We present the orbital solution for the newly discovered transient Be X-ray binary Swift J0243.6+6124 based on the data from the gamma-ray burst monitor on board Fermi obtained during the October ...2017 outburst. We model the Doppler induced and intrinsic spin variations of the neutron star assuming that the latter is driven by accretion torque, and we discuss the implications of the observed spin variations for the parameters of the neutron star and the binary. In particular, we conclude that the neutron star must be strongly magnetized, and estimate the distance to the source at ~5 kpc.
The halo of the Milky Way provides a laboratory to study the properties of the shocked hot gas that is predicted by models of galaxy formation. There is observational evidence of energy injection ...into the halo from past activity in the nucleus of the Milky Way
; however, the origin of this energy (star formation or supermassive-black-hole activity) is uncertain, and the causal connection between nuclear structures and large-scale features has not been established unequivocally. Here we report soft-X-ray-emitting bubbles that extend approximately 14 kiloparsecs above and below the Galactic centre and include a structure in the southern sky analogous to the North Polar Spur. The sharp boundaries of these bubbles trace collisionless and non-radiative shocks, and corroborate the idea that the bubbles are not a remnant of a local supernova
but part of a vast Galaxy-scale structure closely related to features seen in γ-rays
. Large energy injections from the Galactic centre
are the most likely cause of both the γ-ray and X-ray bubbles. The latter have an estimated energy of around 10
erg, which is sufficient to perturb the structure, energy content and chemical enrichment of the circumgalactic medium of the Milky Way.
The soft gamma-ray repeater candidate SGR 0755−2933 was discovered in 2016 by
Swift
/BAT, which detected a short (∼30 ms), powerful burst typical of magnetars. To understand the nature of the source, ...we present here an analysis of follow-up observations of the tentative soft-X-ray counterpart of the source obtained with
Swift
/XRT,
NuSTAR,
and
Chandra
. From our analysis we conclude that, based on the observed counterpart position and properties, SGR 0755−2933 is not a soft gamma-ray repeater but rather a new high-mass X-ray binary. We suggest it be referred to as 2SXPS J075542.5−293353. We therefore conclude that the available data do not allow us to confirm existence and identify the true soft-X-ray counterpart to the burst event. The presence of a soft counterpart is nevertheless essential to unambiguously associate the burst with a magnetar flare, and we conclude that the magnetar origin of the burst and a precise burst location remain uncertain and require further investigation.
ABSTRACT
Motivated by the alleged detection of a cyclotron resonance scattering feature in the X-ray spectrum of the Be-transient KS 1947+300 with NuSTAR, not observed with other observatories, we ...have revisited the available observations of the source to clarify the origin of the reported feature. We focus on the analysis of observations obtained with the BeppoSAX observatory during the 2001 outburst, and by NuSTAR in 2013, when the discovery of the line was reported. We find that in both cases, the source broad-band X-ray continuum can be well described with a two-component Comptonization model, which does not require an additional absorption-like feature. In addition, we show that low-significance residuals mimicking the line, which appear using different continuum models, are consistent with known calibration uncertainties. We therefore conclude that the reported cyclotron line detection is largely questionable, and thus the question on the strength of the source magnetic field remains open. We briefly discuss the origin of the observed broad-band continuum in the context of the pulse-phase-resolved analysis conducted for BeppoSAX data and speculate that the soft component may be associated with the emission from polar areas of the pulsar irradiated by the accretion column.
Aims. We present the results of the monitoring programmes performed with the Swift/XRT telescope and aimed specifically to detect an abrupt decrease of the observed flux associated with a transition ...to the propeller regime in two well-known X-ray pulsars 4U 0115+63 and V 0332+53. Methods. Both sources form binary systems with Be optical companions and undergo so-called giant outbursts every 3−4 years. The current observational campaigns were performed with the Swift/XRT telescope in the soft X-ray band (0.5−10 keV) during the declining phases of the outbursts exhibited by both sources in 2015. Results. The transitions to the propeller regime were detected at the threshold luminosities of (1.4 ± 0.4) × 1036 erg s-1 and (2.0 ± 0.4) × 1036 erg s-1 for 4U 0115+63 and V 0332+53, respectively. Spectra of the sources are shown to be significantly softer during the low state. In both sources, the accretion at rates close to the aforementioned threshold values briefly resumes during the periastron passage following the transition into the propeller regime. The strength of the dipole component of the magnetic field required to inhibit the accretion agrees well with estimates based on the position of the cyclotron lines in their spectra, thus excluding presence of a strong multipole component of the magnetic field in the vicinity of the neutron star.
Aims. The magnetic field of accreting neutron stars determines their overall behavior including the maximum possible luminosity. Some models require an above-average magnetic field strength (≳1013 G) ...in order to explain super-Eddington mass accretion rate in the recently discovered class of pulsating ultraluminous X-ray sources (ULX). The peak luminosity of SMC X-3 during its major outburst in 2016–2017 reached ~2.5 × 1039 erg s-1 comparable to that in ULXs thus making this source the nearest ULX-pulsar. Determination of the magnetic field of SMC X-3 is the main goal of this paper. Methods. SMC X-3 belongs to the class of transient X-ray pulsars with Be optical companions, and exhibited a giant outburst in July 2016–March 2017. The source has been observed over the entire outburst with the Swift/XRT and Fermi/GBM telescopes, as well as the NuSTAR observatory. Collected data allowed us to estimate the magnetic field strength of the neutron star in SMC X-3 using several independent methods. Results. Spin evolution of the source during and between the outbursts, and the luminosity of the transition to the so-called propeller regime in the range of (0.3–7) × 1035 erg s-1 imply a relatively weak dipole field of (1–5) × 1012 G. On the other hand, there is also evidence for a much stronger field in the immediate vicinity of the neutron star surface. In particular, transition from super- to sub-critical accretion regime associated with the cease of the accretion column and very high peak luminosity favor a field that is an order of magnitude stronger. This discrepancy makes SMC X-3 a good candidate for possessing significant non-dipolar components of the field, and an intermediate source between classical X-ray pulsars and accreting magnetars which may constitute an appreciable fraction of ULX population.
The supernova remnant (SNR) HESS J1731−347 is one of the few objects exhibiting emission up to the TeV energy band and it stands as a prime target for the study of cosmic ray acceleration in SNRs. It ...also hosts a central compact object (CCO), which is of interest in the context of the ultra-dense matter equation of state in neutron stars. For both types of studies, however, the parameters of the respective models depend crucially on the assumed distance to the object and are affected to a certain extent by the assumed interstellar medium (ISM) properties around the SNR. Here, we report on the first quantitative analysis of the properties of the compact X-ray dust scattering halo that is assumed to be present around the CCO based on
Chandra
observations of the source. Our findings unambiguously confirm the presence of a compact halo around the CCO, and we show that the observed halo properties are consistent with expectations from independent measurements of the dust distribution along the line of sight and the distance to the source. Although we were not able to significantly improve those constraints, our results are important for future studies of the CCO itself. Indeed, the halo contribution is expected to affect the X-ray spectrum and the derived parameters of the neutron star when observed with moderate angular resolutions. Our results, which offer a quantitative characterization of the halo properties, will be useful in accounting for this effect.
—In total, 7444 fields with a total area of 857.9 thousand hectares were mapped on the territory of five eastern arid regions of the Stavropol krai. As of 2021, arable land occupies more than 55% of ...the study area and is located mainly in its western part. Winter crops occupy 4693 fields with a total area of more than 487 thousand hectares (56.9% of the total field area). Mapping of the contours of the fields was carried out on the basis of satellite images from
Sentinel-2
(natural colors). The morphometric characteristics of the fields were calculated on the basis of the SRTM3 DEM. The mask of winter crops for the period 2011–2021 and weekly composites with data on the NDVI value for spring (March–May) were obtained using the VEGA-Science service. The areas of the fields identified according to remote sensing data are comparable with official statistics. The fields are located on lands with a steepness of up to 5°, the steepness of 1°–2° prevails (about 90% of the total area). Most fields have a predominant southern exposure, there are no fields with a northern exposure. There are 13 kinds of soils on the territory of the study area, chestnut deep soils are predominant. The average NDVI for March–May 2011–2021 shows the highest values in fields located on meadow soils, the lowest NDVI values are observed on salt flats and salt marshes. It was revealed that the NDVI value decreases with increasing field size, the optimal field size is up to 150 hectares. The highest NDVI values were found in fields with a steepness of 1°–2°, southern exposure and meadow, chestnut- and light-chestnut soils. The influence of annual precipitation amounts on the NDVI value is analyzed.
The satellite imagery of the eastern part of the Stavropol region (Russia) was processed and analyzed for the spatial and temporal spread of fires, both landscape and field ones, and open sand ...massifs. Moisture distribution, anthropogenic transformation of the territory, climatic trends, and livestock dynamics were assessed. The agricultural and climatic zones were considered to reconstruct the fire dynamics. No direct relationship was revealed between landscape fire progression and desertification site development. While the advance of open sands naturally prevents the spread of fires, it also contributes to a decrease in the population of large and small livestock. This, in turn, leads to an accumulation of the mortmass and results in a higher fire risk. Our findings show that the areas of open sands increased more than 20-fold from 2013 to 2022, while landscape and field fires tended to become less extensive.
We present the results of the pulse-amplitude-resolved spectroscopy of the accreting pulsar V 0332+53 using the NuSTAR observations of the source in 2015 and 2016. We investigate the dependence of ...the energy of the cyclotron resonant scattering feature (CRSF) as a function of X-ray luminosity on timescales comparable with the spin period of the pulsar within individual observations, and the behavior on longer timescales within and between the two observed outbursts. We confirm that in both cases the CRSF energy is negatively correlated with flux at luminosities higher than the critical luminosity and is positively correlated at lower luminosities. We also confirm the recently reported gradual decrease in the line energy during the giant outburst in 2015. Using the NuSTAR data, we find that this decrease was consistent with a linear decay throughout most of the outburst, and flattened or even reversed at the end of the 2015 outburst, approximately simultaneously with the transition to the subcritical regime. We also confirm that by the following outburst in 2016 the line energy rebounded to previous values. The observed behavior of the CRSF energy with time is discussed in terms of changes in the geometry of the CRSF forming region caused by changes in the effective magnetospheric radius.
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