Search

We present the largest optical photometry compilation of Gamma-Ray Bursts (GRBs) with redshifts (z). We include 64813 observations of 535 events (including upper limits) from 28 February 1997 to 18 August 2023. We also present a user-friendly web tool grbLC which allows users to visualise photometry, coordinates, redshift, host galaxy extinction, and spectral indices for each event in our database. Furthermore, we have added a Gamma-ray Coordinate Network (GCN) scraper that can be used to collect data by gathering magnitudes from the GCNs. The web tool also includes a package for uniformly investigating colour evolution. We compute the optical spectral indices for 138 GRBs, for which we have at least 4 filters at the same epoch in our sample, and craft a procedure to distinguish between GRBs with and without colour evolution. By providing a uniform format and repository for the optical catalogue, this web-based archive is the first step towards unifying several community efforts to gather the photometric information for all GRBs with known redshifts. This catalogue will enable population studies by providing light curves (LCs) with better coverage since we have gathered data from different ground-based locations. Consequently, these LCs can be used to train future LC reconstructions for an extended inference of the redshift. The data gathering also allows us to fill some of the orbital gaps from Swift in crucial points of the LCs, e.g., at the end of the plateau emission or where a jet break is identified.

The Sabzevar ophiolite belt consists of a series of thrust-bound massifs that widen in extent to ∼150 km in NE Iran. The Kuh-Siah harzburgite-dunite massif in the central sector of this belt hosts abundant discontinuous pod-like chromitite deposits. These deposits are characterized by spinels with contrasting and variable compositions, but without any microtextural differences. The chromian spinel in these chromitite bodies displays a wide range of Cr-number (Cr/(Cr + Al)) atomic ratio from 0.50 to 0.77, and reveals a co-occurrence of Al-rich and Cr-rich chromitites within a single ophiolitic massif. Despite these chemical differences, primary spinels from both the high-Al and high-Cr chromitites have similar TiO2 contents, indicating that they formed in a single tectono-magmatic setting. Both high-Al and high-Cr chromitite samples display low to moderate total platinum group element (PGE) abundances (85–537 ppb). Solid phases hosted by Cr-spinel grains in chromitites and their host dunites can be divided into three categories: platinum group minerals (PGM), base-metal minerals (BMM), and silicates. Euhedral quadrangular and round-shaped silicate inclusions consisting of clinopyroxene, orthopyroxene, Na-bearing phlogopite, serpentine and chlorite, are sporadically scattered in the Cr-spinel grains. These inclusions are mainly single crystals and rarely occur as polyphase assemblages. The BMM are mainly euhedral Ni- and Cu-rich sulfides with rare occurrence of pentlandite. The most widespread PGM are crystals of the laurite-erlichmanite series with subordinate malanite, braggite and BM-PGE-rich sulfides. Textural relationships reflect that the PGM are of magmatic origin. The BMM, on the other hand, formed during both magmatic and post-magmatic processes. The occurrence of low-temperature inclusions within Cr-spinel and ferrian Cr-spinel, comprising tremolite, chlorite and serpentine, are interpreted as post-magmatic entrapments of already-formed silicate phases at th

We present analytical and numerical models of the bright long GRB 210822A at $z=1.736$. The intrinsic extreme brightness exhibited in the optical, which is very similar to other bright GRBs (e.g., GRBs 080319B, 130427A, 160625A 190114C, and 221009A), makes GRB 210822A an ideal case for studying the evolution of this particular kind of GRB. We use optical data from the RATIR instrument starting at $T+315.9$ s, with publicly available optical data from other ground-based observatories, as well as Swift/UVOT, and X-ray data from the Swift/XRT instrument. The temporal profiles and spectral properties during the late stages align consistently with the conventional forward shock model, complemented by a reverse shock element that dominates optical emissions during the initial phases ($T<300$ s). Furthermore, we observe a break at $T=80000$s that we interpreted as evidence of a jet break, which constrains the opening angle to be about $\theta_\mathrm{j}=(3-5)$ degrees. Finally, we apply a machine-learning technique to model the multi-wavelength light curve of GRB 210822A using the AFTERGLOWPY library. We estimate the angle of sight $\theta_{obs}=(6.4 \pm 0.1) \times 10^{-1}$ degrees, the energy $E_0=(7.9 \pm 1.6)\times 10^{53}$ ergs, the electron index $p=2.54 \pm 0.10$, the thermal energy fraction in electrons $\epsilon_\mathrm{e}=(4.63 \pm 0.91) \times 10^{-5}$ and in the magnetic field $\epsilon_\mathrm{B}= (8.66 \pm 1.01) \times 10^{-6}$, the efficiency $\chi = 0.89 \pm 0.01$, and the density of the surrounding medium $n_\mathrm{0} = 0.85 \pm 0.01 cm^{-3}$., Comment: Resubmitted to MNRAS after moderate revision, 12 pages, 6 figures

We collected the optical light curve data of 227 gamma-ray bursts (GRBs) observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133 detections and 94 upper limits. We constructed average light curves in the observer and rest frames in both X-rays (from {\itshape Swift}/XRT) and in the optical. Our analysis focused on investigating the observational and intrinsic properties of GRBs. Specifically, we examined observational properties, such as the optical brightness function of the GRBs at $T=1000$ seconds after the trigger, as well as the temporal slope of the afterglow. We also estimated the redshift distribution for the GRBs within our sample. Of the 227 GRBs analysed, we found that 116 had a measured redshift. Based on these data, we calculated a local rate of $\rho_0=0.2$ Gpc$^{-3}$ yr$^{-1}$ for these events with $z<1$. To explore the intrinsic properties of GRBs, we examined the average X-ray and optical light curves in the rest frame. We use the {\scshape afterglowpy} library to generate synthetic curves to constrain the parameters typical of the bright GRB jet, such as energy (${\langle} {E_{0}}{\rangle}\sim 10^{53.6}$~erg), opening angle (${\langle}\theta_\mathrm{core}{\rangle}\sim 0.2$~rad), and density (${\langle}n_\mathrm{0}{\rangle}\sim10^{-2.1}$ cm$^{-3}$). Furthermore, we analyse microphysical parameters, including the fraction of thermal energy in accelerated electrons (${\langle}\epsilon_e{\rangle}\sim 10^{-1.37}$) and in the magnetic field (${\langle}\epsilon_B{\rangle}\sim10^{-2.26}$), and the power-law index of the population of non-thermal electrons (${\langle}p{\rangle}\sim 2.2$)., Comment: Accepted for publication in MNRAS, 13 pages and 9 figures

Kilonovae are a rare class of astrophysical transients powered by the radioactive decay of nuclei heavier than iron, synthesized in the merger of two compact objects. Over the first few days, the kilonova evolution is dominated by a large number of radioactive isotopes contributing to the heating rate. On timescales of weeks to months, its behavior is predicted to differ depending on the ejecta composition and merger remnant. However, late-time observations of known kilonovae are either missing or limited. Here we report observations of a luminous red transient with a quasi-thermal spectrum, following an unusual gamma-ray burst of long duration. We classify this thermal emission as a kilonova and track its evolution up to two months after the burst. At these late times, the recession of the photospheric radius and the rapidly-decaying bolometric luminosity ($L_{\rm bol}\propto t^{-2.7\pm 0.4}$) support the recombination of lanthanide-rich ejecta as they cool., Comment: 47 pages, 14 figures, 9 tables; submitted; a minor typo fixed

GRB~210704A is a burst of intermediate duration ($T_{90} \sim 1-4$~s) followed by a fading afterglow and an optical excess that peaked about 7 days after the explosion. Its properties, and in particular those of the excess, do not easily fit into the well established classification scheme of GRBs as being long or short, leaving the nature of its progenitor uncertain. We present multi-wavelength observations of the GRB and its counterpart, observed up to 160 days after the burst. In order to decipher the nature of the progenitor system, we present a detailed analysis of the GRB high-energy properties (duration, spectral lag, and Amati correlation), its environment, and late-time optical excess. We discuss three possible scenarios: a neutron star merger, a collapsing massive star, and an atypical explosion possibly hosted in a cluster of galaxies. We find that traditional kilonova and supernova models do not match well the properties of the optical excess, leaving us with the intriguing suggestion that this event was an exotic high-energy merger., Comment: Revised version submitted to MNRAS after minor comments, 14 pages, 9 figures

Long duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far the brightest burst ever observed. Due to its enormous energy ($E_\textrm{iso}\!\approx$10$^{55}$ erg) and proximity ($z\!\approx$0.15), GRB 221009A is an exceptionally rare event that pushes the limits of our theories. We present multi-wavelength observations covering the first three months of its afterglow evolution. The X-ray brightness decays as a power-law with slope $\approx\!t^{-1.66}$, which is not consistent with standard predictions for jetted emission. We attribute this behavior to a shallow energy profile of the relativistic jet. A similar trend is observed in other energetic GRBs, suggesting that the most extreme explosions may be powered by structured jets launched by a common central engine., Comment: Submitted version. 53 pages, 9 figures, 6 tables

We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 230812B, and its associated supernova (SN) SN 2023pel. The proximity ($z = 0.36$) and high energy ($E_{\gamma, \rm{iso}} \sim 10^{53}$ erg) make it an important event to study as a probe of the connection between massive star core-collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak $r$-band magnitude of $M_r = -19.46 \pm 0.18$ mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of $M_{\rm{Ni}} = 0.38 \pm 0.01$ $\rm{M_\odot}$, and a peak bolometric luminosity of $L_{\rm{bol}} \sim 1.3 \times 10^{43}$ $\rm{erg}$ $\rm{s^{-1}}$. We confirm SN 2023pel's classification as a broad-lined Type Ic SN with a spectrum taken 15.5 days after its peak in $r$ band, and derive a photospheric expansion velocity of $v_{\rm{ph}} = 11,300 \pm 1,600$ $\rm{km}$ $\rm{s^{-1}}$ at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass $M_{\rm{ej}} = 1.0 \pm 0.6$ $\rm{M_\odot}$ and kinetic energy $E_{\rm{KE}} = 1.3^{+3.3}_{-1.2} \times10^{51}$ $\rm{erg}$. We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and $E_{\gamma, \rm{iso}}$ for their associated GRBs, across a broad range of 7 orders of magnitude, provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems., Comment: 21 pages, 7 Figures, 1 Table, Accepted to ApJ Letters

A significant fraction ($\sim$30\%) of well-localized short gamma-ray bursts (sGRBs) lack a coincident host galaxy. This leads to two main scenarios: \textit{i}) that the progenitor system merged outside of the visible light of its host, or \textit{ii}) that the sGRB resided within a faint and distant galaxy that was not detected by follow-up observations. Discriminating between these scenarios has important implications for constraining the formation channels of neutron star mergers, the rate and environments of gravitational wave sources, and the production of heavy elements in the Universe. In this work, we present the results of our observing campaign targeted at 31 sGRBs that lack a putative host galaxy. Our study effectively doubles the sample of well-studied sGRB host galaxies, now totaling 72 events of which $28\%$ lack a coincident host galaxy to deep limits ($r$\,$\gtrsim$\,$26$ or $F110W$\,$\gtrsim$\,$27$ AB mag), and represents the largest homogeneously selected catalog of sGRB offsets to date. We find that 70\% of sub-arcsecond localized sGRBs occur within 10 kpc of their host's nucleus, with a median projected physical offset of $5.6$ kpc. Using this larger population, we discover a redshift evolution in the locations of sGRBs: bursts at low-$z$ occur at $2\times$ larger offsets compared to those at $z$\,$>$\,$0.5$. Furthermore, we find evidence for a sample of hostless sGRBs at $z$\,$\gtrsim$\,$1$ that are indicative of a larger high-$z$ population, further constraining the sGRB redshift distribution and disfavoring log-normal delay time models., Comment: Submitted to MNRAS. 39 pages, 18 Figures, 4 Tables

Gamma-ray bursts (GRBs) are fascinating events due to their panchromatic nature. We study optical plateaus in GRB afterglows via an extended search into archival data. We comprehensively analyze all published GRBs with known redshifts and optical plateaus observed by many ground-based telescopes (e.g., Subaru Telescope, RATIR) around the world and several space-based observatories such as the Neil Gehrels Swift Observatory. We fit 502 optical light curves (LCs), showing the existence of the plateau in 181 cases. This sample is 77\% larger than the previous one \citep{dainotti2021b}, and it is the largest compilation so far of optical plateaus. We discover the 3D fundamental plane relation at optical wavelengths using this sample. This correlation is between the rest-frame time at the end of the plateau emission, $T^{*}_{\rm opt}$, its optical luminosity, $L_{\rm opt}$, and the peak in the optical prompt emission, $L_{\rm peak, opt}$, thus resembling the three-dimensional (3D) X-ray fundamental plane relation \citep{dainotti2016}. We correct our sample for redshift evolution and selection effects, discovering that this correlation is indeed intrinsic to GRB physics. We investigate the rest-frame end time distributions in X-rays and optical ($T^{*}_{\rm opt}$, $T^{*}_{\rm X}$), and conclude that the plateau is achromatic only when selection biases are not considered. We also investigate if the 3D optical correlation may be a new discriminant between optical GRB classes and {\bf find that there is no significant separation between the classes compared to the Gold sample plane after correcting for evolution.}, Comment: 24 pages, 7 figures and 3 table. Submitted to ApJ. The part in bold is the addition as a response to the referee queries

The geochemical variations of magmas across and along supra-subduction zones (SSZ) have been commonly attributed to profound changes in the phase and chemical compositions of the mantle source and subduction-derived melt and fluid fluxes, as well as the physical parameters (e.g. depth, temperature, oxygen fugacity etc) of slab dehydration, mineral breakdown and melting. Here we test the variability of the Late Quaternary primitive magmas in the southern and northern parts of the meridionally oriented Eastern Volcanic Belt (EVB) of Kamchatka, with a slab depth varying from 60 to 160 km. Eight high-Mg (Mg# > 60 mol%) basalts were characterized for major, trace and platinum-group element (PGE) abundances, as well as the compositions of olivine phenocrysts and olivine-hosted spinel inclusions. The basalts in our study are geochemically typical of SSZ magmas and contain similar liquidus assemblages of forsteritic olivine (Mg# 78–92 mol%), low-Ti Cr-spinel and clinopyroxene. Although the absolute abundances of major and trace elements, and their ratios, in the basalts fluctuate to some extent, the observed variability cannot be correlated with any of considered parameters in the geometry of the Kamchatka SSZ and conditions of melting. This unexpected result led to the evaluation of the platinumgroup element (PGE) systematics against the lithophile and chalcophile trace element geochemistry and the compositions of phenocrysts. Total whole-rock PGE content varies from 2.3 to 11.7 ppb, whereas the normalized PGE concentration patterns are typical for supra-subduction zones magmas and broadly similar in all studied samples. They are enriched in Rh, Pd and Pt relative to mid-ocean ridge basalts (MORB) and have nearly identical concentrations of Ir-group PGE. The only parameter that correlates well with PGE contents is the average Mg# of olivine phenocrysts from 84 to 90.3 mol%. This is interpreted to result from minor cryptic fractionation of sulfide melt, together with pri

Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (greater than two seconds) duration are produced by the core-collapse of massive stars1, and those of short (less than two seconds) duration by the merger of compact objects, such as two neutron stars2. A third class of events with hybrid high-energy properties was identified3, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions4,5,6, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented7,8. Here we report observations of the exceptionally bright GRB 211211A, which classify it as a hybrid event and constrain its distance scale to only 346 megaparsecs. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (approximately 1042 erg per second) kilonova possibly formed in the ejecta of a compact object merger. © 2022, The Author(s).

Gamma-ray bursts (GRBs) are fascinating events due to their panchromatic nature. We study optical plateaus in GRB afterglows via an extended search into archival data. We comprehensively analyze all published GRBs with known redshifts and optical plateaus observed by many ground-based telescopes (e.g., Subaru Telescope, RATIR) around the world and several space-based observatories such as the Neil Gehrels Swift Observatory. We fit 500 optical light curves, showing the existence of the plateau in 179 cases. This sample is 75% larger than the previous one, and it is the largest compilation so far of optical plateaus. We discover the 3D fundamental plane relation at optical wavelengths using this sample. This correlation is between the rest-frame time at the end of the plateau emission, ${T}_{\mathrm{opt}}^{* }$, its optical luminosity, Lopt, and the peak in the optical prompt emission, Lpeak,opt, thus resembling the three-dimensional (3D) X-ray fundamental plane (the so-called 3D Dainotti relation). We correct our sample for redshift evolution and selection effects, discovering that this correlation is indeed intrinsic to GRB physics. We investigate the rest-frame end-time distributions in X-rays and optical (${T}_{\mathrm{opt}}^{* }$, ${T}_{{\rm{X}}}^{* }$), and conclude that the plateau is achromatic only when selection biases are not considered. We also investigate if the 3D optical correlation may be a new discriminant between optical GRB classes and find that there is no significant separation between the classes compared to the Gold sample plane after correcting for evolution. © 2022. The Author(s). Published by the American Astronomical Society.

Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (>2 s) duration are produced by the core-collapse of massive stars, those of short (< 2 s) duration by the merger of two neutron stars (NSs). A third class of events with hybrid high-energy properties was identified, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented. Here we report observations of the exceptionally bright GRB211211A that classify it as a hybrid event and constrain its distance scale to only 346 Mpc. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (~1E42 erg/s) kilonova possibly formed in the ejecta of a compact binary merger., Comment: final version, including supplementary methods

A significant fraction (30\%) of well-localized short gamma-ray bursts (sGRBs) lack a coincident host galaxy. This leads to two main scenarios: \textit{i}) that the progenitor system merged outside of the visible light of its host, or \textit{ii}) that the sGRB resided within a faint and distant galaxy that was not detected by follow-up observations. Discriminating between these scenarios has important implications for constraining the formation channels of neutron star mergers, the rate and environments of gravitational wave sources, and the production of heavy elements in the Universe. In this work, we present the results of our observing campaign targeted at 31 sGRBs that lack a putative host galaxy. Our study effectively doubles the sample of well-studied sGRB host galaxies, now totaling 72 events of which $28\%$ lack a coincident host to deep limits ($r$\,$\gtrsim$\,$26$ or $F110W$\,$\gtrsim$\,$27$ AB mag), and represents the largest homogeneously selected catalog of sGRB offsets to date. We find that 70\% of sub-arcsecond localized sGRBs occur within 10 kpc of their host's nucleus, with a median projected physical offset of $5.6$ kpc. Using this larger population, we discover an apparent redshift evolution in their locations: bursts at low-$z$ occur at $2\times$ larger offsets compared to those at $z$\,$>$\,$0.5$. This evolution could be due to a physical evolution of the host galaxies themselves or a bias against faint high-$z$ galaxies. Furthermore, we discover a sample of hostless sGRBs at $z$\,$\gtrsim$\,$1$ that are indicative of a larger high-$z$ population, constraining the redshift distribution and disfavoring log-normal delay time models., Comment: Accepted by MNRAS

Gamma-ray bursts (GRBs) are fascinating events due to their panchromatic nature. We study optical plateaus in GRB afterglows via an extended search into archival data. We comprehensively analyze all published GRBs with known redshifts and optical plateaus observed by many ground-based telescopes (e.g., Subaru Telescope, RATIR) around the world and several space-based observatories such as the Neil Gehrels Swift Observatory. We fit 500 optical light curves (LCs), showing the existence of the plateau in 179 cases. This sample is 75% larger than the previous one (arXiv:2105.10717), and it is the largest compilation so far of optical plateaus. We discover the 3D fundamental plane relation at optical wavelengths using this sample. This correlation is between the rest-frame time at the end of the plateau emission, $T^{*}_{\rm opt}$, its optical luminosity, $L_{\rm opt}$, and the peak in the optical prompt emission, $L_{\rm peak, opt}$, thus resembling the three-dimensional (3D) X-ray fundamental plane relation (arXiv:1604.06840). We correct our sample for redshift evolution and selection effects, discovering that this correlation is indeed intrinsic to GRB physics. We investigate the rest-frame end time distributions in X-rays and optical ($T^{*}_{\rm opt}$, $T^{*}_{\rm X}$), and conclude that the plateau is achromatic only when selection biases are not considered. We also investigate if the 3D optical correlation may be a new discriminant between optical GRB classes and find that there is no significant separation between the classes compared to the Gold sample plane after correcting for evolution., Comment: 27 pages, 9 figures, 4 tables. Accepted for publication in ApJS. Reworded one sentence for clarity

A significant fraction (30 per cent) of well-localized short gamma-ray bursts (sGRBs) lack a coincident host galaxy. This leads to two main scenarios: (i) that the progenitor system merged outside of the visible light of its host, or (ii) that the sGRB resided within a faint and distant galaxy that was not detected by follow-up observations. Discriminating between these scenarios has important implications for constraining the formation channels of neutron star mergers, the rate and environments of gravitational wave sources, and the production of heavy elements in the Universe. In this work, we present the results of our observing campaign targeted at 31 sGRBs that lack a putative host galaxy. Our study effectively doubles the sample of well-studied sGRB host galaxies, now totaling 72 events of which 28 per cent lack a coincident host to deep limits (r ≳ 26 or F110W ≳ 27 AB mag), and represents the largest homogeneously selected catalogue of sGRB offsets to date. We find that 70 per cent of sub-arcsecond localized sGRBs occur within 10 kpc of their host’s nucleus, with a median projected physical offset of 5.6 kpc. Using this larger population, we discover an apparent redshift evolution in their locations: bursts at low-z occur at 2 × larger offsets compared to those at z > 0.5. This evolution could be due to a physical evolution of the host galaxies themselves or a bias against faint high-z galaxies. Furthermore, we discover a sample of hostless sGRBs at z ≳ 1 that are indicative of a larger high-z population, constraining the redshift distribution and disfavoring lognormal delay time models. © 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

The mafic-ultramafic zoned deposit, in the northern part of the Koryak-Kamchatka Platinum Belt, contains lode platinum mineralisation. The outcrops are crossed by the Snegovaya River, which hosts placer platinum-group minerals occurrences. The primary PGM assemblage is typical for Ural-Alaskan type complexes, dominated by Ir-rich isoferroplatinum which occurs as small euhedral inclusions within chromite. Secondary assemblages form alteration rims around isoferroplatinum or occupy fractures in chromite. The PGM assemblages of the Snegovaya River placer occurrences are comparable with those of the lode chromitites with a predominance of Ir-rich isoferroplatinum and secondary alloys, including tetraferroplatinum, tulameenite, and an unnamed Fe3Pt compound. Similarities between lode and placer mineralisation indicate that the Epilchik complex was the dominant source for the placers. Alteration of isoferroplatinum to secondary intermetallic compounds occurred via progressive development of reduced conditions as a result of serpentinisation. Subsequent pervasive As-mineralisation redistributed PGEs, and a final mineralising pulse deposited sporadic native gold and Pt telluride minerals. A comparison of key mineralogical and physical features between the Epilchik complex and other Ural-Alaskan type complexes is used to determine the economic potential for placers along the Snegovaya River. The occurrences associated with the Epilchik complex are considered prospective for high volume and economic grade accumulations of PGE., The mafic-ultramafic zoned deposit, in the northern part of the Koryak-Kamchatka Platinum Belt, contains lode platinum mineralisation. The outcrops are crossed by the Snegovaya River, which hosts placer platinum-group minerals occurrences. The primary PGM assemblage is typical for Ural-Alaskan type complexes, dominated by Ir-rich isoferroplatinum which occurs as small euhedral inclusions within chromite. Secondary assemblages form alteration rims around isoferroplatinum or occupy fractures in chromite. The PGM assemblages of the Snegovaya River placer occurrences are comparable with those of the lode chromitites with a predominance of Ir-rich isoferroplatinum and secondary alloys, including tetraferroplatinum, tulameenite, and an unnamed Fe3Pt compound. Similarities between lode and placer mineralisation indicate that the Epilchik complex was the dominant source for the placers. Alteration of isoferroplatinum to secondary intermetallic compounds occurred via progressive development of reduced conditions as a result of serpentinisation. Subsequent pervasive As-mineralisation redistributed PGEs, and a final mineralising pulse deposited sporadic native gold and Pt telluride minerals. A comparison of key mineralogical and physical features between the Epilchik complex and other Ural-Alaskan type complexes is used to determine the economic potential for placers along the Snegovaya River. The occurrences associated with the Epilchik complex are considered prospective for high volume and economic grade accumulations of PGE.

We report on observations of the candidate Be/X-ray binary IGR J18219$-$1347 with \textit{Swift}/XRT, \textit{NuSTAR}, and \textit{NICER} during Type-I outbursts in March and June 2020. Our timing analysis revealed the spin period of a neutron star with $P_\textrm{spin}=52.46$ s. This periodicity, combined with the known orbital period of $72.4$ d, indicates that the system is a BeXRB. Furthermore, by comparing the infrared counterpart's spectral energy distribution to known BeXRBs, we confirm this classification and set a distance of approximately $10-15$ kpc for the source. The source's broadband X-ray spectrum ($1.5-50$ keV) is described by an absorbed power-law with photon index $\Gamma$\,$\sim$\,$0.5$ and cutoff energy at $\sim$\,$13$ keV., Comment: Revised manuscript. Accepted to ApJ

We present optical and near-infrared photometric observations of GRB 191016 with the COATLI, DDOTI and RATIR ground-based telescopes over the first three nights. We present the temporal evolution of the optical afterglow and describe 5 different stages that were not completely characterized in previous works, mainly due to scarcity of data points to accurately fit the different components of the optical emission. After the end of the prompt gamma-ray emission, we observed the afterglow rise slowly in the optical and near-infrared (NIR) wavelengths and peak at around T+1450s in all filters. This was followed by an early decay, a clear plateau from T+5000s to T+11000s, and then a regular late decay. We also present evidence of the jet break at later times, with a temporal index in good agreement with the temporal slope obtained from X-ray observations. Although many of the features observed in the optical light curves of GRBs are usually well explained by a reverse shock (RS) or forward shock(FS), the shallowness of the optical rise and enhanced peak emission in the GRB191016A afterglow is not well-fitted by only a FS or a RS. We propose a theoretical model which considers both of these components and combines an evolving FS with a later embedded RS and a subsequent late energy injection from the central engine activity. We use this model to successfully explain the temporal evolution of the light curves and discuss its implications on the fireball properties., Comment: 15 pages, 5 figures, 7 Tables, Submitted to MNRAS

We report the results of our follow-up campaign for the neutron star - black hole (NSBH) merger GW200115 detected during the O3 run of the Advanced LIGO and Advanced Virgo detectors. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering ~20% of the total probability area down to a limiting magnitude of $w$=20.5 AB at ~23 h after the merger. Our search for counterparts returns a single candidate (AT2020aeo), likely not associate to the merger. In total, only 25 sources of interest were identified by the community and later discarded as unrelated to the GW event. We compare our upper limits with the emission predicted by state-of-the-art kilonova simulations and disfavor high mass ejecta (>0.1$M_{\odot}$), indicating that the spin of the system is not particularly high. By combining our optical limits with gamma-ray constraints from $Swift$ and $Fermi$, we disfavor the presence of a standard short duration burst for viewing angles $\lesssim$15 deg from the jet axis. Our conclusions are however limited by the large localization region of this GW event, and accurate prompt positions remain crucial to improving the efficiency of follow-up efforts., Comment: 6 pages, 4 figures, accepted for publication ApJ

We present the results of a multiwavelength campaign of FRB 20201124A, the third closest repeating fast radio burst recently localized in a nearby (z=0.0978) galaxy. Deep VLA observations led to the detection of quiescent radio emission, also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of $\gtrsim$ 1 arcsec and locate it at the position of the FRB, within an error of 0.2 arcsec. EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate of $\approx 10\ {\rm M}_\odot {\rm yr}^{-1}$. The surface star formation rate at the location of FRB 20201124A is two orders of magnitude larger than typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a new-born magnetar produced from a SN explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT and Chandra campaign are consistent with a magnetar scenario., Comment: Accepted by A&A letters

We present optical follow-up observations with the DDOTI telescope of gravitational-wave events detected during the Advanced LIGO and Advanced Virgo O3 observing run. DDOTI is capable of responding to an alert in a few minutes, has an instantaneous field of about 69 deg$^{2}$, and obtains $10\sigma$ upper limits of $w_{\rm lim}=18.5$ to 20.5 AB mag in 1000~s of exposure, depending on the conditions. We observed 54\% (26 out of 48) of the unretracted gravitational-wave alerts and did not find any electromagnetic counterparts. We compare our upper limits to various possible counterparts: the kilonova AT~2017gfo, models of radioactive- and magnetar-powered kilonovae, short gamma-ray burst afterglows, and AGN flares. Although the large positional uncertainties of GW sources do not allow us to place strong constraints during O3, DDOTI observations of well-localized GW events in O4 and beyond could meaningfully constrain models of compact binary mergers. We show that DDOTI is able to detect kilonovae similar to AT~2017gfo up to about 200~Mpc and magnetar-powered kilonovae up to 1~Gpc. We calculate that nearby ($\lesssim$200 Mpc) afterglows have a high chance ($\approx$70\%) to be detected by rapid ($\lesssim$3 hours) DDOTI observations if observed on-axis, whereas off-axis afterglows are unlikely to be seen. Finally, we suggest that long-term monitoring of massive BBH events with DDOTI could confirm or rule out late AGN flares associated with these events., Comment: 26 pages, 5 figures. Accepted for publication in MNRAS

Platinum-group elements (PGE) and gold are a promising tool to assess the processes of mantle melting beneath the subduction zones. However, fractionation processes in magmas inevitably overwrite the initial metal budgets of magmas, making constraints on the melting processes inconclusive. Moreover, little is still known about the geochemical behavior of a particular metal in a single arc magmatic system, from mantle melting towards magma solidification. Here we compare noble metals in lavas from several eruptions of the Tolbachik volcano (Kamchatka arc) to better understand the effects of magma differentiation, estimate primary melt compositions and make constraints on the mantle melting. We show that Ir, Ru, Rh and, to a lesser extent, Pt are compatible during magmatic differentiation. The pronounced incompatible behavior of Cu and Pd, observed in Tolbachik magmas, rules out the significant influence of sulfide melts on the early magmatic evolution in this particular case. Gold is also incompatible during magmatic differentiation; however, its systematics can be affected by the inferred gold recycling in the plumbing system of Tolbachik. Although the Tolbachik lavas show only slightly higher PGE fractionation than in MORB, a notable negative Ru anomaly (higher Pt/Ru and Ir/Ru) is observed. We attribute this to be a result of greater oxidation in the subarc mantle (by 1–4 log units), which promotes crystallization of Ru-bearing phases such as Fe3+-rich Cr-spinel and laurite. The estimated Pd contents for the parental melt of the Tolbachik lavas approaches 6.5 ppb. This is several times higher than reported MORB values (1.5 ± 0.5 ppb), suggesting the enrichment of Pd in the mantle wedge. Our results highlight the influence of the subduction-related processes and mantle wedge refertilization on the noble metal budgets of arc magmas.

We present optical and near-infrared photometric observations of GRB 191016 with the COATLI, DDOTI and RATIR ground-based telescopes over the first three nights. We present the temporal evolution of the optical afterglow and describe 5 different stages that were not completely characterized in previous works, mainly due to scarcity of data points to accurately fit the different components of the optical emission. After the end of the prompt gamma-ray emission, we observed the afterglow rise slowly in the optical and near-infrared (NIR) wavelengths and peak at around T+1450s in all filters. This was followed by an early decay, a clear plateau from T+5000s to T+11000s, and then a regular late decay. We also present evidence of the jet break at later times, with a temporal index in good agreement with the temporal slope obtained from X-ray observations. Although many of the features observed in the optical light curves of GRBs are usually well explained by a reverse shock (RS) or forward shock(FS), the shallowness of the optical rise and enhanced peak emission in the GRB191016A afterglow is not well-fitted by only a FS or a RS. We propose a theoretical model which considers both of these components and combines an evolving FS with a later embedded RS and a subsequent late energy injection from the central engine activity. We use this model to successfully explain the temporal evolution of the light curves and discuss its implications on the fireball properties., Comment: 15 pages, 5 figures, 7 Tables, Submitted to MNRAS

We report on observations of the candidate Be/X-ray binary IGR J18219$-$1347 with \textit{Swift}/XRT, \textit{NuSTAR}, and \textit{NICER} during Type-I outbursts in March and June 2020. Our timing analysis revealed the spin period of a neutron star with $P_\textrm{spin}=52.46$ s. This periodicity, combined with the known orbital period of $72.4$ d, indicates that the system is a BeXRB. Furthermore, by comparing the infrared counterpart's spectral energy distribution to known BeXRBs, we confirm this classification and set a distance of approximately $10-15$ kpc for the source. The source's broadband X-ray spectrum ($1.5-50$ keV) is described by an absorbed power-law with photon index $\Gamma$\,$\sim$\,$0.5$ and cutoff energy at $\sim$\,$13$ keV., Comment: Revised manuscript. Accepted to ApJ

We report the results of our follow-up campaign for the neutron star - black hole (NSBH) merger GW200115 detected during the O3 run of the Advanced LIGO and Advanced Virgo detectors. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering ~20% of the total probability area down to a limiting magnitude of $w$=20.5 AB at ~23 h after the merger. Our search for counterparts returns a single candidate (AT2020aeo), likely not associate to the merger. In total, only 25 sources of interest were identified by the community and later discarded as unrelated to the GW event. We compare our upper limits with the emission predicted by state-of-the-art kilonova simulations and disfavor high mass ejecta (>0.1$M_{\odot}$), indicating that the spin of the system is not particularly high. By combining our optical limits with gamma-ray constraints from $Swift$ and $Fermi$, we disfavor the presence of a standard short duration burst for viewing angles $\lesssim$15 deg from the jet axis. Our conclusions are however limited by the large localization region of this GW event, and accurate prompt positions remain crucial to improving the efficiency of follow-up efforts., Comment: 6 pages, 4 figures, accepted for publication ApJ

We present the results of a multiwavelength campaign of FRB 20201124A, the third closest repeating fast radio burst recently localized in a nearby (z=0.0978) galaxy. Deep VLA observations led to the detection of quiescent radio emission, also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of $\gtrsim$ 1 arcsec and locate it at the position of the FRB, within an error of 0.2 arcsec. EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate of $\approx 10\ {\rm M}_\odot {\rm yr}^{-1}$. The surface star formation rate at the location of FRB 20201124A is two orders of magnitude larger than typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a new-born magnetar produced from a SN explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT and Chandra campaign are consistent with a magnetar scenario., Comment: Accepted by A&A letters

We present optical follow-up observations with the DDOTI telescope of gravitational-wave events detected during the Advanced LIGO and Advanced Virgo O3 observing run. DDOTI is capable of responding to an alert in a few minutes, has an instantaneous field of about 69 deg$^{2}$, and obtains $10\sigma$ upper limits of $w_{\rm lim}=18.5$ to 20.5 AB mag in 1000~s of exposure, depending on the conditions. We observed 54\% (26 out of 48) of the unretracted gravitational-wave alerts and did not find any electromagnetic counterparts. We compare our upper limits to various possible counterparts: the kilonova AT~2017gfo, models of radioactive- and magnetar-powered kilonovae, short gamma-ray burst afterglows, and AGN flares. Although the large positional uncertainties of GW sources do not allow us to place strong constraints during O3, DDOTI observations of well-localized GW events in O4 and beyond could meaningfully constrain models of compact binary mergers. We show that DDOTI is able to detect kilonovae similar to AT~2017gfo up to about 200~Mpc and magnetar-powered kilonovae up to 1~Gpc. We calculate that nearby ($\lesssim$200 Mpc) afterglows have a high chance ($\approx$70\%) to be detected by rapid ($\lesssim$3 hours) DDOTI observations if observed on-axis, whereas off-axis afterglows are unlikely to be seen. Finally, we suggest that long-term monitoring of massive BBH events with DDOTI could confirm or rule out late AGN flares associated with these events., Comment: 26 pages, 5 figures. Accepted for publication in MNRAS

We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg$^2$, and an estimated distance of ~ 240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of $w$ = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescope (LDT), whereas promising candidate counterparts were characterized through multi-colour photometry with the Reionization and Transients InfraRed (RATIR) and spectroscopy with the Gran Telescopio de Canarias (GTC). We use our optical and near-infrared limits in conjunction with the upper limits obtained by the community to constrain the possible electromagnetic counterparts associated with the merger. A gamma-ray burst seen along its jet's axis is disfavoured by the multi-wavelength dataset, whereas the presence of a burst seen at larger viewing angles is not well constrained. Although our observations are not sensitive to a kilonova similar to AT2017gfo, we can rule out high-mass (> 0.1 M$_{\odot}$) fast-moving (mean velocity >= 0.3c) wind ejecta for a possible kilonova associated with this merger., Comment: 17 pages, 11 figures, 5 tables; updated acknowledgement section. Accepted for publication in MNRAS (10 September 2020)

We present a detailed multi-wavelength analysis of two short Gamma-Ray Bursts (sGRBs) detected by the Neil Gehrels Swift Observatory: GRB 160624A at $z=0.483$ and GRB 200522A at $z=0.554$. These sGRBs demonstrate very different properties in their observed emission and environment. GRB 160624A is associated to a late-type galaxy with an old stellar population ($\approx$3 Gyr) and moderate on-going star formation ($\approx$1 $M_{\odot}$ yr$^{-1}$). Hubble and Gemini limits on optical/nIR emission from GRB 160624A are among the most stringent for sGRBs, leading to tight constraints on the allowed kilonova properties. In particular, we rule out any kilonova brighter than AT2017gfo, disfavoring large masses of wind ejecta ($\lesssim$0.03 $M_\odot$). In contrast, observations of GRB 200522A uncovered a luminous ($L_\textrm{F125W}\approx 10^{42}$ erg s$^{-1}$ at 2.3~d) and red ($r-H\approx 1.3$ mag) counterpart. The red color can be explained either by bright kilonova emission powered by the radioactive decay of a large amount of wind ejecta (0.03 $M_\odot$ $\lesssim$ $M$ $\lesssim$ 0.1 $M_\odot$) or moderate extinction, $E(B-V)\approx0.1-0.2$ mag, along the line of sight. The location of this sGRB in the inner regions of a young ($\approx$0.1 Gyr) star-forming ($\approx$2-6 $M_{\odot}$ yr$^{-1}$) galaxy and the limited sampling of its counterpart do not allow us to rule out dust effects as contributing, at least in part, to the red color., Comment: MNRAS, In Press

The transition from prompt to the afterglow emission is one of the most exciting and least understood phases in gamma-ray bursts (GRBs). Correlations among optical, X-ray and gamma-ray emission in GRBs have been explored, to attempt to answer whether the earliest optical emission comes from internal and/or external shocks. We present optical photometric observations of GRB 180325A collected with the TAROT and RATIR ground-based telescopes. These observations show two strong optical flashes with separate peaks at $\sim50\;$s and $\sim120\;$s, followed by a temporally extended optical emission. We also present X-rays and gamma-ray observations of GRB 180325A, detected by the Burst Alert Telescope (BAT) and X-ray Telescope (XRT), on the Neil Gehrels Swift observatory, which both observed a narrow flash at $\sim80\;$s. We show that the prompt gamma- and X-ray early emission shares similar temporal and spectral features consistent with internal dissipation within the relativistic outflow (e.g. by internal shocks or magnetic reconnection), while the early optical flashes are likely generated by the reverse shock that decelerates the ejecta as it sweeps up the external medium., Comment: Accepted for publication in ApJ

We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg$^2$, and an estimated distance of ~ 240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of $w$ = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescope (LDT), whereas promising candidate counterparts were characterized through multi-colour photometry with the Reionization and Transients InfraRed (RATIR) and spectroscopy with the Gran Telescopio de Canarias (GTC). We use our optical and near-infrared limits in conjunction with the upper limits obtained by the community to constrain the possible electromagnetic counterparts associated with the merger. A gamma-ray burst seen along its jet's axis is disfavoured by the multi-wavelength dataset, whereas the presence of a burst seen at larger viewing angles is not well constrained. Although our observations are not sensitive to a kilonova similar to AT2017gfo, we can rule out high-mass (> 0.1 M$_{\odot}$) fast-moving (mean velocity >= 0.3c) wind ejecta for a possible kilonova associated with this merger., Comment: 17 pages, 11 figures, 5 tables; updated acknowledgement section. Accepted for publication in MNRAS (10 September 2020)

We investigate the prompt emission and the afterglow properties of short-duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012-2015, observed by several multiwavelength facilities including the Gran Canarias Telescope 10.4 m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL-SPI-ACS, Swift-BAT, and Fermi-GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1-10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A, and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB 130603B, our new afterglow photometric data constrain the pre-jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new and previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for eight other sGRBs we are able to: place tight constraints on the non-detection of the afterglow, host galaxy, or any underlying 'kilonova' emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.

Wide-field optical surveys have begun to uncover large samples of fast (trise ≲ 5 d), luminous (Mpeak < -18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at lowredshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of nearrelativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 1014 cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although thiswould require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.

Astrophotonics is the application of versatile photonic technologies to channel, manipulate, and disperse guided light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. The developments and demands from the telecommunication industry have driven a major boost in photonic technology and vice versa in the last 40 years. The photonic platform of guided light in fibers and waveguides has opened the doors to next-generation instrumentation for both ground- and space-based telescopes in optical and near/mid-IR bands, particularly for the upcoming extremely large telescopes (ELTs). The large telescopes are pushing the limits of adaptive optics to reach close to a near-diffraction-limited performance. The photonic devices are ideally suited for capturing this AO-corrected light and enabling new and exciting science such as characterizing exoplanet atmospheres. The purpose of this white paper is to summarize the current landscape of astrophotonic devices and their scientific impact, highlight the key issues, and outline specific technological and organizational approaches to address these issues in the coming decade and thereby enable new discoveries as we embark on the era of extremely large telescopes.

Wide-field optical surveys have begun to uncover large samples of fast (t(rise) less than or similar to 5 d), luminous (M-peak < 18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 10 (14) cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.

The early optical emission of gamma-ray bursts gives an opportunity to understand the central engine and first stages of these events. About 30\% of GRBs present flares whose origin is still a subject of discussion. We present optical photometry of GRB 180620A with the COATLI telescope and RATIR instrument. COATLI started to observe from the end of prompt emission at $T+39.3$~s and RATIR from $T+121.4$~s. We supplement the optical data with the X-ray light curve from \emph{Swift}/XRT. %The optical and X-ray light curves show very unusual behavior with features clearly beyond the standard fireball model. We observe an optical flare from $T+110$ to $T+550$~s, with a temporal index decay $\alpha_\mathrm{O,decay}=1.32\pm 0.01$, and a $\Delta t/t=1.63$, which we interpret as the signature of a reverse shock component. After the initial normal decay the light curves show a long plateau from $T+500$ to $T+7800$~s both in X-rays and the optical before decaying again after an achromatic jet break at $T+7800$~s. Fluctuations are seen during the plateau phase in the optical. Adding to the complexity of GRB afterglows, the plateau phase (typically associated with the coasting phase of the jet) is seen in this object after the ``normal'' decay phase (emitted during the deceleration phase of the jet) and the jet break phase occurs directly after the plateau. We suggest that this sequence of events can be explained by a rapid deceleration of the jet with $t_d\lesssim 40$ s due to the high density of the environment ($\approx 100$ cm$^{-3}$) followed by reactivation of the central engine which causes the flare and powers the plateau phase., Comment: 13 pages, 2 figures, 2 tables, submitted to ApJ

Astrophotonics is the application of versatile photonic technologies to channel, manipulate, and disperse guided light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. The developments and demands from the telecommunication industry have driven a major boost in photonic technology and vice versa in the last 40 years. The photonic platform of guided light in fibers and waveguides has opened the doors to next-generation instrumentation for both ground- and space-based telescopes in optical and near/mid-IR bands, particularly for the upcoming extremely large telescopes (ELTs). The large telescopes are pushing the limits of adaptive optics to reach close to a near-diffraction-limited performance. The photonic devices are ideally suited for capturing this AO-corrected light and enabling new and exciting science such as characterizing exoplanet atmospheres. The purpose of this white paper is to summarize the current landscape of astrophotonic devices and their scientific impact, highlight the key issues, and outline specific technological and organizational approaches to address these issues in the coming decade and thereby enable new discoveries as we embark on the era of extremely large telescopes., Comment: Astro2020 APC white paper, Submitted to the National Academy of Sciences for Astro2020 Decadal Survey, 9 pages (excluding references) and 3 figures

With the epochal first detection of gravitational waves from a binary neutron star (NS) merger with the GW170817 event, and its direct confirmation that NS-NS mergers are significant sources of the of the r-process nucleosynthesis of heavy elements, an immense new arena for prompt EM (X-rays through IR and radio) studies of fundamental physics has been opened. Over the next decade, GW observatories will expand in scale and sensitivity so the need for facilities that can provide prompt, high sensitivity, broad-band EM followup becomes more urgent. NS-NS or NS-black hole (BH) mergers will be instantly recognized (and announced) by the LIGO-international collaboration. LSST will be a prime resource for rapid tiling of what will usually be large (~10-100 degree squared) error boxes. X-ray through IR Telescopes in space with (nearly) full-sky access that can rapidly image and tile are crucial for providing the earliest imaging and spectroscopic studies of the kilonova emission immediately following NS-NS mergers. The Time-domain Spectroscopic Observatory (TSO) is a proposed Probe-class 1.3 m telescope at L2, with imaging and spectroscopy (R = 200, 1800) in 4 bands (0.3 - 5 micron) and rapid slew capability to 90% of sky. TSO nUV-mid-IR spectra will enable new constraints on NS structure and nucleosynthesis., Comment: Science White Paper for the US Astro 2020 Decadal Survey

Long gamma-ray bursts (GRBs) are the most luminous known electromagnetic radiation sources in the Universe for the 3 to 300 sec of their prompt flashes (isotropic X/ gamma-ray luminosities up to 10^53 ergs/sec). Their afterglows have first day rest-frame UV/optical absolute magnitudes AB = -30 to -23. This luminous continuum nUV-nIR back-light provides the ultimate probe of the SFR(z) back to the first Pop III to II.5 stars, expected to be massive and GRB progenitors. GRB afterglow spectra in the first 1 to 3 hours will directly measure their host galaxy ionization fraction x_i vs. z in the Epoch of Reionization (EOR), tracing the growth of structure. Only 28% of Swift GRBs have measured redshifts due to limited followup at R, J >21. Some ~25% of GRBs are optically dark due to dust absorption in their host galaxies, but those with low NH in their X-ray spectra are likely at z >7. Current 8-10m telescopes and coming ELTs cannot pursue optically dark GRBs promptly, nor can JWST or WFIRST slew within 0.5 to 1 days of a GRB. The Time-domain Spectroscopic Observatory (TSO) is a proposed Probe-class 1.3m telescope at L2, with imaging and spectroscopy (R = 200, 1800) in 4 bands (0.3 to 5um) and rapid slew capability to 90% of sky. TSO would finally utilize z > 6 to 12 GRBs as the most direct probe of the SFR(z), EOR(z), and possibly the first direct detection of the core collapse of the very first (Pop III) stars., Comment: 5 pages, 3 figures, Science White Paper submitted to the Astro2020 Decadal Survey

Time-domain Astrophysics (TDA), a foundation of Astronomy, has become a major part of current and projected (2020s) astrophysics. While much has been derived from temporal measures of flux and color, the real physics comes from spectroscopy. With LSST coming on line in 2022, with TDA as one of its original drivers, the deluge of Transients and new types of variables will be truly astronomical. With multi-wavelength targeted EM surveys and multi-messenger (e.g. LIGO-international and advanced ICECUBE), and the possibility of full-sky and full-time X-ray imagers, the discovery of new Transients and Variables will flood telescopes on the ground and in space, and this just for multi-band imaging without spectroscopy. In this White Paper we briefly summarize several long-standing major science objectives that can be realized with TDA imaging and spectroscopy (near UV to mid IR) from space. We provide a brief description of how these can be achieved with the Time-domain Spectroscopic Observatory (TSO), a Probe-Class mission concept that ELTs on the ground and Flagship missions in space can not achieve on their own., Comment: Science White Paper submitted (edited) to Astro2020 Decadal Survey. 4 pages, 2 figures, 2 Tables

We present observations of the possible short GRB 180418A in $\gamma$-rays, X-rays, and in the optical. Early optical photometry with the TAROT and RATIR instruments show a bright peak ($\approx$ 14.2 AB mag) between $T+28$ and $T+90$ seconds that we interpret as the signature of a reversal shock. Later observations can be modeled by a standard forward shock model and show no evidence of jet break, allowing us to constrain the jet collimation to $\theta_j> 7^\circ$. Using deep late-time optical observations we place an upper limit of $r>24$ AB mag on any underlying host galaxy. The detection of the afterglow in the \textit{Swift} UV filters constrains the GRB redshift to $z<1.3$ and places an upper bound on the $\gamma$-ray isotropic equivalent energy $E_{\rm{\gamma,iso}} < 3 \times 10^{51}$ erg. The properties of this GRB (e.g. duration, hardness ratio, energetic, and environment) lie at the intersection between short and long bursts, and we can not conclusively identify its type. We estimate that the probability that it is drawn from the population of short GRBs is 10\%-30\%., Comment: Accepted por publication in ApJ

The ubiquitous variability of quasars across a wide range of wavelengths and timescales encodes critical information about the structure and dynamics of the circumnuclear emitting regions that are too small to be directly resolved, as well as detailed underlying physics of accretion and feedback processes in these active supermassive black holes. We emphasize the importance of studying quasar variability with time-domain spectroscopy, focusing on two science cases: (1) reverberation mapping (RM) to measure the broad-line region sizes and black hole masses in distant quasars; (2) spectroscopic follow-up of extreme variability quasars that dramatically change their continuum and broad-line flux within several years. We highlight the need for dedicated optical-infrared spectroscopic survey facilities in the coming decades to accompany wide-area time-domain imaging surveys, including: (1) the next phase of the Sloan Digital Sky Survey (SDSS-V; ~2020-2025), an all-sky, time-domain multi-object spectroscopic survey with 2.5m-class telescopes; (2) the planned Maunakea Spectroscopic Explorer, a dedicated 10m-class spectroscopic survey telescope with a 1.5 sq. deg field-of-view and multiplex of thousands of fibers in both optical and near-IR (J+H) to begin operations in 2029; (3) the Time-domain Spectroscopic Observatory (TSO), a proposed Probe-class ~1.3m telescope at L2, with imaging and spectroscopy (R=200, 1800) in 4 bands (0.3 - 5 micron) and rapid slew capability to 90% of sky, which will extend the coverage of Hbeta to z=8., Comment: Science White Paper for the US Astro 2020 Decadal Survey

We describe the results of principal component analysis (PCA) of up-the-ramp sampled IR array data from the HST WFC3 IR, JWST NIRSpec, and prototype WFIRST WFI detectors. These systems use respectively Teledyne H1R, H2RG, and H4RG-10 near-IR detector arrays with a variety of IR array controllers. The PCA shows that the Legendre polynomials approximate the principal components of these systems (i.e. they roughly diagonalize the covariance matrix). In contrast to the monomial basis that is widely used for polynomial fitting and linearization today, the Legendre polynomials are an orthonormal basis. They provide a quantifiable, compact, and (nearly) linearly uncorrelated representation of the information content of the data. By fitting a few Legendre polynomials, nearly all of the meaningful information in representative WFC3 astronomical datacubes can be condensed from 15 up-the-ramp samples down to 6 compressible Legendre coefficients per pixel. The higher order coefficients contain time domain information that is lost when one projects up-the-ramp sampled datacubes onto 2-dimensional images by fitting a straight line, even if the data are linearized before fitting the line. Going forward, we believe that this time domain information is potentially important for disentangling the various non-linearities that can affect IR array observations, i.e. inherent pixel non-linearity, persistence, burn in, brighter-fatter effect, (potentially) non-linear inter-pixel capacitance (IPC), and perhaps others., Comment: 26 pages, 10 figures, accepted by Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

We present optical photometry of the afterglow of the long GRB 180205A with the COATLI telescope from 217 seconds to about 5 days after the {\itshape Swift}/BAT trigger. We analyse this photometry in the conjunction with the X-ray light curve from {\itshape Swift}/XRT. The late-time light curves and spectra are consistent with the standard forward-shock scenario. However, the early-time optical and X-ray light curves show non-typical behavior; the optical light curve exhibits a flat plateau while the X-ray light curve shows a flare. We explore several scenarios and conclude that the most likely explanation for the early behavior is late activity of the central engine.

We investigate the prompt emission and the afterglow properties of short duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012-2015, observed by several multi-wavelength facilities including the GTC 10.4m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL/SPI/ACS, Swift/BAT and Fermi/GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1-10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB130603B, our new afterglow photometric data constraints the pre jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new as well as previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for 8 other sGRBs we are able to; place tight constraints on the non-detection of the afterglow, host galaxy or any underlying kilonova emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs., Comment: 24 pages, 22 figures, Accepted to MNRAS, 2019 February 19. Received 2019 February 19; in original form 2018 August 30

Wide-field optical surveys have begun to uncover large samples of fast (trise ≲ 5 d), luminous (Mpeak < -18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at lowredshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of nearrelativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 1014 cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although thiswould require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.

We investigate the prompt emission and the afterglow properties of short-duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012-2015, observed by several multiwavelength facilities including the Gran Canarias Telescope 10.4 m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL-SPI-ACS, Swift-BAT, and Fermi-GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1-10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A, and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB 130603B, our new afterglow photometric data constrain the pre-jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new and previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for eight other sGRBs we are able to: place tight constraints on the non-detection of the afterglow, host galaxy, or any underlying 'kilonova' emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.