Search

We present a detailed spectral-timing analysis of the normal branch oscillations (NBOs) observed in two Z sources, Cyg X−2 and Sco X−1, using the data of the Neutron star Interior Composition Explorer (NICER). This is the first study of the NBO properties down to ∼0.4 keV. For Cyg X−2, we confirm the presence of a pivot energy at around 5 keV in the root mean square (rms) spectrum and the phase jump at the pivot energy. In addition, we find a positive phase lag of lower energy (down to 0.4 keV) photons with respect to photons in 2–2.5 keV. For Sco X−1, a rms pivot energy at ∼1.5 keV is detected for the first time, and at the pivot energy a large phase shift is observed. These results indicate that the NBO signal is associated with two different spectral components. By fitting the energy spectra of the states with and without the NBO signal using a two-COMPTB model, we find that the emission of the NBO below or above ∼1.5 keV is mainly related to the Comptonization of the transition layer with the photons from the accretion disc or the neutron star, respectively. In addition, we suggest that if the accretion rate in a Z source is high enough to change the optical depth of the transition layer significantly, a phase jump will occur. A phase shift will be present due to the mixing of the two Comptonization components. [ABSTRACT FROM AUTHOR]

Fast transitions between different types of power density spectra (PDS) happening over time-scales of several tens of seconds are rare phenomena in black hole X-ray binaries. In this paper, we report a broad-band spectral-timing analysis of the fast transitions observed in the 2021 outburst of GX 339−4 using NICER and Insight -HXMT observations. We observe transitions between band-limited noise-dominated PDS and type-B quasi-periodic oscillations (QPOs), and their rapid appearance or disappearance. We also make a detailed comparison between the fast transitions in GX 339−4 with those seen in MAXI J1820+070 and MAXI J1348−630. By comparing the spectra of the periods with and without type-B QPOs, we find that the spectral ratios above 10 keV are nearly constant or slightly decreasing, and the values are different between sources. Below 10 keV, the flux change of the Comptonization component is inversely proportional to the flux change of the thermal component, suggesting that the appearance of type-B QPOs is associated with a redistribution of the accretion power between the disc and the Comptonizing emission region. The spectral ratios between the periods with type-B QPO and those with broad-band noise are significantly different from that with type-B QPO and without type-B QPO, where the ratios (type-B QPO/broad-band noise) show a maximum at around 4 keV and then decrease gradually towards high energies. Finally, we discuss the possible change of the geometry of the inner accretion flow and/or jet during the transitions. [ABSTRACT FROM AUTHOR]

We report the evolution of the X-ray pulsations of EXO 2030+375 during its 2021 outburst using the observations from Insight -HXMT. Based on the accretion torque model, we study the correlation between the spin frequency derivatives and the luminosity. Pulsations can be detected in the energy band of 1–160 keV. The pulse profile evolves significantly with luminosity during the outburst, leading to that the whole outburst can be divided into several parts with different characteristics. The evolution of the pulse profile reveals the transition between the supercritical (fan-beam dominated) and the subcritical accretion (pencil-beam dominated) mode. From the accretion torque model and the critical luminosity model, based on a distance of 7.1 kpc, the inferred magnetic fields are (0.41 − 0.74) × 1012 and (3.48 − 3.96) × 1012 G, respectively, or based on a distance of 3.6 kpc, the estimated magnetic fields are (2.4 − 4.3) × 1013 and (0.98 − 1.11) × 1012 G, respectively. Two different sets of magnetic fields both support the presence of multipole magnetic fields of the neutron star. [ABSTRACT FROM AUTHOR]

Using wavelet analysis and power density spectrum, we investigate two transient quasi-periodic oscillations (QPOs) observed in MAXI J1535−571 observed with Insight - HXMT. The transient QPOs have a centroid frequency of ∼10 Hz with an FWHM ∼0.6 Hz, and an rms amplitude |$\sim 14{{\ \rm per\ cent}}$|⁠. Energy spectra of QPO and non-QPO regimes are also separated and analysed, and the spectra become softer with higher E cut in the non-QPO regime compared to the QPO regime. Our results suggest that the transient QPOs detected in MJD 58016 and 58017 are still the type-C QPO, and the source remains in its HIMS. The duration of all type-C QPO signals based on wavelet is positively correlated with the mean count rate above ∼10 keV, implying appearance of QPOs in different time-scales should be coupled with the corona. The transient QPO properties could be related to the jet or flares, perhaps the partial ejection of the corona is responsible for the disappearance of the type-C QPO. [ABSTRACT FROM AUTHOR]

We investigated the quasi-periodic oscillation (QPO) features in the accretion-powered X-ray pulsar Cen X-3 observed by Insight-HXMT. For two observations in 2020 when Cen X-3 was in an extremely soft state, the power density spectrum revealed the presence of obvious QPO features at ∼40 mHz with an averaged fractional rms amplitude of ∼9 per cent. We study the mHz QPO frequency and rms amplitude over orbital phases, and find that the QPO frequency is ∼33–39 mHz at the orbital phase of 0.1–0.4, increasing to ∼37–43 mHz in the orbital phase of 0.4–0.8, but has no strong dependence on X-ray intensity. We also carried out an energy-dependent QPO analysis, the rms amplitude of the mHz QPOs have a decreasing trend as the energy increases from 2 to 20 keV. In addition, the QPO time-lag analysis shows that the time-delay is ∼20 ms (a hard lag) in the range of ∼5–10 keV, and becomes negative [time-lag of −(20–70) ms] above ∼10 keV. The different QPO theoretical models are summarized and discussed. In the end, we suggest that these energy-dependent timing features as well as the origin of mHz QPOs in Cen X-3 may be ascribed to an instability when the accretion disc is truncated near the corotation radius. [ABSTRACT FROM AUTHOR]

We studied the transient Galactic black hole candidate MAXI J0637−430 with data from Insight-HXMT, Swift , and XMM–Newton. The broad-band X-ray observations from Insight-HXMT help us constrain the power-law component. MAXI J0637–430 is located at unusually high Galactic latitude; if it belongs to the Galactic thick disc, we suggest a most likely distance ≲7 kpc. Compared with other black hole transients, MAXI J0637–430 is also unusual for other reasons: a fast transition to the thermal dominant state at the start of the outburst; a low peak temperature and luminosity (we estimate them at ≈0.7 keV and ≲0.1 times Eddington, respectively); a short decline time-scale; a low soft-to-hard transition luminosity (≲0.01 times Eddington). We argue that such properties are consistent with a small binary separation, short binary period (P ∼ 2 h), and low-mass donor star (M 2 ∼ 0.2 M⊙). Moreover, spectral modelling shows that a single disc blackbody component is not a good fit to the thermal emission. Soft spectral residuals, and deviations from the standard |$L_{\rm disc} \propto T_{\rm in}^4$| relation, suggest the need for a second thermal component. We propose and discuss various scenarios for such component, in addition to those presented in previous studies of this source. For example, a gap in the accretion disc between a hotter inner ring near the innermost stable orbit, and a cooler outer disc. Another possibility is that the second thermal component is the thermal plasma emission from an ionized outflow. [ABSTRACT FROM AUTHOR]

We present a detailed study of the high-mass X-ray binary Vela X-1, using observations performed by Insight-HXMT in 2019 and 2020, concentrating on timing analysis and spectral studies including pulse phase-resolved spectroscopy. The cyclotron line energy is found to be ∼21–27 and 43–50 keV for the fundamental and first harmonic, respectively. We present the evolution of spectral parameters and find that the two line centroid energy ratio E 2/ E 1 evolved from ∼2 before MJD 58900 to ∼1.7 after that. The harmonic cyclotron line energy has no relation to the luminosity but the fundamental line energy shows a positive correlation with X-ray luminosity, suggesting that Vela X-1 is located in the sub-critical accreting regime. In addition, the pulse phase-resolved spectroscopy in Vela X-1 is performed. Both the cyclotron resonant scattering feature and continuum parameters show strong variability over the pulse phase with the ratio of two line energies about 2 near the peak phases and down to ∼1.6 around off-peak phases. Long-term significant variations of the absorption column density and its evolution over the pulse phase may imply the existence of the clumpy wind structure near the neutron star. [ABSTRACT FROM AUTHOR]

In this paper, wavelet analysis is used to study the spectral-timing properties of MAXI J1535–571 observed by the Hard X-ray Modulation Telescope (Insight -HXMT). Low-frequency quasi-periodic oscillations (QPOs) are detected in nine observations. Based on wavelet analysis, the time intervals with QPOs and non-QPOs are isolated, and the corresponding spectra with QPOs and non-QPOs are analysed. We find that the spectra with QPOs (hereafter QPO spectra) are softer than those without QPOs (hereafter non-QPO spectra) in the hard intermediate state (HIMS), while in the soft intermediate state (SIMS), the QPO spectra are slightly harder. The disc temperature of the QPO regime is slightly lower during the HIMS, but becomes higher during the SIMS. The cutoff energies of QPO spectra and non-QPO spectra do not show significant differences. The flux ratio of the disc to total flux is higher for the time intervals with non-QPOs than that in the QPO regime. We propose that these differences in the spectral properties between QPO and non-QPO regimes could be explained through the scenario of Lense–Thirring precession, and the reversal of the QPO/non-QPO behaviour between the HIMS and SIMS may be associated with the appearance/disappearance of a type-B QPO, which might originate in the precession of the jet. [ABSTRACT FROM AUTHOR]

The High Energy (HE) X-ray telescope on board the Hard X-ray Modulation Telescope (Insight -HXMT) can serve as a wide field of view (FOV) gamma-ray monitor with high time resolution (μs) and large effective area (up to thousands cm2). We developed a pipeline to search for gamma-ray bursts (GRBs), using the traditional signal-to-noise ratio (SNR) method for blind search and the coherent search method for targeted search. By taking into account the location and spectrum of the burst and the detector response, the targeted coherent search is more powerful to unveil weak and sub-threshold bursts, especially those in temporal coincidence with gravitational wave (GW) events. Based on the original method in literature, we further improved the coherent search to filter out false triggers caused by spikes in light curves, which are commonly seen in gamma-ray instruments (e.g. Fermi /GBM, POLAR). We show that our improved targeted coherent search method could eliminate almost all false triggers caused by spikes. Based on the first two years of Insight -HXMT/HE data, our targeted search recovered 40 GRBs, which were detected by either Swift /BAT or Fermi /GBM but too weak to be found in our blind search. With this coherent search pipeline, the GRB detection sensitivity of Insight -HXMT/HE is increased to about 1.5E-08 erg cm−2 (200 keV–3 MeV). We also used this targeted coherent method to search Insight -HXMT/HE data for electromagnetic counterparts of LIGO-Virgo GW events (including O2 and O3a runs). However, we did not find any significant burst associated with GW events. [ABSTRACT FROM AUTHOR]

Peroral endoscopic myotomy (POEM) in patients with achalasia who are status post bariatric surgery may be technically challenging due to postsurgical scarring and altered anatomy. The aim of the study was to assess the efficacy and safety of POEM for achalasia in patients with prior bariatric surgery. A review of prospectively maintained databases at three tertiary referral centers from January 2015 to January 2021 was performed. The primary outcome of interest was clinical success, defined as a post-treatment Eckardt score ≤ 3 or improvement in Eckardt score by ≥ 1 when the baseline score was <3, and improvement of symptoms. Secondary outcomes were adverse event rates and symptom recurrence. Sixteen patients status post Roux-en-Y gastric bypass (n  = 14) and sleeve gastrectomy (n  = 2) met inclusion criteria. Indications for POEM were achalasia type I (n  = 2), type II (n  = 9), and type III (n  = 5). POEM was performed either by anterior or posterior approach. The pre-POEM mean integrated relaxation pressure was 26.2 ± 7.6 mm Hg. The mean total myotomy length was 10.2 ± 2.7 cm. The mean length of hospitalization was 1.4 ± 0.7 days. Pre- and postprocedure Eckardt scores were 6.1 ± 2.1 and 1.7 ± 1.8, respectively. The overall clinical success rate was 93.8% (15/16) with mean follow-up duration of 15.5 months. One patient had esophageal leak on postprocedure esophagram and managed endoscopically. Dysphagia recurred in two patients, which was successfully managed with pneumatic dilation with or without botulinum toxin injection. POEM appears to be safe and effective in the management of patients with achalasia who have undergone prior bariatric surgery. [ABSTRACT FROM AUTHOR]

We report the orbital X-ray variability of the high-mass X-ray binary (HMXB) GX 301−2. GX 301−2 underwent a spin-up process in 2018–2020 with the period evolving from ∼685–670 s. The energy-resolved pulse profiles of the pulsar at 1–60 keV varied from single-peaked and sinusoidal shapes to multipeaked ones across different orbital phases. Pulse fractions evolving over the orbit had negative correlations with the X-ray flux. The broad-band X-ray energy spectrum of the pulsar can be described with a partially covered negative–positive cut-off power-law continuum model. Near the periastron passage of the pulsar we found strong variation in the additional column density (⁠|$N_{\mathrm{H}_{2}}$|⁠), which correlated with variation of the flux. Curves of growth for both Fe Kα and Fe Kβ lines were plotted to investigate the distribution of matter around the neutron star. We also found evidence for two cyclotron absorption lines in the phase-averaged spectra in GX 301−2, with one line of 30–42 keV and the other line varying over 48–56 keV. The centroid energies of both lines show a similar relationship with X-ray luminosity: positive correlation in the lower luminosity range, and a negative relation above a critical luminosity of |$10^{37}\, \rm erg\, s^{-1}$|⁠. We estimate the surface magnetic field of the neutron star in GX 301−2 to be ∼(0.5–2) × 1013 G. The two cyclotron line energies have a nearly fixed ratio of ∼1.63 while having a low strength ratio (∼0.05), suggesting that these two features may actually be one line. [ABSTRACT FROM AUTHOR]

We report on the Insight -HXMT observations of the new black hole X-ray binary MAXI J1820+070 during its 2018 outburst. Detailed spectral analysis via the continuum fitting method shows an evolution of the inferred spin during its high soft sate. Moreover, the hardness ratio, the non-thermal luminosity and the reflection fraction also undergo an evolution, exactly coincident to the period when the inferred spin transition takes place. The unphysical evolution of the spin is attributed to the evolution of the inner disc, which is caused by the collapse of a hot corona due to condensation mechanism or may be related to the deceleration of a jet-like corona. The studies of the inner disc radius and the relation between the disc luminosity and the inner disc radius suggest that, only at a particular epoch, did the inner edge of the disc reach the innermost stable circular orbit and the spin measurement is reliable. We then constrain the spin of MAXI J1820 + 070 to be |$a_*=0.2^{+0.2}_{-0.3}$|⁠. Such a slowly spinning black hole possessing a strong jet suggests that its jet activity is driven mainly by the accretion disc rather than by the black hole spin. [ABSTRACT FROM AUTHOR]

We systematically analyse two GRB samples with radio-loud and radio-quiet afterglows, respectively. It is interestingly found that the radio-selected GRB samples exhibit a clear dichotomy in terms of their distributions of intrinsic durations (T int), isotropic energies in γ-rays (E γ, iso), the circum-burst medium density (n), the spectral radio peak luminosity (L ν, p ) and flux densities (F host) of host galaxies. On average, the values of T int, E γ, iso, n, L ν, p , and F host of radio-quiet GRBs are relatively smaller than those of radio-loud ones. However, the redshifts and host flux densities of both samples are similarly distributed. In addition, a positive power-law correlation of |$L_{\nu ,p}\propto E_{\gamma ,\rm iso}^{0.41\pm 0.04}$| is found for the radio-loud sample, especially in accord with the supernova-associated GRBs, which is marginally consistent with that of the radio-quiet GRB sample. A negative correlation between T int and z is confirmed to similarly hold for both radio-loud and radio-quiet GRBs. The dividing line between short and long GRBs in the rest frame is at T int ≃1 s. Consequently, we propose that the radio-selected GRBs could be originated from distinct progenitors and central engines, together with environments. [ABSTRACT FROM AUTHOR]

We investigate the absorption and emission features in observations of GX 301-2 detected with Insight -HXMT/LE in 2017–2019. At different orbital phases, we found prominent Fe Kα, Kβ, and Ni Kα lines, as well as Compton shoulders and Fe K-shell absorption edges. These features are due to the X-ray reprocessing caused by the interaction between the radiation from the source and surrounding accretion material. According to the ratio of iron lines (Kα and Kβ), we infer the accretion material is in a low ionization state. We find an orbital-dependent local absorption column density, which has a large value and strong variability around the periastron. We explain its variability as a result of inhomogeneities of the accretion environment and/or instabilities of accretion processes. In addition, the variable local column density is correlated with the equivalent width of the iron Kα lines throughout the orbit, which suggests that the accretion material near the neutron star is spherically distributed. [ABSTRACT FROM AUTHOR]

Context. Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%. Aims. We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux. Methods. A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (3ML), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the Fermi Gamma-ray Burst Monitor (Fermi-GBM) and the Neil Gehrels Swift Observatory to jointly model the spectral and polarimetric parameters. Results. The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when time-resolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP. [ABSTRACT FROM AUTHOR]

Based on Insight-HXMT data, we report on the pulse fraction evolution during the 2017–2018 outburst of the newly discovered first Galactic ultraluminous X-ray (ULX) source Swift J0243.6+6124. The pulse fractions of 19 observation pairs selected in the rising and fading phases with similar luminosity are investigated. The results show a general trend of the pulse fraction increasing with luminosity and energy at supercritical luminosity. However, the relative strength of the pulsation between each pair evolves strongly with luminosity. The pulse fraction in the rising phase is larger at luminosity below 7.71 × 1038 erg s−1, but smaller at above. A transition luminosity is found to be energy independent. Such a phenomenon is first confirmed by Insight-HXMT observations and we speculate that it may have relation with the radiation-pressure-dominated accretion disc. [ABSTRACT FROM AUTHOR]

We report on our analysis of the 2019 outburst of the X-ray accreting pulsar 4U 1901+03 observed with Insight-HXMT and NICER. Both spectra and pulse profiles evolve significantly in the decaying phase of the outburst. Dozens of flares are observed throughout the outburst. They are more frequent and brighter at the outburst peak. We find that the flares, which have a duration from tens to hundreds of seconds, are generally brighter than the persistent emission by a factor of ∼1.5. The pulse-profile shape during the flares can be significantly different from that of the persistent emission. In particular, a phase shift is clearly observed in many cases. We interpret these findings as direct evidence of changes of the pulsed beam pattern, due to transitions between the sub- and supercritical accretion regimes on a short time-scale. We also observe that at comparable luminosities the flares' pulse profiles are rather similar to those of the persistent emission. This indicates that the accretion on the polar cap of the neutron star is mainly determined by the luminosity, i.e. the mass accretion rate. [ABSTRACT FROM AUTHOR]

It is well known that ordinary supernovae (SNe) are powered by 56Ni cascade decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not all exclusively powered by 56Ni decay. It was suggested that some SNe Ic-BL are powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic supernova discovered by the intermediate Palomar Transient Factory. With a rest-frame rise time of only 4 d, iPTF16asu challenges the existing popular models, for example, the radioactive heating (56Ni-only) and the magnetar +56Ni models. Here we show that this rapid rise could be attributed to interaction between the SN ejecta and a pre-existing circumstellar medium ejected by the progenitor during its final stages of evolution, while the late-time light curve can be better explained by energy input from a rapidly spinning magnetar. This model is a natural extension to the previous magnetar model. The mass-loss rate of the progenitor and ejecta mass are consistent with a progenitor that experienced a common envelope evolution in a binary. An alternative model for the early rapid rise of the light curve is the cooling of a shock propagating into an extended envelope of the progenitor. It is difficult at this stage to tell which model (interaction+magnetar + 56Ni or cooling+magnetar + 56Ni) is better for iPTF16asu. However, it is worth noting that the inferred envelope mass in the cooling+magnetar + 56Ni is very high. [ABSTRACT FROM AUTHOR]

Based on the model of the accretion-induced magnetic field decay of a neutron star (NS), millisecond pulsars (MSPs) will obtain their minimum magnetic field when the NS magnetosphere radius shrinks to the stellar surface during the binary accretion phase. We find that this minimum magnetic field is related to the accretion rate $$\dot{M}$$ as $$B_{\rm min}\sim 2.0\times 10^7{\, \rm G}\, (\dot{M}/\dot{M}_{\rm min})^{1/2}$$, where $$\dot{M}_{\rm min}=4.6\times 10^{15}\rm \, g\,s^{-1}$$ is the average minimum accretion rate required for MSP formation and is constrained by the long-term accretion time, which corresponds to the companion lifetime, being less than the Hubble time. The value of B min is consistent with that of observed radio MSPs and accreting MSPs in low-mass X-ray binaries, which can be found the illustrated case of the minimum and present field strength of SAX J1808.4–3658. The prediction of the minimum magnetic field of MSPs would be the lowest field strength of NSs in the Universe, which could constrain the evolution mechanism of the magnetic field of accreting NSs. [ABSTRACT FROM AUTHOR]

'Internal plateau' followed by a sharp decay is commonly seen in short gamma-ray burst (GRB) light curves. The plateau component is usually interpreted as the dipole emission from a supra-massive magnetar, and the sharp decay may imply the collapse of the magnetar to a black hole (BH). Fall-back accretion on to the new-born BH could produce long-lasting activities via the Blandford-Znajek (BZ) process. The magnetic flux accumulated near the BH would be confined by the accretion discs for a period of time. As the accretion rate decreases, the magnetic flux is strong enough to obstruct gas infall, leading to a magnetically arrested disc. Within this scenario, we show that the BZ process could produce two types of typical X-ray light curves: type I exhibits a long-lasting plateau, followed by a power-law (PL) decay with slopes ranging from 5/3 to 40/9; type II shows roughly a single PL decay with a slope of 5/3. The former requires low magnetic field strength, while the latter corresponds to relatively high values. We search for such signatures of the new-born BH from a sample of short GRBs with an internal plateau, and find two candidates: GRB 101219A and GRB 160821B, corresponding to type II and type I light curves, respectively. It is shown that our model can explain the data very well. [ABSTRACT FROM AUTHOR]

Ultraluminous X-ray sources are usually believed to be black holes with mass about 102-3 M⊙. However, the recent discovery of NuSTAR J095551+6940.8 in M82 by Bachetti et al. shows that it holds the spin period P = 1.37 s and period derivative Ṗ≈-2×10-10ss-1, which provides a strong evidence that some ultraluminous X-ray sources could be neutron stars. We obtain that the source may be an evolved magnetar according to our simulation by employing the model of accretion induced the polar magnetic field decay and standard spin-up torque of an accreting neutron star. The results show that NuSTAR J095551+6940.8 is still in the spin-up process, and the polar magnetic field decays to about 4.5 × 1012 G after accreting ~10-2.5 M⊙, while the strong magnetic field exists in the out-polar region, which could be responsible for the observed low field magnetar. The ultra luminosity of the source can be explained by the beaming effect and two kinds of accretion-radial random accretion and disc accretion. Since the birth rate of magnetars is about ten per cent of the normal neutron stars, we guess that several ultraluminous X-ray sources should share the similar properties to that of NuSTAR J095551+6940.8. [ABSTRACT FROM AUTHOR]

We infer the emission positions of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs) based on the Alfvén wave oscillation model (AWOM). For most sources, the emission radii of kHz QPOs cluster around a region of 16-19 km with the assumed NS radii of 15 km. Cir X-1 has the larger emission radii of 23 ~ 38 km than those of the other sources, which may be ascribed to its large magnetosphere-disc radius or strong NS surface magnetic field. SAX J1808.4-3658 is also a particular source with the relative large emission radii of kHz QPOs of 20 ~ 23 km, which may be due to its large inferred NS radius of 18 ~ 19 km. The emission radii of kHz QPOs for all the sources are larger than the NS radii, and the possible explanations of which are presented. The similarity of the emission radii of kHz QPOs (~16-19 km) for both the low/high luminosity Atoll/Z sources is found, which indicates that both sources share the similar magnetosphere-disc radii. [ABSTRACT FROM AUTHOR]

By means of the Monte Carlo method, we simulate the evolutionary distribution of accreting neutron stars (NSs) in the magnetic field versus spin period ( B-P) diagram where the accretion induced magnetic-field decay model is exploited. The simulated results show that by mass accretion the B-P distribution of the accreting NS would evolve along the equilibrium period line to a region with low field and short period. The B-P distributions of the simulated accreting NSs are consistent with those of the observed millisecond pulsars (MSPs) after accretion of ∼ 0.1-0.2 M⊙. We also test the effects of the initial magnetic field and the spin period on the evolved B-P distribution of the accreting NSs. It is shown that the evolved distributions of the simulated samples are independent of the selection of the initial condition when the NS magnetic field decays to a value less than ∼1010 G. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Endoscopic retrograde cholangiopancreatography (ERCP) remains technically challenging following Roux-en-Y gastric bypass (RYGB). Various techniques have been described to access the excluded stomach. We describe our experience using percutaneous-assisted transprosthetic endoscopic therapy (PATENT) to perform antegrade ERCP. Balloon enteroscopy was used to access the excluded stomach. Direct retrograde percutaneous endoscopic gastrostomy (RPEG) was performed and an esophageal self-expandable metal stent (SEMS) was deployed within the gastrostomy tract. A duodenoscope was advanced through the SEMS and antegrade ERCP was performed. Following ERCP, a gastrostomy tube was placed through the SEMS to maintain patency. Five patients underwent successful antegrade ERCP using PATENT. All patients had a diagnosis of sphincter of Oddi dysfunction. Biliary sphincterotomy was performed in all patients and liver enzymes normalized in four patients with preprocedural elevations. In conclusion, antegrade ERCP employing PATENT is feasible and can be performed during a single endoscopic session in patients with previous RYGB. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the energy dependence of the centroid frequency of the low-frequency quasi-periodic oscillations (QPOs; 0.08–20 Hz) in XTE J1550–564. We have used the observational data from the Rossi X-ray Timing Explorer during the first half part of the 1998–1999 outburst. We have found that the centroid frequency of the fundamental QPO did not vary with photon energy when its QPO frequency was less than ∼0.4–0.8 Hz and it did not increase much when its frequency was between ∼0.8 and ∼3.3 Hz. However, it clearly increased with photon energy when it was larger than ∼3.3 Hz. The most interesting point is that it increased much more quickly with photon energy when its centroid frequency was between ∼6 and ∼8.5 Hz. Subsequently, its rising rate dropped sharply when its frequency was larger than ∼8.5 Hz. We have also investigated the dependence of the first-harmonic and subharmonic QPO frequency on photon energy. We have found that for more than 70 per cent of the subharmonic QPO observations, the frequency increased with the photon energy, while the rest did not change obviously. Meanwhile, ∼60 per cent of the first-harmonic QPOs exhibited a negative correlation between their frequencies and photon energy, while the remaining correlations were irregular. For the amplitudes of the QPOs, complicated dependences on photon energy were also found. The amplitudes of the first-harmonic and subharmonic QPOs have shown a similar correlation with photon energy (i.e. their amplitudes increased with photon energy until ∼6–7 keV, beyond which the amplitudes decreased). By contrast, the fundamental QPO amplitude increased until ∼10 keV and became saturated toward higher energies. These newly discovered patterns of the dependence of QPOs on photon energy cannot be easily explained in the currently existing frames of QPO models. Therefore, they provide an important insight into our understanding of QPO physics. [ABSTRACT FROM PUBLISHER]

The article offers information on the study that focuses on the environmental preferences of Alopias superciliosus and Alopias vulpinus in waters near Marshall Islands. It highlights the materials and methods used in the study including the fishing vessel and fishing grounds, and the fishing gear and operations.

The complete nucleotide sequence of a Beijing isolate of Wisteria vein mosaic virus was determined to be 9695 nucleotides in length excluding the poly(A) tail. Sequence analysis predicted a single large open reading frame of 9279 nucleotides potentially encodes a polyprotein of 3092 amino acids. Phylogenetic analysis based on the genomic and deduced amino acid sequences support the current status of Wisteria vein mosaic virus (WVMV) as a distinct virus of the genus Potyvirus and a member of the Bean common mosaic virus (BCMV) subgroup. Sequence comparisons of WVMV and other members of the BCMV subgroup showed that WVMV is most closely related to both soybean mosaic virus and watermelon mosaic virus. [ABSTRACT FROM AUTHOR]

We analyzed the recently published kHz quasi-period oscillaiton (QPO) data in the neutron star low-mass X-ray binaries (LMXBs), in order to investigate the different correlations of the twin-peak kHz QPOs in bright Z sources and in the less luminous Atoll sources. We find a power-law relation between the upper and the lower kHz QPOs with different indices: b≃ 1.5 for the Atoll source 4U 1728-34 and b≃ 1.9 for the Z source Sco X-1. The implications of our results for the theoretical models for kHz QPOs are discussed. [ABSTRACT FROM AUTHOR]

We consider in this paper the effect of the synchrotron self-Compton process on X-ray afterglows of gamma-ray bursts. We find that, for a wide range of parameter values, especially for the standard values which imply that the energy in the electrons behind the afterglow shock is tens of times as large as that in the magnetic field, the electron cooling is dominated by Compton cooling rather than synchrotron one. This leads to a different evolution of cooling frequency in the synchrotron emission component, and hence a different (flatter) light-curve slope in the X-ray range. This effect should be taken into account when estimating the afterglow parameters by X-ray observational data. For somewhat higher ambient density, the synchrotron self-Compton emission may be directly detected in the X-ray range, showing varying spectral slopes and quite a steep light-curve slope. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 20-year-old man who underwent complex thoraco-abdominal surgery after traumatic injury that resulted in a cervical esophagus disconnected from the remaining gut. He was diagnosed through the use of slim endoscopes passed through a mature percutaneous endoscopic gastronomy trace, which revealed intermittent bleeding from a gastrojejunal anastomic ulcer. The use of innovative endoscopic approach for the management of recurrent massive bleeding is discussed.

We investigate the radius of the recycled pulsar in double pulsar PSR J0737-3039. In the standard accretion spin-up model, the recycled pulsar spin up continues until arriving at a minimum spin period, or so-called “equilibrium period”, which is related to stellar magnetic field, accretion rate, mass and radius. If present spin period is much longer than that at birth, the spin-down age can give the realistic true age estimation for normal pulsar J0737-3039B. Base on the above conditions, we estimate the radius of millisecond pulsar (MSP) J0737-3039A by assuming its true age is same as the spin-down age of its companion J0737-3039B. We obtained that the radius of J0737-3039A ranges approximately from 5 to 27 km. [ABSTRACT FROM PUBLISHER]