J/A+A/601/A83 GRB 140506A X-shooter spectra (Heintz+, 2017)
Steep extinction towards GRB 140506A reconciled from host galaxy observations:
Evidence that steep reddening laws are local.
Heintz K.E., Fynbo J.P.U., Jakobsson P., Kruehler T., Christensen L.,
Perley D.A., Ledoux C., Noterdaeme P., Watson D., Selsing J., Rhodin H.,
Schulze S., Tanvir N.R., Moller P., Goldoni P., Xu D., Milvang-Jensen B.
<Astron. Astrophys. 601, A83 (2017)>
=2017A&A...601A..83H 2017A&A...601A..83H (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; Spectroscopy
Keywords: gamma-ray burst: general - gamma-ray burst: individual: GRB140506A -
dust, extinction - galaxies: individual: GRB 140506A host
Abstract:
We present the spectroscopic and photometric late-time follow-up of
the host galaxy of the long-duration Swift γ-ray burst
GRB140506A 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 8000Å (4000Å 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 <8000Å and rise at <4000Å (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 2175Å extinction
bump can be excluded. We localise the GRB to be at a projected
distance of approximately 4kpc from the centre of the host galaxy.
Based on emission-line diagnostics of the four detected nebular lines,
Hα, Hβ, [OII] and [OIII], we find the host to be a modestly
star forming (SFR=1.34±0.04M☉/yr) and relatively metal poor
(Z=0.35+0:150.11Z☉) galaxy with a large dust content,
characterised by a measured visual attenuation of AV=1.74±0.41mag.
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.
Description:
We acquired late-time photometry with the FOcal Reducer and low
dispersion Spectrograph 2 (FORS2) instrument at the ESO/VLT on 2015
April 29 and June 16.
To supplement the FORS2 and Spitzer imaging we acquired additional
spectra centred on the host galaxy using the X-shooter spectrograph
mounted at the ESO/VLT, covering a wavelength range of 3000-24800Å
(3000-5600, 5500-10200 and 10200-24800Å for the UVB, VIS and NIR
arm, respectively). The follow-up observations of this host were
spread out over three nights, on 2015 May 15, June 15 and September
30.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
18 27 06.04 -55 38 08.7 GRB140506A = GRB 140506A
----------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
nir.dat 44 18355 X-shooter NIR spectrum
uvb.dat 44 6399 X-shooter UVB spectrum
vis.dat 44 11750 X-shooter VIS spectrum
--------------------------------------------------------------------------------
Byte-by-byte Description of file: nir.dat uvb.dat vis.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 E11.6 0.1nm Lambda Wavelength
13- 24 E12.6 0.1mW/m2/nm Flux Flux (in erg/s/cm2/Å)
26- 36 E11.6 0.1mW/m2/nm e_Flux rms uncertainty on Flux
38- 44 F7.5 --- Corr Error slit loss correction
--------------------------------------------------------------------------------
Acknowledgements:
Kasper Elm Heintz, heintz(at)dark-cosmology.dk
(End) Patricia Vannier [CDS] 28-Apr-2017