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1,087 results on '"CRAB PULSAR"'

1. On a Theory of the Origin of Quasi-Harmonic Bursts on the Crab Pulsar.

Author

Zheleznyakov, V. V. and Shaposhnikov, V. E.

Subjects
*ELECTRON-positron plasmas, *PULSARS, *CURRENT sheets, *CRABS, *GEOMETRICAL optics, *POSITRONS
Abstract

The propagation and conditions for the escape of microwave radio emission from the local source of quasi-harmonic bursts that is a current sheet filled with an electron–proton or electron–positron plasma have been studied in the geometrical optics approximation. A comparative analysis of these corpuscular compositions has shown that in the electron–proton plasma, in contrast to the ordinary component that freely escapes from the source, the escape of the extraordinary radiation component into the magnetosphere is impossible. In the electron–positron plasma the situation with the escape of the extraordinary component is retained. However, a criterion for efficient escape from the current sheet into the surrounding magnetosphere has been established for the ordinary radiation. In both cases of the corpuscular composition, the escaping radiation is polarized identically (linearly, in accordance with the well-known results of the observations by Hankins and Eilek). Our analysis does not allow one to make a definite choice between both plasma compositions in the source using one object, the Crab pulsar, as an example. Further studies, a search for other objects like the Crab pulsar, are needed. [ABSTRACT FROM AUTHOR]

Published
2022
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2. Simulation-based discrimination of Crab pulsar models with XL-Calibur

Author

Åkerström, Dennis and Åkerström, Dennis

Abstract

Polarisation of X-ray light is being investigated with polarimeters to extend the borders of what can be observed. Distant compact objects, such as pulsars, that are to small on the sky to be analysed with imaging can be investigated by analysing the polarisation of the emitted light. This can reveal physics previously hidden by their small nature. There are many models that aim to describe the polarisation of these compact objects to make sense of what is measured. Two examples are the outer gap and two-pole caustic models. The X-ray polarimeter XL-Calibur is a balloon-borne telescope capable of detecting X-rays in the $15-80$ keV energy range. In this thesis details on the polarisation of light, how it can be measured and some principles of X-ray polarimetery is discussed. A new feature in the simulation of XL-Calibur in Geant4 is also described and used to investigate the possibility for XL-Calibur to distinguish between different Crab pulsar polarisation models at different signal rates. The results show that signal rates under 2 Hz yield insufficient data to distinguish between the two models using the measured polarisation fraction and angle. For greater signal rates XL-Calibur does in fact differentiate between the models correctly. New methods for the statistical analysis of data can be explored to allow more data to be salvaged, even for low signal rates. The derivation of polarisation parameters is fixed through Stokes parameters in this thesis., Polarisationen av röntgenljus undersöks med polarimetrar för att utvidga gränserna för vad som kan observeras. Avlägsna kompakta objekt, såsom pulsarer, som är för små och för långt borta på himlen för att analyseras med optiska metoder, kan undersökas genom att analysera polarisationen av det utstrålade ljuset. Detta kan avslöja fysik som tidigare var dold på grund av deras storlek. Det finns många modeller som syftar till att beskriva polarisationen av dessa kompakta objekt för att förstå vad som mäts. Två exempel är modellerna: outer gap och two-pole caustic. Röntgenpolarimetern XL-Calibur är ett ballongburet teleskop som kan detektera röntgenstrålning i energiområdet $15-80$ keV. I denna avhandling diskuteras detaljer om ljusets polarisation, hur det kan mätas och några principer för röntgenpolarimetri. En ny funktion i simuleringen av XL-Calibur i Geant4 beskrivs också. Den används för att undersöka möjligheten för XL-Calibur att särskilja mellan olika polariseringsmodeller för Krabbpulsaren vid olika signaltakter. Resultaten visar att för signaltakter under 2 Hz, blir datan otillräcklig för att särskilja mellan de två modellerna både för polarisationsgraden och vinkeln. För högre signaltakter kan XL-Calibur skilja mellan modellerna. Nya metoder för statistisk analys av data kan utforskas för att möjliggöra att mer data kan användas, även för låga signaltakter. I denna avhandling beräknas polarisationsparametrarna genom Stokesparametrarna.

Published
2024

4. Building the Crab Pulsar Timing Model with XPNAV-1 Observations

Author

Sun, Hai-feng, Su, Jian-yu, Zhao, Liang, Liu, Zhi-wei, Fang, Hai-yan, Angrisani, Leopoldo, Series Editor, Arteaga, Marco, Series Editor, Panigrahi, Bijaya Ketan, Series Editor, Chakraborty, Samarjit, Series Editor, Chen, Jiming, Series Editor, Chen, Shanben, Series Editor, Chen, Tan Kay, Series Editor, Dillmann, Ruediger, Series Editor, Duan, Haibin, Series Editor, Ferrari, Gianluigi, Series Editor, Ferre, Manuel, Series Editor, Hirche, Sandra, Series Editor, Jabbari, Faryar, Series Editor, Jia, Limin, Series Editor, Kacprzyk, Janusz, Series Editor, Khamis, Alaa, Series Editor, Kroeger, Torsten, Series Editor, Liang, Qilian, Series Editor, Ming, Tan Cher, Series Editor, Minker, Wolfgang, Series Editor, Misra, Pradeep, Series Editor, Möller, Sebastian, Series Editor, Mukhopadhyay, Subhas, Series Editor, Ning, Cun-Zheng, Series Editor, Nishida, Toyoaki, Series Editor, Pascucci, Federica, Series Editor, Qin, Yong, Series Editor, Seng, Gan Woon, Series Editor, Veiga, Germano, Series Editor, Wu, Haitao, Series Editor, Zhang, Junjie James, Series Editor, Sun, Jiadong, editor, Yang, Changfeng, editor, and Guo, Shuren, editor

Published
2018
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7. The crab nebula and its mysteries: some facts and puzzles.

Author

Weisskopf, Martin C.

Abstract

We discuss and summarize five results that we and various colleagues have produced over the last few years in the study of the wonderful, yet enigmatic, Crab Nebula and its pulsar. The results, in turn, have to do with the geometry inferred from Chandra X-ray observations, the surprising results of pulse phase polarimetry at 1.4 GHz, the search for an X-ray location of the γ-ray flares for which we have Agile and Fermi to thank, and seeing if the optical and infrared inner knot might be the location of these flares. [ABSTRACT FROM AUTHOR]

Published
2019
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8. Search for VHE gamma-ray emission from Geminga pulsar and nebula with the MAGIC telescopes

Author

Antoranz Canales, Pedro, Barrio Uña, Juan Abel, Bonnefoy, Simon Francois Albert, Contreras González, José Luis, Fonseca González, Mª Victoria, López Moya, Marcos, Miranda Pantoja, José Miguel, Nievas Rosillo, Mireia, Antoranz Canales, Pedro, Barrio Uña, Juan Abel, Bonnefoy, Simon Francois Albert, Contreras González, José Luis, Fonseca González, Mª Victoria, López Moya, Marcos, Miranda Pantoja, José Miguel, and Nievas Rosillo, Mireia

Abstract

© ESO, 2016. Artículo firmado por 155 autores. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2012-39502), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Centro de Excelencia Severo Ochoa SEV-2012- 0234, CPAN CSD2007-00042, and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant 268740 of the Academy of Finland, by the Croatian Science Foundation (HrZZ) Project 09/176 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESS-MAGIC/2010/0., The Geminga pulsar, one of the brighest gamma-ray sources, is a promising candidate for emission of very-high-energy (VHE > 100 GeV) pulsed gamma rays. Also, detection of a large nebula have been claimed by water Cherenkov instruments. We performed deep observations of Geminga with the MAGIC telescopes, yielding 63 hours of good-quality data, and searched for emission from the pulsar and pulsar wind nebula. We did not find any significant detection, and derived 95% confidence level upper limits. The resulting upper limits of 5.3 × 10^(−13) TeV cm^(−2)s^(−1) for the Geminga pulsar and 3.5 × 10^(−12) TeV cm^(−2)s^(−1) for the surrounding nebula at 50 GeV are the most constraining ones obtained so far at VHE. To complement the VHE observations, we also analyzed 5 years of Fermi-LAT data from Geminga, finding that the sub-exponential cut-off is preferred over the exponential cut-off that has been typically used in the literature. We also find that, above 10 GeV, the gamma-ray spectra from Geminga can be described with a power law with index softer than 5. The extrapolation of the power-law Fermi-LAT pulsed spectra to VHE goes well below the MAGIC upper limits, indicating that the detection of pulsed emission from Geminga with the current generation of Cherenkov telescopes is very difficult., Ministerio de Economía y Competitividad (MINECO), German BMBF and MPG, Italian INFN and INAF, Swiss National Fund SNF, Japanese JSPS and MEXT, Centro de Excelencia Severo Ochoa, Spanish Consolider-Ingenio 2010 programme, Academy of Finland, Croatian Science Foundation (HrZZ), University of Rijeka, DFG Collaborative Research Centers, Polish MNiSzW, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Published
2023

9. Search for very high energy gamma-ray emission from pulsar-pulsar wind nebula systems with the Magic telescope

Author

Antoranz Canales, Pedro, Barrio Uña, Juan Abel, Contreras González, José Luis, Fonseca González, Mª Victoria, Miranda Pantoja, José Miguel, Nieto, Daniel, Antoranz Canales, Pedro, Barrio Uña, Juan Abel, Contreras González, José Luis, Fonseca González, Mª Victoria, Miranda Pantoja, José Miguel, and Nieto, Daniel

Abstract

© The American Astronomical Society. We thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, and the Spanish MICINN is gratefully acknowledged. This work was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW Grant NN203 390834, and by theYIP of the Helmholtz Gemeinschaft. We thank D.A. Smith and the Nancay Radio Observatory operated by the Paris Observatory (associated with the French CNRS) for the ephemerides of PSR J0218+4232, and also S. M. Ransom (NRAO) for the ephemerides of PSR J0205+6449., The MAGIC collaboration has searched for high-energy gamma-ray emission of some of the most promising pulsar candidates above an energy threshold of 50 GeV, an energy not reachable up to now by other ground-based instruments. Neither pulsed nor steady gamma-ray emission has been observed at energies of 100 GeV from the classical radio pulsars PSR J0205+6449 and PSR J2229+6114 (and their nebulae 3C58 and Boomerang, respectively) and the millisecond pulsar PSR J0218+4232. Here, we present the flux upper limits for these sources and discuss their implications in the context of current model predictions., German BMBF, German MPG, Italian INFN, Spanish MICINN, ETH Research Grant, Polish MNiSzW, YIP of the Helmholtz Gemeinschaft, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Published
2023

23. A new explorer mission for soft X-ray timing - Observation of the Crab pulsar.

Author

Huang, Liangwei, Shuai, Ping, Zhang, Xinyuan, and Chen, Shaolong

Subjects
*SPACE exploration, *EPHEMERIDES, *PLANET ephemerides, *ENERGY bands, *ELECTRONIC structure
Abstract

Abstract We discusse the current X-ray observation results of Crab pulsar obtained with the Time-resolved soft X-ray spectrometer, X-ray pulsar navigation 1 satellite launched on Nov. 10, 2016, summarize the 162 observations of the TSXS from MJD 57709 to MJD 57872, and introduce the propositional method of data reduction. We compare these observation results in the 0.5–9.0 keV energy band with the radio timing parameters by folding the profiles with radio timing ephemerides derived from Jodrell Bank and estimating the phase delay results. The statistical error of post fit time correction is 55.94 μs (root mean square). These achievements verify the effectiveness of the Time-resolved soft X-ray spectrometer and laid the foundation of the future work of the X-ray pulsar navigation 1 mission. Highlights • Report the 162 observations of the Crab pulsar collected by TSXS of the XPNAV-I. • Introduce the data analysis method for the data collected by TSXS. • Publish the Crab X-ray timing result achieved with data from MJD 57709 to 57872. [ABSTRACT FROM AUTHOR]

Published
2018
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24. A Model for the Source of Quasi-Harmonic Bursts on the Crab Pulsar.

Author

Zheleznyakov, V. V. and Bespalov, P. A.

Subjects
*PULSARS, *MICROWAVES, *PLASMA waves, *ELECTROMAGNETIC waves, *PLASMA resonance, *MAGNETOSPHERE
Abstract

A model for the source of microwave bursts from the Crab pulsar in the form of a current sheet with a transversemagnetic field has been investigated. The emission generation mechanism is based on the excitation of plasma waves at the double plasma resonance frequencies in a nonrelativistic nonequilibrium plasma followed by their scattering into electromagnetic waves that escape from the current sheet into the neutron star magnetosphere. The basic parameters of the source explaining the observed characteristics of quasi-harmonic bursts in the interpulses of radio emission from this pulsar have been established. [ABSTRACT FROM AUTHOR]

Published
2018
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25. Building X-ray pulsar timing model without the use of radio parameters.

Author

Sun, Hai-feng, Sun, Xiong, Fang, Hai-yan, Shen, Li-rong, Cong, Shao-peng, Liu, Yan-ming, Li, Xiao-ping, and Bao, Wei-min

Subjects
*PULSARS, *FOURIER transforms, *MAXIMUM likelihood statistics, *COMPUTATIONAL complexity
Abstract

This paper develops a timing solution for the X-ray pulsar timing model without the use of the initial radio model parameters. First, we address the problem of phase ambiguities for the pre-fit residuals in the construction of pulsar timing model. To improve the estimation accuracy of the pulse time of arrival (TOA), we have deduced the general form of test statistics in Fourier transform, and discussed their estimation performances. Meanwhile, a fast maximum likelihood (FML) technique is presented to estimate the pulse TOA, which outperforms cross correlation (CC) estimator and exhibits a performance comparable with maximum likelihood (ML) estimator in spite of a much less reduced computational complexity. Depending on the strategy of the difference minimum of pre-fit residuals, we present an effective forced phase-connected technique to achieve initial model parameters. Then, we use the observations with the Rossi X-Ray Timing Explorer (RXTE) and X-ray pulsar navigation-I (XPNAV-1) satellites for experimental studies, and discuss main differences for the root mean square (RMS) residuals calculated with the X-ray and radio ephemerides. Finally, a chi-square value (CSV) of pulse profiles is presented as a complementary indicator to the RMS residuals for evaluating the model parameters. The results show that the proposed timing solution is valid and effective, and the obtained model parameters can be a reasonable alternative to the radio ephemeris. [ABSTRACT FROM AUTHOR]

Published
2018
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26. Gravitational Waves from Spinning Neutron Stars

Author

Prix, Reinhard, Burton, W. B., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Bertola, F., editor, Cassinelli, J. P., editor, Engvold, O., editor, Heck, A., editor, Heuvel, E. P. J. Van Den, editor, Kaspi, V. M., editor, Kuijpers, J. M. E., editor, Laan, H. Van Der, editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, and Becker, Werner, editor

Published
2009
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27. Radio Emission Properties of Pulsars

Author

Manchester, Richard N., Burton, W. B., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Bertola, F., editor, Cassinelli, J. P., editor, Engvold, O., editor, Heck, A., editor, Heuvel, E. P. J. Van Den, editor, Kaspi, V. M., editor, Kuijpers, J. M. E., editor, Laan, H. Van Der, editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, and Becker, Werner, editor

Published
2009
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28. GeV Gamma-Ray Pulsar Detection

Author

Smith, David A., Thompson, David J., Burton, W. B., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Bertola, F., editor, Cassinelli, J. P., editor, Engvold, O., editor, Heck, A., editor, Heuvel, E. P. J. Van Den, editor, Kaspi, V. M., editor, Kuijpers, J. M. E., editor, Laan, H. Van Der, editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, and Becker, Werner, editor

Published
2009
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29. High Energy Emission from Pulsars and Pulsar Wind Nebulae

Author

Cheng, Kwong Sang, Burton, W. B., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Bertola, F., editor, Cassinelli, J. P., editor, Engvold, O., editor, Heck, A., editor, Heuvel, E. P. J. Van Den, editor, Kaspi, V. M., editor, Kuijpers, J. M. E., editor, Laan, H. Van Der, editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, and Becker, Werner, editor

Published
2009
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30. Pulsar Spin, Magnetic Fields, and Glitches

Author

Ruderman, Malvin, Burton, W. B., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Bertola, F., editor, Cassinelli, J. P., editor, Engvold, O., editor, Heck, A., editor, Heuvel, E. P. J. Van Den, editor, Kaspi, V. M., editor, Kuijpers, J. M. E., editor, Laan, H. Van Der, editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, and Becker, Werner, editor

Published
2009
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31. Photonic Astronomy and Quantum Optics

Author

Dravins, Dainis, Burton, W. B., editor, Bertola, F., editor, Cassinelli, J. P., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Engvold, O., editor, Heck, A., editor, Van Den Heuvel, E.P.J., editor, Kaspi, V. M., editor, Kuijpers, J.M.E., editor, Van Der Laan, H., editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, Phelan, Don, editor, Ryan, Oliver, editor, and Shearer, Andrew, editor

Published
2008
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32. ULTRACAM: An Ultra-Fast, Triple-Beam CCD Camera for High-Speed Astrophysics

Author

Dhillon, V. S., Burton, W. B., editor, Bertola, F., editor, Cassinelli, J. P., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Engvold, O., editor, Heck, A., editor, Van Den Heuvel, E.P.J., editor, Kaspi, V. M., editor, Kuijpers, J.M.E., editor, Van Der Laan, H., editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, Phelan, Don, editor, Ryan, Oliver, editor, and Shearer, Andrew, editor

Published
2008
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33. Imaging Photon Counting Detectors for High Time Resolution Astronomy

Author

Siegmund, O. H. W., Vallerga, J. V., Welsh, B., Tremsin, A. S., McPhate, J. B., Burton, W. B., editor, Bertola, F., editor, Cassinelli, J. P., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Engvold, O., editor, Heck, A., editor, Van Den Heuvel, E.P.J., editor, Kaspi, V. M., editor, Kuijpers, J.M.E., editor, Van Der Laan, H., editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, Phelan, Don, editor, Ryan, Oliver, editor, and Shearer, Andrew, editor

Published
2008
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34. Fast Spectroscopy and Imaging with the FORS2 HIT Mode

Author

O’Brien, Kieran, Burton, W. B., editor, Bertola, F., editor, Cassinelli, J. P., editor, Cesarsky, C. J., editor, Ehrenfreund, P., editor, Engvold, O., editor, Heck, A., editor, Van Den Heuvel, E.P.J., editor, Kaspi, V. M., editor, Kuijpers, J.M.E., editor, Van Der Laan, H., editor, Murdin, P. G., editor, Pacini, F., editor, Radhakrishnan, V., editor, Somov, B. V., editor, Sunyaev, R. A., editor, Phelan, Don, editor, Ryan, Oliver, editor, and Shearer, Andrew, editor

Published
2008
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36. Coherent curvature radiation: maximum luminosity and high-energy emission

Author

Ralph A. M. J. Wijers, A. J. Cooper, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Crab Pulsar, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Radiation, Curvature, Charged particle, Magnetic field, Luminosity, Neutron star, Pulsar, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena
Abstract

High brightness temperature radio transients such as pulsars and fast radio bursts require the coherent radiation of particles. The antenna class of coherent radiation models require a large number of charged particles radiating in phase, therefore the particles must be spatially confined and have well-aligned velocities. Given these necessary conditions, we look at the magnetic field induced by the currents associated with coherently emitting accelerated particles and consider the interaction between the radiating particles and the induced magnetic field. We find a maximum luminosity of coherent curvature radiation that depends on source parameters such as surface magnetic field and neutron star spin period. We find that coherent radio emission across all luminosities can be explained by coherent curvature radiation and suggest it could be universally responsible for both FRBs and extreme galactic sources. Using the Crab Pulsar as an example, we constrain the emission parameters and origin of the most extreme nanoshots to within 60km of the pulsar surface assuming coherent curvature radiation. In agreement with recent observations, we also predict simultaneous X-ray emission from small-scale particle gyration due to the induced field., Comment: Accepted to MNRAS Letters

Published
2021

40. Superfluidity in Relativistic Neutron Stars

Author

Langlois, David, Cardona, Manuel, editor, Fulde, Peter, editor, von Klitzing, Klaus, editor, Merlin, Roberto, editor, Queisser, Hans-Joachim, editor, Störmer, Horst, editor, Huebener, R. P., editor, Schopohl, N., editor, and Volovik, G. E., editor

Published
2002
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42. The Sun as a Gamma-Ray Source

Author

Rieger, Erich, Rank, Gerhard, Appenzeller, I., editor, Börner, G., editor, Harwit, M., editor, Kippenhahn, R., editor, Lequeux, J., editor, Strittmatter, P. A., editor, Trimble, V., editor, and Schönfelder, Volker, editor

Published
2001
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48. Excitation of the main giant pulses from the Crab pulsar

Author

P. A. Bespalov and O. N. Savina

Subjects
Physics, Space and Planetary Science, Crab Pulsar, Astrophysics::High Energy Astrophysical Phenomena, 0103 physical sciences, Astronomy and Astrophysics, Astrophysics, Plasma, 010306 general physics, 010303 astronomy & astrophysics, 01 natural sciences, Excitation
Abstract

A model for the source of microwave main giant pulses (GPs) from the Crab pulsar is proposed and partly investigated. Pulse excitation takes place in a relativistic pair plasma with a strong magnetic field through the beam pulse amplifier (BPA) mechanism, in which short noise pulses of a certain type are amplified by energetic electrons at the Cherenkov resonance, even without strong anisotropy in the distribution function. The wave gain is shown to be as high as with an instability of hydrodynamic type, and wave escaping from the excitation region into the pulsar magnetosphere may not involve significant attenuation. The basic parameters of the source which explains the observed characteristics of the GP electromagnetic bursts have been analysed and are consistent with accepted ideas about physical conditions in the pulsar magnetosphere. The BPA mechanism explains the important properties of the GPs, such as the extremely short pulse duration (extreme nanoshots), the extremely high brightness temperature of the radiation source, the formation of radiation in a wide frequency range, and the possibility of radiation reaching the periphery of the pulsar magnetosphere.

Published
2020

49. X-ray photolysis of CH3COCH3 ice: implications for the radiation effects of compact objects towards astrophysical ices

Author

G. A. Carvalho and Sergio Pilling

Subjects
Earth and Planetary Astrophysics (astro-ph.EP), Physics, 010308 nuclear & particles physics, Crab Pulsar, Interstellar ice, Photodissociation, Gamma ray, FOS: Physical sciences, White dwarf, Astronomy and Astrophysics, Astrophysics, Vela, 01 natural sciences, Space Physics (physics.space-ph), Stars, Astrophysics - Solar and Stellar Astrophysics, Physics - Space Physics, Pulsar, Space and Planetary Science, 0103 physical sciences, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics - Earth and Planetary Astrophysics
Abstract

In this study, we employed broadband X-rays ($6-2000$ eV) to irradiate the frozen acetone CH$_3$COCH$_3$, at the temperature of 12 K, with different photon fluences up to $2.7\times 10^{18}$ photons cm$^{-2}$. Here, we consider acetone as a representative complex organic molecule (COM) present on interstellar ice grains. The experiments were conduced at the Brazilian synchrotron facility (LNLS/CNPEN) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation in the ice sample. We determined the effective destruction cross-section of the acetone molecule and the effective formation cross-section for daughter species. Chemical equilibrium, obtained for fluence $2\times 10^{18}$ photons cm$^{-2}$, and molecular abundances at this stage were determined, which also includes the estimates for the abundance of unknown molecules, produced but not detected, in the ice. Timescales for ices, at hypothetical snow line distances, to reach chemical equilibrium around several compact and main-sequence X-ray sources are given. We estimate timescales of 18 days, 3.6 and 1.8 months, $1.4\times 10^9-6\times 10^{11}$ years, 600 and $1.2\times 10^7$ years, and $10^7$ years, for the Sun at 5 AU, for O/B stars at 5 AU, for white dwarfs at 1 LY, for the Crab pulsar at 2.25 LY, for Vela pulsar at 2.25 LY, and for Sagittarius A* at 3 LY, respectively. This study improves our current understanding about radiation effects on the chemistry of frozen material, in particular, focusing for the first time, the effects of X-rays produced by compact objects in their eventual surrounding ices., Comment: Accepted in MNRAS. This is a preprint. 14 pages, 7 figures

Published
2020

50. Frequency Domain Design Method of Wavelet Basis Based on Pulsar Signal

Author

Qiang Xu, Sihai You, Yiyang He, Lei Feng, and Hongli Wang

Subjects
010504 meteorology & atmospheric sciences, Lifting scheme, Computer science, Noise (signal processing), Crab Pulsar, Wavelet transform, Ocean Engineering, Oceanography, 01 natural sciences, Signal, Wavelet, Pulsar, Frequency domain, 0103 physical sciences, 010306 general physics, Algorithm, 0105 earth and related environmental sciences
Abstract

During pulsar navigation, the high-frequency noise carried by the pulsar profile signal reduces the accuracy of the pulse TOA (Time of Arrival) estimation. At present, the main method to remove signal noise by using wavelet transform is to redesign the function of the threshold and level of wavelet transform. However, the signal-to-noise ratio and other indicators of the filtered signal need to be further optimised, so a more appropriate wavelet basis needs to be designed. This paper proposes a wavelet basis design method based on frequency domain analysis to improve the denoising effect of pulsar signals. This method first analyses the pulsar contour signal in the frequency domain and then designs a Crab pulsar wavelet basis (CPn, where n represents the wavelet basis length) based on its frequency domain characteristics. In order to improve the real-time performance of the algorithm, a wavelet lifting scheme is implemented. Through simulation, this method analyses the pulsar contour signal data at home and abroad. Results show the signal-to-noise ratio can be increased by 4 dB, the mean square error is reduced by 61% and the peak error is reduced by 45%. Therefore, this method has better filtering effect.

Published
2020

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