Frequency dependence of pulsar radiation patterns

We report on new results from simultaneous, dual frequency, single pulse observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find that the longitude separation of subpulses at two different frequencies (238 and 612 MHz) is less than that for the corresponding components in the average profile. A similar behaviour has been noticed before in a number of pulsars. We argue that subpulses are emitted within narrow flux tubes of the dipolar field lines and that the mean pulsar beam has a conal structure. In such a model the longitudes of profile components are determined by the intersection of the line of sight trajectory with subpulse-associated emission beams. Thus, we show that the difference in the frequency dependence of subpulse and profile component longitudes is a natural property of the conal model of pulsar emission beam. We support our conclusions by numerical modelling of pulsar emission, using the known parameters for this pulsar, which produce results that agree very well with our dual frequency observations.Comment: 24 pages, 8 figures. Accepted for publication in Ap

Detection of Giant Pulses from the Pulsar PSR B0031-07

Giant pulses have been detected from the pulsar PSR B0031-07. A pulse with an intensity higher than the intensity of the average pulse by a factor of 50 or more is encountered approximately once per 300 observed periods. The peak flux density of the strongest pulse is 530 Jy, which is a factor of 120 higher than the peak flux density of the average pulse. The giant pulses are a factor of 20 narrower than the integrated profile and are clustered about its center.Comment: 7 pages, 2 figures, to appear in: Pis'ma v Astronomicheskii Zhurnal, 2004, v.30, No.4, and will be translated as: Astronomy Letters, v.30, No.

Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights

In this paper we return to the old problem of conal component-pair widths and profile dimensions. Observationally, we consider a set of 10 pulsars with prominent conal component pairs, for which well measured profiles exist over the largest frequency range now possible. Apart from some tendency to narrow at high frequency, the conal components exhibit almost constant widths. We use all three profile measures, the component separation as well as the outside half-power and 10% widths, to determine conal beam radii, which are the focus of our subsequent analysis. These radii at different frequencies are well fitted by a relationship introduced by Thorsett (1991), but the resulting parameters are highly correlated. Three different types of behavior are found: one group of stars exhibits a continuous variation of beam radius which can be extrapolated down to the stellar surface along the ``last open field lines''; a second group exhibits beam radii which asymptotically approach a minimum high frequency value that is 3--5 times larger; and a third set shows almost no spectral change in beam radius at all. The first two behaviors are associated with outer-cone component pairs; whereas the constant separation appears to reflect inner-cone emission.Comment: 21 pages, 11 figures, accepted for publication in Astrophysical Journal, uses aaste

Observations of Non-radial Pulsations in Radio Pulsars

We introduce a model for pulsars in which non-radial oscillations of high spherical degree (l) aligned to the magnetic axis of a spinning neutron star reproduce the morphological features of pulsar beams. In our model, rotation of the pulsar carries a pattern of pulsation nodes underneath our sightline, reproducing the longitude stationary structure seen in average pulse profiles, while the associated time-like oscillations reproduce "drifting subpulses"--features that change their longitude between successive pulsar spins. We will show that the presence of nodal lines can account for observed 180 degree phase jumps in drifting subpulses and their otherwise poor phase stability, even if the time-like oscillations are strictly periodic. Our model can also account for the "mode changes" and "nulls" observed in some pulsars as quasiperiodic changes between pulsation modes of different l or radial overtone n, analogous to pulsation mode changes observed in oscillating white dwarf stars. We will discuss other definitive and testable requirements of our model and show that they are qualitatively supported by existing data. While reserving judgment until the completion of quantitative tests, we are inspired enough by the existing observational support for our model to speculate about the excitation mechanism of the non-radial pulsations, the physics we can learn from them, and their relationship to the period evolution of pulsars.Comment: 28 pages, 9 figures (as separate png files), Astrophysical Journal, in pres

Finding Radio Pulsars in and Beyond the Galactic Center

Radio-wave scattering is enhanced dramatically for Galactic center sources in a region with radius >~ 15 arc min. Using scattering from Sgr A* and other sources, we show that pulse broadening for pulsars in the Galactic center is {\em at least} 6.3 \nu^{-4} seconds (\nu = radio frequency in GHz) and is most likely 50--200 times larger because the relevant scattering screen appears to be within the Galactic center region itself. Pulsars beyond---but viewed through---the Galactic center suffer even greater pulse broadening and are angularly broadened by <~ 2 {\em arc min}. Periodicity searches at radio frequencies are likely to find only long period pulsars and, then, only if optimized by using frequencies >~ 7 GHz and by testing for small numbers of harmonics in the power spectrum. The optimal frequency is $\nu ~ 7.3 GHz (\Delta_{0.1}P\sqrt{\alpha})^{-1/4}$ where \Delta_{0.1} is the distance of the scattering region from Sgr A* in units of 0.1 kpc, P is the period (seconds), and \alpha is the spectral index. A search for compact sources using aperture synthesis may be far more successful than searches for periodicities because the angular broadening is not so large as to desensitize the survey. We estimate that the number of {\em detectable} pulsars in the Galactic center may range from <= 1 to 100, with the larger values resulting from recent, vigorous starbursts. Such pulsars provide unique opportunities for probing the ionized gas, gravitational potential, and stellar population near Sgr A*.Comment: 13 pages, 4 PS figures, LaTeX and requires AASTeX macro aas2pp4, accepted by ApJ, also available as http://astrosun.tn.cornell.edu/SPIGOT/papers/pulsar/gc_psr.web

Arecibo 430 MHz Pulsar Polarimetry: Faraday Rotation Measures and Morphological Classifications

We have measured Faraday Rotation Measures (RMs) at Arecibo Observatory for 36 pulsars, 17 of them new. We combine these and earlier measurements to study the galactic magnetic field and its possible temporal variations. Many RM values have changed significantly on several-year timescales, but these variations probably do not reflect interstellar magnetic field changes. By studying the distribution of pulsar RMs near the plane in conjunction with the new NE2001 electron density model, we note the following structures in the first galactic longitude quadrant: (1) The local field reversal can be traced as a null in RM in a 0.5-kpc wide strip interior to the Solar Circle, extending \~7 kpc around the Galaxy. (2) Steadily increasing RMs in a 1-kpc wide strip interior to the local field reversal, and also in the wedge bounded by 42<l<52 deg, indicate that the large-scale field is approximately steady from the local reversal in to the Sagittarius arm. (3) The RMs in the 1-kpc wide strip interior to the Sagittarius arm indicate another field reversal in this strip. (4) The RMs in a final 1-kpc wide interior strip, straddling the Scutum arm, also support a second field reversal interior to the Sun,between the Sagittarius and Scutum arms. (5) Exterior to the nearby reversal, RMs from 60<l<78 deg show evidence for two reversals, on the near and far side of the Perseus arm. (6) In general, the maxima in the large-scale fields tend to lie along the spiral arms, while the field minima tend to be found between them. We have also determined polarized profiles of 48 pulsars at 430 MHz. We present morphological pulse profile classifications of the pulsars, based on our new measurements and previously published data.Comment: Accepted by Astrophysical Journal Supplement, 56 pages, 22 fig

Менингококковая инфекция у детей в период 2012–2021 гг. Основные итоги ретроспективного многоцентрового исследования, проблемы сегодняшнего дня

The heavy burden of meningococcal infection is associated not only with life-threatening complications in the acute period and high mortality in invasive forms of the disease, but also with severe consequences in survivors, who are not recorded in our country.The aim of study: to analyze clinical manifestations, complications of the acute period and outcomes of invasive forms of meningococcal disease in children in various regions of the Russian Federation.Materials and methods: an analysis of data from 1327 inpatient medical records of children with an invasive meningococcal infection from 14 regional centers of the Russian Federation for 2012-2021 was carried out (28.3% of cases of the disease in children in the represented federal districts).Results: it was found that young children predominated among the patients – the median was 27.4 (10.7-70.4) months. Complications of the acute period, often combined, were observed in 47.6% of cases. The development of septic shock was noted in 30.4%, Waterhouse-Friderichsen syndrome in 6.6%, carditis in 2.9%, cerebral edema in 15.7%, arthritis in 1.4% of cases; the formation of hydrocephalus, subdural effusion, sensorineural hearing loss in 1.8%, 0.6%, 1% of children, respectively. The presence of soft tissue necrosis requiring surgical intervention was noted in 3.5% of cases. Mortality rate was 10.1%. At the time of discharge from the hospital, 30% of children had complications associated with meningococcal infection: organ dysfunction/ failure in 13.2% of patients (severe in 1.3%), cerebral insufficiency in 19.6%; severe psycho-neurological deficits, sensorineural hearing loss, problems associated with the need for orthopedic/surgical interventions accounted for 0.7%, 0.6% and 0.8%, respectively.Conclusion. Considering the epidemiological features of meningococcal infection – the risk of a sharp increase in morbidity in short periods of time, the life-threatening nature of the disease itself, it is necessary to remain alert to these risks and take all possible measures to prevent the disease using all available means, the most effective of which is vaccine prevention.Тяжелое бремя менингококковой инфекции связано не только с жизнеугрожающими осложнениями острого периода и высокой летальностью при генерализованных формах заболевания, но и с тяжелыми последствиями у выживших, учет которых в нашей стране не ведется.Цель: проведение анализа клинических проявлений, осложнений острого периода и исходов генерализованных форм менингококковой инфекции у детей в различных регионах Российской Федерации.Материалы и методы: проведен анализ данных 1327 медицинских карт (форма 003/у) детей с генерализованной формой менингококковой инфекции из 14 региональных центров Российской Федерации за 2012– 2021 гг. (28,3% случаев заболевания у детей в представляемых федеральных округах).Результаты: установлено, что среди больных преобладали дети раннего возраста – медиана составила 27,4 (10,7–70,4) месяцев. Осложнения, часто сочетанные, в остром периоде заболевания наблюдались в 47,6% случаев: септический шок в 30,4%, синдром Уотерхауза – Фридериксена в 6,6%, кардит в 2,9%, отек головного мозга в 15,7%, артриты в 1,4%, гидроцефалия в 1,8%, сенсоневральная тугоухость в 1%, субдуральный выпот в 0,6% случаев. Наличие некрозов мягких тканей, требовавших хирургического вмешательства, отмечено в 3,5% случаев. Летальность составила 10,1%. На момент выписки из стационара у 30% детей выявлялись осложнения, в том числе выраженная органная дисфункция в 1,3%, грубый психоневрологический дефицит, сенсоневральная тугоухость; осложнения, требующие проведения ортопедических/хирургических вмешательств, составили 0,7%, 0,6% и 0,8% соответственно.Анализ полученных данных позволил вскрыть существующие проблемы, касающиеся клинической и этиологической диагностики заболевания, возможностей выявления осложнений острого периода и учета последствий генерализованных форм менингококковой инфекции.Заключение. Учитывая эпидемиологические особенности менингококковой инфекции (риск резкого подъема заболеваемости в короткие временные промежутки, жизнеугрожающий характер самого заболевания), необходимо сохранять настороженность в отношении данных рисков и предпринимать все возможные меры для профилактики заболевания с использованием всех доступных средств, наиболее эффективным из которых является вакцинопрофилактика

A census of the pulsar population observed with the international LOFAR station FR606 at low frequencies (25–80 MHz)

ontext. To date, only 69 pulsars have been identified with a detected pulsed radio emission below 100 MHz. A LOFAR-core LBA census and a dedicated campaign with the Nançay LOFAR station in stand-alone mode were carried out in the years 2014–2017 in order to extend the known population in this frequency range. Aims. In this paper, we aim to extend the sample of known radio pulsars at low frequencies and to produce a catalogue in the frequency range of 25–80 MHz. This will allow future studies to probe the local Galactic pulsar population, in addition to helping explain their emission mechanism, better characterising the low-frequency turnover in their spectra, and obtaining new information about the interstellar medium through the study of dispersion, scattering, and scintillation. Methods. We observed 102 pulsars that are known to emit radio pulses below 200 MHz and with declination above −30°. We used the Low Band Antennas (LBA) of the LOw Frequency ARray (LOFAR) international station FR606 at the Nançay Radio Observatory in stand-alone mode, recording data between 25 and 80 MHz