We study the distribution of long gamma‐ray bursts in the Epeak–Eiso and in the Eobspeak–fluence planes through an updated sample of 76 bursts, with measured redshift and spectral parameters, detected up to 2007 September. We confirm the existence of a strong rest‐frame correlation Epeak∝E0.54±0.01iso. Contrary to previous studies, no sign of evolution with redshift of the Epeak–Eiso correlation (either its slope and its normalization) is found. The 76 bursts define a strong Eobspeak–fluence correlation in the observer frame (Eobspeak∝F0.32±0.05bol) with redshifts evenly distributed along this correlation. We study possible instrumental selection effects in the observer frame Eobspeak–fluence plane. In particular, we concentrate on the minimum peak flux necessary to trigger a given gamma‐ray burst (GRB) detector (trigger threshold) and the minimum fluence a burst must have to determine the value of Eobspeak (spectral analysis threshold). We find that the latter dominates in the Eobspeak–fluence plane over the former. Our analysis shows, however, that these instrumental selection effects do not dominate for bursts detected before the launch of the Swift satellite, while the spectral analysis threshold is the dominant truncation effect of the Swift GRB sample (27 out of 76 events). This suggests that the Eobspeak–fluence correlation defined by the pre‐Swift sample could be affected by other, still not understood, selection effects. Besides, we caution about the conclusions on the existence of the Eobspeak–fluence correlation based on our Swift sample alone.

For a sample of long γ‐ray bursts (GRBs) with known redshift, we study the distribution of the evolutionary tracks on the rest‐frame luminosity‐peak energy Liso−E′p diagram. We are interested in exploring the extension of the ‘Yonetoku’ correlation to any phase of the prompt light curve, and in verifying how the high‐signal prompt duration time, T′f, in the rest frame correlates with the residuals of such correlation. For our purpose, we separately analyse two samples of time‐resolved spectra corresponding to 32 GRBs with peak fluxes Fp > 1.8 phot cm−2 s−1 from the Swift‐BAT detector, and seven bright GRBs from the Compton Gamma‐ray Observatory (CGRO)‐BATSE detector previously processed by Kaneko et al. After constructing the Liso−E′p diagram, we discuss the relevance of selection effects, finding that they could significantly affect the correlation. However, we find that these effects are much less significant in the Liso T′f−E′p diagram, where the intrinsic scatter reduces significantly. We apply further corrections in order to reduce the intrinsic scatter even more. For the subsamples of GRBs (seven from Swift and five from CGRO) with measured jet break time, tj, we analyse the effects of correcting Liso by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time‐integrated ‘Amati’ and ‘Ghirlanda’ correlations are consequences of the time‐resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.

We explore the possibility of formation of steady internal shocks in jets around black holes. We consider a fluid described by a relativistic equation of state, flowing about the axis of symmetry (θ = 0) in a Schwarzschild metric. We use two models for the jet geometry, (i) a conical geometry and (ii) a geometry with non-conical cross-section. Jet with conical geometry is smooth flow. While the jet with non-conical cross section undergoes multiple sonic point and even standing shock. The jet shock becomes stronger, as the shock location is situated further from the central black hole. Jets with very high energy and very low energy do not harbour shocks, but jets with intermediate energies do harbour shocks. One advantage of these shocks, as opposed to shocks mediated by external medium is that, these shocks have no effect on the jet terminal speed, but may act as possible sites for particle acceleration. Typically , a jet with energy 1.8 c 2 , will achieve a terminal speed of v ∞ = 0.813c for jet with any geometry. But for a jet of non-conical cross-section for which the length scale of the inner torus of the accretion disc is 40r g , then in addition, a steady shock will form at r sh ∼ 7.5r g and compression ratio of R ∼ 2.7. Moreover , electron-proton jet seems to harbour the strongest shock. We discuss possible consequences of such a scenario.

We study the spectral and energetics properties of 47 long‐duration gamma‐ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15–150 keV) of the Swift‐BAT detector, the spectral fitting is reliable only for fitting models with two or three parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, two parameters) and cut‐off power law (CPL, three parameters) models to the time‐integrated spectra of the 47 bursts, and we present the corresponding parameters, their uncertainties and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the νfν peak energy Epk. For these GRBs, we calculate the energy fluence and the rest‐frame isotropic‐equivalent radiated energy, Eγ,iso, as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest‐frame diagram E′pk versus Eγ,iso. We confirm a significant correlation between these two quantities (the ‘Amati’ relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high‐energy PL index frozen to −2.3, obtaining a rather good agreement with the ‘Amati’ relation of non‐Swift GRBs.

A detailed analysis of the optical polarimetric variability of the TeV blazar 1ES 1959+650 from 2007 October 18 to 2011 May 5 is presented. The source showed a maximum and minimum brightness states in the R-band of 14.08±0.03 mag and 15.20±0.03 mag, respectively, with a maximum variation of 1.12 mag, and also a maximum polarization degree of P =(12.2±0.7)%, with a maximum variation of 10.7%. From August to November 2009, a correlation between the optical R-band flux and the degree of linear polarization was found, with a correlation coefficient r pol =0.984±0.025. The source presented a preferential position angle of optical polarization of ∼153 • , with variations of 10 • -50 • , that is in agreement with the projected position angle of the parsec scale jet found at 43 GHz. From the Stokes parameters we infer the existence of two optically-thin synchrotron components that contribute to the polarized flux. One of them is stable, with a constant polarization degree of 4%. Assuming a stationary shock for the variable component, we estimated some parameters associated with the physics of the relativistic jet: the magnetic field, B ∼0.06 G, the Doppler factor, δ 0 ∼23, the viewing angle, Φ ∼2.4 • , and the size of the emission region r b ∼5.6×10 17 cm. Our study is consistent with the spine-sheath model to explain the polarimetric variability displayed by this source during our monitoring.

The early X‐ray light curve of gamma‐ray bursts (GRBs) is complex, and shows a typical steep–flat–steep behaviour. The time Ta at which the flat (plateau) part ends may bear some important physical information, especially if it plays the same role of the so called jet break‐time tjet. To this aim, stimulated by the recent analysis of Willingale et al., we have assembled a sample of GRBs of known redshifts, spectral parameters of the prompt emission, and Ta. By using Ta as a jet angle indicator, and then estimating the collimation‐corrected prompt energetics, we find a correlation between the latter quantity and the peak energy of the prompt emission. However, this correlation has a large dispersion, similar to the dispersion of the Amati correlation and it is not parallel to the Ghirlanda correlation. Furthermore, we show that the correlation itself results mainly from the dependence of the jet opening angle on the isotropic prompt energy, with the time Ta playing no role, contrary to what we find for the jet break‐time tjet. We also find that for the bursts in our sample Ta weakly correlates with Eγ,iso of the prompt emission, but that this correlation disappears when considering all bursts of known redshift and Ta. There is no correlation between Ta and the isotropic energy of the plateau phase.

An R-band photopolarimetric variability analysis of the TeV bright blazar W Comae, between 2008 February 28 and 2013 May 17, is presented. The source showed a gradual tendency to decrease its mean flux level with a total change of 3 mJy. A maximum and minimum brightness states in the R-band of 14.25±0.04 and 16.52±0.1 mag respectively were observed, corresponding to a maximum variation of ∆F = 5.40 mJy.We estimated a minimum variability timescale of ∆t=3.3 days. A maximum polarization degree P=33.8%±1.6%, with a maximum variation of ∆P = 33.2%, was found.One of our main results is the detection of a large rotation of the polarization angle from 78 • to 315 • (∆θ ∼237 • ) that coincides in time with the γ-ray flare observed in 2008 June. This result indicates that both optical and γ-ray emission regions could be co-spatial. During this flare, a correlation between the R-band flux and polarization degree was found with a correlation coefficient of r F−p = 0.93±0.11. From the Stokes parameters we infer the existence of two optically thin synchrotron components that contribute to the polarized flux. One of them is stable with a constant polarization degree of 11%. Assuming a shock-in jet model during the 2008 flare, we estimated a maximum Doppler factor δ D ∼ 27 and a minimum of δ D ∼ 16; a minimum viewing angle of the jet ∼2 • .0; and a magnetic field B ∼ 0.12 G.

A physical description of the formation and propagation of working surfaces inside the relativistic jet of the Blazar PKS 1510-089 are used to model its γ-ray variability light curve using FERMI-LAT data from 2008 to 2012. The physical model is based on conservation laws of mass and momentum at the working surface as explained by Mendoza et al. (2009). The hydrodynamical description of a working surface is parametrised by the initial velocity and mass injection rate at the base of the jet. We show that periodic variations on the injected velocity profiles are able to account for the observed luminosity, fixing model parameters such as mass ejection rates of the central engine injected at the base of the jet, oscillation frequencies of the flow and maximum Lorentz factors of the bulk flow during a particular burst.