Free Access
Volume 557, September 2013
Article Number A18
Number of page(s) 21
Section Extragalactic astronomy
Published online 14 August 2013

Online material

Appendix A: GROND photometry and multi-color light curves

The temporal evolution of the optical/NIR photometric and X-ray data was fitted simultaneously with a two-fold broken power-law, connected smoothly at the break times following Krühler et al. (2009). The functional form of this empirical fit is provided for example in Schulze et al. (2011). The light curve shape is characterized by a shallow, early rise with an index α1 =  −0.18 ± 0.02, where the sign follows the convention that Fν(t) ∝ t− α. The optical/NIR afterglow peaks at t1 = 440 ± 30 s after the BAT trigger time. Afterwards the light curve decays with an index of α2 = 0.52 ± 0.01, before another breaking to

Table A.1

Optical magnitudes of the afterglow of GRB 120815A as measured by GROND.

a steeper decay of α3 = 0.86 ± 0.03 at ks. The light curve is reasonably well fitted with this phenomenological model (χ2 = 261 for 242 degrees of freedom), and no chromatic evolution is apparent within our data set. The overall light curve behavior is reminiscent of GRB 080710 (Krühler et al. 2009), in particular the achromatic and shallow, early rise of the light curve in combination with the soft γ-ray emission detected by BAT (Markwardt et al. 2012).

All magnitudes in Fig. A.1 and Tables A.1, A.2 are in the AB system and uncorrected for the expected Galactic foreground extinction, corresponding to a reddening of EB − V = 0.10 mag (Schlafly & Finkbeiner 2011).

Table A.2

Near-infrared magnitudes of the afterglow of GRB 120815A as measured by GROND.

thumbnail Fig. A.1

GROND optical/NIR and XRT 0.3−10 keV light curves of the afterglow of GRB 120815A in the top panel. The data were fitted with a three-segment, smoothly broken power-law, with residuals shown in the bottom panel. The grey shaded area represents the time interval in which the X-shooter spectroscopy was obtained. X-ray data were converted into a flux density at 3 keV using a spectral index of β = 0.78, and scaled by a factor of 20 to enhance clarity.

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thumbnail Fig. B.1

X-shooter UVB-arm spectrum of the afterglow of GRB 120815A. Black lines show the spectral data, grey lines the noise level, the green line is the GRB afterglow model, and the red-line shows the DLA modeling. The position of absorption lines that are typically associated with GRB-DLAs (taken from Christensen et al. 2011) are indicated by brown lines and ions. Individual lines associated with intervening absorbers are labeled with colored lines and labels.

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thumbnail Fig. B.2

X-shooter VIS-arm spectrum of the afterglow of GRB 120815A. Lines and labels are the same as in Fig. B.1. Additionally, strong telluric lines are indicated by circles in the upper part of each panel.

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thumbnail Fig. B.3

X-shooter NIR-arm spectrum of the afterglow of GRB 120815A. Lines and labels are the same as in Fig. B.2.

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thumbnail Fig. B.4

X-shooter spectrum between 4100 and 5600 Å showing the presence of H lines. The uppermost, blue-framed panel shows an overview over the whole spectral range, while the lower 5 panels zoom in of 180 Å each. We selected regions where most of the absorption bands of H are located. Light-grey lines always show the normalized spectrum, while dark-grey lines indicate the error spectrum. Red lines denote the best-fit H model. In the top panel, we also mark prominent metal absorption lines previously detected in GRB-DLAs (Christensen et al. 2011). In the lower panels, several individual H transitions are identified using standard nomenclature with lower and upper vibrational and rotational quantum numbers.

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© ESO, 2013

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