ABSTRACT
The study of polarization and micro-structure is very important for understanding the radiation mechanism of Rotating Radio Transients (RRATs). Due to the limitations of telescope ...sensitivity and time resolution, studies of the polarization and micro-structure of RRATs have been rare in the past. In this work, we report on a high-time resolution and full polarization observation of RRAT J0139+3336 with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). A total of 96 burst pulses were detected in the 3-h observation. The degrees of linear and circular polarization and the shape of the polarization position angle (PPA) of the single pulses vary significantly. The average profile displays a small degree of linear and circular polarization, and the PPA exhibits a remarkably smooth and steep S-shaped curve, which are also characteristics of pulsars. The circular polarization in some single pulses demonstrates a clear sign change. We discuss the geometric structure of the emission beam based on the results from fitting the RVM model to the changes in the PPA. Using an autocorrelation analysis, the quasi-periodic micro-structure in the single pulse emission is detected with a median period of about 0.91 ms. We show that the position of RRAT J0139+3336 on the P–Pμ diagram falls in the normal pulsar (NP) region . The radio emission of RRAT J0139+3336 shows unique properties, such as the sign change in the circular polarization and quasi-periodicity in the micro-structure, which will provide important clues to the emission mechanism of RRATs.
The low emission mode in PSR B0329+54 Tu, Z Y; Yuen, R; Wen, Z G ...
Monthly notices of the Royal Astronomical Society,
03/2022, Letnik:
512, Številka:
2
Journal Article
Recenzirano
ABSTRACT
We investigate properties of the low emission mode in PSR B0329+54 based on four single-pulse observations at frequency centred at 1.54 GHz using Nanshan radio telescope in Urumqi. The low ...emission mode is characterized by an intensity drop in the central component below that of the other two components. Referred here as the low mode, it has an average duration of 3P0 and is observed in both abnormal and normal emission modes of the pulsar occupying 3.6 per cent of the observed pulses. We demonstrate that the properties of low modes are related to the two modes. We find that the integrated profile of low modes is unique to the two modes, and that low modes occur more frequently when the pulsar is in the normal mode. Analysis of the energy distribution for normal low modes suggests that the cause for the intensity drop in the central component is separated from the emission of the other two components. We demonstrate that the pulse emission characteristics in the normal emission mode shortly after a low-mode bears some similarities with the abnormal mode and gradually recovering to the original normal emission in about three pulsar periods. In addition, the occurrence rate for low modes in different normal modes is mostly consistent, which implies that the duration of low modes is related to a normal mode for this pulsar. Our results imply profile modes each corresponds to specific magnetospheric plama density in particular geometric configuration, and profile mode changing signifies distinct changes of both at different parts of the profile.
Abstract
We report on the detection of 146 (0.96%) bright pulses with a peak flux density >0.86 Jy from PSR B0031–07 in 4 hr of continuous observations made at 4.82 GHz, with a bandwidth of 1 GHz, ...using the Shanghai Tian Ma 65 m radio telescope. We find that the peak flux density distribution follows a power law with index
α
= −3.6 ± 0.2, while the pulse energy appears to follow a logarithmic normal distribution. The bright pulses from PSR B0031–07 were observed to repeat in an irregular fashion. The intervals between bright pulses can be described with an exponentiated Weibull distribution. Furthermore, the sensitive observations at higher frequency with a short time resolution of 65.54
μ
s form a reliable basis for detailed microstructure studies. Close inspection of the detected bright pulses reveals that 38 pulses exhibit well-defined quasi-periodicities. No unanimous period for the quasi-periodicities is found, and the peak flux density is independent of the micropulse width. Finally, possible physical mechanisms are discussed.
A purely magnetospheric model is introduced for observed abrupt changes in pulsar radio profile. Motion of magnetospheric plasma is described by a drift frequency, ωdr, that depends on a parameter 0 ...≤ y ≤ 1, and a change in the magnetospheric state corresponds to a change in y. Emission is assumed to arise from m spots distributed uniformly around the magnetic axis, so that spots drift by at the rate mωdr. Observable features, such as subpulses, appear to rotate as ωR = ωdr − mωV. The motion of the visible point, ωV, is ignored in a "standard" version of the viewing geometry that assumes a fixed line of sight (rather than a fixed line-of-sight direction), implying ωV = 0. With ωV ≠ 0, the apparent motion of subpulses is not constant. An abrupt (or more gradual) change in y implies a change in ωR, which affects the observed pulse structure and the average profile. We apply the model for profile shifts observed with PSR B0919+06.
ABSTRACT
The follow-up timing observations were carried out for 24 pulsars discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Commensal Radio Astronomy FAST Survey. ...We report their phase-connected timing ephemeris, polarization pulse profiles, and Faraday rotation measurements. With their spin periods spanning from 2.995 ms to 4.34 s, their period derivatives were determined to spread between 7.996(8) × 10−21 and 9.83(3) × 10−15 s s−1, which imply that they have characteristic ages from 1.97 × 106 to 5.93 × 109 yr. It is inferred that PSRs J0211+4235 and J0518+2431 are beyond the ‘traditional death line’. PSR J0211+4235 is beyond the ‘death valley’. The death line model of Zhang et al. also cannot explain the radio presence of PSR J0211+4235. This suggests that radiation theory needs to be improved. Besides, ten of the 22 canonical pulsars show nulling phenomena. Moreover, PSR J1617+1123 exhibits variation of emission and J0540+4542 shows subpulse drifting. The DM of five pulsars is larger than the estimated by the YMW16 electron density model, which could suggest that electron density models need updates for higher Galactic latitude regions. PSRs J0447+2447 and J1928−0548 are isolated millisecond pulsars. With their flux densities spanning from 5(1)–553(106) μJy, some of these new pulsars found by FAST are distant, dim, and low-$\dot{E}$ ones and are suitable for testing pulsar emission theories.
Abstract
We report on the interstellar scintillation from pulsar J2048−1616 for the first time at 732, 1369, and 3100 MHz observed with the Parkes 64 m radio telescope. Dynamic spectra are obtained ...and diffractive parameters are derived from two-dimensional autocorrelation analyses. The frequency dependencies of the observed diffractive scintillation timescale and decorrelation bandwidth indicate that the electron density fluctuations in the interstellar medium (ISM) do not follow the Kolmogorov spectrum. The secondary spectra are calculated by forming the Fourier power spectra of the corresponding dynamic spectra. Prominent parabolic arcs are revealed in the secondary spectra at three frequencies, which indicate that they originated from scattering by a thin screen. The scattering screen is approximately located centrally between the pulsar and Earth assuming that the ISM is stationary.
The COVID-19 pandemic has drastically impacted work, economy, and way of life. Sensitive measurement of SARS-CoV-2 specific antibodies would provide new insight into pre-existing immunity, virus ...transmission dynamics, and the nuances of SARS-CoV-2 pathogenesis. To date, existing SARS-CoV-2 serology tests have limited utility due to insufficient reliable detection of antibody levels lower than what is typically present after several days of symptoms. To measure lower quantities of SARS-CoV-2 IgM, IgG, and IgA with higher resolution than existing assays, we developed a new ELISA protocol with a distinct plate washing procedure and timed plate development
use of a standard curve. Very low optical densities from samples added to buffer coated wells at as low as a 1:5 dilution are reported using this 'BU ELISA' method. Use of this method revealed circulating SARS-CoV-2 receptor binding domain (RBD) and nucleocapsid protein (N) reactive antibodies (IgG, IgM, and/or IgA) in 44 and 100 percent of pre-pandemic subjects, respectively, and the magnitude of these antibodies tracked with antibody levels of analogous viral proteins from endemic coronavirus (eCoV) strains. The disease status (HIV, SLE) of unexposed subjects was not linked with SARS-CoV-2 reactive antibody levels; however, quantities were significantly lower in subjects over 70 years of age compared with younger counterparts. Also, we measured SARS-CoV-2 RBD- and N- specific IgM, IgG, and IgA antibodies from 29 SARS-CoV-2 infected individuals at varying disease states, including 10 acute COVID-19 hospitalized subjects with negative serology results by the EUA approved Abbott IgG chemiluminescent microparticle immunoassay. Measurements of SARS-CoV-2 RBD- and N- specific IgM, IgG, IgA levels measured by the BU ELISA revealed higher signal from 9 of the 10 Abbott test negative COVID-19 subjects than all pre-pandemic samples for at least one antibody specificity/isotype, implicating improved serologic identification of SARS-CoV-2 infection
multi-parameter, high sensitive antibody detection. We propose that this improved ELISA protocol, which is straightforward to perform, low cost, and uses readily available commercial reagents, is a useful tool to elucidate new information about SARS-CoV-2 infection and immunity and has promising implications for improved detection of all analytes measurable by this platform.
We present here the analysis of giant micropulses from the Vela pulsar. A total of 4187 giant micropulses with peak flux density >2.5 Jy were detected during almost 4 hr of observations carried out ...with the Yunnan 40 m radio telescope at 6800 MHz. Nine of the giant micropulses arrived approximately 3-4 ms earlier than the peak of average pulse profile, longer than that at lower frequencies. The remaining giant micropulses were clustered into three distributions that correspond to three main emission regions, including four giant micropulses occurring on the trailing edge of the averaged profile. We find that the peak flux density distribution follows a power law with index −4. Furthermore, a certain amount of memory is present from the giant micropulse waiting time distribution. Possible emission mechanisms are discussed.
Variations of P 2 in subpulse drifting pulsars Yuen, R; Melrose, D. B; Samsuddin, M. A ...
Monthly notices of the Royal Astronomical Society,
06/2016, Letnik:
459, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We develop a model for subpulse separation period, P
2, taking into account both the apparent motion of the visible point as a function of pulsar phase, ψ, and the possibility of abrupt jumps between ...different rotation states in non-corotating pulsar magnetospheres. We identify three frequencies: (i) the spin frequency of the star, (ii) the drift frequency of the magnetospheric plasma in the source region and (iii) the angular frequency of the visible point around its trajectory. We show how the last of these, which is neglected in traditional models by implicitly assuming the line of sight through the centre of the star, affects the interpretation of P
2. We attribute the subpulse structure to emission from m antinodes distributed uniformly in azimuthal angle about the magnetic axis. We show that variations of P
2 as a function of rotational phase or observing frequency arise naturally when the motion of the visible point is taken into account. We discuss possible application of our model in signifying overall field-line distortion at the emitting region. Abrupt changes in P
2 can occur during state switching in the magnetosphere. We demonstrate that the unique value of P
2 in each rotation state can be used, in principle, to relate the rotation state of the magnetospheres to subpulse drifting.
This paper proposes an intelligence-based approach to predict passengers' route choice behavior, which is crucial to the effective utilization of transportation stations and affects passenger comfort ...and safety. The actual route choice decisions of passengers are extremely difficult to mimic as they involve human behavior. A comprehensive methodology for capturing route choice behavior is still lacking because extensive labor and time resources are required to collect passenger movement data from different stations. In this paper, a four-month site survey was carried out to collect actual route choice behavior information in nine transportation stations in Hong Kong during peak hours. We developed an intelligent model to capture passengers' route choice decision-making that achieved prediction accuracy of 86%. The applicability of this intelligent route choice model is demonstrated by optimizing the number of gates in a transportation station to inform the spatial design of the station.
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