Variability Modes of Blazars from Intensive Optical Monitoring

We report the main results of our six year long intensive optical monitoring on blazars ON 231 (W Com), BL Lac, and 3C 273. Intensive optical monitoring is an indispensable tool to obtain well sampled light curves and thus to understand the correlation with the variability in other bands and to discriminate among the proposed emission models. The curves based on our work show different variability modes: intermittent mode, quasi-regular mode and mixed mode. It is not clear if different variability modes can be present, at various times, in the life of an object suggesting that their occurrence can be related to the evolution of blazars. An optimized and nearly continuous optical monitoring is the only way to know the activity status of the sources and to retrieve useful information on their physical dynamics. Also, the rapid availability of information about the luminosity of a source is very important to trigger space based observations and to activate large multifrequency collaborations. We stress that a significant sample of blazars can be observed with small size telescopes (0.35-0.80 cm) equipped with CCD cameras. A world-wide network of several instruments in different countries, is very useful to increase the time coverage and to reduce the number of nights lost for bad meteorological conditions.Comment: Paper submitted to the AIP Conference Proceedings "High Energy Gamma-Ray Astronomy" - Conf. Proc. of the gamma-2000 symposium held in Heidelberg. 4 pages, doc format source (AIP Proc.), 1 gif figur

The Intra-Night Optical Variability of the bright BL Lac object S5 0716+714

We address the topic of the Intra-Night Optical Variability of the BL Lac object S5 0716+714. To this purpose a long term observational campaign was performed, from 1996 to 2003, which allowed the collection of a very large data set, containing 10,675 photometric measurements obtained in 102 nights. The source brightness varied in a range of about 2 mag, although the majority of observations were performed when it was in the range 13.0 < R < 13.75. Variability time scales were estimated from the rates of magnitude variation, which were found to have a distribution function well fitted by an exponential law with a mean value of 0.027 mag/h, corresponding to an e-folding time scale of the flux tau_F = 37.6 h. The highest rates of magnitude variation were around 0.10--0.12 mag/h and lasted less than 2 h. These rates were observed only when the source had an R magnitude < 13.4, but this finding cannot be considered significant because of the low statistical occurrence. The distribution of tau_F has a well defined modal value at 19 h. Assuming the recent estimate of the beaming factor delta about 20, we derived a typical size of the emitting region of about 5 times 10^{16}/(1 + z) cm. The possibility to search for a possible correlation between the mean magnitude variation rate and the long term changes of the velocity of superluminal components in the jet is discussed.Comment: 12 pages, 10 figures, accepted for Astronomy and Astrophysic

The Long Term Optical Variability of the BL Lac object S5 0716+714: Evidence for a Precessing Jet

We present the historic light curve of the BL Lac object S5 0716+714, spanning the time interval from 1953 to 2003, built using Asiago archive plates and our recent CCD observations, together with literature data. The source shows an evident long term variability, over which well known short term variations are superposed. In particular, in the period from 1961 to 1983 the mean brightness of S5 0716+714 remained significantly fainter than that observed after 1994. Assuming a constant variation rate of the mean magnitude we can estimate a value of about 0.11 magnitude/year. The simultaneous occurrence of decreasing ejection velocities of superluminal moving components in the jet reported by Bach et al. (2005) suggests that both phenomena are related to the change of the direction of the jet to the line of sight from about 5 to 0.7 degrees for an approximately constant bulk Lorentz factor of about 12. A simple explanation is that of a precessing relativistic jet, which should presently be close to the smallest orientation angle. One can therefore expect in the next ten years a decrease of the mean brightness of about 1 magnitude.Comment: to appear on The Astronomical Journal, 17 pages, 7 figures. Fig.2 is given as a separated jpg fil

BMJ Open

Objectives To investigate authors’ awareness and use of authorship guidelines, and to assess their perceptions of the fairness of authorship decisions. Design A cross-sectional online survey. Setting and participants Corresponding authors of research papers submitted in 2014 to 18 BMJ journals. Results 3859/12 646 (31%) researchers responded. They worked in 93 countries and varied in research experience. Of these, 1326 (34%) reported their institution had an authorship policy providing criteria for authorship; 2871 (74%) were ‘very familiar’ with the International Committee of Medical Journal Editors’ authorship criteria and 3358 (87%) reported that guidelines were beneficial when preparing manuscripts. Furthermore, 2609 (68%) reported that their use was ‘sometimes’ or ‘frequently’ encouraged in their research setting. However, 2859 respondents (74%) reported that they had been involved in a study at least once where someone was added as an author who had not contributed substantially (honorary authorship), and 1305 (34%) where someone was not listed as an author but had contributed substantially (ghost authorship). Only 740 (19%) reported that they had never experienced either honorary or ghost authorship; 1115 (29%) reported that they had experienced both at least once. There was no clear pattern in experience of authorship misappropriation by continent. For their last coauthored article, 2187 (57%) reported that explicit authorship criteria had been used to determine eligibility, and 3088 (80%) felt that the decision made was fair. When institutions frequently encouraged use of authorship guidelines, authorship eligibility was more likely to be discussed early (817 of 1410, 58%) and perceived as fairer (1273 of 1410, 90%) compared with infrequent encouragement (974 of 2449, 40%, and 1891 of 2449, 74%). Conclusions Despite a high level of awareness of authorship guidelines and criteria, these are not so widely used; more explicit encouragement of their use by institutions may result in more favourable use of guidelines by authors

Variability of the Spectral Energy Distribution of the Blazar S5 0716+714

The emission from blazars is known to be variable at all wavelengths. The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra of emitting electrons and/or the physical parameters of the jet. Meaningful modeling of blazar broadband spectra is required to understand the extreme conditions within the emission region. Not only is the broadband SED crucial, but also information about its variability is needed to understand how the highest states of emission occur and how they differ from the low states. This may help in discriminating between models. Here we present the results of our SED modeling of the blazar S5 0716+714 during various phases of its activity. The SEDs are classified into different bins depending on the optical brightness state of the source.Comment: 4 pages, 3 figures, contributed talk presented at the conference Multifrequency Variability of Blazars, Guangzhou, China, September 22-24, 2010. To appear in Journal of Astrophysics and Astronomy (JAA

The historical light curve of the symbiotic star AG Draconis: intense, magnetically induced cyclic activity

We analyze an optical light curve of the symbiotic system AG Draconis covering the last 120 years of its history. During the first 32 years the system was in a quiescence state. Around the year 1922 the star's quiescence luminosity brightened by 0.29 mag. The last 82 years of the light curve (LC) are characterized by a series of outbursts of 1-2 magnitude in brightness and about 100 days in duration. The outbursts are distributed along the time axis in 6 clusters with a quasi-periodic cycle of some 5300 days. The time intervals among the outbursts themselves are integral numbers of the period 373.5 days. During quiescence states the LC oscillates with the binary period of the system of 550 d. The LC contains also a weak periodic signal with a period of 350 d, attributed to pulsations of the giant star. Another period of 1160 d is also present in the light curve, being the sidereal rotation period of the giant star. We suggest that the outbursts are events of intense mass transfer from the giant onto the hot component. These are modulated by an interplay between a solar-like magnetic dynamo cycle operating in the outer layers of the giant, and a tidal deformation of these layers that circulates the surface of the giant with the synodic diurnal period of 373.5 Earth days. AG Dra is the 5th symbiotic system with a light curve that reflects such an intense magnetic and magnetically modulated activity. (Abridged)Comment: 10 pages, 4 figures. Accepted for publication in MNRA