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Your search keyword '"O'BRIEN P., T"' showing total 26 results
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26 results on '"O'BRIEN P., T"'

1. A NEW POPULATION OF ULTRA-LONG DURATION GAMMA-RAY BURSTS.

Author

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., and Bersier, D.

Subjects
GAMMA ray bursts, REDSHIFT, DWARF galaxies, SUPERNOVAE, BLACK holes
Abstract

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 (<105M☼). [ABSTRACT FROM AUTHOR]

Published
2014
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5. Swift Observations of the X-Ray-Bright GRB 050315.

Author

Vaughan, S., Goad, M. R., Beardmore, A. P., O’Brien, P. T., Osborne, J. P., Page, K. L., Barthelmy, S. D., Burrows, D. N., Campana, S., Cannizzo, J. K., Capalbi, M., Chincarini, G., Cummings, J. R., Cusumano, G., Giommi, P., Godet, O., Hill, J. E., Kobayashi, S., Kumar, P., and Parola, V. La

Published
2006
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10. STAR FORMATION IN THE EARLY UNIVERSE: BEYOND THE TIP OF THE ICEBERG.

Author

Tanvir, N. R., Levan, A. J., Fruchter, A. S., Fynbo, J. P. U., Hjorth, J., Wiersema, K., Bremer, M. N., Rhoads, J., Jakobsson, P., O'Brien, P. T., Stanway, E. R., Bersier, D., Natarajan, P., Greiner, J., Watson, D., Castro-Tirado, A. J., Wijers, R. A. M. J., Starling, R. L. C., Misra, K., and Graham, J. F.

Subjects
GAMMA ray bursts, STAR formation, PHYSICAL cosmology, STELLAR luminosity function, GALACTIC evolution
Abstract

We present late-time Hubble Space Telescope (HST) imaging of the fields of six Swift gamma-ray bursts (GRBs) lying at 5.0 ≲ z ≲ 9.5. Our data include very deep observations of the field of the most distant spectroscopically confirmed burst, GRB 090423, at z = 8.2. Using the precise positions afforded by their afterglows, we can place stringent limits on the luminosities of their host galaxies. In one case, that of GRB 060522 at z = 5.11, there is a marginal excess of flux close to the GRB position which may be a detection of a host at a magnitude JAB ≈ 28.5. None of the others are significantly detected, meaning that all the hosts lie below L* at their respective redshifts, with star formation rates (SFRs) ≲ 4 M☼ yr–1 in all cases. Indeed, stacking the five fields with WFC3-IR data, we conclude a mean SFR <0.17 M☼ yr–1 per galaxy. These results support the proposition that the bulk of star formation, and hence integrated UV luminosity, at high redshifts arises in galaxies below the detection limits of deep-field observations. Making the reasonable assumption that GRB rate is proportional to UV luminosity at early times allows us to compare our limits with expectations based on galaxy luminosity functions (LFs) derived from the Hubble Ultra-Deep Field and other deep fields. We infer that an LF, which is evolving rapidly toward steeper faint-end slope (α) and decreasing characteristic luminosity (L*), as suggested by some other studies, is consistent with our observations, whereas a non-evolving LF shape is ruled out at ≳ 90% confidence. Although it is not yet possible to make stronger statements, in the future, with larger samples and a fuller understanding of the conditions required for GRB production, studies like this hold great potential for probing the nature of star formation, the shape of the galaxy LF, and the supply of ionizing photons in the early universe. [ABSTRACT FROM AUTHOR]

Published
2012
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11. THE LATE PEAKING AFTERGLOW OF GRB 100418A.

Author

Marshall, F. E., Antonelli, L. A., Burrows, D. N., Covino, S., de Pasquale, M., Evans, P. A., Fugazza, D., Holland, S. T., Liang, E. W., O'Brien, P. T., Oates, S. R., Osborne, J. P., Pagani, C., Sakamoto, T., Siegel, M. H., Wu, X. F., and Zhang, B.

Published
2011
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16. Line Searches in Swift X-Ray Spectra.

Author

Hurkett, C. P., Vaughan, S., Osborne, J. P., O’Brien, P. T., Page, K. L., Beardmore, A., Godet, O., Burrows, D. N., Capalbi, M., Evans, P., Gehrels, N., Goad, M. R., Hill, J. E., Kennea, J., Mineo, T., Perri, M., and Starling, R.

Published
2008
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19. The Early X-Ray Emission from GRBs.

Author

O’Brien, P. T., Willingale, R., Osborne, J., Goad, M. R., Page, K. L., Vaughan, S., Rol, E., Beardmore, A., Godet, O., Hurkett, C. P., Wells, A., Zhang, B., Kobayashi, S., Burrows, D. N., Nousek, J. A., Kennea, J. A., Falcone, A., Grupe, D., Gehrels, N., and Barthelmy, S.

Published
2006
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25. Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet Observations of the Broad-Line Radio Galaxy 3C 390.3.

Author

O'Brien, P. T., Dietrich, M., Leighly, K., Alloin, D., Clavel, J., Crenshaw, D. M., Horne, K., Kriss, G. A., Krolik, J. H., Malkan, M. A., Netzer, H., Peterson, B. M., Reichert, G. A., Rodríguez-Pascual, P. M., Wamsteker, W., Anderson, K. S. J., Bochkarev, N. G., Cheng, F. -Z, Filippenko, A. V., and Gaskell, C. M.

Published
1998
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26. Detection of GRB 060927 at z = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages

Author

J. Gorosabel, P. M. Vreeswijk, D. Bersier, C. Ledoux, Eleonora Troja, D. Malesani, R. L. C. Starling, Pall Jakobsson, H. A. Krimm, Jesper Sollerman, Ersin Gogus, Ralph A. M. J. Wijers, A. J. Levan, Yuji Urata, Tolga Guver, Carl W. Akerlof, P. T. O'Brien, Ü. Kızıloǧlu, B. Milvang-Jensen, Nial R. Tanvir, Chryssa Kouveliotou, Dieter Horns, E. S. Rykoff, H. F. Swan, M. Özel, S. A. Yost, Michael C. B. Ashley, Jens Hjorth, J. Wren, Meng Zhai, Fang Yuan, A. E. Ruiz-Velasco, A. Melandri, John C Wheeler, B. L. Jensen, Johan P. U. Fynbo, A. J. Castro-Tirado, Wiphu Rujopakarn, S. D. Barthelmy, Carole Mundell, B. E. Schaefer, Dong Xu, Felix Aharonian, J. M. Castro Cerón, Christina C. Thöne, W. K. Zheng, N. Gehrels, T. R. Marsh, K. Y. Huang, W. T. Vestrand, R. M. Quimby, Michael I. Andersen, Darach Watson, C. Guidorzi, Gavin Rowell, Timothy A. McKay, Andrew C. Phillips, High Energy Astrophys. & Astropart. Phys (API, FNWI), RUIZ-VELASCO A E, SWAN H, TROJA E, MALESANI D, FYNBO J P U, STARLING R L C, XU D, AHARONIAN F, AKERLOF C, ANDERSEN M I, ASHLEY M C B, BARTHELMY S D, BERSIER D, CERN J M CASTRO, CASTRO-TIRADO A J, GEHRELS N, GUFUF E, GOROSABEL J, GUIDORZI C, GVER T, HJORTH J, HORNS D, HUANG K Y, JAKOBSSON P, JENSEN B L, KUZULOUFLU, KOUVELIOTOU C, KRIMM H A, LEDOUX C, LEVAN A J, MARSH T, MCKAY T, MELANDRI A, MILVANG-JENSEN B, MUNDELL C G, O'BRIEN P T, ZEL M, PHILLIPS A, QUIMBY R, ROWELL G, RUJOPAKARN W, RYKOFF E S, SCHAEFER B E, SOLLERMAN J, TANVIR N R, THNE C C, URATA Y, VESTRAND W T, VREESWIJK P M, WATSON D, WHEELER J C, WIJERS R A M J, WREN J, YOST S A, YUAN F, ZHAI M, and ZHENG W K

Subjects
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Cosmology: Observations, Spectral line, law.invention, Telescope, gamma rays: bursts (GRB 060927), law, 0103 physical sciences, 010303 astronomy & astrophysics, Reionization, Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, Astrophysics (astro-ph), Astronomy and Astrophysics, Galaxy, Redshift, Afterglow, QC Physics, 13. Climate action, Space and Planetary Science, Dark Ages, gamma rays: bursts(GRB 060927), Gamma-ray burst
Abstract

We report on follow-up observations of the GRB 060927 using the ROTSE-IIIa telescope and a suite of larger aperture ground-based telescopes. An optical afterglow was detected 20 s after the burst, the earliest rest-frame detection of optical emission from any GRB. Spectroscopy performed with the VLT about 13 hours after the trigger shows a continuum break at lambda ~ 8070 A produced by neutral hydrogen absorption at z~5.6. We also detect an absorption line at 8158 A which we interpret as SiII at z=5.467. Hence, GRB 060927 is the second most distant GRB with a spectroscopically measured redshift. The shape of the red wing of the spectral break can be fitted by a damped Lyalpha profile with a column density with log(N_HI/cm^-2) ~ 22.5. We discuss the implications of this work for the use of GRBs as probes of the end of the dark ages and draw three main conclusions: i) GRB afterglows originating from z>6 should be relatively easy to detect from the ground, but rapid NIR monitoring is necessary to ensure that they are found; ii) The presence of large HI column densities in some GRBs host galaxies at z>5 makes the use of GRBs to probe the reionization epoch via spectroscopy of the red damping wing challenging; iii) GRBs appear crucial to locate typical star-forming galaxies at z>5 and therefore the type of galaxies responsible for the reionization of the universe., 15 pages, 6 figures, 2 tables, accepted for publication in ApJ, uses emulateapj

Published
2007
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