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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., 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., D.A.K. acknowledges support from Spanish National Research Project RTI2018-098104-J-I00 (GRBPhot). S.Y. and D.L. acknowledge the support by the United States Department of Energy in funding the Science Undergraduate Laboratory Internship (SULI) program. S.Y. gratefully acknowledges the support of the Vagelos Challenge Award at the University of Pennsylvania. R.L.B. acknowledges support from the DGAPA/UNAM IG100820 and the DGAPA/UNAM postdoctoral fellowship. N.F. acknowledges support from the DGAPA/UNAM IN106521. Some of the data used in this paper were acquired with the RATIR instrument, funded by the University of California and NASA Goddard Space Flight Center, and the 1.5-meter Harold L. Johnson telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, operated and maintained by the Observatorio Astronómico Nacional and the Instituto de Astronomía of the Universidad Nacional Autónoma de México. Operations are partially funded by the Universidad Nacional Autónoma de México (DGAPA/PAPIIT IG100414, IT102715, AG100317, IN109418, IG100820, IN106521, and IN105921). We acknowledge the contribution of Leonid Georgiev and Neil Gehrels to the development of RATIR. M.F., L.Z., and A.Z. are grateful for the support from the Scientific Caribbean Foundation. E.S. thanks the Latino Education Advancement Foundation for their support., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of seven compact low-mass star-forming galaxies at redshifts, z,in the range 0.3161-0.4276, with various O3Mg2=[OIII]5007/MgII 2796+2803 and Mg2=MgII 2796/MgII 2803 emission-line ratios. We aim to study the dependence of leaking Lyman continuum (LyC) emission on the characteristics of MgII emission together with the dependences on other indirect indicators of escaping ionizing radiation. LyC emission with escape fractions fesc(LyC)=3.1-4.6 per cent is detected in four galaxies, whereas only 1sigma upper limits of fesc(LyC) in the remaining three galaxies were derived. A strong narrow Ly-alpha emission line with two peaks separated by Vsep~298-592 km/s was observed in four galaxies with detected LyC emission and very weak Ly-alpha emission is observed in galaxies with LyC non-detections. Our new data confirm the tight anti-correlation between fesc(LyC) and Vsep found for previous low-redshift galaxy samples. Vsep remains the best indirect indicator of LyC leakage among all considered indicators. It is found that escaping LyC emission is detected predominantly in galaxies with Mg2>1.3. A tendency of an increase of fesc(LyC) with increasing of both the O3Mg2 and Mg2 is possibly present. However, there is substantial scatter in these relations not allowing their use for reliable prediction of fesc(LyC)., 19 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society. arXiv admin note: substantial text overlap with arXiv:2103.01514

We report a Karl G. Jansky Very Large Array search for redshifted CO(1-0) emission from three HI-absorption-selected galaxies at $z \approx 2$, identified earlier in their CO(3-2) or CO(4-3) emission. We detect CO(1-0) emission from DLA B1228-113 at $z\approx2.1933$ and DLA J0918+1636 at $z\approx2.5848$; these are the first detections of CO(1-0) emission in high-$z$ HI-selected galaxies. We obtain high molecular gas masses, $\rm M_{mol}\approx10^{11}\times(\alpha_{\rm CO}/4.36)\ M_\odot$, for the two objects with CO(1-0) detections, which are a factor of $\approx1.5-2$ lower than earlier estimates. We determine the excitation of the mid$-J$ CO rotational levels relative to the $J=1$ level, r$_{ J1}$, in HI-selected galaxies for the first time, obtaining r$_{\rm 31}=1.00\pm0.20$ and r$_{\rm 41}=1.03\pm0.23$ for DLA J0918+1636, and r$_{\rm 31}=0.86\pm0.21$ for DLA B1228-113. These values are consistent with thermal excitation of the $J=3,4$ levels. The excitation of the $J=3$ level in the HI-selected galaxies is similar to that seen in massive main-sequence and sub-mm galaxies at $z\gtrsim2$, but higher than that in main-sequence galaxies at $z\approx1.5$; the higher excitation of the galaxies at $z\gtrsim2$ is likely to be due to their higher star-formation rate (SFR) surface density. We use Hubble Space Telescope Wide Field Camera 3 imaging to detect the rest-frame near-ultraviolet emission of DLA B1228-113, obtaining an NUV SFR of $4.44\pm0.47$ M$_{\odot}$ yr$^{-1}$, significantly lower than that obtained from the total infrared luminosity, indicating significant dust extinction in the $z\approx2.1933$ galaxy., Comment: 9 pages, 4 figures, and 2 tables. Accepted for publication in ApJL

We constrain the Hubble constant H$_0$ using Fast Radio Burst (FRB) observations from the Australian Square Kilometre Array Pathfinder (ASKAP) and Murriyang (Parkes) radio telescopes. We use the redshift-dispersion measure (`Macquart') relationship, accounting for the intrinsic luminosity function, cosmological gas distribution, population evolution, host galaxy contributions to the dispersion measure (DM$_{\rm host}$), and observational biases due to burst duration and telescope beamshape. Using an updated sample of 16 ASKAP FRBs detected by the Commensal Real-time ASKAP Fast Transients (CRAFT) Survey and localised to their host galaxies, and 60 unlocalised FRBs from Parkes and ASKAP, our best-fitting value of H$_0$ is calculated to be $73_{-8}^{+12}$ km s$^{-1}$ Mpc$^{-1}$. Uncertainties in FRB energetics and DM$_{\rm host}$ produce larger uncertainties in the inferred value of H$_0$ compared to previous FRB-based estimates. Using a prior on H$_0$ covering the 67--74 km s$^{-1}$ Mpc$^{-1}$ range, we estimate a median DM$_{\rm host} = 186_{-48}^{+59}$ km s$^{-1}$ Mpc$^{-1}$, exceeding previous estimates. We confirm that the FRB population evolves with redshift similarly to the star-formation rate. We use a Schechter luminosity function to constrain the maximum FRB energy to be $\log_{10} E_{\rm max}=41.26_{-0.22}^{+0.27}$ erg assuming a characteristic FRB emission bandwidth of 1 GHz at 1.3 GHz, and the cumulative luminosity index to be $\gamma=-0.95_{-0.15}^{+0.18}$. We demonstrate with a sample of 100 mock FRBs that H$_0$ can be measured with an uncertainty of $\pm 2.5$ km s$^{-1}$ Mpc$^{-1}$, demonstrating the potential for clarifying the Hubble tension with an upgraded ASKAP FRB search system. Last, we explore a range of sample and selection biases that affect FRB analyses., Comment: 21 pages, 19 figures, 6 tables, accepted by MNRAS, updated Table 5 and Figure 5

Fast radio bursts (FRBs) are extremely powerful sources of radio waves observed at cosmological distances. We use a sophisticated model of FRB observations -- presented in detail in a companion paper -- to fit FRB population parameters using large samples of FRBs detected by ASKAP and Parkes, including seven sources with confirmed host galaxies. Our fitted parameters demonstrate that the FRB population evolves with redshift in a manner consistent with, or faster than, the star-formation rate (SFR), ruling out a non-evolving population at 99.9\% C.L. Our estimated maximum FRB energy is $\log_{10} E_{\rm max} [{\rm erg}] = 41.84_{-0.18}^{+0.49}$ (68\% C.L.) assuming a 1\,GHz emission bandwidth, with slope of the cumulative luminosity distribution $\gamma=-1.16_{-0.12}^{+0.11}$. We find a log-mean host DM contribution of $145_{-60}^{+64}$\,pc\,cm$^{-3}$ on top of a typical local (ISM and halo) contribution of $\sim80$\,pc\,cm$^{-3}$, which is higher than most literature values. These results are consistent with the model of FRBs arising as the high-energy limit of magnetar bursts, but allow for FRB progenitors that evolve faster than the SFR., Comment: 8 pages, 2 tables, 3 figures. Revised from v1 to include (1+z)^-1 time dilation in FRB rate

We present the first detailed dissection of the circumgalactic medium (CGM) of massive starburst galaxies at z > 2. Our target is a submillimeter galaxy (SMG) at z = 2.674 that has a star formation rate of 1200 $M_\odot$/yr and a molecular gas reservoir of $1.3\times10^{11} M_\odot$. We characterize its CGM with two background QSOs at impact parameters of 93 kpc and 176 kpc. We detect strong HI and metal-line absorption near the redshift of the SMG towards both QSOs, each consisting of three main subsystems spanning over 1500 km/s. The absorbers show remarkable kinematic and metallicity coherence across a separation of 86 kpc. In particular, the cool gas in the CGM of the SMG exhibits high HI column densities ($\log N_{\rm HI}/{\rm cm}^{-2} = 20.2, 18.6$), low metallicities ([M/H] $\approx$ -2.0), and similar radial velocities ($\approx$ -300 km/s). While the HI column densities match previous results on the CGM around QSOs at z > 2, the metallicities are lower by more than an order of magnitude, making it an outlier in the line width$-$metallicity relation of damped Ly$��$ absorbers. The large physical extent, the velocity coherence, the high surface density, and the low metallicity are all consistent with the cool, inflowing, and near-pristine gas streams predicted to penetrate hot massive halos at z > 1.5. We estimate a total gas accretion rate of ~100 $M_\odot$/yr from three such streams, which falls short of the star formation rate but is consistent with simulations. At this rate, it takes about a gigayear to acquire the molecular gas reservoir of the central starburst., ApJ in press. Data files available at https://github.com/fuhaiastro/data

We present a preliminary data release from our multi-year campaign at Keck Observatory to study the host galaxies of a large sample of Swift-era gamma-ray bursts via multi-color ground-based optical imaging and spectroscopy. With over 160 targets observed to date (and almost 100 host detections, most of which have not previously been reported in the literature) our effort represents the broadest GRB host survey to date. While targeting was heterogeneous, our observations span the known diversity of GRBs including short bursts, long bursts, spectrally soft GRBs (XRFs), ultra-energetic GRBs, X-ray faint GRBs, dark GRBs, SN-GRBs, and other sub-classes. We also present a preview of our database (currently available online via a convenient web interface) including a catalog of multi-color photometry, redshifts and line ID’s. Final photometry and reduced imaging and spectra will be available in the near future.

We have been undertaking a systematic survey at 850 $\mu$m based on a sample of four prototypical $z\sim2-3$ enormous Ly$\alpha$ nebulae (ELANe) as well as their megaparsec-scale (Mpc-scale) environments to study the physical connections between ELANe and their coeval dusty submillimeter galaxies (SMGs). By analysing the SCUBA-2 data with self-consistent Monte Carlo simulations to construct the number counts, here, we report on the overabundance of 850 $\mu$m-selected submillimeter sources around all the four ELANe, by a factor of 3.6$\pm$0.6 (weighted average) compared to the blank fields. This suggests that the excessive number of submillimeter sources are likely to be part of the Mpc-scale environment around the ELANe, corroborating the co-evolution scenario for SMGs and quasars; this is a process which may be more commonly observed in the ELAN fields. If the current form of the underlying count models continues toward the fainter end, our results would suggest an excess of the 850 $\mu$m extragalactic background light by a factor of between 2-10, an indication of significant background light fluctuations on the survey scales. Finally, by assuming that all the excessive submillimeter sources are associated with their corresponding ELAN environments, we estimate the SFR densities of each ELAN field, as well as a weighted average of $\Sigma$SFR=1200$\pm$300 $M_\odot$ yr$^{-1}$ Mpc$^{-3}$, consistent with that found in the vicinity of other quasar systems or proto-clusters at similar redshifts; in addition, it is a factor of about 300 greater than the cosmic mean., Comment: 11 pages, 5 pages, A&A in press

More than three-quarters of the baryonic content of the Universe resides in a highly diffuse state that is difficult to detect, with only a small fraction directly observed in galaxies and galaxy clusters

We use MUSE/VLT to conduct a survey of $z\sim3$ physical quasar pairs at close separation with a fast observation strategy. Our aim is twofold: (i) explore the Ly$\alpha$ glow around the faint-end of the quasar population; (ii) take advantage of the combined illumination of a quasar pair to unveil large-scale intergalactic structures extending between the two quasars. Here, we report the results for a quasar pair ($z=3.020,3.008$; $i=21.84,22.15$), separated by 11.6 arcsec (or 89 projected kpc). MUSE reveals filamentary Ly$\alpha$ structures extending between the two quasars with an average surface brightness of SB$_{\rm Ly\alpha}=1.8\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Photoionization models of the constraints in the Ly$\alpha$, HeII, and CIV line emissions show that the emitting structures are intergalactic bridges with an extent between $\sim89$ and up to $\sim600$ kpc. Our models rule out the possibility that the structure extends for $\sim 2.9$ Mpc, i.e., the separation inferred from the uncertain systemic redshift difference of the quasars if the difference was only due to the Hubble flow. At the current spatial resolution and surface brightness limit, the average projected width of an individual bridge is about 35 kpc. We also detect a strong absorption in HI, NV, and CIV along the background sight-line at higher $z$, which we interpret as due to at least two components of cool, metal enriched, and relatively ionized CGM or IGM surrounding the quasar pair. Two additional HI absorbers are detected along both quasar sight-lines at $\sim -900$ and $-2800$ km s$^{-1}$ from the system, with the latter having associated CIV absorption only along the foreground quasar sight-line. The absence of galaxies in the MUSE field of view at the redshifts of these two absorbers suggests that they trace large-scale structures or expanding shells in front of the quasar pair., Comment: 24 Pages, 24 Figures, 6 Appendices; Accepted for publication in A&A

The W. M. Keck Observatory is committed to maintaining the scientific leadership of our observing community by matching our observers' skills and passions in their fields of astronomical science with a continuing dedication by the Observatory and its collaborators to the development of state of the art instrumentation and systems. Our science driven strategic plan guides these developments and informs our plans for the future. In this paper we describe the performance of recently completed new instruments, instrument upgrades, and infrastructure upgrade projects. We also describe the expected performance of projects currently in the development or construction phases. Projects recently completed include a new laser for the Keck II AO system, the upgrade of the spectrograph detector in the OSIRIS instrument, and the upgrade to the telescope control system on the Keck II telescope. Projects in development include an upgrade to the telescope control system on the Keck I telescope, the blue channel of the Keck Cosmic Web Imager, the red channel of the Keck Cosmic Web Imager, the Keck Planet Finder, a deployable tertiary mirror for the Keck I telescope, an upgrade to the imager of OSIRIS, a major upgrade to the NIRSPEC instrument, and a fiber feed from the Keck II AO system to NIRSPEC.

We show in this paper why molecular millimeter absorption line searches in DLAs have been unsuccessful. We use CO emission line maps of local galaxies to derive the H2 column density distribution function f(N_H2) at z=0. We show that it forms a natural extension to f(N_HI): the H2 distribution exceeds f(N_HI) at N_H ~ 10^22 cm^-2 and exhibits a power law drop-off with slope ~ -2.5. Approximately 97% of the H2 mass density rho_H2 is in systems above N_H2=10^21 cm^-2. We derive a value rho_H2 = 1.1 x 10^7 h_70 M_sun Mpc^-3, which is ~25% the mass density of atomic hydrogen. Yet, the redshift number density of H2 above this N_H2 limit is only ~3 x 10^-4, a factor 150 lower than that for HI in DLAs at z=0. Furthermore, we show that the median impact parameter between a N_H2>10^21 cm^-2 absorber and the centre of the galaxy hosting the H2 gas is only 2.5 kpc. Based on arguments related to the Schmidt law, we argue that H2 gas above this column density limit is associated with a large fraction of the integral star formation rate density. Even allowing for an increased molecular mass density at higher redshifts, the derived cross-sections indicate that it is very unlikely to identify the bulk of the molecular gas in present quasar absorption lines samples. We discuss the prospects for identifying this molecular mass in future surveys.

The rapid succession of discovery of short--duration hard--spectrum GRBs has led to unprecedented insights into the energetics of the explosion and nature of the progenitors. Yet short of the detection of a smoking gun, like a burst of coincident gravitational radiation or a Li-Paczynski mini-supernova, it is unlikely that a definitive claim can be made for the progenitors. As was the case with long--duration soft--spectrum GRBs, however, the expectation is that a systematic study of the hosts and the locations of short GRBs could begin to yield fundamental clues about their nature. We present the first aggregate study of the host galaxies of short--duration hard--spectrum GRBs. In particular, we present the Gemini--North and Keck discovery spectra of the galaxies that hosted three short GRBs and a moderate--resolution (R~6000) spectrum of a fourth host. We find that these short--hard GRBs originate in a variety of low-redshift (z, 8 pages, 2 figures. Accepted to ApJ

We employ observationally determined intrinsic velocity widths and column densities of damped Lyman-alpha systems at high redshift to investigate the distribution of baryons in protogalaxies within the context of a standard cold dark matter model. We proceed under the assumption that damped Lyman alpha systems represent a population of cold, rotationally supported, protogalactic disks and that the abundance of protogalactic halos is well approximated by a cold dark matter model with critical density and vanishing cosmological constant. Using conditional cross sections to observe a damped system with a given velocity width and column density, we compare observationally inferred velocity width and column density distributions to the corresponding theoretically determined distributions for a variety of disk parameters and CDM normalizations. In general, we find that the observations can not be reproduced by the models for most disk parameters and CDM normalizations. Whereas the column density distribution favors small disks with large neutral gas fraction, the velocity width distribution favors large and thick disks with small neutral gas fraction. The possible resolutions of this problem in the context of this CDM model may be: (1) an increased contribution of rapidly rotating disks within massive dark matter halos to damped Lyman-alpha absorption or (2) the abandoning of simple disk models within this CDM model for damped Lyman-alpha systems at high redshift. Here the first possibility may be achieved by supposing that damped Lya system formation only occurs in halos with fairly large circular velocities and the second possibility may result from a large contribution of mergers and double-disks to damped Lya absorption at high redshift.

The mean metallicity of the thick disk of the Galaxy is 0.5 dex higher than that of the damped Lyman alpha systems. This has been interpreted to argue that stars in the former do not arise out of gas in the latter. Using new metallicity and H I column-density data we show the metal-rich damped systems do contain sufficient baryons at the thick-disk metallicity to account for the stellar masses of thick disks. Comparing our kinematic data with the metallicities we show that damped Lyman alpha systems exhibiting the largest profile velocity widths span a narrow range of high metallicities, while systems with small velocity widths span a wider range of metallicities. This is naturally explained by passage of the damped Lyman alpha sightlines through rapidly rotating disks with negative radial gradients in metallicity. The systematically lower N(H I) of systems with high velocity widths indicates (a) the gaseous disks have centrally located holes, and (b) an apparent inconsistency with the protogalactic clump model for damped Lyman alpha systems. The higher metallicity of systems with low N(H I) further implies that stars rather than gas dominate the baryonic content of the most metal-rich damped systems.

We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs;GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (1054 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB090926A) exceeds the canonical value of 1051erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or a neutrino-driven collapsar, but remain compatible with theoretical expectations for magnetohydrodynamical collapsar models (e.g., the Blandford-Znajek mechanism). Our jet opening angles (θ) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors (Γ0) inferred from the detection of GeV photons imply θΓ0 ≈ 70-90, values which are above those predicted in magnetohydrodynamic models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows at radio wavelengths with the order-of-magnitude improvement in sensitivity offered by the Extended Very Large Array should definitively establish the relativistic energy budgets of these events. © 2011. The American Astronomical Society. All rights reserved.

The O VI absorber at z = 0.2028 detected in the spectrum of the QSO PKS 0312–77 is the strongest discovered so far in the low redshift Universe (logN(OVI) = 14.95±0.05,) and is observed near a Lyman limit system (LLS). We present an analysis of these absorbers and their connection to galaxies based on a combination of FUV and NUV spectra of PKS 0312–77 obtained from FUSE and HST/STIS E140M/E230M and optical imaging and spectroscopy of galaxies in the field. Based on O I/H I and a photoionization model, we find a metallicity of 0.25 solar for the LLS, too enriched to be pristine IGM gas. We find that the gas resulting from the merger of a 0.7L* galaxy (impact parameter of 38 kpc) is the likely origin for the LLS. At −190 km/s from the LLS, another absorber is found with a supersolar metallicity. Outflow from this galaxy is likely responsible for this supersolar, fully ionized absorber. The metallicity variation is a possible evidence for poor mixing of metals on galactic structure as observed in the Milky ...

We review current research related to spectroscopy of gamma-ray burst (GRB) afterglows with particular emphasis on the interstellar medium (ISM) of the galaxies hosting these high redshift events. These studies reveal the physical conditions of star-forming galaxies and yield clues to the nature of the GRB progenitor. We offer a pedagogical review of the experimental design and review current results. The majority of sightlines are characterized by large HI column densities, negligible molecular fraction, the ubiquitous detection of UV pumped fine-structure transitions, and metallicities ranging from 1/100 to nearly solar abundance., Conference procedings for Gamma Ray Bursts 2007 November 5-9, 2007 Santa Fe, New Mexico (8 pages, 4 figures)

With a column density log N(OVI) = 14.95+/-0.05, the OVI absorber at z_abs~0.2028 observed toward the QSO PKS0312-77 (z_em=0.223) is the strongest yet detected at z, Comment: Accepted for publication in the ApJ

Recent observations suggest that global properties of the host galaxies for long-duration gamma-ray bursts (GRBs) are particularly well-suited for creating the massive star progenitors of these GRBs. Motivated by the hypothesis that massive young star clusters located in metal-poor, low-metallicity galaxies are a natural birthsite for GRB progenitors, we present a comparison study of the ISM properties along the sightline toward the super star cluster, NGC1705-1, and those in distant GRB hosts. Using the same set of metal transitions in the UV and applying known ISM structures in NGC1705, we find that NGC1705-1 resembles distant GRB host galaxies in its high neutral gas column, low molecular gas fraction, low metallicity, alpha-element enhancement,and low dust depletion. The lack of molecular gas is due to the enhanced UV radiation field in the starburst environment, consistent with the expectations for GRB progenitors. In addition, the known presence of dense neutral gas clouds at r, 20 pages, including 3 figurs. ApJ in press

We report on observations of a gamma-ray burst (GRB 061126) with an extremely bright (R ~ 12 mag at peak) early-time optical afterglow. The optical afterglow is already fading as a power law 22 seconds after the trigger, with no detectable prompt contribution in our first exposure, which was coincident with a large prompt-emission gamma-ray pulse. The optical--infrared photometric spectral energy distribution is an excellent fit to a power law, but it exhibits a moderate red-to-blue evolution in the spectral index at about 500 s after the burst. This color change is contemporaneous with a switch from a relatively fast decay to slower decay. The rapidly decaying early afterglow is broadly consistent with synchrotron emission from a reverse shock, but a bright forward-shock component predicted by the intermediate- to late-time X-ray observations under the assumptions of standard afterglow models is not observed. Indeed, despite its remarkable early-time brightness, this burst would qualify as a dark burst at later times on the basis of its nearly flat optical-to-X-ray spectral index. Our photometric spectral energy distribution provides no evidence of host-galaxy extinction, requiring either large quantities of grey dust in the host system (at redshift 1.1588 +/- 0.0006, based upon our late-time Keck spectroscopy) or separate physical origins for the X-ray and optical afterglows., Comment: Revised version submitted to ApJ. Contains significantly expanded discussion, an additional figure, and numerous other changes

Even with the renaissance in gamma-ray burst (GRB) research fostered by the Swift satellite, few bursts have both contemporaneous observations at long wavelengths and exquisite observations at later times across the electromagnetic spectrum. We present here contemporaneous imaging with the KAIT robotic optical telescope, dense optical sampling with Lulin, supplemented with infrared data from PAIRITEL and radio to gamma-ray data from the literature. For the first time, we can test the constancy of microphysical parameters in the internal-external shock paradigm and carefully trace the flow of energy from the GRB to the surrounding medium. KAIT data taken P1 minute after the start of GRB 051111 and coinciding with the fading gamma-ray tail of the prompt emission indicate a smooth reinjection of energy into the shock. No color change is apparent in observations beginning similar to 1.5 minutes after the GRB and lasting for the first hour after the burst. There are achromatic flux modulations about the best-fit model at late (t approximate to 10(4) s) times, possibly due to variations in the external density. We find that the host galaxy extinction is well fit by a curve similar to that of the Small Magellanic Cloud. Low visual extinction, A(V) approximate to 0.2 mag, combined with high column densities determined from the X-ray and optical spectroscopy (N-H > 10(21) cm(-2)), indicate a low dust-to-metals ratio and a possible overabundance of the light metals. An apparent small ratio of total to selective extinction (R-V approximate to 2) argues against dust destruction by the GRB. Time constancy of both the IR/optical/UV spectral energy distribution and the soft X-ray absorption suggests that the absorbing material is not local to the GRB., copyright(c)2006 American Astronomical Society

We present a survey for z~3 Lyman break galaxies (LBGs) associated with damped Lyman alpha systems (DLAs) with the primary purpose of determining the DLA-LBG cross-correlation. This paper describes the acquisition and analysis of imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343 sources detected in the field. Spectroscopic observations of 529 LBG candidates using Keck LRIS yielded 339 redshifts. We have conservatively identified 211 z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG identification and present a model of the u'BVRI photometric selection function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break photometric selection technique., Comment: 26 pages, 6 tables, 11 figures, accepted for publication in ApJ

We present early optical photometry and spectroscopy of the afterglow and host galaxy of the bright short-duration gamma-ray burst GRB 130603B discovered by the Swift satellite. Using our Target of Opportunity program on the Gemini South telescope, our prompt optical spectra reveal a strong trace from the afterglow superimposed on continuum and emission lines from the z = 0.3568 ± 0.0005 host galaxy. The combination of a relatively bright optical afterglow (r′ = 21.52 at Δt = 8.4 hr), together with an observed offset of 0.″9 from the host nucleus (4.8 kpc projected distance at z = 0.3568), allow us to extract a relatively clean spectrum dominated by afterglow light. Furthermore, the spatially resolved spectrum allows us to constrain the properties of the explosion site directly, and compare these with the host galaxy nucleus, as well as other short-duration GRB host galaxies. We find that while the host is a relatively luminous (), star-forming (SFR = 1.84 M yr-1) galaxy with almost solar metallicity, the spectrum of the afterglow exhibits weak Ca II absorption features but negligible emission features. The explosion site therefore lacks evidence of recent star formation, consistent with the relatively long delay time distribution expected in a compact binary merger scenario. The star formation rate (SFR; both in an absolute sense and normalized to the luminosity) and metallicity of the host are both consistent with the known sample of short-duration GRB hosts and with recent results which suggest GRB 130603B emission to be the product of the decay of radioactive species produced during the merging process of a neutron-star-neutron-star binary ("kilonova"). Ultimately, the discovery of more events similar to GRB 130603B and their rapid follow-up from 8 m class telescopes will open new opportunities for our understanding of the final stages of compact-objects binary systems and provide crucial information (redshift, metallicity, and chemical content of their explosion site) to characterize the environment of one of the most promising gravitational wave sources. © 2013. The American Astronomical Society. All rights reserved..

Starting with the first detection of an afterglow from a short-duration hard-spectrum gamma-ray burst (SHB) by Swift last year, a growing body of evidence has suggested that SHBs are associated with an older and lower-redshift galactic population than long-soft GRBs and, in a few cases, with large (>~ 10 kpc) projected offsets from the centers of their putative host galaxies. Here we present observations of the field of GRB 060502B, a SHB detected by Swift and localized by the X-ray Telescope (XRT). We find a massive red galaxy at a redshift of z=0.287 at an angular distance of 17.1 arcsec from our revised XRT position. Using associative and probabilistic arguments we suggest that this galaxy hosted the progenitor of GRB 060502B. If true, this offset would correspond to a physical displacement of 73 +- 19 kpc in projection, about twice the largest offset inferred for any SHB to date and almost an order of magnitude larger than a typical long-soft burst offset. Spectra and modeling of the star-formation history of this possible host show it to have undergone a large ancient starburst. If the progenitor of GRB 060502B was formed in this starburst episode, the time of the GRB explosion since birth is tau = 1.3 +- 0.2 Gyr and the minimum kick velocity of the SHB progenitor is v_kick = 55 +- 15 km/s., Accepted to the Astrophysical Journal. 18 pages, 3 figures; expanded discussion of alternative host possibilities

We present early-time optical through infrared photometry of the bright gamma-ray burst GRB 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric dataset allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information on the ultraviolet continuum absorption properties of any sightline outside our Local Group to date. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175-Angstrom feature (while present) is weaker by about a factor of two than when seen under similar circumstances locally. However, the spectral energy distribution is exquisitely fitted by the more general Fitzpatrick & Massa (1990) parameterization of Local-Group extinction, putting it in the same family as some peculiar Milky Way extinction curves. After correcting for this (considerable, A_V = 3.3 +/- 0.4 mag) extinction, GRB 080607 is revealed to have been among the most optically luminous events ever observed, comparable to the naked-eye burst GRB 080319B. Its early peak time (t_rest < 6 s) indicates a high initial Lorentz factor (Gamma > 600), while the extreme luminosity may be explained in part by a large circumburst density. Only because of its early high luminosity could the afterglow of GRB 080607 be studied in such detail in spite of the large attenuation and great distance, making this burst an excellent prototype for the understanding of other highly obscured extragalactic objects, and of the class of "dark" GRBs in particular., Submitted to AJ. 15 pages, 6 tables, 9 figures

Understanding the origin and diversity of emission processes responsible for gamma-ray bursts (GRBs) remains a pressing challenge. While prompt and contemporaneous panchromatic observations have the potential to test predictions of the internal-external shock model, extensive multiband imaging has been conducted for only a few GRBs. We present rich, early-time, multiband data sets for two Swift events, GRB 110205A and GRB 110213A. The former shows optical emission since the early stages of the prompt phase, followed by the steep rising in flux up to 1000s after the burst (t -α with α = -6.13 ± 0.75). We discuss this feature in the context of the reverse-shock scenario and interpret the following single power-law decay as being forward-shock dominated. Polarization measurements, obtained with the RINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the nature of the emitting ejecta. The latter event, instead, displays a very peculiar optical to near-infrared light curve, with two achromatic peaks. In this case, while the first peak is probably due to the onset of the afterglow, we interpret the second peak to be produced by newly injected material, signifying a late-time activity of the central engine. © 2011. The American Astronomical Society. All rights reserved.