Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH (Cluster Lensing and Supernovae with Hubble) clusters, we perform a first pilot study to see whether standardizable candles can ...be used to calibrate cluster mass maps created from strong lensing observations. Such calibrations will be crucial when next-generation Hubble Space Telescope cluster surveys (e.g. Frontier) provide magnification maps that will, in turn, form the basis for the exploration of the high-redshift Universe. We classify SNe using combined photometric and spectroscopic observations, finding two of the three to be clearly of Type Ia and the third probable. The SNe exhibit significant amplification, up to a factor of 1.7 at ... significance (SN-L2). We conducted this as a blind study to avoid fine-tuning of parameters, finding a mean amplification difference between SNe and the cluster lensing models of 0.09 ± 0.09stat ± 0.05sys mag. This impressive agreement suggests no tension between cluster mass models and high-redshift-standardized SNe Ia. However, the measured statistical dispersion of ... = 0.21 mag appeared large compared to the dispersion expected based on statistical uncertainties (0.14). Further work with the SN and cluster lensing models, post-unblinding, reduced the measured dispersion to ... = 0.12. An explicit choice should thus be made as to whether SNe are used unblinded to improve the model, or blinded to test the model. As the lensed SN samples grow larger, this technique will allow improved constraints on assumptions regarding e.g. the structure of the dark matter halo. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT There is now strong evidence that long-duration gamma-ray bursts (LGRBs) are preferentially formed in low-metallicity environments. However, the magnitude of this effect and its functional ...dependence on metallicity have not been well characterized. In our previous paper, we compared the metallicity distribution of LGRB host galaxies to that of star-forming galaxies in the local universe. Here we build upon this work by in effect dividing one distribution by the other, and thus directly determine the relative rate of LGRB formation as a function of metallicity in the low-redshift universe. We find a dramatic cutoff in LGRB formation above a metallicity of in the KK04 scale, with LGRBs forming between 10 and 50 times more frequently per unit star formation below this cutoff than above. Furthermore, our data suggest that the rate of LGRB formation per unit star formation continues to fall above this break. We estimate that the LGRB formation rate per unit star formation may drop by as much as a factor of 100 between one-third solar and solar metallicity.
We detect the optical afterglow and host galaxy of GRB 070714B. Our observations of the afterglow show an initial plateau in the light curve for approximately the first 5-25 minutes, and then ...steepening to a power-law decay with index alpha = 0.86 - 0.10 for the period between 1 and 24 hr postburst. This is consistent with the X-ray light curve which shows an initial plateau followed by a similar subsequent decay. At late time, we detect a host galaxy at the location of the optical transient. Gemini Nod & Shuffle spectroscopic observations of the host show a single emission line at 7167 A which, based on a griz JHK photometric redshift, we conclude is the 3727 A O II line. We therefore find a redshift of z = 0.923. This redshift, as well as a subsequent probable spectroscopic redshift determination of GRB 070429B at z = 0.904 by two other groups significantly exceeds the previous highest spectroscopically confirmed short burst redshift of z = 0.546 for GRB 051221. This dramatically moves back the time at which we know short bursts were being formed and suggests that the present evidence for an old progenitor population may be observationally biased.
We present observations of the optical afterglow of GRB 170817A, made by the Hubble Space Telescope, between 2018 February and August, up to one year after the neutron star merger GW170817. The ...afterglow shows a rapid decline beyond 170 days, and confirms the jet origin for the observed outflow, in contrast to more slowly declining expectations for "failed-jet" scenarios. We show here that the broadband (radio, optical, X-ray) afterglow is consistent with a structured outflow where an ultra-relativistic jet, with a Lorentz factor of Γ 100, forms a narrow core (∼5°) and is surrounded by a wider angular component that extends to ∼15°, which is itself relativistic (Γ 5). For a two-component model of this structure, the late-time optical decline, where F ∝ t− , is = 2.20 0.18, and for a Gaussian structure the decline is = 2.45 0.23. We find the Gaussian model to be consistent with both the early ∼10 days and late 290 days data. The agreement of the optical light curve with the evolution of the broadband spectral energy distribution, and its continued decline, indicates that the optical flux is arising primarily from the afterglow and not any underlying host system. This provides the deepest limits on any host stellar cluster with a luminosity 4000 L (MF606W −4.3).
We present Hubble Space Telescope (HST) Wide Field Camera 3 UV and near-IR (nIR) imaging of 21 Superluminous Supernovae (SLSNe) host galaxies, providing a sensitive probe of star formation and ...stellar mass within the hosts. Comparing the photometric and morphological properties of these host galaxies with those of core-collapse supernovae (CCSNe) and long-duration gamma-ray bursts (LGRBs), we find SLSN hosts are fainter and more compact at both UV and nIR wavelengths, in some cases we barely recover hosts with absolute magnitude around MV ≈ −14. With the addition of ground based optical observations and archival results, we produce spectral energy distribution fits to these hosts, and show that SLSN hosts possess lower stellar mass and star formation rates. This is most pronounced for the hydrogen deficient Type-I SLSN hosts, although Type-II H-rich SLSN host galaxies remain distinct from the bulk of CCSNe, spanning a remarkably broad range of absolute magnitudes, with ∼30 per cent of SLSNe-II arising from galaxies fainter than M
nIR ∼ −14. The detection of our faintest SLSN hosts increases the confidence that SLSNe-I hosts are distinct from those of LGRBs in star formation rate and stellar mass, and suggests that apparent similarities in metallicity may be due to the limited fraction of hosts for which emission line metallicity measurements are feasible. The broad range of luminosities of SLSN-II hosts is difficult to describe by metallicity cuts, and does not match the expectations of any reasonable UV-weighted luminosity function, suggesting additional environmental constraints are likely necessary to yield hydrogen rich SLSNe.
Abstract
The number of long-duration gamma-ray burst (LGRB) host galaxies with measured metallicities and host masses has expanded sufficiently to investigate how the distributions of these ...properties change with redshift. Using the combined host galaxy metallicity sample from Graham & Fruchter and Krühler et al., we find a surprising lack of evolution in the LGRB metallicity distribution across different redshifts. In particular, the fraction of LGRB hosts with relatively high metallicity (12+log(O/H) ≥ 8.4) remains essentially constant out to
z
= 2.5. This result is at odds with the evolution in the mass–metallicity relation of typical galaxies, which become progressively more metal poor with increasing redshift. A similar result is found when converting the LGRB host galaxy mass distribution taken from the Swift GRB Host Galaxy Legacy Survey (SHOALS) sample to a corresponding metallicity distribution by applying a redshift-dependent mass–metallicity relation. The SHOALS sample is compiled using an unbiased selection function implying that the observed lack of evolution in the host galaxy high-metallicity distribution is not caused by selection effects. However, the LGRB host galaxy metallicities estimated from the stellar mass are typically a quarter dex higher at all redshifts than the metallicity we measure spectroscopically. This implies that using mass–metallicity relationships to estimate host metallicities will thus produce a substantial systematic bias.
The historic first joint detection of both gravitational-wave and electromagnetic emission from a binary neutron star merger cemented the association between short gamma-ray bursts (SGRBs) and ...compact object mergers, as well as providing a well-sampled multi-wavelength light curve of a radioactive kilonova (KN) for the first time. Here, we compare the optical and near-infrared light curves of this KN, AT 2017gfo, to the counterparts of a sample of nearby (z < 0.5) SGRBs to characterize their diversity in terms of their brightness distribution. Although at similar epochs AT 2017gfo appears fainter than every SGRB-associated KN claimed so far, we find three bursts (GRBs 050509B, 061201, and 080905A) where, if the reported redshifts are correct, deep upper limits rule out the presence of a KN similar to AT 2017gfo by several magnitudes. Combined with the properties of previously claimed KNe in SGRBs this suggests considerable diversity in the properties of KN drawn from compact object mergers, despite the similar physical conditions that are expected in many NS-NS mergers. We find that observer angle alone is not able to explain this diversity, which is likely a product of the merger type (NS-NS versus NS-BH) and the detailed properties of the binary (mass ratio, spins etc.). Ultimately disentangling these properties should be possible through observations of SGRBs and gravitational-wave sources, providing direct measurements of heavy element enrichment throughout the universe.
Recently, it has been suggested that the metallicity aversion of Long-duration Gamma Ray Bursts (LGRBs) is not intrinsic to their formation, but rather a consequence of the anti-correlation between ...star formation and metallicity seen in the general galaxy population. To investigate this proposal, we compare the metallicity of the hosts of LGRBs, broad-lined Type Ic (Ic-bl) supernovae (SNe), and Type II SNe to each other and to the metallicity distribution of star-forming galaxies using the Sloan Digital Sky Survey (SDSS) to represent galaxies in the local universe and the Team Keck Redshift Survey (TKRS) for galaxies at intermediate redshifts. The differing metallicity distributions of LGRB hosts and the star formation in local galaxies forces us to conclude that the low-metallicity preference of LGRBs is not primarily driven by the anti-correlation between star formation and metallicity, but rather must be overwhelmingly due to the astrophysics of the LGRBs themselves. Three quarters of our LGRB sample are found at metallicities below 12+log(O/H) < 8.6, while less than a one-tenth of local star formation is at similarly low metallicities. However, our SN samples are statistically consistent with the metallicity distribution of the general galaxy population. Additionally, we show that the star formation rate distribution of the LGRB and SNe host populations are consistent with the star formation rate distribution of the SDSS galaxy sample. This provides further evidence that the low-metallicity distribution of LGRBs is not caused by the general properties of star-forming galaxies. Using the TKRS population of galaxies, we can exclude the possibility that the LGRB host metallicity aversion is caused by the decrease in galaxy metallicity with redshift, as this effect is clearly much smaller than the observed LGRB host metallicity bias over the redshift span of our sample. The presence of the strong metallicity difference between LGRBs and Type Ic-bl SNe largely eliminates the possibility that the observed LGRB metallicity bias is a byproduct of a difference in the initial mass functions of the galaxy populations. Rather, metallicity below half-solar must be a fundamental component of the evolutionary process that separates LGRBs from the vast majority of Type Ic-bl SNe and from the bulk of local star formation.
We present a comparative study of the galactic and small-scale environments of gamma-ray bursts (GRBs) and core-collapse supernovae (CCSNe). We use a sample of 34 GRB hosts at z < 1.2, and a ...comparison sample of 58 supernova hosts located within the Great Observatories Origins Deep Survey footprint. We fit template spectra to the available photometric data, which span the range 0.45–24 μm, and extract absolute magnitudes, stellar masses and star formation rates from the resulting fits. Our results broadly corroborate previous findings, but offer significant enhancements in spectral coverage and a factor 2–3 increase in sample size. Specifically, we find that CCSNe occur frequently in massive spirals (spiral fraction ∼50 per cent). In contrast GRBs occur in small, relatively low mass galaxies with high specific and surface star formation rates, and have a spiral fraction of only ∼10 per cent. A comparison of the rest-frame absolute magnitudes of the GRB and CCSN sample is less conclusive than found in previous work, suggesting that while GRB hosts are typically both smaller and bluer than those of CCSN their total blue light luminosities are only slightly lower. We suggest this is likely due to rapid periods of intensified star formation activity, as indicated by the high specific SFRs, which both create the GRB progenitors and briefly significantly enhance the host galaxy blue luminosity. Finally, our analysis of local environments of GRBs and CCSNe shows that GRBs are highly concentrated on their host light, and further occur in regions of higher absolute surface luminosity than CCSNe.
We report our identification of the optical afterglow and host galaxy of the short-duration gamma-ray burst sGRB 160821B. The spectroscopic redshift of the host is z = 0.162, making it one of the ...lowest redshift short-duration gamma-ray bursts (sGRBs) identified by Swift. Our intensive follow-up campaign using a range of ground-based facilities as well as Hubble Space Telescope, XMM-Newton, and Swift, shows evidence for a late-time excess of optical and near-infrared emission in addition to a complex afterglow. The afterglow light curve at X-ray frequencies reveals a narrow jet, deg, that is refreshed at >1 day post-burst by a slower outflow with significantly more energy than the initial outflow that produced the main GRB. Observations of the 5 GHz radio afterglow shows a reverse shock into a mildly magnetized shell. The optical and near-infrared excess is fainter than AT2017gfo associated with GW170817, and is well explained by a kilonova with dynamic ejecta mass Mdyn = (1.0 0.6) × 10−3 M and a secular (post-merger) ejecta mass with Mpm = (1.0 0.6) × 10−2 M , consistent with a binary neutron star merger resulting in a short-lived massive neutron star. This optical and near-infrared data set provides the best-sampled kilonova light curve without a gravitational wave trigger to date.
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