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Journal ArticleDOI

A γ-ray burst at a redshift of z ≈ 8.2

29 Oct 2009-Nature (Nature Publishing Group)-Vol. 461, Iss: 7268, pp 1254-1257

AbstractLong-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars(1), and some are bright enough that they should be observable out to redshifts of z > 20 using current technology(2-4). Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy(5). Here we report that GRB 090423 lies at a redshift of z approximate to 8.2, implying that massive stars were being produced and dying as GRBs similar to 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

Topics: Redshift survey (64%), GRB 090423 (62%), Redshift (59%), Gamma-ray burst (59%), Galaxy (57%)

Summary (1 min read)

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Summary

  • Hitherto, the highest redshift measured for any object was z 5 6.96, for a Lyman-a emitting galaxy5.
  • The full grizYJHK spectral energy distribution (SED) obtained ,17 h after burst gives a photometric redshift of z 5 8:06z0:21{0:28, assuming a simple intergalactic medium (IGM) absorption model.
  • 21CRESST and NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
  • Finding such events is not an unreasonable hope: the most extreme GRBs have had afterglows that were intrinsically significantly brighter than that of GRB 090423 at the same rest-frame time3,4, and their first spectra were recorded more than 15 h after the burst.
  • The infrared light curve was obtained using UKIRT, Gemini North, the MPI/ESO 2.2-m telescope and the VLT.
  • Error bars are 1s (68% confidence level) and the absolute magnitude scale corresponds to absolute AB magnitudes at 0.136mm.
  • Probing the neutral fraction of the IGM with GRBs during the epoch of reionization.

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LETTERS
A c-ray burst at a redshift of z < 8.2
N. R. Tanvir
1
, D. B. Fox
2
, A. J. Levan
3
, E. Berger
4
, K. Wiersema
1
, J. P. U. Fynbo
5
, A. Cucchiara
2
, T. Kru
¨
hler
6,7
,
N. Gehrels
8
, J. S. Bloom
9
, J. Greiner
6
, P. A. Evans
1
, E. Rol
10
, F. Olivares
6
, J. Hjorth
5
, P. Jakobsson
11
, J. Farihi
1
,
R. Willingale
1
, R. L. C. Starling
1
, S. B. Cenko
9
, D. Perley
9
, J. R. Maund
5
, J. Duke
1
, R. A. M. J. Wijers
10
, A. J. Adamson
12
,
A. Allan
13
, M. N. Bremer
14
, D. N. Burrows
2
, A. J. Castro-Tirado
15
, B. Cavanagh
12
, A. de Ugarte Postigo
16
,
M. A. Dopita
17
, T. A. Fatkhullin
18
, A. S. Fruchter
19
, R. J. Foley
4
, J. Gorosabel
15
, J. Kennea
2
, T. Kerr
12
, S. Klose
20
,
H. A. Krimm
21,22
, V. N. Komarova
18
, S. R. Kulkarni
23
, A. S. Moskvitin
18
, C. G. Mundell
24
, T. Naylor
13
, K. Page
1
,
B. E. Penprase
25
, M. Perri
26
, P. Podsiadlowski
27
, K. Roth
28
, R. E. Rutledge
29
, T. Sakamoto
21
, P. Schady
30
, B. P. Schmidt
17
,
A. M. Soderberg
4
, J. Sollerman
5,31
, A. W. Stephens
28
, G. Stratta
26
, T. N. Ukwatta
8,32
, D. Watson
5
, E. Westra
4
,
T. Wold
12
& C. Wolf
27
Long-duration c-ray bursts (GRBs) are thought to result from the
explosions of certain massive stars
1
, and some are bright enough
that they should be observable out to redshifts of z . 20 using
current technology
2–4
. Hitherto, the highest redshift measured
for any object was z 5 6.96, for a Lyman-a emitting galaxy
5
.
Here we report that GRB 090423 lies at a redshift of z < 8.2, imply-
ing that massive stars were being produced and dying as GRBs
630 Myr after the Big Bang. The burst also pinpoints the location
of its host galaxy.
GRB 090423 was detected by the Burst Alert Telescope (BAT) on
NASA’s Swift satellite
6
at 07:55:19 UT on 23 April 2009. Observations
with Swift’s X-ray Telescope (XRT), which began 73 s after the trig-
ger, revealed a variable X-ray counterpart and localized its position to
a precision of 2.3 arcsec (at the 90% confidence level). Ground-based
optical observations in the r, i and z filters starting within a few min-
utes of the burst revealed no counterpart at these wavelengths
(Supplementary Information).
The United Kingdom Infrared Telescope (UKIRT), Hawaii, began
imaging about 20 min after the burst, in response to an automated
request, and provided the first infrared (2.15-m m) detection of the
GRB afterglow. In parallel, observations in other near-infrared (NIR)
filters using the Gemini North 8-m telescope, Hawaii, showed that
the counterpart was only visible at wavelengths greater than about
1.2 mm (Fig. 1). In this range, the afterglow was relatively bright and
exhibited a shallow spectral slope, F
n
/ n
20.26
, in contrast to the deep
limit on any flux at 1.02 mm. Later observations from Chile using the
MPI/ESO 2.2-m telescope, Gemini South and the Very Large
Telescope (VLT) confirmed this finding. Such a sharp spectral break
cannot be produced by dust absorption at any redshift, and is a
textbook case of a short-wavelength ‘drop-out’ source. The full
grizYJHK spectral energy distribution (SED) obtained ,17 h after
burst gives a photometric redshift of z 5 8:06
z0:21
{0:28
, assuming a simple
intergalactic medium (IGM) absorption model. Complete details of
our imaging campaign are given in Supplementary Table 1.
Our first NIR spectroscopy was performed with the European
Southern Observatory (ESO) 8.2-m VLT, starting about 17.5 h after
the burst. These observations revealed a flat continuum that abruptly
disappeared at wavelengths less than about 1.13 mm, confirming the
origin of the break as being due to Lyman-a absorption by neutral
1
Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK.
2
Department of Astronomy & Astrophysics, Pennsylvania State University,
University Park, Pennsylvania 16802, USA.
3
Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
4
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, Massachusetts 02138, USA.
5
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark.
6
Max-Planck-
Institut fu¨r Extraterrestrische Physik, Giessenbachstraße 1, 85740 Garching, Germany.
7
Universe Cluster, Technische Universita
¨
tMu¨nchen, Boltzmannstrasse 2, 85748 Garching,
Germany.
8
NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
9
Department of Astronomy, University of California, Berkeley, California 94720-3411, USA.
10
Astronomical Institute ‘‘Anton Pannekoek’’, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands.
11
Centre for Astrophysics and Cosmology, Science
Institute, University of Iceland, Dunhagi 5, 107 Reykjavı
´
k, Iceland.
12
Joint Astronomy Centre, 660 North A’ohoku Place, University Park, Hilo, Hawaii 96720, USA.
13
School of Physics,
University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
14
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
15
Instituto de Astrofı
´
sica de
Andalucı
´
a del Consejo Superior de Investigaciones Cientı
´
ficas, PO Box 03004, 18080 Granada, Spain.
16
European Southern Observatory, Casilla 19001, Santiago 19, Chile.
17
Research
School of Astronomy & Astrophysics, The Australian National University, Cotter Road, Weston Creek, Australian Capital Territory 2611, Australia.
18
Special Astrophysical
Observatory, Nizhnij Arkhyz, Karachai-Cirkassian Republic, 369167, Russia.
19
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA.
20
Thu¨ringer
Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany.
21
CRESST and NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
22
Universities Space
Research Association, 10211 Wincopin Circle, Suite 500, Columbia, Maryland 21044, USA.
23
Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena,
California 91125, USA.
24
Astrophysics Research Institute, Liverpool John Moores University, Birkenhead CH41 1LD, UK.
25
Department of Physics and Astronomy, Pomona College,
Claremont, California 91711, USA.
26
ASI Science Data Center, Via Galileo Galilei, 00044 Frascati, Italy.
27
Department of Physics, Oxford University, Keble Road, Oxford OX1 3RH, UK.
28
Gemini Observatory, Hilo, Hawaii 96720, USA.
29
Physics Department, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada.
30
The UCL Mullard Space
Science Laboratory, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK.
31
The Oskar Klein Centre, Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden.
32
The
George Washington University, Washington DC 20052, USA.
Figure 1
|
Multiband images of the afterglow of GRB 090423. The right-
most panel shows the discovery image made using the UKIRT Wide Field
Infrared Camera with the K filter (centred at 2.15 mm) at a mid-time of about
30 min after the burst. The other three images (Y, 1.02 mm; J, 1.26 mm;
H, 1.65 mm) were obtained approximately 1.5 h after the burst using Gemini
North’s Near Infrared Imager and Spectrometer (NIRI). The main panels are
40 arcsec to a side, oriented with north to the top and east to the left. Insets,
regions around the GRB, smoothed and at higher contrast. The absence of
any flux in Y implies a power-law spectral slope between Y and J steeper than
F
n
/ n
218
and, coupled with the blue colour at longer wavelengths
(J2H(AB) < 0.15 mag), immediately implies a redshift greater than about
7.8 for GRB 090423.
Vol 461
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29 October 2009
|
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Macmillan Publishers Limited. All rights reserved
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hydrogen, with a redshift of z < 8.2. The spectrum and broadband
photometric observations, plotted over model data, are shown in
Fig. 2. To obtain a more quantitative estimate of the redshift, we fit
the spectra in redshift versus log[N
H
I
(cm
22
)] space, assuming a flat
prior likelihood value for log[N
H
I
(cm
22
)] of between 19 and 23,
which is broadly consistent with the distribution observed for
lower-redshift GRB hosts
7–9
. We take the neutral fraction of the
IGM to be 10%, although our conclusions depend only weakly on
this assumption. We find the redshift from ISAAC spectroscopy to be
z 5 8:19
z0:03
{0:06
. An additional spectrum, recorded ,40 h after the
burst using the VLT’s Spectrograph for INtegral Field Observations
in the Near Infrared confirms this analysis, yielding z 5 8:33
z0:06
{0:11
(Supplementary Information). Fitting simultaneously to both spec-
tra and the photometric data points gives our best estimate of the
redshift, z 5 8:23
z0:06
{0:07
. The low signal-to-noise ratio means we that
are unable to detect metal absorption features in either spectrum—
which would provide a more precise value of the redshift—and pre-
vents a meaningful attempt to measure the IGM H
I column density
in this instance. Our three independent redshift measures are con-
sistent with that reported from a low-resolution spectrum obtained
with the Telescopio Nazionale Galileo, La Palma
10
.
The X-ray and NIR light curves of GRB 090423 (Fig. 3) show a
broken power-law decay, with evidence of flares in both the X-ray
and the infrared bands. The spectral energy distribution is consistent
with the presence of the cooling break between the X-ray and optical
bands. Apart from the unusually shallow spectral slope of the con-
tinuum at wavelengths greater than 1.2 mm, its afterglow properties in
general appear to be consistent with the bulk GRB population (see
Supplementary Information for further discussion).
With the standard cosmological parameters (Hubble parameter,
H
0
5 71 km s
21
Mpc
21
; total matter density, V
M
5 0.27; dark-
energy density, V
L
5 0.73) a redshift of z 5 8.2 corresponds to a time
of only 630 Myr after the Big Bang, when the Universe was just 4.6%
of its current age. GRB 090423’s inferred isotropic equivalent energy,
E
iso
5 1 3 10
53
erg (8–1,000 keV)
11
, indicates that it was a bright, but
not extreme, GRB. Thus, we find no evidence of exceptional beha-
viour that might indicate an origin in a population III progenitor.
First-generation stars are thought more likely to collapse into par-
ticularly massive black holes, which in turn may produce unusually
long-lived GRBs
12
; this seems not to be the case for GRB 090423.
Indeed, we note that the c-ray duration of GRB 090423,
t
90
5 10.3 s, corresponds in the rest frame to only 1.1 s, and the peak
energy measured by BAT, 49 keV, is moderately hard in the rest
frame. Two other GRBs with z . 5 (GRB 060927 and GRB 080913)
had similarly short rest-frame durations, leading to some debate
13
as
to whether their progenitors were similar to those of the ‘short-hard’
class of GRBs, which are not thought to be directly related to core
collapse. However, in the case of GRB 090423, a more careful extra-
polation of the observed c-ray and X-ray light curves to lower red-
shifts shows that its duration would have appeared significantly
longer than suggested by naive time-dilation considerations
14
.In
any event, short GRBs probably have their origins in compact objects
that are themselves the end products of massive stars, so the above
conclusions will hold irrespective of the population from which
GRB 090423 derives.
It has long been recognized that GRBs have the potential to be power-
ful probes of the early Universe
15
. Their association with individual stars
means that they serve as a signpost of star formation, even if their host
0.1
12
Flux density at 16 h (μJy)
20
10
0
–10
–20
0.2
Rest-frame wavelength (μm)
Observed wavelength (μm)
SZ J
23
22
21
20
19
8 8.5
Redshift
H
K
J
z
Y
log[N
H I
(cm
–2
)]
Figure 2
|
The composite infrared spectrum of the GRB 090423 afterglow.
SZ-band (0.98–1.1 mm) and J-band (1.1–1.4 mm) one- and two-dimensional
spectra obtained with the VLT using the Infrared Spectrometer And Array
Camera (ISAAC). Also plotted are the sky-subtracted photometric data
points obtained using Gemini North’s NIRI (red) and the VLT’s High Acuity
Wide field K-band Imager and Gemini South’s Gemini Multi-Object
Spectrograph (blue) (scaled to 16 h after the burst and expressed in
microjanskys; 1 Jy 5 10
226
Wm
22
Hz
21
). The vertical error bars show the
2s (95%) confidence level, and the horizontal lines indicate the widths of the
filters. The shorter-wavelength measurements are non-detections, and
emphasize the tight constraints on any transmitted flux below the break. The
break itself, at an observed wavelength of about 1.13 mm, is seen to occur
close to the short-wavelength limit of the J-band spectrum, below which,
although noisy, the spectrum shows no evidence of any detected continuum.
Details of the data-reduction steps and adaptive binning used to construct
these spectra are given in Supplementary Information. A model spectrum
showing the H
I damping wing for a host galaxy with a hydrogen column
density of N
H
I
5 10
21
cm
22
at a redshift of z 5 8.23 is also plotted (solid
black line), and provides a good fit to the data. Inset, allowing for a wider
range in possible host N
H
I
values gives the 1s (68%) and 2s confidence
contours shown. The fact that no deviation is seen from a power-law
spectrum at wavelengths greater than 1.2 mm, together with its shallow
spectral slope, suggests that there is little or no dust along the line of sight
through the GRB host galaxy (unless it is ‘grey’), consistent with the galaxy
being relatively unevolved, and having a low abundance of metals.
NATURE
|
Vol 461
|
29 October 2009 LETTERS
1255
Macmillan Publishers Limited. All rights reserved
©2009

galaxies are too faint to detect directly. Equally important, precise deter-
mination of the hydrogen Lyman-a absorption profile can provide a
measure of the neutral fraction of the IGM at the location of the
burst
16–20
. With multiple GRBs at redshifts of z . 7, and the associated
information about the IGM, we could therefore trace the process of
reionization from its early stages
21
.
The high redshift of GRB 090423 has several crucial implications.
Predictions based on extrapolating the global star-formation-rate
density suggest that the observed rate of GRBs at z < 8 should be about
40% of that at z < 6 (ref. 12). Given the extra difficulty of identifying
afterglows at higher redshifts, our finding is broadly consistent with
these predictions. This is extremely encouraging for the prospects of
future initiatives aimed at finding high-redshift GRBs and using them
to locate and study primordial galaxies and measure the history of star
formation at early times
22–24
. Furthermore, it is close to the redshift
range in which the bulk of the cosmic reionization is thought to have
taken place
25–27
. Very high-redshift GRBs for which infrared spectro-
scopy was possible earlier, or which had brighter afterglows, would
provide a direct probe of the progress of reionization. Finding such
events is not an unreasonable hope: the most extreme GRBs have had
afterglows that were intrinsically significantly brighter than that of
GRB 090423 at the same rest-frame time
3,4
, and our first spectra were
recorded more than 15 h after the burst. Spectroscopy with a high
signal-to-noise ratio would also provide a measure of the metallicity
of the host galaxy, which potentially offers important clues to the
nature of any earlier generations of stars. Because the massive stars
that yield GRBs are also likely to belong to the same population that is
responsible for reionization, this suggests that GRBs will ultimately be
used to constrain both sides—supply and demand—of the cosmic
ionization budget in the early Universe.
Received 3 June; accepted 19 August 2009.
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0.1
10
5
10
4
1,000
100
10
1
0.1
0.01
19
20
21
22
23
24
25
26
1 10 100 1,000
J band
H band
K band
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Rest-frame time since GRB 090423 (s)
Observer time since GRB 090423 (s)
X-ray
Luminosity (erg s
–1
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Flux (10
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AB magnitude
M
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Infrared
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Figure 3
|
The X-ray and infrared light curves of GRB 090423. The axes
show both observed (left-hand and bottom axes) and rest-frame (right-hand
and top axes) quantities. The X-ray light curve was obtained using Swift’s
BAT (cyan) and XRT (magenta), where the BAT observations have been
extrapolated into the X-ray band. The fitted function represents a
phenomenological model
28
of the prompt and afterglow components. The
infrared light curve was obtained using UKIRT, Gemini North, the MPI/ESO
2.2-m telescope and the VLT. For consistency, although individual bands are
plotted, they have been transformed into absolute magnitudes in the J band
by means of the best-fitting SED (F
n
/ n
20.26
). We show two illustrative fits
to the infrared light curve. The solid line shows a plateau, breaking at
24,000 s to a steeper slope proportional to ,t
21.4
. This underestimates the
late time points, which must then be interpreted as a flare. The dashed line
shows an alternative model, in which mid-time points at ,60,000 s are
instead interpreted as a flare; this is more consistent with the later time
points and the X-ray break time at the end of the plateau. However, in this
case the post-break slope, proportional to ,t
20.7
, is much slower than the
X-ray decay at comparable times, and it further requires a additional break in
the light curve to accommodate the late-time upper limit. Error bars are 1s
(68% confidence level) and the absolute magnitude scale corresponds to
absolute AB magnitudes at 0.136 mm. See Supplementary Information for
further details.
LETTERS NATURE
|
Vol 461
|
29 October 2009
1256
Macmillan Publishers Limited. All rights reserved
©2009

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Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements We thank Ph. Yock, B. Allen, P. Kubanek, M. Jelinek and
S. Guziy for their assistance with the BOOTES-3 YA telescope observations
(Supplementary Information). This work was partly based on observations
obtained at the Gemini Observatory, which is operated by the Association of
Universities for Research in Astronomy, Inc., under a cooperative agreement with
the US National Science Foundation on behalf of the Gemini partnership: the
National Science Foundation (United States), the Science and Technology Facilities
Council (United Kingdom), the National Research Council (Canada), CONICYT
(Chile), the Australian Research Council (Australia), the Ministe
´
rio da Cie
ˆ
ncia e
Tecnologia (Brazil) and SECYT (Argentina). This work was also partly based on
observations made using ESO telescopes at the La Silla or Paranal observatories by
G. Carraro, L. Schmidtobreick, G. Marconi, J. Smoker, V. Ivanov, E. Mason and
M. Huertas-Company. The UKIRT is operated by the Joint Astronomy Centre on
behalf of the UK Science and Technology Facilities Council. R.J.F. acknowledges a
Clay Fellowship.
Author Contributions Triggering observations: N.R.T., D.B.F., A.J.L., E.B., J.S.B.,
D.P., J. Greiner, A.J.C.-T., A.d.U.P.; analysis of ground-based data: N.R.T., D.B.F.,
A.J.L., E.B., K.W., J.P.U.F., A.C., J.S.B., J.F., J.D., J. Gorosabel, B.C., D.P., J.R.M.,
T. Kru¨hler, A.J.C.-T., A.d.U.P., C.G.M.; Swift analysis: P.A.E., R.L.C.S., K.P., R.W.,
A.J.L., N.R.T., N.G., D.W., P.S., T.S.; observations at various observatories and their
automation to accept GRB overrides: A.J.A., A.A., T. Kerr, T.N., A.W.S., K.R., T.W.
All authors made contributions through their involvement in the programmes from
which the data derive, and contributed to the interpretation, content and
discussion presented here. Writing was led by N.R.T., A.J.L., D.B.F. and E.B.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. Correspondence and requests for materials should be
addressed to N.R.T. (nrt3@star.le.ac.uk).
NATURE
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Vol 461
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29 October 2009 LETTERS
1257
Macmillan Publishers Limited. All rights reserved
©2009
Citations
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Journal ArticleDOI
30 Jun 2011-Nature
TL;DR: Observations of a quasar at a redshift of 7.3 are reported, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.
Abstract: Quasars have historically been identified in optical surveys, which are insensitive to sources at z > 6.5. Infrared deep-sky survey data now make it possible to explore higher redshifts, with the result that a luminous quasar (ULAS J1120+0641) with a redshift z = 7.085, beyond the previous high of z = 6.44, has now been identified. Further observations of this and other distant quasars should reveal the ionization state of the Universe as it was only about 0.75 billion years after the Big Bang. The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed1 by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified2,3,4 in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 1013L⊙ and hosts a black hole with a mass of 2 × 109M⊙ (where L⊙ and M⊙ are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing5, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

1,406 citations


Journal ArticleDOI
Abstract: The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of “dark energy” with exotic physical properties, or that Einstein’s theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious efforts to understand its origin, with experiments that aim to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and the abundance of galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit “Stage IV” dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We briefly review a number of other approaches including redshift-space distortions, the Alcock–Paczynski effect, and direct measurements of the Hubble constant H_0. We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from General Relativity, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and cosmic microwave background data. We also show the level of precision required for clusters or other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets that support a wide range of scientific investigations, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.

1,111 citations


Journal ArticleDOI
Abstract: The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit Multi-Cycle Treasury Program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of structure formation models. The CLASH cluster sample is larger and less biased than current samples of space-based imaging studies of clusters to similar depth, as we have minimized lensing-based selection that favors systems with overly dense cores. Specifically, 20 CLASH clusters are solely X-ray selected. The X-ray-selected clusters are massive (kT > 5 keV) and, in most cases, dynamically relaxed. Five additional clusters are included for their lensing strength (θ_Ein > 35" at z_s = 2) to optimize the likelihood of finding highly magnified high-z (z > 7) galaxies. A total of 16 broadband filters, spanning the near-UV to near-IR, are employed for each 20-orbit campaign on each cluster. These data are used to measure precise (σ_z ~ 0.02(1 + z)) photometric redshifts for newly discovered arcs. Observations of each cluster are spread over eight epochs to enable a search for Type Ia supernovae at z > 1 to improve constraints on the time dependence of the dark energy equation of state and the evolution of supernovae. We present newly re-derived X-ray luminosities, temperatures, and Fe abundances for the CLASH clusters as well as a representative source list for MACS1149.6+2223 (z = 0.544).

826 citations


Journal ArticleDOI
Abstract: Understanding massive stars is essential for a variety of branches of astronomy including galaxy and star cluster evolution, nucleosynthesis and supernovae, pulsars, and black holes. It has become evident that massive star evolution is very diverse, being sensitive to metallicity, binarity, rotation, and possibly magnetic fields. Although the problem to obtain a good statistical observational database is alleviated by current large spectroscopic surveys, it remains a challenge to model these diverse paths of massive stars toward their violent end stage. I show that the main sequence stage offers the best opportunity to gauge the relevance of the various possible evolutionary scenarios. This also allows sketching the post-main-sequence evolution of massive stars, for which observations of Wolf-Rayet stars give essential clues. Recent supernova discoveries owing to the current boost in transient searches allow tentative mappings of progenitor models with supernova types, including pair-instability supernova...

737 citations


Journal ArticleDOI
Abstract: We provide a comprehensive review of major developments in our understanding of gamma-ray bursts, with particular focus on the discoveries made within the last fifteen years when their true nature was uncovered. We describe the observational properties of photons from the radio to 100s GeV bands, both in the prompt emission and the afterglow phases. Mechanisms for the generation of these photons in GRBs are discussed and confronted with observations to shed light on the physical properties of these explosions, their progenitor stars and the surrounding medium. After presenting observational evidence that a powerful, collimated, jet moving at close to the speed of light is produced in these explosions, we describe our current understanding regarding the generation, acceleration, and dissipation of the jet. We discuss mounting observational evidence that long duration GRBs are produced when massive stars die, and that at least some short duration bursts are associated with old, roughly solar mass, compact stars. The question of whether a black-hole or a strongly magnetized, rapidly rotating neutron star is produced in these explosions is also discussed. We provide a brief summary of what we have learned about relativistic collisionless shocks and particle acceleration from GRB afterglow studies, and discuss the current understanding of radiation mechanism during the prompt emission phase. We discuss theoretical predictions of possible high-energy neutrino emission from GRBs and the current observational constraints. Finally, we discuss how these explosions may be used to study cosmology, e.g. star formation, metal enrichment, reionization history, as well as the formation of first stars and galaxies in the universe.

725 citations


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Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent limits on deviations from the minimal, six-parameter Λ cold dark matter model. We report these limits and use them to constrain the physics of cosmic inflation via Gaussianity, adiabaticity, the power spectrum of primordial fluctuations, gravitational waves, and spatial curvature. We also constrain models of dark energy via its equation of state, parity-violating interaction, and neutrino properties, such as mass and the number of species. We detect no convincing deviations from the minimal model. The six parameters and the corresponding 68% uncertainties, derived from the WMAP data combined with the distance measurements from the Type Ia supernovae (SN) and the Baryon Acoustic Oscillations (BAO) in the distribution of galaxies, are: Ω b h 2 = 0.02267+0.00058 –0.00059, Ω c h 2 = 0.1131 ± 0.0034, ΩΛ = 0.726 ± 0.015, ns = 0.960 ± 0.013, τ = 0.084 ± 0.016, and at k = 0.002 Mpc-1. From these, we derive σ8 = 0.812 ± 0.026, H 0 = 70.5 ± 1.3 km s-1 Mpc–1, Ω b = 0.0456 ± 0.0015, Ω c = 0.228 ± 0.013, Ω m h 2 = 0.1358+0.0037 –0.0036, z reion = 10.9 ± 1.4, and t 0 = 13.72 ± 0.12 Gyr. With the WMAP data combined with BAO and SN, we find the limit on the tensor-to-scalar ratio of r 1 is disfavored even when gravitational waves are included, which constrains the models of inflation that can produce significant gravitational waves, such as chaotic or power-law inflation models, or a blue spectrum, such as hybrid inflation models. We obtain tight, simultaneous limits on the (constant) equation of state of dark energy and the spatial curvature of the universe: –0.14 < 1 + w < 0.12(95%CL) and –0.0179 < Ω k < 0.0081(95%CL). We provide a set of WMAP distance priors, to test a variety of dark energy models with spatial curvature. We test a time-dependent w with a present value constrained as –0.33 < 1 + w 0 < 0.21 (95% CL). Temperature and dark matter fluctuations are found to obey the adiabatic relation to within 8.9% and 2.1% for the axion-type and curvaton-type dark matter, respectively. The power spectra of TB and EB correlations constrain a parity-violating interaction, which rotates the polarization angle and converts E to B. The polarization angle could not be rotated more than –59 < Δα < 24 (95% CL) between the decoupling and the present epoch. We find the limit on the total mass of massive neutrinos of ∑m ν < 0.67 eV(95%CL), which is free from the uncertainty in the normalization of the large-scale structure data. The number of relativistic degrees of freedom (dof), expressed in units of the effective number of neutrino species, is constrained as N eff = 4.4 ± 1.5 (68%), consistent with the standard value of 3.04. Finally, quantitative limits on physically-motivated primordial non-Gaussianity parameters are –9 < f local NL < 111 (95% CL) and –151 < f equil NL < 253 (95% CL) for the local and equilateral models, respectively.

5,716 citations


Journal ArticleDOI
20 Aug 2004
Abstract: The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr � 1 and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to (1) determine the origin of GRBs, (2) classify GRBs and search for new types, (3) study the interaction of the ultrarelativistic outflows of GRBs with their surrounding medium, and (4) use GRBs to study the early universe out to z >10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a newgeneration wide-field gamma-ray (15‐150 keV) detector that will detect bursts, calculate 1 0 ‐4 0 positions, and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5 00 positions and perform spectroscopy in the 0.2‐10 keV band; and a narrow-field UV/optical telescope that will operate in the 170‐ 600 nm band and provide 0B3 positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of � 1m crab (� 2;10 � 11 ergs cm � 2 s � 1 in the 15‐150 keV band), more than an order of magnitude better than HEAO 1 A-4. A flexible data and operations system will allow rapid follow-up observations of all types of

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Journal ArticleDOI
TL;DR: A homogeneous X-rays analysis of all 318 gamma-ray bursts detected by the X-ray telescope (XRT) on the Swift satellite up to 2008 July 23 is presented; this represents the largest sample ofX-ray GRB data published to date.
Abstract: We present a homogeneous X-ray analysis of all 318 gamma-ray bursts detected by the X-ray telescope (XRT) on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB data published to date. In Sections 2-3, we detail the methods which the Swift-XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift-XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4-6, we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light-curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks.

1,420 citations


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