On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40 − 8 + 8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M ⊙ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 Mpc ) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

We present multi-wavelength observations and modeling of the exceptionally bright long γ-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of 3 . 6 j q »  and kinetic energy of E 2 10»´erg, propagating into a low-density (n 5 10 5 »´-cm −3 ) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of 100 0  G and an ejecta magnetization of R 1 100 B » -. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

After the initial burst of γ-rays that defines a γ-ray burst (GRB), expanding ejecta collide with the circumburst medium and begin to decelerate at the onset of the afterglow, during which a forward shock travels outwards and a reverse shock propagates backwards into the oncoming collimated flow, or 'jet'. Light from the reverse shock should be highly polarized if the jet's magnetic field is globally ordered and advected from the central engine, with a position angle that is predicted to remain stable in magnetized baryonic jet models or vary randomly with time if the field is produced locally by plasma or magnetohydrodynamic instabilities. Degrees of linear polarization of P ≈ 10 per cent in the optical band have previously been detected in the early afterglow, but the lack of temporal measurements prevented definitive tests of competing jet models. Hours to days after the γ-ray burst, polarization levels are low (P < 4 per cent), when emission from the shocked ambient medium dominates. Here we report the detection of P =28(+4)(-4) per cent in the immediate afterglow of Swift γ-ray burst GRB 120308A, four minutes after its discovery in the γ-ray band, decreasing to P = 16(+5)(-4) per cent over the subsequent ten minutes. The polarization position angle remains stable, changing by no more than 15 degrees over this time, with a possible trend suggesting gradual rotation and ruling out plasma or magnetohydrodynamic instabilities. Instead, the polarization properties show that GRBs contain magnetized baryonic jets with large-scale uniform fields that can survive long after the initial explosion.

We present ground-based and HST optical and infrared observations of Swift XRF 100316D / SN 2010bh. It is seen that the optical light curves of SN 2010bh evolve at a faster rate than the archetype GRB-SN 1998bw, but at a similar rate to SN 2006aj, a supernova that was spectroscopically linked with XRF 060218, and at a similar rate to non-GRB associated type Ic SN 1994I. We estimate the rest-frame extinction of this event from our optical data to be E(B − V ) = 0.18 ± 0.08 mag. We find the V -band absolute magnitude of SN 2010bh to be M V = −18.62 ± 0.08, which is the faintest peak V -band magnitude observed to-date for a spectroscopicallyconfirmed GRB-SNe. When we investigate the origin of the flux at t − t o = 0.598 days, it is shown that the light is not synchrotron in origin, but is likely coming from the supernova shock break-out. We then use our optical and infrared data to create a quasi-bolometric light curve of SN 2010bh which we model with a simple analytical formula. The results of our modeling imply that SN 2010bh synthesized a nickel mass of M Ni ≈ 0.1M ⊙ , ejected M ej ≈ 2.2M ⊙ and has an explosion energy of E k ≈ 1.4 × 10 52 erg. Thus, while SN 2010bh is an energetic explosion, the amount of nickel created during the explosion is much less than that of SN 1998bw, and only marginally more than SN 1994I. Finally, for a sample 22 GRB-SNe we check for a correlation between the stretch factors and luminosity factors in the R band and conclude that no statisticallysignificant correlation exists.

2Long-duration Gamma-Ray Bursts (GRBs) are an extremely rare outcome of the collapse of massive stars, and are typically found in the distant Universe.Because of its intrinsic luminosity (L ∼ 3 × 10 53 erg s −1 ) and its relative proximity (z = 0.34), GRB 130427A was a unique event that reached the highest fluence observed in the γ-ray band. Here we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-m Liverpool and Faulkes telescopes and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs,suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early Universe and over the full range of GRB isotropic energies.GRB 130427A was the brightest burst detected by Swift (1) as well as by several γ-ray detectors onboard other space missions. It was also the brightest and longest burst detected above 100 MeV, with the most energetic photon detected at 95 GeV (2). It was detected by Fermi-GBM (3) at T 0,GBM = 07:47:06.42 UT on April 27 2013. Hereafter this time will be our reference time T 0 . The Burst Alert Telescope (BAT, (4)) onboard Swift triggered on GRB 130427Aat t = 51.1 s, when Swift completed a pre-planned slew. The Swift slew to the source started at t = 148 s and ended at t = 192 s. The Swift UltraViolet Optical Telescope (UVOT, (5)) began observations at t = 181 s while observations by the Swift X-ray Telescope (XRT, (6)) started at t = 195 s (see (7) for more details). The structure of the γ-ray light curve revealed by the Swift-BAT in the 15-350 keV band ( Fig. 1) can be divided in three main episodes: an initial peak, beginning at t = 0.1 s and peaking at t = 0.5 s; a second large peak showing a complex 3 structure with a duration of ∼ 20 s and a third, much weaker episode, starting at t ∼120 s showing a fast rise/exponential decay behavior. The overall duration of the prompt emission was T 90(15−150 keV) = 276 ± 5 s (i.e. the time containing 90% of the fluence) calculated over the first 1830 s of BAT observation from T 0,GBM . During the early phases of the γ-ray emission strong spectral variability is observed (Fig. 1). A marked spectral hardening is observed during is (2.68 ± 0.01) × 10 −3 erg cm −2 , with a spectrum peaking at E peak = 1028 ± 8 keV, while the fluence of the emission episode at (120 -250 s) is ∼ 9 × 10 −5 erg cm −2 , with a spectrum peaking at ∼240 keV (9).This event was extremely bright also in the optical and it was immediately detected by various robotic telescopes: in particular, the Raptor robotic telescope detected a bright optical counterpart already at t = 0.5 s (10). Optical spectroscopy of the afterglow determined the redshift to be z = 0.34 (11); an UVOT UV grism spectrum (7) was also acquired. At this distance the rest frame 1 keV-10 MeV isotropic energy is E iso = 8.1 × 10 53 erg and the peak luminosity is L iso = 2.7 × 10 53 erg s −1 . Acc...