Andrew Yee
March 2nd 06, 05:08 PM
Issac Newton Group of Telescopes
Santa Cruz de La Palma, Canary Islands, Spain
Contact:
Javier Méndez, Public Relations Officer
jma @ ing.iac.es
Release date: 2nd March, 2006
WHT and NOT Observations Probing Cosmic Evolution with Gamma-Ray Bursts:
GRB 060206 at Redshift 4.048
Gamma-ray bursts (GRBs) are very bright flashes of radiation, that are
detected approximately 100 times per year by satellites. For a long time
it was a mystery where these flashes originated from and how they were
produced. In 1997 astronomers using the William Herschel Telescope
discovered that GRBs show a so-called "afterglow": radiation in other
wavelengths following the gamma-rays. This afterglow can be studied with
telescopes from the Earth, and allowed astronomers to find that GRBs
originate in the violent deaths of massive stars, in star-forming galaxies
far away.
GRBs have proven to be excellent probes of the distant Universe. The high
luminosities of GRB afterglows allow absorption line studies of the
interstellar medium at high redshift up to redshifts larger than six. The
decrease in brightness of GRB afterglows means that a rapid response is
essential: the afterglow can be "caught" when it is still bright. To
exploit this benefit, the William Herschel Telescope (WHT) and the Nordic
Optical Telescope (NOT) have implemented rapid response GRB programmes.
Early in the morning of February the 6th, 2006 a GRB was detected by the
Swift satellite. The GRB was at that time high in the sky over La Palma
and the weather was good. Within 15 minutes the NOT was pointed towards
this burst by the Danish GRB follow-up group. Using ALFOSC a bright
optical afterglow was discovered in the R band. Directly after the
detection had been made, a low-resolution spectrum was acquired using the
same instrument. The latter spectrum rapidly determined the redshift of
GRB 060206 at z=4.048. Meanwhile, the WHT had been alerted through our
collaboration of the NOT and WHT, involving GRB follow-up teams from the
Netherlands, the United Kingdom and Denmark. Starting at just 1.6 hours
after the burst a medium-resolution spectrum could be obtained using WHT's
ISIS spectrograph.
The combination of the NOT and WHT provides a unique window on this
afterglow. The low resolution and broad wavelength coverage of the NOT
spectrum allowed an accurate determination of the column density of
neutral hydrogen (HI), redshifted to optical wavelengths. The high
resolution of the WHT spectra meant an accurate study of metal lines in
the spectrum was possible. A large number of metal lines are found in the
spectra, including (forbidden) fine-structure lines. Based on the
measurement of the neutral hydrogen column density and the metal content
from weak, unsaturated singly-ionised sulphur (SII) lines, a metallicity
of [S/H] = -0.84 ± 0.10, or ~0.14 times solar metallicity, was derived.
This is in fact one of the highest metallicities measured from absorption
lines at redshift around 4. From the very high column densities for the
forbidden singly-ionised silicon (SiII*), neutral oxygen (OI* and and
OI**) lines the researchers infer very high densities in the system,
significantly larger than 10^4 cm-3.
The high-resolution spectra also allows the astronomers to study the
kinematics of the absorption systems: several different, discrete velocity
systems can be distinguished, with velocities up to 500 km/s. Most
surprising however, was the tentative detection of molecular hydrogen in
the ISIS spectrum. This is the very first detection of molecular lines in
an optical GRB afterglow spectrum. Especially remarkable is the fact that
this possible detection has been done with a 4-metre telescope, proving
that medium size telescopes can compete when response times are short. The
joint study of the afterglow of GRB 060206 with WHT ISIS and NOT ALFOSC
shows the power of a multi-national collaboration coordinating GRB
follow-up at the Roque de Los Muchachos Observatory on La Palma.
The authors acknowledge the indispensable assistance given by both
observers and staff at WHT and NOT.
More information:
Fynbo, J.P.U., et al., 2006, "Probing Cosmic Chemical Evolution with
Gamma-Ray Bursts: GRB060206 at z=4.048",
http://xxx.unizar.es/abs/astro-ph?papernum=0602444
IMAGE CAPTIONS:
[Figure 1:
http://www.ing.iac.es/PR/press/DLA_NOT.gif ()]
Portion of the NOT ALFOSC spectrum showing the Damped Lyman-alpha line at
the GRB redshift and the best fitting profile. A column density of neutral
hydrogen log N(HI)=20.85 ± 0.10 is derived. Credit: Isaac Newton Group of
Telescopes, La Palma
[Figure 2:
http://www.ing.iac.es/PR/press/finestructure_WHT.gif ()]
Portions of the ISIS spectrum showing the OI, OI*, OI**, SiII, SiII* and
SII lines. It is clearly visible that there are four discrete velocity
components, with velocity differences up to ~500 km/s. Credit: Isaac
Newton Group of Telescopes, La Palma
Santa Cruz de La Palma, Canary Islands, Spain
Contact:
Javier Méndez, Public Relations Officer
jma @ ing.iac.es
Release date: 2nd March, 2006
WHT and NOT Observations Probing Cosmic Evolution with Gamma-Ray Bursts:
GRB 060206 at Redshift 4.048
Gamma-ray bursts (GRBs) are very bright flashes of radiation, that are
detected approximately 100 times per year by satellites. For a long time
it was a mystery where these flashes originated from and how they were
produced. In 1997 astronomers using the William Herschel Telescope
discovered that GRBs show a so-called "afterglow": radiation in other
wavelengths following the gamma-rays. This afterglow can be studied with
telescopes from the Earth, and allowed astronomers to find that GRBs
originate in the violent deaths of massive stars, in star-forming galaxies
far away.
GRBs have proven to be excellent probes of the distant Universe. The high
luminosities of GRB afterglows allow absorption line studies of the
interstellar medium at high redshift up to redshifts larger than six. The
decrease in brightness of GRB afterglows means that a rapid response is
essential: the afterglow can be "caught" when it is still bright. To
exploit this benefit, the William Herschel Telescope (WHT) and the Nordic
Optical Telescope (NOT) have implemented rapid response GRB programmes.
Early in the morning of February the 6th, 2006 a GRB was detected by the
Swift satellite. The GRB was at that time high in the sky over La Palma
and the weather was good. Within 15 minutes the NOT was pointed towards
this burst by the Danish GRB follow-up group. Using ALFOSC a bright
optical afterglow was discovered in the R band. Directly after the
detection had been made, a low-resolution spectrum was acquired using the
same instrument. The latter spectrum rapidly determined the redshift of
GRB 060206 at z=4.048. Meanwhile, the WHT had been alerted through our
collaboration of the NOT and WHT, involving GRB follow-up teams from the
Netherlands, the United Kingdom and Denmark. Starting at just 1.6 hours
after the burst a medium-resolution spectrum could be obtained using WHT's
ISIS spectrograph.
The combination of the NOT and WHT provides a unique window on this
afterglow. The low resolution and broad wavelength coverage of the NOT
spectrum allowed an accurate determination of the column density of
neutral hydrogen (HI), redshifted to optical wavelengths. The high
resolution of the WHT spectra meant an accurate study of metal lines in
the spectrum was possible. A large number of metal lines are found in the
spectra, including (forbidden) fine-structure lines. Based on the
measurement of the neutral hydrogen column density and the metal content
from weak, unsaturated singly-ionised sulphur (SII) lines, a metallicity
of [S/H] = -0.84 ± 0.10, or ~0.14 times solar metallicity, was derived.
This is in fact one of the highest metallicities measured from absorption
lines at redshift around 4. From the very high column densities for the
forbidden singly-ionised silicon (SiII*), neutral oxygen (OI* and and
OI**) lines the researchers infer very high densities in the system,
significantly larger than 10^4 cm-3.
The high-resolution spectra also allows the astronomers to study the
kinematics of the absorption systems: several different, discrete velocity
systems can be distinguished, with velocities up to 500 km/s. Most
surprising however, was the tentative detection of molecular hydrogen in
the ISIS spectrum. This is the very first detection of molecular lines in
an optical GRB afterglow spectrum. Especially remarkable is the fact that
this possible detection has been done with a 4-metre telescope, proving
that medium size telescopes can compete when response times are short. The
joint study of the afterglow of GRB 060206 with WHT ISIS and NOT ALFOSC
shows the power of a multi-national collaboration coordinating GRB
follow-up at the Roque de Los Muchachos Observatory on La Palma.
The authors acknowledge the indispensable assistance given by both
observers and staff at WHT and NOT.
More information:
Fynbo, J.P.U., et al., 2006, "Probing Cosmic Chemical Evolution with
Gamma-Ray Bursts: GRB060206 at z=4.048",
http://xxx.unizar.es/abs/astro-ph?papernum=0602444
IMAGE CAPTIONS:
[Figure 1:
http://www.ing.iac.es/PR/press/DLA_NOT.gif ()]
Portion of the NOT ALFOSC spectrum showing the Damped Lyman-alpha line at
the GRB redshift and the best fitting profile. A column density of neutral
hydrogen log N(HI)=20.85 ± 0.10 is derived. Credit: Isaac Newton Group of
Telescopes, La Palma
[Figure 2:
http://www.ing.iac.es/PR/press/finestructure_WHT.gif ()]
Portions of the ISIS spectrum showing the OI, OI*, OI**, SiII, SiII* and
SII lines. It is clearly visible that there are four discrete velocity
components, with velocity differences up to ~500 km/s. Credit: Isaac
Newton Group of Telescopes, La Palma