The black hole candidate and X-ray binary MAXI J1535−571 was discovered in 2017
September. During the decay of its discovery outburst, and before returning to quiescence,
the source underwent at ...least four reflaring events, with peak luminosities of ∼1035–36 erg s−1
(d/4.1 kpc)2. To investigate the nature of these flares, we analysed a sample of NICER (Neutron
star Interior Composition Explorer) observations taken with almost daily cadence. In this work,
we present the detailed spectral and timing analysis of the evolution of the four reflares. The
higher sensitivity of NICER at lower energies, in comparison with other X-ray detectors,
allowed us to constrain the disc component of the spectrum at ∼0.5 keV. We found that during
each reflare the source appears to trace out a q-shaped track in the hardness–intensity diagram
similar to those observed in black hole binaries during full outbursts. MAXI J1535−571 transits
between the hard state (valleys) and softer states (peaks) during these flares. Moreover, the
Comptonized component is undetected at the peak of the first reflare, while the disc component
is undetected during the valleys. Assuming the most likely distance of 4.1 kpc, we find that
the hard-to-soft transitions take place at the lowest luminosities ever observed in a black
hole transient, while the soft-to-hard transitions occur at some of the lowest luminosities ever
reported for such systems.
Objectives
To determine how general practice veterinarians make weight loss recommendations for dogs and if nutrients become deficient when following these recommendations.
Materials and Methods
A ...questionnaire of general practice veterinarians was conducted to characterise weight loss recommendations made to clients. Using this data, progressive levels of caloric restriction were applied to top‐selling commercial non‐therapeutic adult maintenance diets and non‐therapeutic weight management diets. Nutrient intakes were compared to the National Research Council's Recommended Allowances for metabolic body weight using a theoretical current weight and ideal body weight for an obese dog. Nutrient intakes were also compared to recommendations from the Association of American Feed Control Officials using current body weight.
Results
Several nutrients were found at risk of deficiency, including choline, methionine, cysteine, selenium, eicosapentanoic acid, docosahexanoic acid, riboflavin, pantothenic acid and cobalamin in both non‐therapeutic adult maintenance diets and non‐therapeutic weight management diets.
Clinical Significance
Caution is warranted when making weight loss recommendations using commercial diets until further research on the nutrient needs of obese dogs undergoing weight loss is undertaken. Restriction of commercial diets to achieve weight loss in dogs may result in nutrient deficiencies.
Slim-disk models describe advective accretion flows at high luminosities, while reducing to the standard thin disk form in the low luminosity limit. We have developed a new spectral model, slimbb, ...within the framework of XSPEC, which describes fully relativistic slim-disk accretion and includes photon ray-tracing that starts from the disk photosphere, rather than the equatorial plane. We demonstrate the features of this model by applying it to RXTE spectra of the persistent black-hole X-ray binary LMC X-3. LMC X-3 has the virtues of exhibiting large intensity variations while maintaining itself in soft spectral states which are well described using accretion-disk models, making it an ideal candidate to test the aptness of slimbb. Our results demonstrate consistency between the low-luminosity (thin-disk) and high luminosity (slim-disk) regimes. The results also illustrate that advection alone does not solve the problem of the origin of the surprisingly soft high-luminosity spectra in LMC X-3. We show that X-ray continuum-fitting in the high accretion rate regime can powerfully test black-hole accretion disk models.
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 ∼0.4 keV, at the moment of maximum luminosity, to ∼0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broad-band noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broad-band 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.
Swift J1858.6–0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors of >100 in soft X-rays) in its discovery state. We present the detection of five ...thermonuclear (Type I) X-ray bursts from Swift J1858.6–0814, implying that the compact object in the system is a neutron star (NS). Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, D = 12.8+0.8−0.6 kpc, although systematic effects allow a conservative range of 9–18 kpc. Before one burst, we detect a QPO at 9.6 ± 0.5 mHz with a fractional rms amplitude of 2.2 ± 0.2 per cent (0.5–10 keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15 per cent fractional amplitude (over 1–8 keV). Finally, we discuss the implications of the NS accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6–0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst.
We present the discovery of eclipses in the X-ray light curves of the X-ray binary Swift J1858.6–0814. From these, we find an orbital period of P= 76841.3(+1.3,−1.4) s (≈21.3 hours) and an eclipse ...duration of t(ec)= 4098(+17,−18) s (≈1.14 hours).We also find several absorption dips during the pre-eclipse phase. From the eclipse duration to orbital period ratio, the inclination of the binary orbit is constrained to i >70◦. The most likely range for the companion mass suggests that the inclination is likely to be closer to this value than 90◦. The eclipses are also consistent with earlier data, in which strong variability (‘flares’) and the long orbital period prevent clear detection of the period or eclipses. We also find that the bright flares occurred preferentially in the post-eclipse phase of the orbit, likely due to increased thickness at the disc-accretion stream interface preventing flares being visible during the pre-eclipse phase. This supports the notion that variable obscuration is responsible for the unusually strong variability in Swift J1858.6–0814.
Accretion disks around compact objects are expected to enter an unstable phase at high luminosity
. One instability may occur when the radiation pressure generated by accretion modifies the disk ...viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales
. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole
. Although there are hints of these cycles in a few isolated cases
, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle
. Here we report the presence of the same multiwavelength instability around an accreting neutron star. Moreover, we show that the variability across the electromagnetic spectrum-from radio to X-ray-of both black holes and neutron stars at high accretion rates can be explained consistently if the accretion disks are unstable, producing relativistic ejections during transitions that deplete or refill the inner disk. Such a new association allows us to identify the main physical components responsible for the fast multiwavelength variability of highly accreting compact objects.
In Casares et al. we presented the first radial velocity curve of the companion star to BW Cir which demonstrates the presence of a black hole in this historical X-ray transient. But these data were ...affected by aliasing and two possible periods at 2.5445 days and 2.5635 days were equally possible. Here we present new spectroscopic data that enable us to break the 1-year aliasing and confirm 2.5445 days as the correct orbital period. We also present R-band photometry over 14 years, which reveals the presence of important flaring activity dominating the light curves.
We present an analysis of the Swift Burst Alert Telescope (BAT) and X-ray telescope (XRT) data of GRB060602B, which is most likely an accreting neutron star in a binary system and not a gamma-ray ...burst. Our analysis shows that the BAT burst spectrum is consistent with a thermonuclear flash (type I X-ray burst) from the surface of an accreting neutron star in a binary system. The X-ray binary nature is further confirmed by the report of a detection of a faint point source at the position of the XRT counterpart of the burst in archival XMM–Newton data approximately six year before the burst and in more recent XMM–Newton data obtained at the end of 2006 September (nearly four months after the burst). Since the source is very likely not a gamma-ray burst, we rename the source Swift J1749.4−2807, based on the Swift/BAT discovery coordinates. Using the BAT data of the type I X-ray burst, we determined that the source is at most at a distance of 6.7 ± 1.3 kpc. For a transiently accreting X-ray binary, its soft X-ray behaviour is atypical: its 2–10 keV X-ray luminosity (as measured using the Swift/XRT data) decreased by nearly three orders of magnitude in about 1 day, much faster than what is usually seen for X-ray transients. If the earlier phases of the outburst also evolved this rapidly, then many similar systems might remain undiscovered because the X-rays are difficult to detect and the type I X-ray bursts might be missed by all the sky surveying instruments. This source might be part of a class of very fast transient low-mass X-ray binary systems of which there may be a significant population in our Galaxy.
The 2009 November outburst of the neutron star X-ray binary Aquila X-1 (Aql X-1) was observed with unprecedented radio coverage and simultaneous pointed X-ray observations, tracing the radio emission ...around the full X-ray hysteresis loop of the outburst for the first time. We use these data to discuss the disk-jet coupling, finding the radio emission to be consistent with being triggered at state transitions, both from the hard to the soft spectral state and vice versa. Our data appear to confirm previous suggestions of radio quenching in the soft state above a threshold X-ray luminosity of {approx}10% of the Eddington luminosity. We also present the first detections of Aql X-1 with very long baseline interferometry, showing that any extended emission is relatively diffuse and consistent with steady jets rather than arising from discrete, compact knots. In all cases where multi-frequency data were available, the source radio spectrum is consistent with being flat or slightly inverted, suggesting that the internal shock mechanism that is believed to produce optically thin transient radio ejecta in black hole X-ray binaries is not active in Aql X-1.
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