Browsing by Author "Starling, R. L. C."

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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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    The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
    (OXFORD UNIV PRESS, 2015) Friis, M.; De Cia, A.; Kruehler, T.; Fynbo, J. P. U.; Ledoux, C.; Vreeswijk, P. M.; Watson, D. J.; Malesani, D.; Gorosabel, J.; Starling, R. L. C.; Jakobsson, P.; Varela, K.; Wiersema, K.; Drachmann, A. P.; Trotter, A.; Thoene, C. C.; de Ugarte Postigo, A.; D'Elia, V.; Elliott, J.; Maturi, M.; Goldoni, P.; Greiner, J.; Haislip, J.; Kaper, L.; Knust, F.; LaCluyze, A.; Milvang Jensen, B.; Reichart, D.; Schulze, S.; Sudilovsky, V.; Tanvir, N.; Vergani, S. D.
    We present the first reported case of the simultaneous metallicity determination of a gamma- ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission- line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long- duration Swift GRB 121024A at z = 2.30, we give one of the most complete views of a GRB host/ environment to date. We observe a strong damped Lya absorber (DLA) with a hydrogen column density of log N(H i) = 21.88 +/- 0.10, H-2 absorption in the Lyman- Werner bands (molecular fraction of log(f) approximate to- 1.4; fourth solid detection of molecular hydrogen in a GRB- DLA), the nebular emission lines H alpha, H beta, [OII], [O III] and [N II], as well as metal absorption lines. We find aGRB host galaxy that is highly star forming (SFR similar to 40M circle dot yr(-1)), with a dust- corrected metallicity along the line of sight of [Zn/ H](corr) =- 0.6 +/- 0.2 ([O/H]similar to- 0.3 from emission lines), and a depletion factor [Zn/ Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400 km s(-1) (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log(M*/M-circle dot) = 9.9(-0.3)(+0.2). We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line- emitting star- forming regions. The extinction curve for the line of sight is found to be unusually flat (R-V similar to 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.