Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late 2017 September in a giant outburst with a peak luminosity of 2 × 1039(d/7 kpc)2 erg s−1 (0.1-10 keV), with no ...formerly reported activity. At this luminosity, Swift J0243.6+6124 is the first known galactic ultraluminous X-ray pulsar. We describe Neutron star Interior Composition Explorer (NICER) and Fermi Gamma-ray Burst Monitor (GBM) timing and spectral analyses for this source. A new orbital ephemeris is obtained for the binary system using spin frequencies measured with GBM and 15-50 keV fluxes measured with the Neil Gehrels Swift Observatory Burst Alert Telescope to model the system's intrinsic spin-up. Power spectra measured with NICER show considerable evolution with luminosity, including a quasi-periodic oscillation near 50 mHz that is omnipresent at low luminosity and has an evolving central frequency. Pulse profiles measured over the combined 0.2-100 keV range show complex evolution that is both luminosity and energy dependent. Near the critical luminosity of L ∼ 1038 erg s−1, the pulse profiles transition from single peaked to double peaked, the pulsed fraction reaches a minimum in all energy bands, and the hardness ratios in both NICER and GBM show a turnover to softening as the intensity increases. This behavior repeats as the outburst rises and fades, indicating two distinct accretion regimes. These two regimes are suggestive of the accretion structure on the neutron star surface transitioning from a Coulomb collisional stopping mechanism at lower luminosities to a radiation-dominated stopping mechanism at higher luminosities. This is the highest observed (to date) value of the critical luminosity, suggesting a magnetic field of B ∼ 1013 G.
ABSTRACT
OAO 1657−415 is an atypical supergiant X-ray binary among wind- and disc-fed systems, showing alternate spin-up/spin-down intervals lasting of the order of tens of days. We study different ...torque states of OAO 1657−415 based on the spin history monitored by Fermi/Gamma-Ray Burst Monitor, together with fluxes from Swift/Burst Alert Telescope (BAT) and Monitor of All-sky X-ray Image/Gas Slit Camera. Its spin frequency derivatives are well correlated with Swift/BAT fluxes during rapid spin-up episodes, anticorrelated with Swift/BAT fluxes during rapid spin-down episodes, and not correlated in between. The orbital profile of spin-down episodes is reduced by a factor of 2 around orbital phases of 0.2 and 0.8 compared to that of spin-up episodes. The orbital hardness ratio profile of spin-down episodes is also lower than that of spin-up episodes around phases close to the mid-eclipse, implying that there is more material between the neutron star and the observer for spin-down episodes than for spin-up episodes around these phases. These results indicate that the torque state of the neutron star is connected with the material flow on orbital scale and support the retrograde/prograde disc accretion scenario for spin-down/spin-up torque reversal.
ABSTRACT
We present a detailed timing study of the pulse profile of Swift J0243.6+6124 with Hard X-ray Modulation Telescope (HXMT) and Fermi/GBM (Gamma-ray Burst Monitor) data during its 2017 giant ...outburst. The double-peak profile at luminosity above 5 × 1038 erg s−1 is found to be 0.25 phase offset from that below 1.5 × 1038erg s−1, which strongly supports for a transition from a pencil beam to a fan beam, and thus for the formation of shock dominated accretion column. During the rising stage of the high double-peak regime, the faint peak got saturated in 10–100 keV band above a luminosity of Lt ∼ 1.3 × 1039erg s−1, which is coincident with sudden spectral changes of both the main and faint peaks. They imply a sudden change of emission pattern around Lt. The spin-up rate ($\dot{\nu }$) is linearly correlated with luminosity (L) below Lt, consistent with the prediction of a radiation pressure dominated disc. The $\dot{\nu }-L$ relation flattens above Lt, indicating a less efficient transfer of angular momentum and a change of accretion disc geometry above Lt. It is likely due to irradiation of the disc by the central accretion column and indicates significant radiation feedback well before the inner disc radius reaching the spherization radius.
ABSTRACT Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two γ-ray bursts (GRBs) every three days. Here, we present the third of a ...series of catalogs of GRBs detected by GBM, extending the second catalog by two more years through the middle of 2014 July. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM-detected GRBs. For each GRB, the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10 to 1000 keV, exploiting the full energy range of GBM's low-energy NaiTl) detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fit by a two-component model with short-hard and long-soft bursts than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
ABSTRACT
GX 301-2 provides a rare opportunity to study both disc and wind accretion in a same target. We report Insight-Hard X-ray Modulation Telescope observations of the spin-up event of GX 301-2 ...that happened in 2019 and compare with those of wind-fed state. The pulse profiles of the initial rapid spin-up period are dominated by one main peak, while those of the later slow spin-up period are composed of two similar peaks, as those of wind-fed state. These behaviours are confirmed by Fermi/Gamma-ray Burst Monitor data, which also show that during the rapid spin-up period, the main peak increases with luminosity up to 8 × 1037 erg s−1, but the faint peak remains almost constant. The absorption column densities during the spin-up period are ∼1.5 × 1023 cm−2, much less than those of wind-fed state at similar luminosity (∼9 × 1023 cm−2), supporting the scenario that most of material is condensed into a disc during the spin-up period. We discuss possible differences between disc and wind accretion that may explain the observed different trends of pulse profiles.
ABSTRACT We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku during an outburst decline in 2010 October and compare with previous results. XTE J1946+274 ...is a transient X-ray binary consisting of a Be-type star and a neutron star with a 15.75 s pulse period in a 172 days orbit with 2-3 outbursts per orbit during phases of activity. We improve the orbital solution using data from multiple instruments. The X-ray spectrum can be described by an absorbed Fermi-Dirac cut-off power-law model along with a narrow Fe K line at 6.4 keV and a weak Cyclotron Resonance Scattering Feature (CRSF) at ∼35 keV. The Suzaku data are consistent with the previously observed continuum flux versus iron line flux correlation expected from fluorescence emission along the line of sight. However, the observed iron line flux is slightly higher, indicating the possibility of a higher iron abundance or the presence of non-uniform material. We argue that the source most likely has only been observed in the subcritical (non-radiation dominated) state since its pulse profile is stable over all observed luminosities and the energy of the CRSF is approximately the same at the highest (∼5 × 1037 erg s−1) and lowest (∼5 × 1036 erg s−1) observed 3-60 keV luminosities.
Development of the sensor head for the StarBurst multimessenger pioneer Woolf, Richard S.; Kocevski, Daniel; Grove, J. Eric ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
July 2024, 2024-07-00, Letnik:
1064
Journal Article
Recenzirano
The StarBurst Multimessenger Pioneer is a highly sensitive wide-field gamma-ray monitor designed to detect the prompt emission of short gamma-ray bursts, a key electromagnetic signature of neutron ...star mergers. StarBurst is designed to enhance the new era of multimessenger astronomy by using the advancements in gamma-ray detectors made over the past decade, namely in silicon photomultipliers (SiPMs) for light readout. With >400% the effective area of the Fermi Gamma-ray Burst Monitor and full coverage of the unocculted sky, the StarBurst observations of electromagnetic counterparts to neutron star mergers make it a key partner to the gravitational wave network in discovering these mergers at a fraction of the cost of currently operating gamma-ray missions. The StarBurst Sensor Head consists of 12 thallium-doped cesium iodide (CsI:Tl) scintillation detectors, each of which uses a custom array of low-mass, low-voltage SiPMs to cover an energy range 50 keV–2000 keV. The manuscript outlines the science of StarBurst; the predecessor technology demonstrator instrument, Glowbug; instrument design including mechanical, electrical, and data acquisition; and, the performance results from a crystal detector unit.
Summary
Purpose: Data on epileptiform electroencephalography (EEG) discharges in healthy children are limited, with published studies dating back more than 20 years. Moreover, analyses have been ...performed exclusively using paper‐recorded EEG, and reported prevalences differ significantly. With recent reports using these data as reference suggesting an increased prevalence of epileptiform EEG discharges in children with behavioral disturbances, acquisition of exact prevalence data has become even more critical. The aim of our study was to analyze the frequency of epileptiform EEG discharges in healthy children using digitally recorded EEG (DEEG) and to compare these data to those of previously published studies.
Methods: Prospective analysis of DEEG was performed in 382 healthy children (226 male, 156 female) ages 6–13 years admitted to our hospital for minor head trauma. Recording was carried out for a minimum of 20 min including hyperventilation and photic stimulation. Analysis was carried out by two board‐certified clinical neurophysiologists.
Results: Epileptiform EEG discharges were detected in 25 of 382 children (11 of 226 male, 14 of 156 female) corresponding to an overall prevalence of 6.5%. Of these 25 children, 4 had either generalized or bifrontal spikes, 12 showed constant localized focal discharges, and 9 showed multifocal discharges. Compared to previous studies using non‐DEEG recording, the prevalence of epileptiform EEG discharges in our population was significantly higher. No significant difference was found when comparing our data to prevalences recently reported in children with behavioral disturbances using DEEG.
Conclusions: Our study further highlights the urgent need to reevaluate the prevalence of epileptiform EEG discharges in healthy children using DEEG recordings in a large cohort.
Spectroscopy is a method typically used to assess an unknown quantity of energy by means of a frequency measurement. In many problems, resonance techniques enable high-precision measurements, but the ...observables have generally been restricted to electromagnetic interactions. Here we report the application of resonance spectroscopy to gravity. In contrast to previous resonance methods, the quantum mechanical transition is driven by an oscillating eld that does not directly couple an electromagnetic charge or moment to an electromagnetic field.
The standard model of cosmology provides a robust description of the evolution of the Universe. Nevertheless, the small magnitude of the vacuum energy is troubling from a theoretical point of view9. ...An appealing resolution to this problem is to introduce additional scalar fields. However, these have so far escaped experimental detection, suggesting some kind of screening mechanism may be at play. Although extensive exclusion regions in parameter space have been established for one screening candidate—chameleon fields10,17—another natural screening mechanism based on spontaneous symmetry breaking has also been proposed, in the form of symmetrons11. Such fields would change the energy of quantum states of ultracold neutrons in the gravitational potential of the Earth. Here, we demonstrate a spectroscopic approach based on the Rabi resonance method that probes these quantum states with a resolution of ΔE =2 × 10−15 eV. This allows us to exclude the symmetron as the origin of dark energy for a large volume of the three-dimensional parameter space.
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