1,721,113 research outputs found
Science objectives of the Einstein Probe mission
No full textWeimin Yuan et al.The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5–4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the EP mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects and phenomena revealed in the dynamic X-ray universe, and their underlying physical processes. Besides EP’s strength in time-domain science, its follow-up telescope, with excellent performance, will also enable advances in many areas of X-ray astronomy.We would like to thank a large number of colleagues, many of whom are not listed as co-authors of this paper, for stimulating discussions on the science objectives and science cases of the EP mission over the past ten years. EP is a space mission supported by Strategic Priority Program on Space Science of Chinese Academy of Sciences, in collaboration with ESA, MPE and CNES (Grant Nos. XDA15310000, and XDA15052100). This work was supported by the National Natural Science Foundation of China (Grant Nos. 61234003, 61434004, and 61504141), and CAS Interdisciplinary Project (Grant No. KJZD-EW-L11-04). We gratefully acknowledge the China National Astronomical Data Center (NADC), the Astronomical Data Center of the Chinese Academy of Sciences, and the Chinese Virtual Observatory (China-VO) for providing data resources and technical support.Peer reviewe
Accreting Pulsars: Mixing-up Accretion Phases in Transitional Systems
Full text linkIn the last 20 years our understanding of the millisecond pulsar (MSP)
population changed dramatically. Thanks to RXTE, we discovered that neutron
stars in LMXBs spins at 200-750 Hz frequencies, and indirectly confirmed the
recycling scenario, according to which neutron stars are spun up to ms periods
during the LMXB-phase. In the meantime, the continuous discovery of
rotation-powered MSPs in binary systems in the radio and gamma-ray band (mainly
with the Fermi LAT) allowed us to classify these sources into two "spiders"
populations, depending on the mass of their companion stars: Black Widow, with
very low-mass companion stars, and Redbacks, with larger companions possibly
filling their Roche lobes but without accretion. It was soon regained that MSPs
in short orbital period LMXBs are the progenitors of the spider populations of
rotation-powered MSPs, although a direct link between accretion- and
rotation-powered MSPs was still missing. In 2013 XMM-Newton spotted the X-ray
outburst of a new accreting MSP (IGR J18245-2452) in a source that was
previously classified as a radio MSP. Follow up observations of the source when
it went back to X-ray quiescence showed that it was able to swing between
accretion- to rotation-powered pulsations in a relatively short timescale (few
days), promoting this source as the direct link between the LMXB and the radio
MSP phases. Following discoveries showed that there exists a bunch of sources,
which alternates X-ray activity phases, showing X-ray pulsations, to radio-loud
phases, showing radio pulsations, establishing a new class of MSPs: the
Transitional MSP. In this review we describe these exciting discoveries and the
properties of accreting and transitional MSPs, highlighting what we know and
what we have still to learn about in order to fully understand the (sometime
puzzling) behavior of these systems and their evolutive connection (abridged)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
The 11 yr of low activity of the magnetar XTE J1810−197
Full text linkIn 2003, the magnetar XTE J1810-197 started an outburst that lasted until early 2007. In the following 11 yr, the source stayed in a quiescent/low-activity phase. XTE J1810-197 is one of the closest magnetars, hence its X-ray properties can be studied in detail even in quiescence and an extended monitoring has been carried out to study its long-term timing and spectral evolution. Here, we report the results of new X-ray observations, taken between 2017 September and 2018 April, with XMM-Newton, Chandra, and NICER. We derived a phase-connected timing solution yielding a frequency derivative of -9.26(6) × 10-14 Hz s-1. This value is consistent with that measured between 2009 and 2011, indicating that the pulsar spin-down rate remained quite stable during the long quiescent period. A spectral analysis of all the X-ray observations taken between 2009 and 2018 does not reveal significant spectral and/or flux variability. The spectrum of XTE J1810-197 can be described by the sum of two thermal components with temperatures of 0.15 and 0.3 keV, plus a power-law component with photon index 0.6. We also found evidence for an absorption line at ∼1.2 keV and width of 0.1 keV. Due to the long exposure time of the summed XMM-Newton observations, we could also carry out a phase-resolved spectral analysis for this source in quiescence. This showed that the flux modulation can be mainly ascribed to the warmer of the two thermal components, whose flux varies by ∼45 per cent along the pulse phase
Dense matter in neutron stars with eXTP
No full textAng Li et al.In this white paper, we present the potential of the enhanced X-ray timing and polarimetry (eXTP) mission to constrain the equation of state of dense matter in neutron stars, exploring regimes not directly accessible to terrestrial experiments. By observing a diverse population of neutron stars—including isolated objects, X-ray bursters, and accreting systems—eXTP’s unique combination of timing, spectroscopy, and polarimetry enables high-precision measurements of compactness, spin, surface temperature, polarimetric signals, and timing irregularity. These multifaceted observations, combined with advances in theoretical modeling, pave the way toward a comprehensive description of the properties and phases of dense matter from the crust to the core of neutron stars. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is planned to be launched in early 2030.This work was supported by China’s Space Origins Exploration Program. Ang Li was supported by the National Natural Science Foundation of China (Grant No. 12273028). Anna L. Watts, Bas Dorsman, and Tuomo Salmi acknowledged support from ERC Consolidator (Grant No. 865768) AEONS. Anna L. Watts also acknowledged support from NWO grant ENW-XL OCENW.XL21.XL21.038. Sebastien Guillot acknowledged the support of the CNES. Shuang-Nan Zhang was supported by the National Natural Science Foundation of China (Grant No. 12333007), the International Partnership Program of Chinese Academy of Sciences (Grant No. 113111KYSB20190020), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA15020100). Zhiqiang Miao was supported by the China National Postdoctoral Program for Innovation Talents (Grant No. BX20240223), and the China Postdoctoral Science Foundation Funded Project (Grant No. 2024M761948). Yuri Cavecchi acknowledged support from a Ramon y Cajal fellowship (Grant No. RYC2021-032718-I) financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. Xia Zhou was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No. 2023D01E20), and the National SKA Program of China (Grant No. 2020SKA0120300). Xiaoping Zheng and Xuezhi Liu were supported by the National Natural Science Foundation of China (Grant Nos. 12033001, and 12473039), and Weihua Wang was supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LQ24A030002). Quan Cheng was supported by the National Natural Science Foundation of China (Grant No. 12003009). Weiwei Zhu was supported by the National SKA Program of China (Grant No. 2020SKA0120200), and the National Natural Science Foundation of China (Grant No. 12041303). Zhaosheng Li was supported by the National Natural Science Foundation of China (Grant No. 1227303). Lijing Shao was supported by the National SKA Program of China (Grant No. 2020SKA0120300), the Beijing Natural Science Foundation (Grant No. 1242018), and the Max Planck Partner Group Program funded by the Max Planck Society. Akira Dohi was supported by JSPS KAKENHI (the Japan Society for the Promotion of Science, Grantsin-Aid for Scientific Research) (Grant Nos. 23K19056, and 25K17403). Hong Shen was supported by the National Natural Science Foundation of China (Grant No. 12175109). Constan¸c˜a Providˆencia acknowledged support from FCT (Funda¸c˜ao para a Ciˆencia e a Tecnologia, I.P., Portugal) (Grant Nos. UIDB/04564/2020, and 2022.06460.PTDC). Laura Tolos was supported from the program Unidad de Excelencia Mar´ıa de Maeztu CEX2020-001058-M, from the project PID2022-139427NB-I00 financed by the Spanish MCIN/AEI/10.13039/501100011033/FEDER, UE (FSE+), and by the CRC-TR 211 “Strong-interaction matter under extreme conditions” – project Nr. 315477589 – TRR 211. Alessandro Patruno acknowledged support from grant PID2021-124581OB-I0, PID2024-155316NB-I00, and 2021SGR00426. Li Li was supported by the National Natural Science Foundation of China (Grant No. 12122513). The work of Kai Hebeler, Melissa Mendes, Achim Schwenk, and Isak Svensson was supported in part by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant No. 101020842), and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 279384907 – SFB 1245. Manuel Linares acknowledged support from the ERC Consolidator (Grant No. 101002352) (LOVENEST). Nanda Rea was supported by the European Research Council (ERC) via the Consolidator Grant “MAGNESIA” (Grant No. 817661) and the Proof of Concept “DeepSpacePulse” (Grant No. 101189496), the Catalan grant SGR2021-01269, the Spanish grant ID2023-153099NA-I00, and the program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M. Aleksi Vuorinen was supported by the Research Council of Finland (Grant No. 354533).With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (CEX2020-001058-M)Peer reviewe
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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