-
A. J. Levan,
N. R. Tanvir,
R. L. C. Starling,
K. Wiersema,
K. L. Page,
D. A. Perley,
S. Schulze,
G. A. Wynn,
R. Chornock,
J. Hjorth, [......],
J. P. Osborne,
E. Pian,
R. Sanchez-Ramirez,
B. Schmidt,
I. Skillen,
G. Tagliaferri,
C. Thone,
O. Vaduvescu,
R. A. M. J. Wijers,
B. A. Zauderer
[show abstract]
[hide abstract]
ABSTRACT: We present comprehensive multiwavelength observations of three gamma-ray
bursts (GRBs) with durations of several thousand seconds. We demonstrate that
these events are extragalactic transients; in particular we resolve the
long-standing conundrum of the distance of GRB 101225A (the "Christmas-day
burst"), finding it to have a redshift z=0.847, and showing that two apparently
similar events (GRB 111209A and GRB 121027A) lie at z=0.677 and z=1.773
respectively. The systems show extremely unusual X-ray and optical lightcurves,
very different from classical GRBs, with long lasting highly variable X-ray
emission and optical light curves that exhibit little correlation with the
behaviour seen in the X-ray. Their host galaxies are faint, compact, and highly
star forming dwarf galaxies, typical of "blue compact galaxies". We propose
that these bursts are the prototypes of a hitherto largely unrecognized
population of ultra-long GRBs, that while observationally difficult to detect
may be astrophysically relatively common. The long durations may naturally be
explained by the engine driven explosions of stars of much larger radii than
normally considered for GRB progenitors which are thought to have compact
Wolf-Rayet progenitor stars. However, we cannot unambiguously identify
supernova signatures within their light curves or spectra. We also consider the
alternative possibility that they arise from the tidal disruption of stars by
supermassive black holes.
02/2013;
-
J Hjorth,
D Malesani,
P Jakobsson,
A ~O Jaunsen,
J ~P ~U Fynbo,
J Gorosabel,
T Krühler,
A ~J Levan,
M ~J Michalowski,
B Milvang-Jensen,
P Møller,
S Schulze,
N ~R Tanvir, D Watson
apj. 09/2012; 756:187.
-
T Zafar, D Watson,
Á {El'i}asdóttir,
J ~P ~U Fynbo,
T Krühler,
P Schady,
G Leloudas,
P Jakobsson,
C ~C Thöne,
D ~A Perley,
A ~N Morgan,
J Bloom,
J Greiner
apj. 07/2012; 753:82.
-
C. C. Thoene,
J. P. U. Fynbo,
P. Goldoni,
A. de Ugarte Postigo,
S. Campana,
S. D. Vergani,
S. Covino,
T. Kruehler,
L. Kaper,
N. Tanvir, [......],
S. Klose,
A. J. Levan,
B. Milvang-Jensen,
A. Nicuesa Guelbenzu,
E. Palazzi,
S. Piranomonte,
G. Tagliaferri, D. Watson,
K. Wiersema,
R. A. M. J. Wijers
[show abstract]
[hide abstract]
ABSTRACT: Abundances of galaxies at redshifts z > 4 are difficult to obtain from damped
Ly {\alpha} (DLA) systems in the sightlines of quasars (QSOs) due to the Ly
{\alpha} forest blanketing and the low number of high-redshift quasars
detected. Gamma-ray bursts (GRBs) with their higher luminosity are well suited
to study galaxies out to the formation of the first stars at z > 10. Its large
wavelength coverage makes the X-shooter spectrograph an excellent tool to study
the interstellar medium (ISM) of high redshift galaxies, in particular if the
redshift is not known beforehand. Here we determine the properties of a GRB
host at z = 4.66723 from a number of resonant low- and high ionization and
fine-structure absorption lines. This is one of the highest redshifts where a
detailed analysis with medium-resolution data has been possible. We detect one
intervening system at z = 2.18. The velocity components of the absorption lines
are fitted with Voigt-profiles and we determine a metallicity of [M/H] = -1.0
\pm 0.1 using S. The absorption lines show a complicated kinematic structure
which could point to a merger in progress. Si II* together with the restframe
UV energy release determined from GROND data gives us the distance of 0.3 to 1
kpc of the absorbing material from the GRB. We measure a low extinction of AV =
0.24 \pm 0.06 mag using X-ray spectral information and the flux calibrated
X-shooter spectrum. GRB-DLAs have a shallower evolution of metallicity with
redshift than QSO absorbers and no evolution in HI column density or ionization
fraction. GRB hosts at high redshift might continue the trend towards lower
metallicities in the LZ-relation with redshift, but the sample is still too
small to draw a definite conclusion. While the detection of GRBs at z > 4 with
current satellites is still difficult, they are very important for our
understanding of the early epochs of star- and galaxy-formation.
06/2012;
-
Jan-Willem den Herder,
Luigi Piro,
Takaya Ohashi,
Chryssa Kouveliotou,
Dieter H. Hartmann,
Jelle S. Kaastra,
L. Amati,
M. I. Andersen,
M. Arnaud,
J. -L. Attéia, [......],
S. Wachter, D. Watson,
M. Weisskopf,
N. Werner,
N. White,
R. Willingale,
R. Wijers,
N. Yamasaki,
K. Yoshikawa,
S. Zane
[show abstract]
[hide abstract]
ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using
high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements
between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal
content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and
evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in
their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying
the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts
(z ∼0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument,
we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part
of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a
Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm2/s in 10s in the 5–150keV band) to identify and localize 2000GRBs over a five year mission, of which ∼65GRBs have a redshift
>7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5eV, a field of view of 30arcmin and large effective
area below 1keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser
parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed
Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes
the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background
is achieved by the selected low Earth orbit.
KeywordsX-ray–Mission–Gamma-ray bursts–Clusters of galaxies–Warm-hot intergalactic medium–Chemical evolution
Experimental Astronomy 04/2012; · 1.82 Impact Factor
-
D. Watson,
J. French,
L. Christensen,
B. O'Halloran,
M. Michałowski,
J. Hjorth,
D. Malesani,
J. P. U. Fynbo,
K. D. Gordon,
J. M. Castro Cerón,
S. Covino,
and R. F. Reinfrank
[show abstract]
[hide abstract]
ABSTRACT: Gamma-ray burst (GRB) host galaxies have been studied extensively in optical photometry and spectroscopy. Here we present the first mid-infrared spectrum of a GRB host, HG 031203. It is one of the nearest GRB hosts at z = 0.1055, allowing both low- and high-resolution spectroscopy with the Spitzer Infrared Spectrograph (IRS). Medium-resolution UV to K-band spectroscopy with the X-shooter spectrograph on the Very Large Telescope is also presented, along with Spitzer IRAC and MIPS photometry, as well as radio and submillimeter observations. These data allow us to construct a UV to radio spectral energy distribution with almost complete spectroscopic coverage from 0.3 to 35 μm of a GRB host galaxy for the first time, potentially valuable as a template for future model comparisons. The IRS spectra show strong, high-ionization fine structure line emission indicative of a hard radiation field in the galaxy—in particular the [S IV]/[S III] and [Ne III]/[Ne II] ratios—suggestive of strong ongoing star formation and a very young stellar population. The absence of any polycyclic aromatic hydrocarbon emission supports these conclusions, as does the probable hot peak dust temperature, making HG 031203 similar to the prototypical blue compact dwarf galaxy (BCD), II Zw 40. The selection of HG 031203 via the presence of a GRB suggests that it might be a useful analog of very young star-forming galaxies in the early universe, and hints that local BCDs may be used as more reliable analogs of star formation in the early universe than typical local starbursts. We look at the current debate on the ages of the dominant stellar populations in z ~ 7 and z ~ 8 galaxies in this context. The nebular line emission is so strong in HG 031203 that at z ~ 7, it can reproduce the spectral energy distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 μm fluxes without the need to invoke a 4000 Å break. Indeed, photometry of HG 031203 shows elevation of the broadband V-magnitude at a level similar to the IRAC elevation in stacked z-band dropouts, solely due to its strong [O III] line emission.
The Astrophysical Journal 10/2011; 741(1):58. · 6.02 Impact Factor
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R. Amanullah,
A Goobar,
B. Clément,
J. -G. Cuby,
H. Dahle,
T. Dahlén,
J. Hjorth,
S. Fabbro,
J. Jönsson,
J. -P. Kneib,
C. Lidman,
M. Limousin,
B. Milvang-Jensen,
E. Mörtsell,
J. Nordin,
K. Paech,
J. Richard,
T. Riehm,
V. Stanishev, D. Watson
[show abstract]
[hide abstract]
ABSTRACT: Our ability to study the most remote supernova explosions, crucial for the
understanding of the evolution of the high-redshift universe and its expansion
rate, is limited by the light collection capabilities of telescopes. However,
nature offers unique opportunities to look beyond the range within reach of our
unaided instruments thanks to the light-focusing power of massive galaxy
clusters. Here we report on the discovery of one of the most distant supernovae
ever found, at redshift, z=1.703. Due to a lensing magnification factor of
4.3\pm0.3, we are able to measure a lightcurve of the supernova, as well as
spectroscopic features of the host galaxy with a precision comparable to what
will otherwise only be possible with future generation telescopes.
09/2011;
-
K. M. Svensson,
N. R. Tanvir,
D. A. Perley,
M. J. Michalowski,
K. L. Page,
J. S. Bloom,
S. B. Cenko,
J. Hjorth,
P. Jakobsson, D. Watson,
P. J. Wheatley
[show abstract]
[hide abstract]
ABSTRACT: [Abridged] We present comprehensive X-ray, optical, near- and mid-infrared,
and sub-mm observations of GRB 080207 and its host galaxy. The afterglow was
undetected in the optical and near-IR, implying an optical to X-ray index <0.3,
identifying GRB 080207 as a dark burst. Swift X-ray observations show extreme
absorption in the host, which is confirmed by the unusually large optical
extinction found by modelling the X-ray to nIR afterglow spectral energy
distribution. Our Chandra observations obtained 8 days post-burst allow us to
place the afterglow on the sky to sub-arcsec accuracy, enabling us to pinpoint
an extremely red galaxy (ERO). Follow-up host observations with HST, Spitzer,
Gemini, Keck and the James Clerk Maxwell Telescope (JCMT) provide a photometric
redshift solution of z ~1.74 (+0.05,-0.06) (1 sigma), 1.56 < z < 2.08 at 2
sigma) for the ERO host, and suggest that it is a massive and morphologically
disturbed ultra-luminous infrared galaxy (ULIRG) system, with L_FIR ~ 2.4 x
10^12 L_solar. These results add to the growing evidence that GRBs originating
in very red hosts always show some evidence of dust extinction in their
afterglows (though the converse is not true -- some extinguished afterglows are
found in blue hosts). This indicates that a poorly constrained fraction of GRBs
occur in very dusty environments. By comparing the inferred stellar masses, and
estimates of the gas phase metallicity in both GRB hosts and sub-mm galaxies we
suggest that many GRB hosts, even at z>2 are at lower metallicity than the
sub-mm galaxy population, offering a likely explanation for the dearth of
sub-mm detected GRB hosts. However, we also show that the dark GRB hosts are
systematically more massive than those hosting optically bright events, perhaps
implying that previous host samples are severely biased by the exclusion of
dark events.
09/2011;
-
J. W. den Herder,
L. Piro,
T. Ohashi,
C. Kouveliotou,
D. H. Hartmann,
J. S. Kaastra,
L. Amati,
M. I. Andersen,
M. Arnaud,
J-L. Attéia, [......],
S. Wachter, D. Watson,
M. Weisskopf,
N. Werner,
N. White,
R. Willingale,
R. Wijers,
N. Yamasaki,
K. Yoshikawa,
S. Zane
[show abstract]
[hide abstract]
ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of
metal creation from the epoch of cosmic dawn. Using high-spectral resolution in
the soft X-ray band, ORIGIN will be able to identify the physical conditions of
all abundant elements between C and Ni to red-shifts of z=10, and beyond. The
mission will answer questions such as: When were the first metals created? How
does the cosmic metal content evolve? Where do most of the metals reside in the
Universe? What is the role of metals in structure formation and evolution? To
reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to
study their local environments in their host galaxies. This requires the
capability to slew the satellite in less than a minute to the GRB location. By
studying the chemical composition and properties of clusters of galaxies we can
extend the range of exploration to lower redshifts (z ~ 0.2). For this task we
need a high-resolution spectral imaging instrument with a large field of view.
Using the same instrument, we can also study the so far only partially detected
baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the
WHIM will be studied using absorption lines at low redshift in the spectra for
GRBs.
Experimental Astronomy 04/2011; 34(2):519. · 1.82 Impact Factor
-
GRB Coordinates Network. 01/2011; 12542:1.
-
D. A. Kann,
S. Klose,
B. Zhang,
D. Malesani,
E. Nakar,
A. Pozanenko,
A. C. Wilson,
N. R. Butler,
P. Jakobsson,
S. Schulze, [......],
L. Stella,
G. Tagliaferri,
N. R. Tanvir,
J. Telting,
V. Testa,
A. C. Updike,
A. Volnova, D. Watson,
K. Wiersema,
and D. Xu
[show abstract]
[hide abstract]
ABSTRACT: We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
The Astrophysical Journal 08/2010; 720(2):1513. · 6.02 Impact Factor
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N R Tanvir,
D B Fox,
A J Levan,
E Berger,
K Wiersema,
J P U Fynbo,
A Cucchiara,
T Krühler,
N Gehrels,
J S Bloom, [......],
B P Schmidt,
A M Soderberg,
J Sollerman,
A W Stephens,
G Stratta,
T N Ukwatta, D Watson,
E Westra,
T Wold,
C Wolf
[show abstract]
[hide abstract]
ABSTRACT: Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approximately 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.
Nature 10/2009; 461(7268):1254-7. · 36.28 Impact Factor
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N. R. Tanvir,
D. B. Fox,
A. J. Levan,
E. Berger,
K. Wiersema,
J. P. U. Fynbo,
A. Cucchiara,
T. Kruehler,
N. Gehrels,
J. S. Bloom, [......],
B. P. Schmidt,
A. M. Soderberg,
J. Sollerman,
A. W. Stephens,
G. Stratta,
T. N. Ukwatta, D. Watson,
E. Westra,
T. Wold,
C Wolf
[show abstract]
[hide abstract]
ABSTRACT: It is thought that the first generations of massive stars in the Universe were an important, and quite possibly dominant, source of the ultra-violet radiation that reionized the hydrogen gas in the intergalactic medium (IGM); a state in which it has remained to the present day. Measurements of cosmic microwave background anisotropies suggest that this phase-change largely took place in the redshift range z=10.8 +/- 1.4, while observations of quasars and Lyman-alpha galaxies have shown that the process was essentially completed by z=6. However, the detailed history of reionization, and characteristics of the stars and proto-galaxies that drove it, remain unknown. Further progress in understanding requires direct observations of the sources of ultra-violet radiation in the era of reionization, and mapping the evolution of the neutral hydrogen fraction through time. The detection of galaxies at such redshifts is highly challenging, due to their intrinsic faintness and high luminosity distance, whilst bright quasars appear to be rare beyond z~7. Here we report the discovery of a gamma-ray burst, GRB 090423, at redshift z=8.26 -0.08 +0.07. This is well beyond the redshift of the most distant spectroscopically confirmed galaxy (z=6.96) and quasar (z=6.43). It establishes that massive stars were being produced, and dying as GRBs, ~625 million years after the Big Bang. In addition, the accurate position of the burst pinpoints the location of the most distant galaxy known to date. Larger samples of GRBs beyond z~7 will constrain the evolving rate of star formation in the early universe, while rapid spectroscopy of their afterglows will allow direct exploration of the progress of reionization with cosmic time. Comment: Submitted to Nature
06/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: GRB 060505 and GRB 060614 are nearby long-duration gamma-ray bursts (LGRBs) without accompanying supernovae (SNe) down to very strict limits. They thereby challenge the conventional LGRB-SN connection and naturally give rise to the question: are there other peculiar features in their afterglows which would help shed light on their progenitors? To answer this question, we combine new observational data with published data and investigate the multiband temporal and spectral properties of the two afterglows. We find that both afterglows can be well interpreted within the framework of the jetted standard external shock wave model, and that the afterglow parameters for both bursts fall well within the range observed for other LGRBs. Hence, from the properties of the afterglows there is nothing to suggest that these bursts should have another progenitor than other LGRBs. Recently, Swift-discovered GRB 080503 also has the spike + tail structure during its prompt γ-ray emission seemingly similar to GRB 060614. We analyze the prompt emission of this burst and find that this GRB is actually a hard-spike + hard-tail burst with a spectral lag of 0.8 ± 0.4 s during its tail emission. Thus, the properties of the prompt emission of GRB 060614 and GRB 080503 are clearly different, motivating further thinking of GRB classification (and even identification of faint core-collapse SNe). Finally, we note that, whereas the progenitor of the two SN-less bursts remains uncertain, the core-collapse origin for the SN-less bursts would be quite certain if a windlike environment can be observationally established, e.g., from an optical decay faster than the X-ray decay in the afterglow's slow cooling phase.
The Astrophysical Journal 04/2009; 696(1):971. · 6.02 Impact Factor
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J. Greiner,
T. Krühler,
J. P. U. Fynbo,
A. Rossi,
R. Schwarz,
S. Klose,
S. Savaglio,
N. R. Tanvir,
S. McBreen,
T. Totani, [......],
J. Hjorth,
E. Jehin,
A. J. Levan,
E. W. Liang,
D. Malesani,
T.-S. Pyo,
S. Schulze,
G. Szokoly,
K. Terada,
and K. Wiersema
[show abstract]
[hide abstract]
ABSTRACT: We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND, which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i' and z' bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to λ = 9400 Å, and zero flux for 7500 Å<λ < 9400 Å, which we interpret as the onset of a Gunn-Peterson trough at z = 6.695± 0.025 (95.5% confidence level), making GRB 080913 the highest-redshift gamma-ray burst (GRB) to date, and more distant than the highest-redshift QSO. We note that many redshift indicators that are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2 m class telescopes can identify most high-redshift GRBs.
The Astrophysical Journal 03/2009; 693(2):1610. · 6.02 Impact Factor
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C ~C Thoene,
P Goldoni,
S Covino,
L ~A Antonelli,
D Malesani,
J ~P ~U Fynbo,
A ~J Levan,
P Jakobsson,
H Flores,
B Milvang-Jensen,
J Hjorth, D Watson,
K Wiersema,
N ~R Tanvir,
A Ugarte Postigo
GRB Coordinates Network. 01/2009; 10233:1.
-
S. Vaughan,
R. Willingale,
P. T. O'Brien,
J. P. Osborne,
J. N. Reeves,
A. J. Levan,
M. G. Watson,
J. A. Tedds, D. Watson,
M. Santos-Lleó,
P. M. Rodríguez-Pascual,
and N. Schartel
[show abstract]
[hide abstract]
ABSTRACT: We report the first detection of a time-dependent dust-scattered X-ray halo around a gamma-ray burst (GRB). GRB 031203 was observed by XMM-Newton starting 6 hr after the burst. The halo appeared as concentric ringlike structures centered on the GRB location. The radii of these structures increased with time as t1/2, consistent with small-angle X-ray scattering caused by a large column of dust along the line of sight to a cosmologically distant GRB. The rings are due to dust concentrated in two distinct slabs in the Galaxy located at distances of 880 and 1390 pc, consistent with known Galactic features. The halo brightness implies an initial soft X-ray pulse consistent with the observed GRB.
The Astrophysical Journal 12/2008; 603(1):L5. · 6.02 Impact Factor
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D. Watson,
S. A. Vaughan,
R. Willingale,
J. Hjorth,
S. Foley,
J. P. U. Fynbo,
P. Jakobsson,
A. Levan,
P. T. O'Brien,
J. P. Osborne,
K. Pedersen,
J. N. Reeves,
J. A. Tedds,
and M. G. Watson
[show abstract]
[hide abstract]
ABSTRACT: GRB 031203 was a very low apparent luminosity γ-ray burst (GRB). Coincidentally, it was also the first GRB with a dust-scattered X-ray halo. The observation of the halo allowed us to infer the presence of a large soft X-ray fluence in the total burst output. It has also been claimed, however, that GRB 031203 was intrinsically subenergetic, representative of a class of spectrally hard, low-energy bursts quite different from other GRBs. A careful reanalysis of the available data confirms our original finding that GRB 031203 had a very large soft X-ray component, the time of which can be constrained to within a few minutes after the burst, strongly suggesting that while GRB 031203 did indeed have a very low apparent luminosity, it was also very soft. Notions propagated in the literature regarding the uncertainties in the determination of the soft X-ray fluence from the halo data and on the available constraints from the hard X-ray data are addressed: the properties of the scattering dust along the line of sight (grain sizes, precise location, and geometry) are determined directly from the high-quality X-ray data so that there is little uncertainty about the scatterer; constraints on the X-ray light curve from the INTEGRAL spacecraft at the time of the soft X-ray blast are not complete because of a slew in the spacecraft pointing shortly after the burst. Claims that GRB 031203 was intrinsically underenergetic and that it represents a deviation from the luminosity-peak-energy relation do not appear to be substantiated by the data, regardless of whether the soft X-ray component is (arbitrarily) declared part of the prompt emission or the afterglow. We conclude that the difference between the soft and hard X-ray spectra from XMM-Newton and INTEGRAL indicate that a second soft pulse probably occurred in this burst, as has been observed in other GRBs, notably GRB 050502B.
The Astrophysical Journal 12/2008; 636(2):967. · 6.02 Impact Factor
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J. Hjorth,
J. Sollerman,
J. Gorosabel,
J. Granot,
S. Klose,
C. Kouveliotou,
J. Melinder,
E. Ramirez-Ruiz,
R. Starling,
B. Thomsen, [......],
B. L. Jensen,
P. M. Vreeswijk,
J. M. Castro Cerón,
P. Jakobsson,
A. Levan,
K. Pedersen,
J. E. Rhoads,
N. R. Tanvir, D. Watson,
and R. A. M. J. Wijers
[show abstract]
[hide abstract]
ABSTRACT: We have obtained deep optical images with the Very Large Telescope at ESO of the first well-localized short-duration gamma-ray burst, GRB 050509B. From V and R imaging, initiated ~2 days after the GRB trigger and lasting up to three weeks, we detect no variable object inside the small Swift XRT X-ray error circle down to 2 σ limits of V = 26.5 and R = 25.1. The X-ray error circle includes a giant elliptical galaxy at z = 0.225, which has been proposed as the likely host of this GRB. Our limits indicate that if the GRB originated at z = 0.225, any supernova-like event accompanying the GRB would have to be over 100 times fainter than normal Type Ia SNe or Type Ic hypernovae, 5 times fainter than the faintest known Ia or Ic SNe, and fainter than the faintest known Type II SNe. Moreover, we use the optical limits to constrain the energetics of the GRB outflow. Simple models indicate that unless the intrinsic energy in the outflow from GRB 050509B was 1051 ergs, there was very little radioactive material with efficient decay timescales for generating a large luminosity. These limits strongly constrain progenitor models for this short GRB.
The Astrophysical Journal 12/2008; 630(2):L117. · 6.02 Impact Factor
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D. Watson,
J. P. U. Fynbo,
C. Ledoux,
P. Vreeswijk,
J. Hjorth,
A. Smette,
A. C. Andersen,
K. Aoki,
T. Augusteijn,
A. P. Beardmore, [......],
A. Pozanenko,
J. N. Reeves,
V. Rumyantsev,
T. Shahbaz,
D. Sharapov,
J. Sollerman,
R. L. C. Starling,
N. Tanvir,
K. Torstensson,
and K. Wiersema
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ABSTRACT: The optical afterglow spectrum of GRB 050401 (at z = 2.8992 ± 0.0004) shows the presence of a damped Lyα absorber (DLA), with log N = 22.6 ± 0.3. This is the highest column density ever observed in a DLA and is about 5 times larger than the strongest DLA detected so far in any QSO spectrum. From the optical spectrum, we also find a very large Zn column density, implying an abundance of [Zn/H] = -1.0 ± 0.4. These large columns are supported by the early X-ray spectrum from Swift XRT, which shows a column density (in excess of Galactic) of log NH = 22.21 assuming solar abundances (at z = 2.9). The comparison of this X-ray column density, which is dominated by absorption due to α-chain elements, and the H I column density derived from the Lyα absorption line allows us to derive a metallicity for the absorbing matter of [α/H] = -0.4 ± 0.3. The optical spectrum is reddened and can be well reproduced with a power law with SMC extinction, where AV = 0.62 ± 0.06. But the total optical extinction can also be constrained independent of the shape of the extinction curve: from the optical to X-ray spectral energy distribution, we find 0.5 AV 4.5. However, even this upper limit, independent of the shape of the extinction curve, is still well below the dust column that is inferred from the X-ray column density, i.e., AV = 9.1. This discrepancy might be explained by a small dust content with high metallicity (low dust-to-metals ratio). "Gray" extinction cannot explain the discrepancy, since we are comparing the metallicity to a measurement of the total extinction (without reference to the reddening). Little dust with high metallicity may be produced by sublimation of dust grains or may naturally exist in systems younger than a few hundred megayears.
The Astrophysical Journal 12/2008; 652(2):1011. · 6.02 Impact Factor
