We discuss possible association of fast radio bursts (FRBs) with supergiant pulses emitted by young pulsars (ages ∼ tens to hundreds of years) born with regular magnetic field but very short – few ...milliseconds – spin periods. We assume that FRBs are extra-Galactic events coming from distances d ≲ 100 Mpc and that most of the dispersion measure (DM) comes from the material in the freshly ejected SNR shell. We then predict that for a given burst the DM should decrease with time and that FRBs are not expected to be seen below ∼300 MHz due to free–free absorption in the expanding ejecta. A supernova might have been detected years before the burst; FRBs are mostly associated with star-forming galaxies. The model requires that some pulsars are born with very fast spins, of the order of few milliseconds. The observed distribution of spin-down powers
$\dot{E}$
in young energetic pulsars is consistent with equal birth rate per decade of
$\dot{E}$
. Accepting this injection distribution and scaling the intrinsic brightness of FRBs with
$\dot{E}$
, we predict the following properties of a large sample of FRBs: (i) the brightest observed events come from a broad distribution in distances; (ii) for repeating bursts brightness either remains nearly constant (if the spin-down time is longer than the age of the pulsar) or decreases with time otherwise; in the latter case DM
$\propto \dot{E}$
.
Background
Bariatric surgery is endorsed by multiple societies as the most effective treatment for obesity. Psychosocial functioning has also been noted to improve for most patients after bariatric ...surgery. However, some studies have shown an increase in post-operative suicide risk. The aim of this study was to review the published literature and evaluate the association of bariatric surgery with suicide events and suicide/self-harm attempts in patients who have undergone weight loss surgery.
Methods
MEDLINE and Embase were searched from inception through January 2018 for retrospective or prospective studies reporting mortality outcomes and self-harm or suicide rates after bariatric procedures. The primary outcome was the pooled event rate with 95% confidence interval (95% CI) for suicide. Secondary outcomes were suicide/self-harm attempts after bariatric surgery compared to same population prior to surgery and to matched control subjects, with the respective calculated odds ratios (OR) and 95% CI.
Results
From 227 citations, 32 studies with 148,643 subjects were eligible for inclusion. The patients were predominantly females (76.9%). Roux-en-Y gastric bypass (RYGB) was the most commonly performed procedure (58.9%). The post-bariatric suicide event rate was 2.7/1000 patients (95% CI 0.0019–0.0038), while the suicide/self-harm attempt event rate was 17/1000 patients (95% CI 0.01–0.03). The self-harm/suicide attempt risk was higher after bariatric surgery within the same population with OR of 1.9 (95% CI 1.23–2.95), and compared to matched control subjects, OR 3.8 (95% CI, 2.19–6.59).
Conclusions
Post-bariatric surgery patients had higher self-harm/suicide attempt risk compared to age-, sex-, and BMI-matched controls. Various pre- and post-surgical psychosocial, pharmacokinetic, physiologic, and medical factors may be involved.
We present estimates of initial spin periods,
P
0
, for radio pulsars associated with supernova remnants. By using the published data on 30 objects, we were able to derive a reliable estimate for the ...initial spin period, assuming standard magneto-dipole spin-down (braking index
n
=3), in many cases. Our set of estimates is still not sufficient to infer the exact shape of the initial period distribution. However, we show that a gaussian distribution with mean and deviation ∼0.1 s is consistent with our results, while flat, wide distributions and very narrow ones are disfavored.
We discuss identification of possible counterparts and persistent sources related to fast radio bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large ...spin-down luminosities. In particular, we demonstrate that at least some of the sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance (p-value ≈ 4 per cent) of galaxies in error boxes of FRBs. In the very near future with even modestly increased statistics of FRBs and with the help of dedicated X-ray observations and all-sky X-ray surveys it will be possible to decisively prove or falsify the supergiant pulses model.
In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby ...cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. Several scenarios of magneto-rotational evolution are presented. Recent observational data, such as the discovery of long-period radio pulsars, require the non-trivial evolution of magnetic fields, the spin periods of neutron stars, or both. In some detail, I discuss different models of magnetic field decay and interactions of young neutron stars with fallback matter.
Evolution of Neutron Star Magnetic Fields Igoshev, Andrei P.; Popov, Sergei B.; Hollerbach, Rainer
Universe (Basel),
09/2021, Letnik:
7, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Neutron stars are natural physical laboratories allowing us to study a plethora of phenomena in extreme conditions. In particular, these compact objects can have very strong magnetic fields with ...non-trivial origin and evolution. In many respects, its magnetic field determines the appearance of a neutron star. Thus, understanding the field properties is important for the interpretation of observational data. Complementing this, observations of diverse kinds of neutron stars enable us to probe parameters of electro-dynamical processes at scales unavailable in terrestrial laboratories. In this review, we first briefly describe theoretical models of the formation and evolution of the magnetic field of neutron stars, paying special attention to field decay processes. Then, we present important observational results related to the field properties of different types of compact objects: magnetars, cooling neutron stars, radio pulsars, and sources in binary systems. After that, we discuss which observations can shed light on the obscure characteristics of neutron star magnetic fields and their behaviour. We end the review with a subjective list of open problems.
How to make a mature accreting magnetar Igoshev, A. P; Popov, S. B
Monthly notices of the Royal Astronomical Society,
01/2018, Letnik:
473, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
Several candidates for accreting magnetars have been proposed recently by different authors. Existence of such systems contradicts the standard magnetic field decay scenario where a large ...magnetic field of a neutron star reaches ≲a few ×1013 G at ages ≳1 Myr. Among other sources, the high-mass X-ray binary 4U 0114+65 seems to have a strong magnetic field around 1014 G. We develop a new Bayesian estimate for the kinematic age and demonstrate that 4U 0114+65 has kinematic age 2.4–5 Myr (95 per cent credential interval) since the formation of the neutron star. We discuss which conditions are necessary to explain the potential existence of magnetars in accreting high-mass binaries with ages about few Myr and larger. Three necessary ingredients are: the Hall attractor to prevent rapid decay of dipolar field, relatively rapid cooling of the crust in order to avoid Ohmic decay due to phonons, and finally, low values of the parameter Q to obtain long Ohmic time-scale due to impurities. If age and magnetic field estimates for proposed accreting magnetars are correct, then these systems set the strongest limit on the crust impurity for a selected sample of neutron stars and provide evidence in favour of the Hall attractor.
Abstract
X-ray emission from the surface of isolated neutron stars (NSs) has been now observed in a variety of sources. The ubiquitous presence of pulsations clearly indicates that thermal photons ...either come from a limited area, possibly heated by some external mechanism, or from the entire (cooling) surface but with an inhomogeneous temperature distribution. In an NS the thermal map is shaped by the magnetic field topology since heat flows in the crust mostly along the magnetic field lines. Self-consistent surface thermal maps can hence be produced by simulating the coupled magnetic and thermal evolution of the star. We compute the evolution of the NS crust in three dimensions for different initial configurations of the magnetic field and use the ensuing thermal surface maps to derive the spectrum and the pulse profile as seen by an observer at infinity, accounting for general-relativistic effects. In particular, we compare cases with a high degree of symmetry with inherently 3D ones, obtained by adding a quadrupole to the initial dipolar field. Axially symmetric fields result in rather small pulsed fractions (≲5%), while more complex configurations produce higher pulsed fractions, up to ∼25%. We find that the spectral properties of our axisymmetric model are close to those of the bright isolated NS RX J1856.5-3754 at an evolutionary time comparable with the inferred dynamical age of the source.
It has long been unclear if the small-scale magnetic structures on the neutron star (NS) surface could survive the fall-back episode. The study of the Hall cascade by Cumming, Arras & Zweibel hinted ...that energy in small-scales structures should dissipate on short time-scales. Our new 2D magneto-thermal simulations suggest the opposite. For the first ∼10 kyr after the fall-back episode with accreted mass 10−3 M⊙, the observed NS magnetic field appears dipolar, which is insensitive to the initial magnetic topology. In framework of the Ruderman & Sutherland, vacuum gap model during this interval, non-thermal radiation is strongly suppressed. After this time, the initial (i.e. multipolar) structure begins to re-emerge through the NS crust. We distinguish three evolutionary epochs for the re-emergence process: the growth of internal toroidal field, the advection of buried poloidal field, and slow Ohmic diffusion. The efficiency of the first two stages can be enhanced when small-scale magnetic structure is present. The efficient re-emergence of high-order harmonics might significantly affect the curvature of the magnetospheric field lines in the emission zone. So, only after few 104 yr would be the NS starts shining as a pulsar again, which is in correspondence with radio silence of central compact objects. In addition, these results can explain the absence of good candidates for thermally emitting NSs with freshly re-emerged field among radio pulsars (), as NSs have time to cool down, and supernova remnants can already dissipate.
Strong encryption algorithms and reliable anonymity routing have made cybercrime investigation more challenging. Hence, one option for law enforcement agencies (LEAs) is to search through unencrypted ...content on the Internet or anonymous communication networks (ACNs). The capability of automatically harvesting web content from web servers enables LEAs to collect and preserve data prone to serve as potential leads, clues, or evidence in an investigation. Although scientific studies have explored the field of web crawling soon after the inception of the web, few research studies have thoroughly scrutinised web crawling on the "dark web" or via ACNs such as I2P, IPFS, Freenet, and Tor. The current paper presents a systematic literature review (SLR) that examines the prevalence and characteristics of dark web crawlers. From a selection of 58 peer-reviewed articles mentioning crawling and the dark web, 34 remained after excluding irrelevant articles. The literature review showed that most dark web crawlers were programmed in Python, using either Selenium or Scrapy as the web scraping library. The knowledge gathered from the systematic literature review was used to develop a Tor-based web crawling model into an already existing software toolset customised for ACN-based investigations. Finally, the performance of the model was examined through a set of experiments. The results indicate that the developed crawler was successful in scraping web content from both clear and dark web pages, and scraping dark marketplaces on the Tor network. The scientific contribution of this paper entails novel knowledge concerning ACN-based web crawlers. Furthermore, it presents a model for crawling and scraping clear and dark websites for the purpose of digital investigations. The conclusions include practical implications of dark web content retrieval and archival, such as investigation clues and evidence, and the related future research topics.
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