We present the spectroscopic and photometric late-time follow-up of the host galaxy of the long-duration Swift \gamma -ray burst GRB 140506A at z = 0.889 .
The optical and near-infrared afterglow of this GRB had a peculiar spectral energy distribution ( SED ) with a strong flux-drop at 8000 Å ( 4000 Å rest-frame ) suggesting an unusually steep extinction curve .
By analysing the contribution and physical properties of the host galaxy , we here aim at providing additional information on the properties and origin of this steep , non-standard extinction .
We find that the strong flux-drop in the GRB afterglow spectrum at < 8000 Å and rise at < 4000 Å ( observers frame ) is well explained by the combination of a steep extinction curve along the GRB line of sight and contamination by the host galaxy light at short wavelengths so that the scenario with an extreme 2175 Å extinction bump can be excluded .
We localise the GRB to be at a projected distance of approximately 4 kpc from the centre of the host galaxy .
Based on emission-line diagnostics of the four detected nebular lines , H \alpha , H \beta , [ O ii ] and [ O iii ] , we find the host to be a modestly star forming ( SFR = 1.34 \pm 0.04 ~ { } M _ { \odot } yr ^ { -1 } ) and relatively metal poor ( Z = 0.35 ^ { +0.15 } _ { -0.11 } ~ { } Z _ { \odot } ) galaxy with a large dust content , characterised by a measured visual attenuation of A _ { V } = 1.74 \pm 0.41 mag .
We compare the host to other GRB hosts at similar redshifts and find that it is unexceptional in all its physical properties .
We model the extinction curve of the host-corrected afterglow and show that the standard dust properties causing the reddening seen in the Local Group are inadequate in describing the steep drop .
We thus conclude that the steep extinction curve seen in the afterglow towards the GRB is of exotic origin and is sightline-dependent only , further confirming that this type of reddening is present only at very local scales and that it is solely a consequence of the circumburst environment .