The afterglow of GRB 110918A was imaged for over 40 days after the trigger with GROND in the g′r′i′z′JHKS bands (outlined in Sect. 2.2). Using the deep observations of the host, the underlying contribution from the host galaxy was subtracted implementing the High Order Transform of PSF and Template Subtraction package, HOTPANTS11 v5.1.10b. The resulting afterglow light curve can be seen in Fig. A.1, while the raw data can be found in Tables A.2 and A.3 and the host subtracted data in Tables A.4 and A.5. The standard stars used in g′r′i′z′ for relative calibration can be found in Table A.1.
Afterglow light curve of GRB 110918A obtained with the 7-channel imager GROND (host subtracted).
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Optical reference stars.
GROND photometric data g′r′i′z′.
GROND photometric data JHKs.
GROND host-subtracted photometric data g′r′i′z′.
GROND host subtracted photometric data JHKs.
The spectra obtained with GMOS and OSIRIS (see Sect. 2.6) reveal many absorption lines of gas along the line-of-sight toward the afterglow, specifically of the following species: Fe ii (2344, 2374, 2382, 2586, 2600), Mg ii (2803, 2796), Mg i (2853), and Ca ii (3935, 3970). The equivalent widths of the metals are listed in Table B.1.
Equivalent widths measured for the absorption lines of the afterglow.
Two spectra of the host galaxy were obtained with OSIRIS and X-shooter (see Sect. 3.3), showing the following emission lines: Hα and Hβ transitions from the Balmer series and also forbidden transitions of [O ii] and [N ii] (only [O ii] emission was detected with OSIRIS, and so for consistency only the X-shooter emission lines are shown). All of the 2D spectral images and 1D Gaussian fits can be seen in Fig. C.1.
2D spectra of the host of GRB 110918A depicting four different emissions ([N ii], [O ii], Hα, Hβ). Overplotted is our Gaussian fit, where areas that overlay telluric lines are shown in white and excluded from the fit. All the values presented are raw values and do not include slit-loss or extinction corrections. Each image has been smoothed in both pixel directions for presentation purposes. a) The Balmer series transition Hα; b) the Balmer series transition Hβ; c) the forbidden transition [N ii]; d) the forbidden transition [O ii].
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© ESO, 2013