ABSTRACT
We present our broad-band study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 d after the merger, and a multimessenger analysis including LIGO ...constraints. The data are compared with predictions from a wide range of models, providing the first detailed comparison between non-trivial cocoon and jet models. Homogeneous and power-law shaped jets, as well as simple cocoon models are ruled out by the data, while both a Gaussian shaped jet and a cocoon with energy injection can describe the current data set for a reasonable range of physical parameters, consistent with the typical values derived from short GRB afterglows. We propose that these models can be unambiguously discriminated by future observations measuring the post-peak behaviour, with Fν ∝ t∼−1.0 for the cocoon and Fν∝ t∼−2.5 for the jet model.
Abstract
We present the results of our year-long afterglow monitoring of GW170817, the first binary neutron star (NS) merger detected by advanced LIGO and advanced Virgo. New observations with the ...Australian Telescope Compact Array (ATCA) and the Chandra X-ray Telescope were used to constrain its late-time behavior. The broadband emission, from radio to X-rays, is well-described by a simple power-law spectrum with index β ∼0.585 at all epochs. After an initial shallow rise ∝ t0.9, the afterglow displayed a smooth turn-over, reaching a peak X-ray luminosity of LX≈5 ×1039 erg s−1 at 160 d, and has now entered a phase of rapid decline, approximately ∝ t−2. The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ≈22○ from its axis. Within such model, the properties of the explosion (such as its blastwave energy EK ≈ 2 × 1050 erg, jet width θc ≈4○, and ambient density n ≈3 × 10−3 cm−3) fit well within the range of properties of cosmological short GRBs.
Recent observations with the Chandra X-ray telescope continue to detect X-ray emission from the transient GW170817. In a total exposure of 96.6 ks, performed between 2020 March 9 and 16 (935–942 d ...after the merger), a total of 8 photons are measured at the source position, corresponding to a significance of ≈5σ. Radio monitoring with the Australian Telescope Compact Array (ATCA) shows instead that the source has faded below our detection threshold (<33 μJy, 3σ). By assuming a constant spectral index of β = 0.585, we derive an unabsorbed X-ray flux of ≈1.4 × 10−15 erg cm−2 s−1, higher than earlier predictions, yet still consistent with a simple structured jet model. We discuss possible scenarios that could account for prolonged emission in X-rays. The current data set appears consistent both with energy injection by a long-lived central engine and with the onset of a kilonova afterglow, arising from the interaction of the sub-relativistic merger ejecta with the surrounding medium. Long-term monitoring of this source will be essential to test these different models.
Diets used to induce metabolic disease are generally high in fat and refined carbohydrates and importantly, are usually made with refined, purified ingredients. However, researchers will often use a ...low fat grain-based (GB) diet containing unrefined ingredients as the control diet. Such a comparison between two completely different diet types makes it impossible to draw conclusions regarding the phenotypic differences driven by diet. While many compositional differences can account for this, one major difference that could have the greatest impact between GB and purified diets is the fiber content, both in terms of the level and composition. We will review recent data showing how fiber differences between GB diets and purified diets can significantly influence gut health and microbiota, which itself can affect metabolic disease development. Researchers need to consider the control diet carefully in order to make the best use of precious experimental resources.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
ABSTRACT
X-ray emission from the gravitational wave transient GW170817 is well described as non-thermal afterglow radiation produced by a structured relativistic jet viewed off-axis. We show that the ...X-ray counterpart continues to be detected at 3.3 years after the merger. Such long-lasting signal is not a prediction of the earlier jet models characterized by a narrow jet core and a viewing angle ≈20 deg, and is spurring a renewed interest in the origin of the X-ray emission. We present a comprehensive analysis of the X-ray dataset aimed at clarifying existing discrepancies in the literature, and in particular the presence of an X-ray rebrightening at late times. Our analysis does not find evidence for an increase in the X-ray flux, but confirms a growing tension between the observations and the jet model. Further observations at radio and X-ray wavelengths would be critical to break the degeneracy between models.
In the field of rolling element bearing diagnostics envelope analysis, and in particular the squared envelope spectrum, have gained in the last years a leading role among the different digital signal ...processing techniques. The original constraint of constant operating speed has been relaxed thanks to the combination of this technique with the computed order tracking, able to resample signals at constant angular increments. In this way, the field of application of squared envelope spectrum has been extended to cases in which small speed fluctuations occur, maintaining the effectiveness and efficiency that characterize this successful technique. However, the constraint on speed has to be removed completely, making envelope analysis suitable also for speed and load transients, to implement an algorithm valid for all the industrial application. In fact, in many applications, the coincidence of high bearing loads, and therefore high diagnostic capability, with acceleration–deceleration phases represents a further incentive in this direction. This paper is aimed at providing and testing a procedure for the application of envelope analysis to speed transients. The effect of load variation on the proposed technique will be also qualitatively addressed.
► Model of bearing signal in variable operating speed conditions. ► New procedure (RS-SES) coupling squared envelope spectrum and computed order tracking. ► Numerical simulations of effectiveness of RS-SES vs. traditional procedure. ► Considerations on load variability effect.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Observation of the scapular posture is one of the most important components of the physical examination in overhead athletes. Postural asymmetry is typically considered to be associated with ...injuries. However, asymmetry in the overhead athlete's scapula may be normal due to the dominant use of the limb.
To quantify the differences in resting scapular posture between the dominant and nondominant sides in 3 groups of healthy overhead athletes (baseball pitchers, volleyball players, and tennis players) using an electromagnetic tracking device.
Cross-sectional design.
University-based biomechanics laboratory.
A total of 43 players participated, including 15 baseball pitchers, 15 volleyball players, and 13 tennis players. All participants were healthy college-aged men.
Bilateral 3-dimensional scapular kinematics with the arm at rest were measured using an electromagnetic tracking device.
Bilateral scapular position and orientation were measured. Between-groups and between-sides differences in each variable were analyzed using separate analyses of variance.
In tennis players, the scapula was more protracted on the dominant side than on the nondominant side (P < .05). In all overhead athletes, the dominant-side scapula was more internally rotated (P = .001) and anteriorly tilted (P = .001) than the nondominant-side scapula was.
The dominant-side scapula of the overhead athletes was more internally rotated and anteriorly tilted than the nondominant-side scapula. The dominant-side scapula of the tennis players was more protracted than that on the nondominant side. Clinicians evaluating overhead athletes need to recognize that scapular posture asymmetry in unilateral overhead athletes may be normal. Our results emphasize the importance of the baseline evaluation in this population in order to accurately assess pathologic change in bilateral scapular positions and orientations after injury.
We present the results of a multiwavelength campaign targeting FRB 20201124A, the third closest repeating fast radio burst (FRB), which was recently localized in a nearby (
z
= 0.0978) galaxy. Deep ...VLA observations led to the detection of quiescent radio emission, which was also marginally visible in X-rays with
Chandra
. Imaging at 22 GHz allowed us to resolve the source on a scale of ≳1″ and locate it at the position of the FRB, within an error of 0.2″. The EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate (SFR) of ≈10
M
⊙
yr
−1
. The surface SFR at the location of FRB 20201124A is two orders of magnitude larger than what is typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a newborn magnetar produced from a supernova explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT, and
Chandra
campaign are consistent with a magnetar scenario.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
PDF
