1,721,260 research outputs found
A MAGIC view of the Very High-Energy gamma-Ray Sky.
No full textMAGIC is currently the largest single dish Cherenkov telescope operating since September 2004. Since then it has been delivering a wealth of exciting physics results from its observations in the Very High Energy (VHE) region of galactic and extragalactic sky. We present a review of the most recent experimental results obtained using MAGIC
GRB100816A: TNG optical afterglow confirmation.
No full textWe observed the field of the short hard GRB100816A (Swift trigger
431764; Oates et al., GCN 11102) with the Italian 3.6m TNG telescope
(La Palma, Canary Islands) equipped with the DOLORES camera.
Observations started on Aug 16 at 03:22 UT (~2.8 hrs after the burst)
under very poor weather conditions (high cloudiness and high
humidity). We acquired a R band image of the GRB field for a total
exposure time of 180s. We clearly detect a source consistent with the
one reported by (Oates et al., GCN 11102). This souce, located at RA
(J2000)=23:26:57.58; Dec(J2000)=+26:34:42.7 (+/-0.5''), showed a
magnitude R~20.5 (calibrated against USNO B1.0) at the epoch of the
observation. Due to its fading behavior with respect to the UVOT
observation, we confirm that this source is the optical afterglow of
GRB100816A
Short time scale variability at gamma rays in FSRQs and implications on the current models
No full textWe studied the rapid variability at GeV gamma rays of the flat-spectrum
radio quasar PKS 1222+216, which was recently found by the MAGIC
Cerenkov telescope to display very short variability (minutes time
scale) at hundreds of GeV. We analyzed the time period between 2010
April 29 and June 20, when the source generated a few gamma-ray flares
with flux in the MeV-GeV band in excess of 10^-5 ph cm^-2 s^-1 on daily
basis. We set tight upper limits on the observed doubling time scale
(about 1 hour on 2010 April 30), the smallest measured to date at
MeV-GeV energies, which can constrain the size of the gamma-ray emitting
region. We also studied the spectra measured during two flares (2010
April 30 and June 17-18). The combination of spectral and variability
studies obtained in the present work favors the hypothesis that gamma
rays are generally produced inside the broad-line region (BLR), but
sometimes the dissipation can occur at larger distances, nearby the
infrared torus
Search for the shortest variability at gamma rays in flat-spectrum radio quasars
No full textWe report about the search for short-term variability in the high-energy γ-ray energy band of three flat-spectrum radio quasars (3C 454.3, 3C 273, PKS B1222 + 216), whose flux at E > 100 MeV exceeded the value of 10-5 ph cm-2 s-1 for at least one day. Although, the statistics was not yet sufficient to effectively measure the characteristic time scale, it allowed us to set tight upper limits on the observed doubling time scale (<2-3 h) - the smallest measured to date at MeV energies -, which can constrain the size of the γ-ray emitting region. The results obtained in the present work favor the hypothesis that γ rays are generated inside the broad-line region
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
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
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