Assembling the pulsed puzzle of X-ray pulsars.

• Applicant: Dr. Victor Doroshenko
• Subject Area: Astrophysics and Astronomy
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418943601

Accreting X-ray pulsars have been suggested as natural laboratories for physics under extreme conditions of magnetic fields (B≈ 10^12-14 G), gravity (log g ~14) and temperature (T~10^8 K). In these laboratories the interaction of matter with intense radiation and the propagation of light in ultra strong fields, unachievable on earth, might be studied. To fully realize this potential, however, a clear and coherent understanding of the astrophysics of these objects, i.e. of how the observed emission is produced, is an essential preliminary condition. Unfortunately, and despite more than forty years of studies, the emission of the radiation emerging from the neutron star, i.e. its geometry and physical properties, is still unclear and debated. This is largely due to the difficulties in the interpretation of the observations. In fact, the observed X-ray emission is a combination of radiation 1) emerging from most likely independent and not yet understood regions around the two poles of the neutron star; 2) bent by its gravity, and 3) essentially depending on the geometry (i.e. on the angle between the line of sight and the field axis, between the latter and the spin axis, and on pole misalignment). The contributions of individual poles and their intrinsic emission properties have not yet been identified. This step is, however, essential to develop and test theoretical predictions of the formation of the emission in accreting pulsars. With this project we aim at solving this problem using an innovative approach and novel technique, which exploits the properties of the observed X-ray flux variability induced by stochastic accretion rate fluctuations. In essence, we aim to “hear” the individual accretion “voices” of the two poles of the neutron star much like our brain identifies the individual voices in a lively conversation. This will be done through application of state-of-the-art methods developed for the well known “blind source separation” problem encountered in telecommunication, radar/sonar, medical applications, in machine vision, and speech recognition. We will develop and apply these methods to observations obtained with the Rossi X-ray Timing Explorer and the Hard X-ray Modulation Telescope observatories. As shown by our preliminary tests, these techniques will allow for the first time to reconstruct the geometry and intrinsic beam patterns with no additional assumptions, thus enabling a well-grounded comparison of observations with theoretical predictions.

• DFG Programme: Research Grants
• International Connection: China, Netherlands
• Co-Investigator: Professor Dr. Andrea Santangelo
• Cooperation Partners: Alexander Mushtukov, Ph.D.; Professor Shu Zhang