1,354,994 research outputs found
A spectral study of the black hole X-ray binary MAXI J1820+070 with AstroSat and NuSTAR
No full textMAXI J1820+070 is a newly discovered transient black hole X-ray binary, which showed several spectral and temporal features. In this work, we analyse the broad-band X-ray spectra from all three simultaneously observing X-ray instruments onboard AstroSat, as well as contemporaneous X-ray spectra from NuSTAR, observed during the hard state of MAXI J1820+070 in 2018 March. Implementing a combination of multicolour disc model, relativistic blurred reflection model RELXILLLPCP, and a distant reflection in the form of XILLVERCP, we achieve reasonable and consistent fits for AstroSat and NuSTAR spectra. The best-fitting model suggests a low temperature disc (kTin ∼ 0.3 keV), iron overabundance (AFe ∼ 4–5 solar), a short lamp-post corona height (h < 8Rg), and a high corona temperature (kTe ∼ 115–150 keV). Addition of a second Comptonization component leads to a significantly better fit, with the kTe of the second Comptonization component being ∼14–18 keV. Our results from independent observations with two different satellites in a similar source state indicate an inhomogeneous corona, with decreasing temperature attributed to increasing height. Besides, utilizing the broader energy coverage of AstroSat, we estimate the black hole mass to be 6.7–13.9 M, consistent with independent measurements reported in the literature
Universality of coronal properties in accreting black holes across mass and accretion rate
No full textAims: Through their radio loudness, lack of thermal UV emission from the accretion disk, and power-law dominated spectra, low-luminosity active galactic nuclei (LLAGNs) display similarity with the hard state of stellar-mass black hole X-ray binaries (BHBs). In this work we perform a systematic hard X-ray spectral study of a carefully selected sample of unobscured LLAGNs using archival NuSTAR data to understand the central engine properties in the lower accretion regime.
Methods: We analyzed the NuSTAR spectra of a sample of 16 LLAGNs. We modeled the continuum emission with detailed Comptonization models.
Results: We find a strong anti-correlation between the optical depth and the electron temperature of the corona, previously also observed in the brighter Seyferts. This anti-correlation is present irrespective of the shape of the corona, and the slope of this anti-correlation in the log space for LLAGNs (0.68-1.06) closely matches that of the higher accretion rate Seyferts (0.55-1.11) and hard state of BHBs (∼0.87). This anti-correlation may indicate a departure from a fixed disk-corona configuration in radiative balance.
Conclusions: Our result, therefore, demonstrates a possible universality in Comptonization processes of black hole X-ray sources across multiple orders of magnitude in mass and accretion rate
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Exploring the accretion-ejection geometry of GRS 1915+105 in the obscured state with future X-ray spectro-polarimetry
No full textContext. GRS 1915+105 has been in a bright flux state for more than two decades, but in 2018 a significant drop in flux was observed, partly due to changes in the central engine along with increased X-ray absorption. Aims. The aim of this work is to explore how X-ray spectro-polarimetry can be used to derive the basic geometrical properties of the absorbing and reflecting matter. In particular, the expected polarisation of the radiation reflected off the disc and the putative outflow is calculated. Methods. We used NuSTAR data collected after the flux drop to derive the parameters of the system from hard X-ray spectroscopy. The spectroscopic parameters were then used to derive the expected polarimetric signal, using results from a Monte Carlo radiative transfer code, both in the case of neutral and fully ionised matter. Results. From the spectral analysis, we find that the continuum emission becomes softer with increasing flux, and that in all flux levels the obscuring matter is highly ionised. This analysis, on the other hand, confirms that spectroscopy alone is unable to put constraints on the geometry of the reflectors. Simulations show that X-ray polarimetric observations, such as those that will be provided soon by the Imaging X-ray Polarimetry Explorer (IXPE), will help to determine the geometrical parameters which are left unconstrained by the spectroscopic analysis
A variable magnetic disc wind in the black hole X-ray binary GRS 1915+105?
No full textContext. GRS 1915+105 being one of the brightest transient black hole binaries (BHBs) in the X-rays offers a unique testbed for the study of the connection between accretion and ejection mechanisms in BHBs. In particular, this source can be used to study the accretion disc wind and its dependence on the state changes in BHBs. Aims. Our aim is to investigate the origin and geometry of the accretion disc wind in GRS 1915+105. This study will provide a basis for planning future observations with the X-ray Imaging Spectroscopy Mission (XRISM), and may also provide important parameters for estimating the polarimetric signal with the upcoming Imaging X-ray Polarimetry Explorer (IXPE). Methods. We analysed the spectra of GRS 1915+105 in the soft φ and hard χ classes using the high-resolution spectroscopy offered by Chandra HETGS. In the soft state, we find a series of wind absorption lines that follow a non-linear dependence of velocity width, velocity shift, and equivalent width with respect to ionisation, indicating a multiple component or stratified outflow. In the hard state we find only a faint Fe XXVI absorption line. We model the absorption lines in both the states using a dedicated magneto-hydrodynamic (MHD) wind model to investigate a magnetic origin of the wind and to probe the cause of variability in the observed line flux between the two states. Conclusions. The MHD disc wind model provides a good fit for both states, indicating the possibility of a magnetic origin of the wind. The multiple ionisation components of the wind are well characterised as a stratification of the same magnetic outflow. We find that the observed variability in the line flux between soft and hard states cannot be explained by photo-ionisation alone but is most likely due to a large (three orders of magnitude) increase in the wind density. We find the mass outflow rate of the wind to be comparable to the accretion rate, suggesting an intimate link between accretion and ejection processes that lead to state changes in BHBs
Variations on the Author
No full text“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
No full textWe 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
Miliusa gokhalaei Ratheesh, Sujanapal, Anil Kumar & Sivadasan, sp. nov.
No full textMiliusa gokhalaei Ratheesh, Sujanapal, Anil Kumar & Sivadasan, sp. nov., Figs. 1 & 2 Miliusa indicae et M. eriocarpae similis foliis petiolatis nervis pubescentibus floribus axillaribus solitariis carpellis 1- vel 2-ovularibus infundibularibus, sed foliorum basi inaequaliter rotundata floribus sessilibus vel breviter pedicellatis petalis crasse carnosis carpellis glabris antherae connectivo incluso differt. Type:— INDIA: Kerala: Wayanad district, Vythiri Ghat, 11 ° 30' 24.3' N, 76 ° 01' 49.1' E, 490 m, 26 September 2008 (with flowers). Sujanapal & Narayanan MSSH 4312 (holotype MH, isotypes CAbC- MSSRF Herbarium, Wayanad CAL, CAL, KFRI). Evergreen trees, to ca. 5 m high; bark black, branches terete, drooping, young parts densely hairy. Leaves simple, alternate, 6.0–12. 0 × 2.5–4. 0 cm, oblong or obovate, glabrous, midrib pubescent below, slightly unequally rounded at base, apex caudate acuminate, subsessile or petiole to 3 mm long, membranous; lateral nerves 10–14 pairs, intramarginal nerves sub-marginal, looping; margins entire, slightly curved, thickened. Flowers solitary, pseudo-terminal (slightly above and opposite the terminal leaf) greenish-yellow; pedicel 2–4 mm long, glabrous; bracts two, small, ovate; bracteoles two at the base, unequal, ovate-triangular, acute, ca. 1.5 mm long, hairy outside; sepals 3, ca. 1.5 × 2.0 mm, broadly ovate, acute, glabrous; outer petals 3, broadly ovate, acute, hairy on margins, slightly hooded, ca. 2.0 × 1.5 mm; inner petals 3, ovate-lanceolate, 2.0–2.4 × 0.8–1.3 cm, thick, fleshy, glabrous, thickly hooded on the lower half, cohering when young along margins, greenish-yellow with brown streaks inside; torus ovoid, long hairy; stamens many, 40–50, anthers in pairs, ca. 1 mm, connective included; staminodes absent; anthers extrorse; carpels 10–15, linear-oblong in outline, slightly curved, ca. 2 mm long, glabrous; stigma ovoid-acute, about half the height of the ovary, with viscous exudate; ovules 1 or 2. Fruiting stalk terete, 8–11 mm long; monocarps usually 8–12, each 10–12 mm across, obovoid, mammose, apex projecting, more or less obturbinate, glabrous, deep pink; stipe ca. 5 mm long. Seeds 1-2. Phenology:— Flowering and fruiting occur during September to February. Eponymy:— The specific epithet honors Padmashree Mr. A. M. Gokhalae (IAS, Retd.), former Director of the M. S. Swaminathan Research Foundation, Chennai, India, for being a great lover of plants and plant taxonomy; he prepared a detailed electronic database for more than 7000 species of Indian angiosperms, which is one of the pioneering comprehensive efforts in digitization and digital identification of the group in India. Distribution and habitat:— Windward side of Wayanad-Silent Valley-Kodagu sub-cluster in the Nilgiri phytogeographical region of the Western Ghats. The range starts in Nadukani forests of Nilambur (Malappuram district) and extends to the Kakkayam and Thusharagiri forests of Kozhikode district through the evergreen forests in the western side of Wayanad Ghats. Evergreen forests, at elevations of ca. 400–750 m a.s.l. are the ideal habitat of the new species. It is seen mostly along the slopes as a lower stratum tree or shrub with scandent branches. Arenga wightii Griffith (1845: 475) is a common associate in most of its habitats. Rare, endemic and endangered species of Annonaceae such as Desmos lawii Safford (1912: 506), Goniothalamus wynaadensis Beddome (1868 - 1874:13), Meiogyne ramarowii (Dunn1914: 183) Gandhi (1976: 38), Orophea malabarica Sasidharan & Sivarajan (1990: 269), Polyalthia suberosa (Roxburgh 1795: 31.t.34) Thwaites (1864: 398), Sageraea laurina Dalzell (1851: 207), etc. are also found in its northern distributional ranges. Endangered and economically important trees such as Cynometra beddomei Prain (1897: 478), C. travancorica Beddome (1873: 316), Kingiodendron pinnatum Harms (1897: 194), Myristica beddomei King (1891: 291), etc. are common in its habitats. Artabotrys zeylanicus Hooker & Thomson (1855: 128), Desmos lawii, Smythea bombaiensis (Dalzell 1851: 36) Banerjee & Mukherjee (1970: 214), etc. are the woody climbers common in the habitats. In Nadukani forests a critically endangered tree species, Atuna indica (Beddome 1864: 45) Kostermans (1969: 422), is seen along with this new species. Interrelationships:— Miliusa gokhalaei is similar to M. indica and M. eriocarpa in having subsessile or shortly petiolate, hairy-nerved leaves, and axillary solitary flowers, flask-shaped carpel with 1–2 ovules. However, it differs in its unequal rounded leaf bases, sessile or shortly pedicellate flowers, thick fleshy petals, glabrous carpel and included connective of anther. The other related species is Miliusa montana, and the diagnostic morphological characters of the new species and the related species are given in table 1. Van Heusden (1992) studied morphology and evolution of flowers in Annonaceae and assigned key features for Miliusa group. Based on her characterization and structure of inner petals, the southern Indian-Sri Lankan and Andamanese species of Miliusa can be broadly classified into three groups - Miliusa nilagirica group, Miliusa indica group and Miliusa velutina group. Miliusa nilagirica group is peculiar among these because of the presence of recurved petals. However, van Heusden never noticed recurved petals in Miliusa group. This group is distinct from all others of the region in having fewer stamens. The peculiarity of Miliusa velutina group is the presence of flat inner petals. Miliusa mukerjeeana is the only other member of this group. All other species belong to Miliusa indica group in having saccate, sub-saccate or pouched petals. The new species also belongs to the Miliusa indica group in having saccate petals and numerous stamens. Additional specimens examined: — INDIA: Kerala: Wayanad District, Vythiri Ghats, 11 ° 30ʹ 24.3ʹ N, 76 ° 01ʹ 49.1ʹ E, 490 m, 30 September 2008 (with flowers), Sujanapal & Narayanan MSSH 4320; Ibid., 27 August 2009, Sujanapal & Narayanan MSSH 4388 (with flowers); Malappuram District, Nadukani Forests (Nilambur), 11 ° 29ʹ22.6ʹ N, 76 ° 15ʹ 19.4ʹ E, ± 510 m, 01 January 2009, Sujana MSSH 4382 (with fruits); Kozhikode District, Kakkayam Forests 11 ° 32ʹ 12.2ʹ N, 75 ° 55ʹ 12.2ʹ E, ± 525 m, 22 October 2008 (with flowers), Sujanapal & Narayanan MSSH 4378 (with flowers); Thusharagiri Forests, 11 ° 28ʹ 12.7ʹ N, 76 ° 08ʹ 11.2ʹ E, ± 450 m, 12 October 2008, Sujanapal & Narayanan MSSH 4372 (Herbarium of CAbC-MSSRF, Wayanad). Population structure and conservation status:— Populations of the new species are fragmented and seen in the lower storey, mainly along the western slopes of the Western Ghats between 400 m and 750 m a.s.l. in evergreen forests; they are represented by a few scattered mature individuals. There is no continuity in distribution from the southern to the northern populations. The southern-most population is located in the evergreen forests of Nadukani (Nilambur, Malappuram District). The major central population is in the Vythiri Ghats of Wayanad district and Thamarassery Ghats up to Kakkayam and Thusharagiri Range of Kozhikkode district at the northern tip. In all locations, populations of this new species are small. Our observations showed that there were only nine mature individuals in a 1 km 2 area of Nilambur. Compared to Nilambur, the population is comparatively large in Wayanad and Kozhikkode forests with more or less continuous distribution from Thamarassery up to Peruvannamuzhi. Altogether the distribution of this new species is restricted to 50 km 2. None of the localities is protected. The population at Nilambur is adjacent to human habitation, and waste disposal, pollution and degradation of habitat due to the nearby Sate Highway-28 are the main threats to this population. Increased anthropogenic interference in the form of firewood collection deepens the crisis. In Thamarassery Ghats the population is near to the National Highway-212, and the area is highly subject to various kinds of disturbances. The habitats in Kakkayam and Peruvannamuzhi ranges are highly disturbed due to construction activities related to two reservoirs and the forthcoming hydroelectric project. These construction activities promote calamities like landslides, soil erosion, etc. since it is lying along the sharp western slopes. By following IUCN criteria (IUCN, 2001) for assessing the status of Rare and Threatened plants, M. gokhalaei is assessed as belonging to Critically Endangered (CR) category. Its range (extent of occurrence) is less than 100 km 2, the population is severely fragmented and the quality of habitat is declining continuously.Published as part of Ratheesh Narayanan, M. K., Anil Kumar, P. Sujanapal N., Sivadasan, M., Alfarhan, Ahmed H. & Thomas, Jacob, 2012, Miliusa gokhalaei, a new species of Annonaceae from India with notes on interrelationships, population structure and conservation status, pp. 26-34 in Phytotaxa 42 on pages 27-32, DOI: 10.11646/phytotaxa.42.1.4, http://zenodo.org/record/492817
A new species of Sonerila Roxb. (Melastomataceae) from Kerala, India
No full textRatheesh Narayanan, M. K., Mini, V., Shaju, T., Sujana, K. A., Joseph, Jayesh P., Alfarhan, Ahmed H., Sivadasan, M. (2013): A new species of Sonerila Roxb. (Melastomataceae) from Kerala, India. Phytotaxa 110 (1): 55-60, DOI: 10.11646/phytotaxa.110.1.5, URL: http://dx.doi.org/10.11646/phytotaxa.110.1.
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