes a sistemas binarios, son tratados en forma separada y detallada.Fil: GĂłmez, Mercedes. Universidad Nacional de CĂłrdoba. Observatorio AstronĂłmico de CĂłrdoba; Argentina.http://www.astronomiaargentina.org.arAstronomĂa (incluye AstrofĂsica y Ciencias del Espacio
Optical spectroscopy of 4U 1812-12: an ultra-compact X-ray binary seen through an H II region
The persistent, low-luminosity neutron star X-ray binary 4U 1812-12 is a
potential member of the scarce family of ultra-compact systems. We performed
deep photometric and spectroscopic optical observations with the 10.4 m Gran
Telescopio Canarias in order to investigate the chemical composition of the
accreted plasma, which is a proxy for the donor star class. We detect a faint
optical counterpart (g~25, r~23) that is located in the background of the
outskirts of the Sharpless 54 H II region, whose characteristic nebular lines
superimpose on the X-ray binary spectrum. Once this is corrected for, the
actual source spectrum lacks hydrogen spectral features. In particular, the
Halpha emission line is not detected, with an upper limit (3 sigma) on the
equivalent width of <1.3 A. Helium (He I) lines are neither observed, albeit
our constraints are not restrictive enough to properly test the presence of
this element. We also provide stringent upper limits on the presence of
emission lines from other elements, such as C and O, which are typically found
in ultra-compact systems with C-O white dwarfs donors. The absence of hydrogen
features, the persistent nature of the source at low luminosity, as well as the
low optical to X-ray flux ratio confirm 4U 1812-12 as a compelling
ultra-compact X-ray binary candidate, for which we tentatively propose a
He-rich donor based on the optical spectrum and the detection of short
thermonuclear X-ray bursts. In this framework, we discuss the possible orbital
period of the system according to disc instability and evolutionary models.Comment: Accepted for publication in A&
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&
Failed-transition outbursts in black hole low-mass X-ray binaries
Black hole low-mass X-ray binaries (BH LMXBs) evolve in a similar way during outburst. Based on the X-ray spectrum and variability, this evolution can be divided into three canonical states: low/hard, intermediate, and high/soft state. BH LMXBs evolve from the low/hard to the high/soft state through the intermediate state in some outbursts (here called 'full outbursts'). However, in other cases, BH LMXBs undergo outbursts in which the source never reaches the high/soft state, here called 'failed-transition outbursts' (FT outbursts). From a sample of 56 BH LMXBs undergoing 128 outbursts, we find that 36 per cent of these BH LMXBs experienced at least one FT outburst, and that FT outbursts represent ~33 per cent of the outbursts of the sample, showing that these are common events. We compare all the available X-ray data of full and FT outbursts of BH LMXBs from RXTE/PCA, Swift/BAT, and MAXI, and find that FT and full outbursts cannot be distinguished from their X-ray light curves, hardness-intensity diagrams, or X-ray variability during the initial 10-60 d after the outburst onset. This suggests that both types of outbursts are driven by the same physical process. We also compare the optical and infrared (O/IR) data of FT and full outbursts of GX 339-4. We found that this system is generally brighter in O/IR bands before an FT outburst, suggesting that the O/IR flux points to the physical process that later leads to a full or an FT outburst. We discuss our results in the context of models that describe the onset and evolution of outbursts in accreting X-ray binaries.</p
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
CronologĂa de las ocupaciones arqueolĂłgicas del ĂĄrea Los Antiguos-Monte Zeballos y Paso Roballos (NO de Santa Cruz)
Algunas secuencias arqueolĂłgicas del Holoceno medio y tardĂo del N.O. de Santa Cruz muestran discontinuidades temporales de cierta magnitud, de varias centurias o milenios, en la ocupaciĂłn de algunos lugares destacados. Esto vale tambiĂ©n para el Holoceno temprano aunque aquĂ nos concentraremos en los periodos mĂĄs recientes. Estas discontinuidades pueden tener validez local o regional y ser el resultado de perĂodos de abandono de distinta duraciĂłn. Estos aparentes vacĂos ocupacionales podrĂan obedecer a problemas de muestreo: sitios con ocupaciones aĂșn no detectadas o a ocupaciones aĂșn no datadas. No obstante, esto sirve para destacar que aĂșn desconocemos en quĂ© medida estas zonas fueron sucesivamente exploradas y ocupadas de manera continua, o cual fue su papel como vĂas de circulaciĂłn. Dado que para estos momentos se acepta un aumento de poblaciĂłn (Borrero 2004), problematizar el tema de la continuidad en la ocupaciĂłn de los espacios conforma un complemento para ampliar discusiones planteadas en trabajos de sĂntesis recientes para Patagonia (Borrero 2004; Miotti y Salemme 2005). De esta manera, tambiĂ©n se aporta conocimiento para la comprensiĂłn de procesos culturales de corta y larga duraciĂłn y su correlato arqueolĂłgico en diferentes escalas espaciales.PublicaciĂłn original en CD-ROM.Facultad de Ciencias Naturales y Muse
X-ray Spectral and Timing evolution of MAXI J1727-203 with NICER
We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727-203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3-10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727-203 evolved through the soft, intermediate and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from âŒ0.4 keV, at the moment of maximum luminosity, to âŒ0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broadband noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broadband noise at 0.3 - 10 keV of this source. We find that the fractional rms increases with energy in most of the outburst except during the hard state, where the fractional rms remains approximately constant with energy. We also find that, below 3 keV, the fractional rms follows the same trend generally observed at energies >3 keV, a behaviour known from previous studies of black holes and neutron stars. The spectral and timing evolution of MAXI J1727-203, as parametrised by the hardness-intensity, hardness-rms, and rms-intensity diagrams, suggest that the system hosts a black hole, although we could not rule out a neutron star