J/ApJ/860/L21 GROND, NOT & VLT/X-shooter obs. of GRB180325A (Zafar+, 2018)
The 2175Å extinction feature in the optical afterglow spectrum of GRB180325A
at z=2.25.
Zafar T., Heintz K.E., Fynbo J.P.U., Malesani D., Bolmer J., Ledoux C.,
Arabsalmani M., Kaper L., Campana S., Starling R.L.C., Selsing J.,
Kann D.A., de Ugarte Postigo A., Schweyer T., Christensen L., Moller P.,
Japelj J., Perley D., Tanvir N.R., D'Avanzo P., Hartmann D.H., Hjorth J.,
Covino S., Sbarufatti B., Jakobsson P., Izzo L., Salvaterra R., D'Elia V.,
Xu D.
<Astrophys. J., 860, L21 (2018)>
=2018ApJ...860L..21Z 2018ApJ...860L..21Z
ADC_Keywords: GRB; Photometry, ugriz; Photometry, infrared
Keywords: dust, extinction; galaxies: ISM; gamma-ray burst: general;
gamma-ray burst: individual (GRB 180325A)
Abstract:
The ultraviolet (UV) extinction feature at 2175Å is ubiquitously
observed in the Galaxy but is rarely detected at high redshifts. Here
we report the spectroscopic detection of the 2175Å bump on the
sightline to the γ-ray burst (GRB) afterglow GRB180325A at
z=2.2486, the only unambiguous detection over the past 10 years of GRB
follow-up, at four different epochs with the Nordic Optical Telescope
(NOT) and the Very Large Telescope (VLT)/X-shooter. Additional
photometric observations of the afterglow are obtained with the
Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We
construct the near-infrared to X-ray spectral energy distributions
(SEDs) at four spectroscopic epochs. The SEDs are well described by a
single power law and an extinction law with RV∼4.4, Av∼1.5, and the
2175Å extinction feature. The bump strength and extinction curve
are shallower than the average Galactic extinction curve. We determine
a metallicity of [Zn/H]>-0.98 from the VLT/X-shooter spectrum. We
detect strong neutral carbon associated with the GRB with equivalent
width of Wr(λ1656)=0.85±0.05. We also detect optical emission
lines from the host galaxy. Based on the Hα emission-line flux,
the derived dust-corrected star formation rate is ∼46±4M☉/yr
and the predicted stellar mass is log M*/M☉∼9.3±0.4,
suggesting that the host galaxy is among the main-sequence
star-forming galaxies.
Description:
At 01:53:02 UT on 2018 March 25, the Neil Gehrels Swift Observatory
detected GRB 180325A with its Burst Alert Telescope (BAT), and its
X-Ray Telescope (XRT) began observations at 01:54:16.2 UT. At 6
minutes after the burst trigger, the Nordic Optical Telescope (NOT)
equipped with the Andalucia Faint Object Spectrograph and Camera
(AlFOSC) observed the GRB in the R-band.
The Gamma-Ray burst Optical and Near-Infrared Detector (GROND) mounted
at the 2.2m Max Planck Gesellschaft telescope started taking
photometric observations of the afterglow in all seven (g' r' i' z' JH
and K) bands at ∼1.05hr after the burst.
We subsequently observed GRB 180325A at ∼1.84hr after trigger with
the VLT/X-shooter spectrograph. VLT/X-shooter data were obtained as
part of the Stargate VLT proposal (Program ID: 0100.D-0649(A)).
The complete log of GROND, NOT, and VLT/X-shooter photometric
observations is provided in Table 1.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
10 29 42.57 +24 27 48.9 GRB 180325A = GRB 180325A
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 49 62 Multi-band photometric observations of GRB 180325A
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See also:
J/ApJ/663/320 : IR-through-UV extinction curve (Fitzpatrick+, 2007)
J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)
J/ApJ/732/110 : SDSS 2175Å extinction bump candidates (Jiang+, 2011)
J/AJ/141/36 : GRB 080607 multi-band light curves (Perley+, 2011)
J/A+A/572/A12 : GRB 140506A spectra (Fynbo+, 2014)
J/A+A/601/A83 : GRB 140506A X-shooter spectra (Heintz+, 2017)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Facility Facility (1)
7- 7 A1 --- Filt Filter used (RgrizJHK)
9- 20 F12.6 s t-T0 Time since the burst trigger
(2018 March 25 at 01:53:02)
22- 28 F7.2 s Exp [10/1170] Exposure time
30- 35 F6.3 mag omag [16.1/23.6] Observed AB magnitude in Filter
37- 47 F11.9 mag e_omag [0.02/0.3]? Uncertainty in omag
49- 49 I1 --- l_omag [1]? 3σ upper limit flag on omag
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Note (1): Facility as follows:
GROND = Gamma-Ray burst Optical and Near-Infrared Detector, 2.2-m Max
Planck Gesellschaft telescope with g'r'i'z'JH and K filters;
NOT = Andalucia Faint Object Spectrograph and Camera (AlFOSC), Nordic
Optical Telescope with R-band filters;
XSH = X-shooter spectrograph (griz filters), VLT.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Jul-2019