J/A+A/629/A131 Reduced X-shooter spectra of GRB 190114A (Heintz+, 2019)
New constraints on the physical conditions in H2-bearing GRB-host damped
Lyman-alpha absorbers.
Heintz K.E., Bolmer J., Ledoux C., Noterdaeme P., Krogager J.-K.,
Fynbo J.P.U., Jakobsson P., Covino S., D'Elia V., De Pasquale M.,
Hartmann D.H., Izzo L., Japelj J., Kann D.A., Kaper L., Petitjean P.,
Rossi A., Salvaterra R., Schady P., Selsing J., Starling R., Tanvir N.R.,
Thoene C.C., de Ugarte Postigo A., Vergani S.D., Watson D., Wiersema K.,
Zafar T.
<Astron. Astrophys. 629, A131 (2019)>
=2019A&A...629A.131H 2019A&A...629A.131H (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; Spectra, ultraviolet ; Spectra, optical ;
Spectra, infrared
Keywords: galaxies: ISM - galaxies: high-redshift - ISM: molecules - dust -
extinction - gamma-ray burst: general -
gamma-ray burst: individual: 181020A and 190114A
Abstract:
We report the detections of molecular hydrogen (H2),
vibrationally-excited H2 (H2*), and neutral atomic carbon (CI),
an efficient tracer of molecular gas, in two new afterglow spectra of
GRBs 181020A (z=2.938) and 190114A (z=3.376), observed
with X-shooter at the Very Large Telescope (VLT). Both host-galaxy
absorption systems are characterized by strong damped Lyman-alpha
absorbers (DLAs) and substantial amounts of molecular hydrogen with
logN(HI,H2)=22.20±0.05, 20.40±0.04 (GRB 181020A) and
logN(HI, H2)=22.15±0.05, 19.44±0.04 (GRB 190114A). The DLA
metallicites, depletion levels, and dust extinctions are within the
typical regimes probed by GRBs with [Zn/H]=-1.57±0.06,
[Zn/Fe]=0.67±0.03, and AV=0.27±0.02mag (GRB 181020A) and
[Zn/H]=-1.23±0.07, [Zn/Fe]=1.06±0.08, and AV=0.36±0.02mag (GRB
190114A). In addition, we examine the molecular gas content of all
known H2-bearing GRB-DLAs and explore the physical conditions and
characteristics required to simultaneously probe CI and H2*. We
confirm that H2 is detected in all CI- and H2*-bearing GRB
absorption systems, but that these rarer features are not necessarily
detected in all GRB H2 absorbers. We find that a large molecular
fraction of fH2≳10-3 is required for CI to be detected. The
defining characteristic for H2* to be present is less clear, though
a large H2 column density is an essential factor. We also find that
the observed line profiles of the molecular-gas tracers are
kinematically "cold", with small velocity offsets of δv<20km/s
from the bulk of the neutral absorbing gas. We then derive the H2
excitation temperatures of the molecular gas and find that they are
relatively low with Tex~=100-300K, however, there could be
evidence of warmer components populating the high-J H2 levels in
GRBs 181020A and 190114A. Finally, we demonstrate that even though the
X-shooter GRB afterglow campaign has been successful in recovering
several H2-bearing GRB-host absorbers, this sample is still hampered
by a significant dust bias excluding the most dust-obscured H2
absorbers from identification. CI and H2* could open a potential
route to identify molecular gas even in low-metallicity or highly
dust-obscured bursts, though they are only efficient tracers for the
most H2-rich GRB-host absorption systems.
Description:
We obtained optical to near-infrared (NIR) afterglow spectroscopy of
both GRBs with the VLT/X-shooter instrument.
The spectrum of GRB 181020A was acquired (at the start of exposure)
5.7h after the GRB with an acquisition magnitude of R∼17.3mag (Fynbo
et al., 2018GCN.23356....1F 2018GCN.23356....1F). GRB 190114A was observed only 15-min
after trigger with an acquisition magnitude of R∼18.7mag, using the
rapid-response mode (RRM).
The optical to NIR spectra of both GRBs were taken simultaneously in
the ultraviolet (UVB), visual (VIS) and NIR arms of VLT/X-shooter with
slit-widths of 1.0", 0.9", 0.9", respectively. The observations were
performed under excellent conditions with average seeing and airmasses
of 1.02", 1.25 (GRB 181020A) and 0.47", 1.29 (GRB 190114A). Both
spectra show very high signal-to-noise ratios (S/N), with S/N≳30 at
λobs=6700Å in the VIS arm spectra.
Objects:
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RA (2000) DE Designation(s)
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04 22 10.54 +02 11 29.1 GRB190114A = GRB 190114A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 126 3 List of fits spectra
fits/* . 3 Individdal fits spectra
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right Ascension (J2000)
4- 5 I2 min RAm Right Ascension (J2000)
7- 11 F5.2 s RAs Right Ascension (J2000)
12 A1 --- DE- Declination sign (J2000)
13- 14 I2 deg DEd Declination (J2000)
16- 17 I2 arcmin DEm Declination (J2000)
19- 22 F4.1 arcsec DEs Declination (J2000)
24- 30 I7 --- Nx Number of pixels along X-axis
32- 55 A24 "datime" Obs.date Observation date
57- 60 I4 Kibyte size Size of FITS file
62- 83 A22 --- FileName Name of FITS file, in subdirectory fits
85-126 A42 --- Title Title of the FITS file
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Acknowledgements:
Kasper Elm Heintz, keh14(at)hi.is
(End) Patricia Vannier [CDS] 07-Aug-2019