We report multi-color optical imaging and polarimetry observations of the afterglow of the first TeVdetected gamma-ray burst, GRB 190114C, using the RINGO3 polarimeter on the 2-m autonomous robotic Liverpool Telescope. Observations begin 201 s after the onset of the GRB and continue until ∼ 7000 s post-burst. High temporal resolution (∆t 2.3 − 4.6 s) and dense sampling of the RINGO3 light curves reveal a chromatic break at t ∼ 400 − 500 s -with initial temporal decay α ∼ 1.5 flattening to α ∼ 1 post-break -which we model as a combination of reverse and forward-shock components, with magnetization parameter R B ∼ 40. The observed polarization degree P ∼ 2 − 4% remains steady throughout the first ∼ 2000-s observation window, with a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms GRB 190114C is highly obscured (A v,HG = 1.49 ± 0.12 mag; N H,HG = (9.0 ± 0.03) × 10 22 cm −2 ). The measured polarization is therefore dominated by dust scattering and the intrinsic polarization is low -in contrast to P > 10% measured previously for other GRB reverse shocks. We test whether 1st and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and the sub-TeV emission but conclude neither is explained in the reverse shock Inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if largescale jet magnetic fields are distorted on timescales prior to reverse shock emission.

With the discovery of gamma ray bursts1,2, it became clear that our Universe flickers with superfast catastrophic events, sometimes lasting for a thousandths of a second. These ultra-fast transients - the peculiar one-day butterflies of the Universe - shine so brightly that they are noticed even on the other end of the Universe and, moreover, by very small telescopes. But in the radio range, the sky remained silent until the beginning of the 21st century. Only in 2007, radio astronomers analyzing archival observations of the Parkes Radio Telescope first encountered fast transients 3,4 . About a hundred such sources have already been discovered. We report the first optical observation of the closest radio burster FRB 180916.J0158+655-8 synchronously with a radio burst. In total, we obtained about 155,093 images at MASTER Global Robotic Net9*. In the course of our observations, we found a new method for detecting objects deep below the noise level. In addition, using the new method, we found the excess of photons in the FRB direction at a level of 23 m associated with the emission of the host galaxy.

Aims. We investigate the long gamma-ray burst (GRB) 140629A through multiwavelength observations to derive the properties of the dominant jet and its host galaxy. Methods. The afterglow and host galaxy observations were taken in the optical (Swift/UVOT and various facilities worldwide), infrared (Spitzer), and X-rays (Swift/XRT) between 40 s and 3 yr after the burst trigger. Results. Polarisation observations by the MASTER telescope indicate that this burst is weakly polarised. The optical spectrum contains absorption features, from which we confirm the redshift of the GRB as originating at z = 2.276 ± 0.001. We performed spectral fitting of the X-rays to optical afterglow data and find there is no strong spectral evolution. We determine the hydrogen column density NH to be 7.2 × 1021 cm−2 along the line of sight. The afterglow in this burst can be explained by a blast wave jet with a long-lasting central engine expanding into a uniform medium in the slow cooling regime. At the end of energy injection, a normal decay phase is observed in both the optical and X-ray bands. An achromatic jet break is also found in the afterglow light curves ∼0.4 d after trigger. We fit the multiwavelength data simultaneously with a model based on a numerical simulation and find that the observations can be explained by a narrow uniform jet in a dense environment with an opening angle of 6.7° viewed 3.8° off-axis, which released a total energy of 1.4 × 1054 erg. Using the redshift and opening angle, we find GRB 140629A follows both the Ghirlanda and Amati relations. From the peak time of the light curve, identified as the onset of the forward shock (181s after trigger), the initial Lorentz factor (Γ0) is constrained in the range 82–118. Fitting the host galaxy photometry, we find the host to be a low mass, star-forming galaxy with a star formation rate of log (SFR) 1.1+0.9−0.4 M⊙ yr−1. We obtain a value of the neutral hydrogen density by fitting the optical spectrum, log NHI = 21.0 ± 0.3, classifying this host as a damped Lyman-alpha. High ionisation lines (N V, Si IV) are also detected in the spectrum.

We present multiwavelength observations and a model for flat spectrum radio quasar NVSS J141922-083830, originally classified as a blazar candidate of unknown type (BCU II object) in the Third Fermi-LAT AGN Catalog (3LAC). Relatively bright flares (>3 magnitudes) were observed on 21 February 2015 (MJD 57074) and 8 September 2018 (MJD 58369) in the optical band with the MASTER Global Robotic Net (MASTER-Net) telescopes. Optical spectra obtained with the Southern African Large Telescope (SALT) on 1 March 2015 (MJD 57082), during outburst, and on 30 May 2017 (MJD 57903), during quiescence, showed emission lines at 5325Å and at ≈3630Å that we identified as the Mg ii 2798Å and C iii] 1909Å lines, respectively, and hence derived a redshift z = 0.903. Analysis of Fermi-LAT data was performed in the quiescent regime (5 years of data) and during four prominent flaring states in February–April 2014, October–November 2014, February–March 2015 and September 2018. We present spectral and timing analysis with Fermi-LAT. We report a hardening of the gamma-ray spectrum during the last three flaring periods, with a power-law spectral index Γ = 2.0–2.1. The maximum gamma-ray flux level was observed on 24 October 2014 (MJD 56954) at (7.57 ± 1.83) × 10−7 ph cm−2s−1. The multi-wavelength spectral energy distribution during the February–March 2015 flare supports the earlier evidence of this blazar to belong to the FSRQ class. The SED can be well represented with a single-zone leptonic model with parameters typical of FSRQs, but also a hadronic origin of the high-energy emission can not be ruled out.

We report on MASTER optical observations of an afterglow-like optical and X-ray transient AT2021lfa/ZTF21aayokph. We detected the initial steady brightening of the transient at 7σ confidence level. This allowed us to use smooth optical self-similar emission of GRBs model to constrain the explosion time to better than 14 min as well as to estimate its initial Lorentz factor Γ0 = 20 ± 10. Taking into consideration the low Γ0 and non-detection in gamma-rays, we classify this transient as the first failed GRB afterglow.