Browsing by Author "Watson, D. J."

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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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    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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    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.
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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.