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.
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 hard X-ray emission of X Persei Doroshenko, V.; Santangelo, A.; Kreykenbohm, I. ...
Astronomy and astrophysics (Berlin),
04/2012, Letnik:
540
Journal Article
Recenzirano
Odprti dostop
We present an analysis of the spectral properties of the peculiar X-ray pulsar X Per based on INTEGRAL observations. We show that the source exhibits an unusually hard spectrum and is confidently ...detected by ISGRI up to more than 100 keV. We find that two distinct components may be identified in the broadband 4–200 keV spectrum of the source. We interpret these components as the result of thermal and bulk Comptonization in the vicinity of the neutron star and describe them with several semi-phenomenological models. The previously reported absorption feature at ~30 keV is not required in the proposed scenario and therefore its physical interpretation must be taken with caution. We also investigated the timing properties of the source in the framework of existing torque theory, concluding that the observed phenomenology can be consistently explained if the magnetic field of the neutron star is ~1014 G.
We present an analysis of BeppoSAX observations of the unique transient bursting X-ray pulsar GRO J1744−28. The observations took place in 1997 March during the decay phase of the outburst. We find ...that the persistent broad-band X-ray continuum of the source is consistent with a cutoff power law typical for the accreting pulsars. We also detect the fluorescence iron line at 6.7 keV and an absorption feature at ∼4.5 keV, which we interpret as a cyclotron line. The corresponding magnetic field strength in the line-forming region is ∼3.7(1 + z) × 1011 G. Neither line is detected in the spectra of the bursts. However, an additional soft thermal component with kT ∼ 2 keV was required to describe the burst spectrum. We briefly discuss the nature of this component and argue that among other possibilities it might be connected with thermonuclear flashes at the neutron star surface which accompany the accretion-powered bursts in the source.
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.
Beppo SAX observations of XTE J1946+274 Doroshenko, R; Santangelo, A; Doroshenko, V ...
Astronomy and astrophysics (Berlin),
4/2017, Letnik:
600
Journal Article
Recenzirano
We report on the Beppo SAX monitoring of a giant outburst of the transient X-ray pulsar XTE J1946+274 in 1998. The source was detected with a flux of ~4 x 10 super(-9) ergcm super(-2)s super(-1)(in ...0.1-120 keV range). The broadband spectrum, typical for accreting pulsars, is well described by a cutoff power law with a cyclotron resonance scattering feature (CRSF) at ~38 keV. This value is consistent with earlier reports based on the observations with Suzaku at factor of ten lower luminosity, which implies that the feature is formed close to the neutron star surface rather than in the accretion column. Pulsations with P~ 15.82s were observed up to ~70 keV. The pulse profile strongly depends on energy and is characterised by a "soft" and a "hard" peaks shifted by half period, which suggests a strong phase dependence of the spectrum, and that two components with roughly orthogonal beam patterns are responsible for the observed pulse shape. This conclusion is supported by the fact that the CRSF, despite its relatively high energy, is only detected in the spectrum of the soft peak of the pulse profile. Along with the absence of correlation of the line energy with luminosity, this could be explained in the framework of the recently proposed "reflection" model for CRSF formation. However more detailed modelling of both line and continuum formation are required to confirm this interpretation.
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.
Accretion onto magnetized neutron stars is expected to be centrifugally inhibited at low accretion rates. Several sources, however, are known to pulsate in quiescence at luminosities below the ...theoretical limit predicted for the onset of the centrifugal barrier. The source 1A 0535+262 is one of them. Here we present the results of an analysis of a ~50 ks long XMM-Newton observation of 1A 0535+262 in quiescence. At the time of the observation, the neutron star was close to apastron, and the source had remained quiet for two orbital cycles. In spite of this, we detected a pulsed X-ray flux of ~3 × 10-11 erg cm-2 s-1. Several observed properties, including the power spectrum, remained similar to those observed in the outbursts. Particularly, we have found that the frequency of the break detected in the quiescent noise power spectrum follows the same correlation with flux observed when the source is in outburst. This correlation has been associated with the truncation of the accretion disk at the magnetosphere boundary. We argue that our result, along with other arguments previously reported in the literature, suggests that the accretion in quiescence also proceeds from an accretion disk around the neutron star. The proposed scenario consistently explains the energy of the cyclotron line observed in 1A 0535+262, and the timing properties of the source including the spin frequency evolution within and between the outbursts, and the frequency of the break in power spectrum.
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.
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