Browsing by Author "Hjorth, J."

Now showing 1 - 13 of 13
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    A NEW POPULATION OF ULTRA-LONG DURATION GAMMA-RAY BURSTS
    (IOP PUBLISHING LTD, 2014) Levan, A. J.; Tanvir, N. R.; Starling, R. L. C.; Wiersema, K.; Page, K. L.; Perley, D. A.; Schulze, S.; Wynn, G. A.; Chornock, R.; Hjorth, J.; Cenko, S. B.; Fruchter, A. S.; O'Brien, P. T.; Brown, G. C.; Tunnicliffe, R. L.; Malesani, D.; Jakobsson, P.; Watson, D.; Berger, E.; Bersier, D.; Cobb, B. E.; Covino, S.; Cucchiara, A.; de Ugarte Postigo, A.; Fox, D. B.; Gal Yam, A.; Goldoni, P.; Gorosabel, J.; Kaper, L.; Kruehler, T.; Karjalainen, R.; Osborne, J. P.; Pian, E.; Sanchez Ramirez, R.; Schmidt, B.; Skillen, I.; Tagliaferri, G.; Thoene, C.; Vaduvescu, O.; Wijers, R. A. M. J.; Zauderer, B. A.
    We present comprehensive multiwavelength observations of three gamma-ray bursts (GRBs) with durations of several thousand seconds. We demonstrate that these events are extragalactic transients; in particular, we resolve the long-standing conundrum of the distance of GRB 101225A (the "Christmas-day burst"), finding it to have a redshift z = 0.847 and showing that two apparently similar events (GRB 111209A and GRB 121027A) lie at z = 0.677 and z = 1.773, respectively. The systems show extremely unusual X-ray and optical light curves, very different from classical GRBs, with long-lasting, highly variable X-ray emission and optical light curves that exhibit little correlation with the behavior seen in the X-ray. Their host galaxies are faint, compact, and highly star-forming dwarf galaxies, typical of "blue compact galaxies." We propose that these bursts are the prototypes of a hitherto largely unrecognized population of ultra-long GRBs, which while observationally difficult to detect may be astrophysically relatively common. The long durations may naturally be explained by the engine-driven explosions of stars of much larger radii than normally considered for GRB progenitors, which are thought to have compact Wolf-Rayet progenitor stars. However, we cannot unambiguously identify supernova signatures within their light curves or spectra. We also consider the alternative possibility that they arise from the tidal disruption of stars by massive black holes and conclude that the associated timescales are only consistent with the disruption of compact stars (e. g., white dwarfs) by black holes of relatively low mass (<10(5) M-circle dot).
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    DETECTION OF THREE GAMMA-RAY BURST HOST GALAXIES AT z similar to 6
    (IOP PUBLISHING LTD, 2016) McGuire, J. T. W.; Tanvir, N. R.; Levan, A. J.; Trenti, M.; Stanway, E. R.; Shull, J. M.; Wiersema, K.; Perley, D. A.; Starling, R. L. C.; Bremer, M.; Stocke, J. T.; Hjorth, J.; Rhoads, J. E.; Curtis Lake, E.; Schulze, S.; Levesque, E. M.; Robertson, B.; Fynbo, J. P. U.; Ellis, R. S.; Fruchter, A. S.
    Long-duration gamma-ray bursts (GRBs) allow us to pinpoint and study star-forming galaxies in the early universe, thanks to their orders of magnitude brighter peak luminosities compared to other astrophysical sources, and their association with the deaths of massive stars. We present Hubble Space Telescope Wide Field Camera 3 detections of three Swift GRB host galaxies lying at redshifts z = 5.913 (GRB 130606A), z = 6.295 (GRB 050904), and z = 6.327 (GRB 140515A) in the F140W (wide-JH band, lambda(obs) similar to 1.4 mu m) filter. The hosts have magnitudes (corrected for Galactic extinction) of m(lambda obs) = 26.34(-0.16)(+0.14), 27.56(-0.22)(+0.18), and 28.30(-0.33)(+0.25) respectively. In all three cases, the probability of chance coincidence of lower redshift galaxies is less than or similar to 2%, indicating that the detected galaxies are most likely the GRB hosts. These are the first detections of high-redshift (z > 5) GRB host galaxies in emission. The galaxies have luminosities in the range 0.1-0.6 L-z=6* (with M-1600* = -20.95 +/- 0.12) and half-light radii in the range 0.6-0.9 kpc. Both their half-light radii and luminosities are consistent with existing samples of Lyman-break galaxies at z similar to 6. Spectroscopic analysis of the GRB afterglows indicate low metallicities ([M/H] less than or similar to -1) and low dust extinction (AV less than or similar to 0.1) along the line of sight. Using stellar population synthesis models, we explore the implications of each galaxy's luminosity for its possible star-formation history and consider the potential for emission line metallicity determination with the upcoming James Webb Space Telescope.
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    DISCOVERY OF THE BROAD-LINED TYPE Ic SN 2013cq ASSOCIATED WITH THE VERY ENERGETIC GRB 130427A
    (2013) Xu, D.; de Ugarte Postigo, A.; Leloudas, G.; Kruehler, T.; Cano, Z.; Hjorth, J.; Malesani, D.; Fynbo, J. P. U.; Thoene, C. C.; Sanchez-Ramirez, R.; Schulze, S.; Jakobsson, P.; Kaper, L.; Sollerman, J.; Watson, D. J.; Cabrera-Lavers, A.; Cao, C.; Covino, S.; Flores, H.; Geier, S.; Gorosabel, J.; Hu, S. M.; Milvang-Jensen, B.; Sparre, M.; Xin, L. P.; Zhang, T. M.; Zheng, W. K.; Zou, Y. C.
    Long-duration gamma-ray bursts (GRBs) at z < 1 are found in most cases to be accompanied by bright, broadlined Type Ic supernovae (SNe Ic-BL). The highest-energy GRBs are mostly located at higher redshifts, where the associated SNe are hard to detect observationally. Here, we present early and late observations of the optical counterpart of the very energetic GRB 130427A. Despite its moderate redshift, z = 0.3399+/-0.0002, GRB 130427A is at the high end of the GRB energy distribution, with an isotropic-equivalent energy release of E-iso similar to 9.6 x 10(53) erg, more than an order of magnitude more energetic than other GRBs with spectroscopically confirmed SNe. In our dense photometric monitoring, we detect excess flux in the host-subtracted r-band light curve, consistent with that expected from an emerging SN, similar to 0.2 mag fainter than the prototypical SN 1998bw. A spectrum obtained around the time of the SN peak (16.7 days after the GRB) reveals broad undulations typical of SNe Ic-BL, confirming the presence of an SN, designated SN 2013cq. The spectral shape and early peak time are similar to those of the high expansion velocity SN 2010bh associated with GRB 100316D. Our findings demonstrate that high-energy, long-duration GRBs, commonly detected at high redshift, can also be associated with SNe Ic-BL, pointing to a common progenitor mechanism.
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    GRB 140606B/iPTF14bfu: detection of shock-breakout emission from a cosmological gamma-ray burst?
    (OXFORD UNIV PRESS, 2015) Cano, Zach; de Ugarte Postigo, A.; Perley, D.; Kruehler, T.; Margutti, R.; Friis, M.; Malesani, D.; Jakobsson, P.; Fynbo, J. P. U.; Gorosabel, J.; Hjorth, J.; Sanchez Ramirez, R.; Schulze, S.; Tanvir, N. R.; Thoene, C. C.; Xu, D.
    We present optical and near-infrared photometry of GRB 140606B (z = 0.384), and optical photometry and spectroscopy of its associated supernova (SN). The results of our modelling indicate that the bolometric properties of the SN (M-Ni = 0.4 +/- 0.2 M-circle dot, M-ej = 5 +/- 2 M-circle dot, and E-K = 2 +/- 1 x 10(52) erg) are fully consistent with the statistical averages determined for other gamma-ray burst (GRB)-SNe. However, in terms of its gamma-ray emission, GRB 140606B is an outlier of the Amati relation, and occupies the same region as low luminosity (ll) and short GRBs. The gamma-ray emission in llGRBs is thought to arise in some or all events from a shock breakout (SBO), rather than from a jet. The measured peak photon energy (E-p approximate to 800 keV) is close to that expected for. -rays created by an SBO (greater than or similar to 1 MeV). Moreover, based on its position in the M-V,M- (p)- L-iso,L-gamma plane and the E-K-Gamma eta plane, GRB 140606B has properties similar to both SBO-GRBs and jetted-GRBs. Additionally, we searched for correlations between the isotropic gamma-ray emission and the bolometric properties of a sample of GRB-SNe, finding that no statistically significant correlation is present. The average kinetic energy of the sample is (E) over bar (K) = 2.1 x 10(52) erg. All of the GRB-SNe in our sample, with the exception of SN 2006aj, are within this range, which has implications for the total energy budget available to power both the relativistic and non-relativistic components in a GRB-SN event.
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    Molecular hydrogen in the damped Lyman α system towards GRB 120815A at z=2.36
    (2013) Kruhler, T.; Ledoux, C.; Fynbo, J. P. U.; Vreeswijk, P. M.; Schmidl, S.; Malesani, D.; Christensen, L.; De Cia, A.; Hjorth, J.; Jakobsson, P.; Kann, D. A.; Kaper, L.; Vergani, S. D.; Afonso, P. M. J.; Covino, S.; de Ugarte Postigo, A.; D'Elia, V.; Filgas, R.; Goldoni, P.; Greiner, J.; Hartoog, O. E.; Milvang-Jensen, B.; Nardini, M.; Piranomonte, S.; Rossi, A.; Sanchez-Ramirez, R.; Schady, P.; Schulze, S.; Sudilovsky, V.; Tanvir, N. R.; Tagliaferri, G.; Watson, D. J.; Wiersema, K.; Wijers, R. A. M. J.; Xu, D.
    We present the discovery of molecular hydrogen (H-2), including the presence of vibrationally-excited H-2* in the optical spectrum of the of GRB 120815A at z = 2.36 obtained with X-shooter at the VLT. Simultaneous photometric broad-band data from GROND X-ray observations by SwiftXRT place further constraints on the amount and nature of dust along the sightline. The galactic of GRB 120815A is characterized by a strong DLA with log(N(H I) = cm(-2)) = 21.95 +/- 0.10, prominent H-2 absorption the Lyman-Werner bands (log(N(H-2) = cm(-2)) = 20.54 +/- 0.13) and thus a molecular gas fraction log f(H-2) = 1.14 +/- 0.15. The d between the absorbing neutral gas and GRB 120815A is constrained via photo-excitation modeling of fine-structure and stable transitions of Fe II and Ni II to d = 0.5 +/- 0.1 kpc. The DLA metallicity ([Zn = H] = 1.15 +/- 0.12), visual extinction AV less than or similar to 0.15 mag) and dust depletion ([Zn = Fe] = 1.01 +/- 0.10) are intermediate between the values of well-studied, H-2-deficient DLAs observed at high spectral resolution, and the approximately solar metallicity, highly-obscured and H-2-rich GRB 080607 With respect to N(H I), metallicity, as well as dust-extinction and depletion, GRB 120815A is fairly representative of the properties of GRB-DLAs. This demonstrates that molecular hydrogen is present in at least a fraction of the more typical GRB- and H-2 and H-2* are probably more wide-spread among GRB-selected systems than the few examples of previous detections suggest. Because H-2* transitions are located redwards of the Lyman alpha absorption, H-2* opens a second route for positive searches molecular absorption also in GRB afterglows at lower redshifts and observed at lower spectral resolution. Further detections of gas in GRB-DLAs would allow statistical studies, and, coupled with host follow-up and sub-mm spectroscopy, provide insights into the process and conditions of star-formation at high redshift.
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    Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv
    (2020) Ackley, K.; Amati, L.; Barbieri, C.; Bauer, F. E.; Benetti, S.; Bernardini, M. G.; Bhirombhakdi, K.; Botticella, M. T.; Branchesi, M.; Brocato, E.; Bruun, S. H.; Bulla, M.; Campana, S.; Cappellaro, E.; Castro-Tirado, A. J.; Chambers, K. C.; Chaty, S.; Chen, T-W; Ciolfi, R.; Coleiro, A.; Copperwheat, C. M.; Covino, S.; Cutter, R.; D'Ammando, F.; D'Avanzo, P.; De Cesare, G.; D'Elia, V; Della Valle, M.; Denneau, L.; De Pasquale, M.; Dhillon, V. S.; Dyer, M. J.; Elias-Rosa, N.; Evans, P. A.; Eyles-Ferris, R. A. J.; Fiore, A.; Fraser, M.; Fruchter, A. S.; Fynbo, J. P. U.; Galbany, L.; Gall, C.; Galloway, D. K.; Getman, F., I; Ghirlanda, G.; Gillanders, J. H.; Gomboc, A.; Gompertz, B. P.; Gonzalez-Fernandez, C.; Gonzalez-Gaitan, S.; Grado, A.; Greco, G.; Gromadzki, M.; Groot, P. J.; Gutierrez, C. P.; Heikkila, T.; Heintz, K. E.; Hjorth, J.; Hu, Y-D; Huber, M. E.; Inserra, C.; Izzo, L.; Japelj, J.; Jerkstrand, A.; Jin, Z. P.; Jonker, P. G.; Kankare, E.; Kann, D. A.; Kennedy, M.; Kim, S.; Klose, S.; Kool, E. C.; Kotak, R.; Kuncarayakti, H.; Lamb, G. P.; Leloudas, G.; Levan, A. J.; Longo, F.; Lowe, T. B.; Lyman, J. D.; Magnier, E.; Maguire, K.; Maiorano, E.; Mandel, I; Mapelli, M.; Mattila, S.; McBrien, O. R.; Melandri, A.; Michalowski, M. J.; Milvang-Jensen, B.; Moran, S.; Nicastro, L.; Nicholl, M.; Guelbenzu, A. Nicuesa; Nuttal, L.; Oates, S. R.; O'Brien, P. T.; Onori, F.; Palazzi, E.; Patricelli, B.; Perego, A.; Torres, M. A. P.; Perley, D. A.; Pian, E.; Pignata, G.; Piranomonte, S.; Poshyachinda, S.; Possenti, A.; Pumo, M. L.; Quirola-Vasquez, J.; Ragosta, F.; Ramsay, G.; Rau, A.; Rest, A.; Reynolds, T. M.; Rosetti, S. S.; Rossi, A.; Rosswog, S.; Sabha, N. B.; Carracedo, A. Sagues; Salafia, O. S.; Salmon, L.; Salvaterra, R.; Savaglio, S.; Sbordone, L.; Schady, P.; Schipani, P.; Schultz, A. S. B.; Schweyer, T.; Smartt, S. J.; Smith, K. W.; Smith, M.; Sollerman, J.; Srivastav, S.; Stanway, E. R.; Starling, R. L. C.; Steeghs, D.; Stratta, G.; Stubbs, C. W.; Tanvir, N. R.; Testa, V; Thrane, E.; Tonry, J. L.; Turatto, M.; Ulaczyk, K.; van der Horst, A. J.; Vergani, S. D.; Walton, N. A.; Watson, D.; Wiersema, K.; Wiik, K.; Wyrzykowski, L.; Yang, S.; Yi, S-X; Young, D. R.
    Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.
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    Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
    (2023) Agudo, I.; Amati, L.; An, T.; Bauer, F. E.; Benetti, S.; Bernardini, M. G.; Beswick, R.; Bhirombhakdi, K.; de Boer, T.; Branchesi, M.; Brennan, S. J.; Brocato, E.; Caballero-Garcia, M. D.; Cappellaro, E.; Castro Rodriguez, N.; Castro-Tirado, A. J.; Chambers, K. C.; Chassande-Mottin, E.; Chaty, S.; Chen, T. -W.; Coleiro, A.; Covino, S.; D'Ammando, F.; D'Avanzo, P.; D'Elia, V.; Fiore, A.; Floers, A.; Fraser, M.; Frey, S.; Frohmaier, C.; Fulton, M.; Galbany, L.; Gall, C.; Gao, H.; Garcia-Rojas, J.; Ghirlanda, G.; Giarratana, S.; Gillanders, J. H.; Giroletti, M.; Gompertz, B. P.; Gromadzki, M.; Heintz, K. E.; Hjorth, J.; Hu, Y. -D.; Huber, M. E.; Inkenhaag, A.; Izzo, L.; Jin, Z. P.; Jonker, P. G.; Kann, D. A.; Kool, E. C.; Kotak, R.; Leloudas, G.; Levan, A. J.; Lin, C. -C.; Lyman, J. D.; Magnier, E. A.; Maguire, K.; Mandel, I.; Marcote, B.; Sanchez, D. Mata; Mattila, S.; Melandri, A.; Michalowski, M. J.; Moldon, J.; Nicholl, M.; Guelbenzu, A. Nicuesa; Oates, S. R.; Onori, F.; Orienti, M.; Paladino, R.; Paragi, Z.; Perez-Torres, M.; Pian, E.; Pignata, G.; Piranomonte, S.; Quirola-Vasquez, J.; Ragosta, F.; Rau, A.; Ronchini, S.; Rossi, A.; Sanchez-Ramirez, R.; Salafia, O. S.; Schulze, S.; Smartt, S. J.; Smith, K. W.; Sollerman, J.; Srivastav, S.; Starling, R. L. C.; Steeghs, D.; Stevance, H. F.; Tanvir, N. R.; Testa, V.; Torres, M. A. P.; Valeev, A.; Vergani, S. D.; Vescovi, D.; Wainscost, R.; Watson, D.; Wiersema, K.; Wyrzykowski, L.; Yang, J.; Yang, S.; Young, D. R.
    We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (similar to SIM;150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude (M-i similar to -16.7 mag), and the r-band decline rate of similar to 1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only similar to 0.1 M circle dot, with Ni-56 comprising similar to 20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
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    Spectroscopy of the short-hard GRB 130603B The host galaxy and environment of a compact object merger
    (2014) Postigo, A. de Ugarte; Thone, C. C.; Rowlinson, A.; Garcia-Benito, R.; Levan, A. J.; Gorosabel, J.; Goldoni, P.; Schulze, S.; Zafar, T.; Wiersema, K.; Sanchez-Ramirez, R.; Melandri, A.; D'Avanzo, P.; Oates, S.; D'Elia, V.; De Pasquale, M.; Kruehler, T.; van der Horst, A. J.; Xu, D.; Watson, D.; Piranomonte, S.; Vergani, S. D.; Milvang-Jensen, B.; Kaper, L.; Malesani, D.; Fynbo, J. P. U.; Cano, Z.; Covino, S.; Flores, H.; Greiss, S.; Hammer, F.; Hartoog, O. E.; Hellmich, S.; Heuser, C.; Hjorth, J.; Jakobsson, P.; Mottola, S.; Sparre, M.; Sollerman, J.; Tagliaferri, G.; Tanvir, N. R.; Vestergaard, M.; Wijers, R. A. M. J.
    Context. Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational waves. The detection of a "kilonova"-like signature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger.
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    The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars
    (2017) Tanvir, N.; Levan, A.; Gonzalez Fernández, C.; Korobkin, O.; Mandel, I.; Rosswog, S.; Hjorth, J.; D'Avanzo, P.; Fruchter, A. S.; Rabus, Markus
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    The supermassive black hole coincident with the luminous transient ASASSN-15lh.
    (2017) Krühler, Thomas; Kim, Sam; Fraser, M.; Leloudas, G.; Schulze, Steve; Stone, N. C.; Velzen, S. van; Amorin, R.; Hjorth, J.; Jonker, P. G.; Kann, D. A.
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    The swift gamma-ray burst host galaxy legacy survey. I. Sample selection and redshift distribution.
    (2016) Perley, Daniel A.; Kim, Sam; Krühler, Thomas; Schulze, Steve.; Ugarte Postigo, A. de; Hjorth, J.; Berger, E.; Cenko, S. B.; Chary, R.; Cucchiara, A.
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    THE SWIFT GRB HOST GALAXY LEGACY SURVEY. II. REST-FRAME NEAR-IR LUMINOSITY DISTRIBUTION AND EVIDENCE FOR A NEAR-SOLAR METALLICITY THRESHOLD
    (IOP PUBLISHING LTD, 2016) Perley, D. A.; Tanvir, N. R.; Hjorth, J.; Laskar, T.; Berger, E.; Chary, R.; de Ugarte Postigo, A.; Fynbo, J. P. U.; Kruhler, T.; Levan, A. J.; Michalowski, M. J.; Schulze, S.
    We present rest-frame near-IR (NIR) luminosities and stellar masses for a large and uniformly selected population of gamma-ray burst (GRB) host galaxies using deep Spitzer Space Telescope imaging of 119 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and we determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find a rapid increase in the characteristic NIR host luminosity between z similar to 0.5 and z similar to 1.5, but little variation between z similar to 1.5 and z similar to 5. Dust-obscured GRBs dominate the massive host population but are only rarely seen associated with low-mass hosts, indicating that massive star-forming galaxies are universally and (to some extent) homogeneously dusty at high. redshift while low-mass star-forming galaxies retain little dust in their interstellar medium. Comparing our luminosity distributions with field surveys and measurements of the high-z mass-metallicity relation, our results have good consistency with a model in which the GRB rate per unit star formation is constant in galaxies with gas-phase metallicity below approximately the solar value but heavily suppressed in more metal-rich environments. This model also naturally explains the previously reported "excess" in the GRB rate beyond z greater than or similar to 2; metals stifle GRB production in most galaxies at z < 1.5 but have only minor impact at higher redshifts. The metallicity threshold we infer is much higher than predicted by single-star models and favors a binary progenitor. Our observations also constrain the fraction of cosmic star formation in low-mass galaxies undetectable to Spitzer to be small at z < 4.
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    VLT/X-Shooter emission-line spectroscopy of 96 gamma-ray-burst-selected galaxies at 0.1 < z < 3.6
    (EDP SCIENCES S A, 2015) Kruehler, T.; Malesani, D.; Fynbo, J. P. U.; Hartoog, O. E.; Hjorth, J.; Jakobsson, P.; Perley, D. A.; Rossi, A.; Schady, P.; Schulze, S.; Tanvir, N. R.; Vergani, S. D.; Wiersema, K.; Afonso, P. M. J.; Bolmer, J.; Cano, Z.; Covino, S.; D'Elia, V.; de Ugarte Postigo, A.; Filgas, R.; Friis, M.; Graham, J. F.; Greiner, J.; Goldoni, P.; Gomboc, A.; Hammer, F.; Japelj, J.; Kann, D. A.; Kaper, L.; Klose, S.; Levan, A. J.; Leloudas, G.; Milvang Jensen, B.; Guelbenzu, A. Nicuesa; Palazzi, E.; Pian, E.; Piranomonte, S.; Sanchez Ramirez, R.; Savaglio, S.; Selsing, J.; Tagliaferri, G.; Vreeswijk, P. M.; Watson, D. J.; Xu, D.
    We present data and initial results from VLT/X-Shooter emission-line spectroscopy of 96 galaxies selected by long gamma-ray bursts (GRBs) at 0.1 < z < 3.6, the largest sample of GRB host spectra available to date. Most of our GRBs were detected by Swift and 76% are at 0.5 < z < 2.5 with a median z(med) similar to 1.6. Based on Balmer and/or forbidden lines of oxygen, nitrogen, and neon, we measure systemic redshifts, star formation rates (SFR), visual attenuations (A(V)), oxygen abundances (12 + log(O/H)), and emission-line widths (sigma). We study GRB hosts up to z similar to 3.5 and find a strong change in their typical physical properties with redshift. The median SFR of our GRB hosts increases from SFRmed similar to 0.6 M circle dot yr(-1) at z similar to 0.6 up to SFRmed similar to 15 M circle dot yr(-1) at z similar to 2. A higher ratio of [O III]/[O II] at higher redshifts leads to an increasing distance of GRB-selected galaxies to the locus of local galaxies in the Baldwin-Phillips-Terlevich diagram. There is weak evidence for a redshift evolution in A(V) and similar to, with the highest values seen at z similar to 1.5 (A(V)) or z similar to 2 (sigma). Oxygen abundances of the galaxies are distributed between 12 + log(O/H) = 7.9 and 12 + log(O/H) = 9.0 with a median 12 + log(O/H)(med) similar to 8.5. The fraction of GRB-selected galaxies with super-solar metallicities is similar to 20% at z < 1 in the adopted metallicity scale. This is significantly less than the fraction of total star formation in similar galaxies, illustrating that GRBs are scarce in high metallicity environments. At z similar to 3, sensitivity limits us to probing only the most luminous GRB hosts for which we derive metallicities of Z less than or similar to 0.5 Z circle dot. Together with a high incidence of Z similar to 0.5 Z circle dot galaxies at z similar to 1.5, this indicates that a metallicity dependence at low redshift will not be dominant at z similar to 3. Significant correlations exist between the hosts' physical properties. Oxygen abundance, for example, relates to A(V) (12 + log(O/H) proportional to 0.17 A(V)), line width (12 + log(O/H) proportional to sigma(0.6)), and SFR (12 + log(O/H) proportional to SFR0.2). In the last two cases, the normalization of the relations shift to lower metallicities at z > 2 by similar to 0.4 dex. These properties of GRB hosts and their evolution with redshift can be understood in a cosmological context of star-forming galaxies and a picture in which the hosts' properties at low redshift are influenced by the tendency of GRBs to avoid the most metal-rich environments.