Following the discovery of the gravitational-wave source GW170817 by three Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo antennae (Abbott et al., 2017a), the MASTER Global Robotic Net telescopes obtained the first image of the NGC 4993 host galaxy. An optical transient, MASTER OTJ130948.10-232253.3/SSS17a was later found, which appears to be a kilonova resulting from the merger of two neutron stars (NSs). Here we describe this independent detection and photometry of the kilonova made in white light, and in B, V, and R filters. We note that the luminosity of this kilonova in NGC 4993 is very close to those measured for other kilonovae possibly associated with gamma-ray burst (GRB) 130603 and GRB 080503.

We present comprehensive multiwavelength radio to X-ray observations of GRB 181201A spanning from ≈150 s to ≈163 days after the burst, comprising the first joint ALMA–VLA–GMRT observations of a gamma-ray burst (GRB) afterglow. The radio and millimeter-band data reveal a distinct signature at ≈3.9 days, which we interpret as reverse-shock (RS) emission. Our observations present the first time that a single radio-frequency spectral energy distribution can be decomposed directly into RS and forward shock (FS) components. We perform detailed modeling of the full multiwavelength data set, using Markov Chain Monte Carlo sampling to construct the joint posterior density function of the underlying physical parameters describing the RS and FS synchrotron emission. We uncover and account for all discovered degeneracies in the model parameters. The joint RS–FS modeling reveals a weakly magnetized (σ ≈ 3 × 10⁻³), mildly relativistic RS, from which we derive an initial bulk Lorentz factor of Γ₀ ≈ 103 for the GRB jet. Our results support the hypothesis that low-density environments are conducive to the observability of RS emission. We compare our observations to other events with strong RS detections and find a likely observational bias selecting for longer lasting, nonrelativistic RSs. We present and begin to address new challenges in modeling posed by the present generation of comprehensive, multifrequency data sets.

Scientific complementary metal-oxide-semiconductor (CMOS) detectors have developed quickly in recent years thanks to their low cost and high availability. They also have some advantages over charge-coupled devices (CCDs), such as high frame rate or typically lower readout noise. These sensors started to be used in astronomy following the development of the first back-illuminated models. Therefore, it is worth studying their characteristics, advantages, and weaknesses. One of the most widespread CMOS sensors are those from the Sony IMX series, which are included in large astronomical survey projects based on small and fast telescopes because of their low cost, and capability for wide-field and high-cadence surveys. In this paper, we aim to characterize the IMX455M and IMX411M sensors, which are integrated into the QHY600 and QHY411 cameras, respectively, for use in astronomical observations. These are large (36 × 24 and 54 × 40 mm) native 16 bit sensors with 3.76 μm pixels and are sensitive in the optical range. We present the results of the laboratory characterization of both cameras. They showed a very low dark current of 0.011 and 0.007 e⁻ px⁻¹ s⁻¹ @–10°C for the QHY600 and QHY411 cameras, respectively. They also show the presence of warm pixels, ∼0.024% in the QHY600 and 0.005% in the QHY411. Warm pixels proved to be stable and linear with exposure time, and are therefore easily corrected using dark frames. Pixels affected by the Salt & Pepper noise are ∼2% of the total and a method to correct for this effect is presented. Both cameras were attached to night telescopes and several on-sky tests were performed to prove their capabilities. On-sky tests demonstrate that these CMOS behave as well as CCDs of similar characteristics and (for example) they can attain photometric accuracies of a few mili-magnitudes.

Context. Theories of the formation and evolution of small bodies in planetary systems predict that they may escape into interstellar space at any time, leaked from extrasolar Oort clouds or ejected following close encounters with local planets or their host stars. After just two such interlopers – 1I/2017 U1 (‘Oumuamua) and 2I/Borisov – had been characterized, more questions had been raised than answered. Assessing the recently discovered interstellar comet 3I/ATLAS will only broaden our understanding of this complex topic. Aims. Here, we investigate the spectral, cometary, and rotational properties of 3I/ATLAS as well as its dynamical context. Methods. We identified the spectral type of 3I/ATLAS from the visible reflectance spectrum and used photometric observations to derive its level of activity and rotational properties. Observational data were obtained with the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope. We used N-body simulations and statistical analyses of Gaia DR3 data to investigate the origin of 3I/ATLAS and its Galactic background. Results. Interstellar comet 3I/ATLAS has a visible spectrum slightly redder than the ones of D-type asteroids, 1I/‘Oumuamua and 2I/Borisov, with a spectral slope of S′ = 18.3 ± 0.9 %/1000 Å in the 4000–9000 Å range, which is similar to the ones of trans-Neptunian objects and Centaurs. It has a conspicuous coma and its rotation period is 16.79 ± 0.23 h. The heliocentric components of its Galactic velocity are (U,V,W) = (−51.233 ± 0.006, −19.456 ± 0.004, +18.930_−0.006^+0.005) km s⁻¹ with a radiant in Sagittarius of (α, δ) = (295.​​°043_{−0.​​°004}^{+0.​​°003}, −19.​​°0704_{−0.​​°0005}^{+0.​​°0006}). The analysis of a sample of kinematic analogs of 3I/ATLAS extracted from Gaia DR3 suggests that its parent system is part of the Galactic thin disk and includes a solar-like star with a slightly subsolar metallicity. Conclusions. The results from the physical characterization of 3I/ATLAS further support the idea that extrasolar debris is not too different from the debris found in the Solar System and that it is the result of similar formation processes.

We obtain the time delay between the arrival time of the A and B images of the QSO 0957+561. The results of applying two different methods (the discrete cross-correlation function and the dispersion estimation technique) to the observed light curves of the A and B images are presented. The adopted value (time delay) is of Δτ_BA = 424 ± 3 days (1 σ). We have used this time delay as well as a recent measurement of the one-dimensional velocity dispersion of the main lensing galaxy (σ_gal) to estimate H₀. Two H₀ = H₀(Δτ_BA, σ_gal) relations based on different pictures of the lens galaxy, lead to H₀ = 64^{+ 14}₋₁₅ km s^-1 Mpc^-1 (2 σ) (softened power-law sphere) and H₀ = 66^{+ 15}₋₁₄ km s^-1 Mpc^-1 (2 σ) (King profile plus a point-mass at the center).