1,721,169 research outputs found
<i>IXPE</i> Observations of Magnetar Sources
Get PDFAmong the more than 60 sources observed in the first two years of operations, IXPE addressed four magnetars, neutron stars believed to host ultra-strong magnetic fields. We report here the main implication coming from IXPE measurements for the physics of magnetars. Polarimetric observations confirmed the expectations of high polarization degrees, up to ≈80%, values which have not been detected in any other source so far, providing further proof (independent from the P-P˙ estimate) that magnetars host indeed ultra-magnetized neutron stars. Polarization measurements also indicate that softer X-rays likely come from surface regions where the overlying atmosphere underwent magnetic condensation. The agreement of the phase-dependent polarization angle with a simple rotating vector model strongly supports the presence of vacuum birefringence around the star
Complex rotational dynamics of the neutron star in Hercules X-1 revealed by X-ray polarization
No full textHeyl, Jeremy et al.-- Full list of authors: Heyl, Jeremy; Doroshenko, Victor; González-Caniulef, Denis; Caiazzo, Ilaria; Poutanen, Juri; Mushtukov, Alexander; Tsygankov, Sergey S.; Kirmizibayrak, Demet; Bachetti, Matteo; Pavlov, George G.; Forsblom, Sofia V.; Malacaria, Christian; Suleimanov, Valery F.; Agudo, Iván; Antonelli, Lucio Angelo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolò; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Chen, Chien-Ting; Ciprini, Stefano; Costa, Enrico; De Rosa, Alessandra; Del Monte, Ettore; Di Gesu, Laura; Di Lalla, Niccolò; Di Marco, Alessandro; Donnarumma, Immacolata; Dovčiak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Iwakiri, Wataru; Jorstad, Svetlana G.; Kaaret, Philip; Karas, Vladimir; Kislat, Fabian; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, Henric; La Monaca, Fabio; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Frédéric; Marinucci, Andrea; Marscher, Alan P.; Marshall, Herman L.; Massaro, Francesco; Matt, Giorgio; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Muleri, Fabio; Negro, Michela; Ng, C. -Y.; O'Dell, Stephen L.; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro; Peirson, Abel Lawrence; Perri, Matteo; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, Maura; Possenti, Andrea; Puccetti, Simonetta; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Roberts, Oliver J.; Romani, Roger W.; Sgrò, Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria; Swartz, Douglas A.; Tamagawa, Toru; Tavecchio, Fabrizio; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei; Zane, Silvia.In an accreting X-ray pulsar, a neutron star accretes matter from a companion star through an accretion disk. The magnetic field of the rotating neutron star disrupts the inner edge of the disk, funnelling the gas to flow onto the poles on its surface. Hercules X-1 is a prototypical persistent X-ray pulsar about 7 kpc from Earth. Its emission varies on three distinct timescales: the neutron star rotates every 1.2 s, it is eclipsed by its companion each 1.7 d, and the system exhibits a superorbital period of 35 d, which has remained stable since its discovery. Several lines of evidence point to the source of this variation as the precession of the accretion disk or that of the neutron star. Despite the many hints over the past 50 yr, the precession of the neutron star itself has yet not been confirmed or refuted. X-ray polarization measurements (probing the spin geometry of Her X-1) with the Imaging X-ray Polarimetry Explorer suggest that free precession of the neutron star crust sets the 35 d period; this has the important implication that its crust is somewhat asymmetric by a few parts per ten million. © 2024 Springer Nature LimitedIXPE is a joint US and Italian mission. The US contribution is supported
by the National Aeronautics and Space Administration (NASA)
and led and managed by its Marshall Space Flight Center, with
industry partner Ball Aerospace (Contract NNM15AA18C). The Italian
contribution is supported by the Italian Space Agency (Contract
ASI-ASI-OHBI-2022-13-I.0 and Agreements ASI-INAF-2022-19-HH.0 and
ASI-INFN-2017.13-H0) and its Space Science Data Center (Agreements
ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0), and by the Italian
National Institute for Astrophysics and the Italian National Institute
for Nuclear Physics. This research used data products provided by
the IXPE Team (Marshall Space Flight Center, Space Science Data
Center, Italian National Institute for Astrophysics and Italian National
Institute for Nuclear Physics) and distributed with additional software
tools by the High-Energy Astrophysics Science Archive Research
Center at NASA’s Goddard Space Flight Center. J.H. acknowledges
support from the Natural Sciences and Engineering Research Council
of Canada through a discovery grant, the Canadian Space Agency
through the co-investigator grant program, and computational
resources and services provided by Compute Canada, Advanced
Research Computing at the University of British Columbia, and the
SciServer science platform (www.sciserver.org). D.G.-C. acknowledges
support from a fellowship grant from the French National Centre
for Space Studies. J.P. and S.S.T. were supported by the Academy of
Finland (Grant Nos. 333112 and 349144) and the Väisälä Foundation.
V.D. and V.F.S. thank the German Academic Exchange Service (Travel
Grant No. 57525212). We used Astropy (http://www.astropy.org), a
community-developed core Python package and an ecosystem of
tools and resources for astronomy.Peer reviewe
White dwarfs as probes of novel physical phenomena
No full textWhite dwarfs are the final state of most stars once nuclear burning in the core has finished, leaving a remnant that evolves through a straightforward cooling process that is largely thought to be well-understood. The electron-degenerate core of a white dwarf is an extreme environment that provides a testbed of physics in regimes not achievable with ground-based experiments. In this dissertation, observations of white dwarfs are used to test white dwarf cooling theory and look for evidence of novel physical phenomena. The cooling and kinematics of ultramassive white dwarfs in the solar neighbourhood are analysed using Gaia EDR3 observations to reinvestigate an anomalous cooling delay previously reported based on earlier Gaia DR2 observations, which challenged the conventional understanding of white dwarf cooling. The cooling of white dwarfs in the globular cluster 47 Tucanae is also analysed in detail by comparing cooling models to HST data to both test the implementation of element diffusion in stellar evolution simulations and determine the values of parameters important for modelling white dwarf cooling like the white dwarf mass and envelope thickness. A thorough understanding of these properties enables the cooling of white dwarfs to be used to indirectly search for evidence of novel particles such as axions. The emission of axions produced in the core of a white dwarf via axion bremsstrahlung would provide an additional energy loss mechanism and thus affect the cooling rate. A new bound on the axion-electron coupling of gₐₑₑ ≤ 0.81 × 10⁻¹³ is derived from the cooling of white dwarfs in 47 Tucanae. This improves upon previous constraints by nearly a factor of two and excludes the range of values favoured by the hints of axions suggested by galactic white dwarf luminosity functions. Axions could also be produced in the core of a very hot, magnetic white dwarf like ZTF J1901+1458 via the ⁵⁷Fe transition and then convert to photons in the magnetosphere, and it is shown that X-ray observations of ZTF J1901+1458 by NuSTAR to search for the corresponding signal could probe the coupling of axions to nucleons with better sensitivity than both current and future planned ground-based observations.Science, Faculty ofPhysics and Astronomy, Department ofGraduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
New tricks for old stars : studying compact objects through novel methodologies in timing, energy and imaging
No full textTo understand astronomical objects and their environments, it is essential to study their behavior across time, energy and space. For compact objects, these analyses provide a unique window into physics in extreme environments, probing transient behavior, accretion processes, and tests of spacetime and gravity in the high field regime. In this dissertation, I discuss novel approaches for timing and spectral analysis and imaging with polarimetry in astronomy.
I first discuss two methodologies with respect to their use for astronomical timing analysis: 1) Wiener Deconvolution to resolve the response function generating time lags across different energy bands and 2) Mutual Information as a powerful tool to identify time lags without assuming underlying linearity. I establish a methodological framework and demonstrate efficacy of Wiener Deconvolution for generalized utilization of astronomical timing and lag analysis through toy models and discuss our algorithm to obtain time lags using Mutual Information. I then present the results of these methodologies applied to radio data from the black hole binary MAXI J1820+070. These approaches not only help in identifying time lags with high accuracy and precision, but also reveal numerous previously undetected lags, offering new insights into how the compact jet in MAXI J1820+070 behaves across different energies.
I then extend the astronomical application of Wiener Deconvolution to 2D, enabling estimates of the first ever high resolution X-ray polarimetry images, and present preliminary results for the Supernova Remnant Cas A. Finally, I explore magnetar spectral line analysis and modeling, and show how we can learn about the behaviour of magnetic fields at their most intense through spectral lines detected from magnetars with current and future detectors.Science, Faculty ofPhysics and Astronomy, Department ofGraduat
Studies of evolved stellar populations : from giants to remnants
No full textStudying galaxies helps scientists understand better the structure and history of the Universe. The properties of galaxies, such as their dynamics and evolution, can be inferred through studying the age, composition, and distribution of the different stellar populations (from young stars to their remnants) that constitute them, using multi-wavelength observations. In this thesis, we focus on the study of old stellar populations and their remnants, from X-rays to the near infrared. Superconducting transition-edge sensors carried by X-ray telescopes, such as Colibrì, are powerful tools for the study of neutron stars’ and black holes’ fundamental properties. We develop a low-computational-cost technique that optimizes energy and time resolution to levels of about 1 eV and 100 ns, respectively, over a wide range of energies (0–30 keV). Such sensitivities will give new insights on the physics of dense matter and extreme magnetic fields. Using 2MASS near-infrared photometry and the Gaia Data Release 2, we identify carbon stars in the Large Magellanic Cloud, Small Magellanic Cloud and Milky Way (MW), and we derive the corresponding carbon-star luminosity function (CSLF). Due to its limited dispersion in the J band, the CSLF is a promising rung in the cosmic distance ladder (up to 50–60 Mpc). Thanks to the next generation of telescopes (e.g. James Webb Space Telescope), the CSLF could replace the Cepheid–Type-Ia supernova pair rung, thus enabling the derivation of an independent measurement of the Hubble constant. We identify galactic white dwarfs (WDs) thanks to their colours, in the Canada-France-Hawai‘i Telescope Large Area U-band Deep Survey, at unprecedented faint magnitudes (27 mag). The U-band and optical photometry allows us to fit for the physical properties of the white dwarfs, such as surface temperature, mass, surface gravity, cooling age, and distance. We find a main mass peak consistent with globular-cluster studies, making our sample the largest and deepest old stellar-halo WD population. Finally, we derive a typical age of the MW stellar halo consistent with previous studies, as well as the typical age of the oldest WDs in the MW, putting further constraints on the history of our Galaxy.Science, Faculty ofPhysics and Astronomy, Department ofGraduat
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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