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M. De Pasquale, P. Schady,
N. P. M. Kuin,
M. J. Page,
P. A. Curran,
S. Zane,
S. R. Oates,
S. T. Holland,
A. A. Breeveld,
E. A. Hoversten, [......],
V. Vitale,
A. von Kienlin,
A. P. Waite,
P. Wang,
B. L. Winer,
K. S. Wood,
X. F. Wu,
R. Yamazaki,
T. Ylinen,
and M. Ziegler
[show abstract]
[hide abstract]
ABSTRACT: We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the gamma-ray burst outflow, poorly known in short bursts. We discuss internal and external shock models for the broadband energy emission of this object.
The Astrophysical Journal Letters 01/2010; 709(2):L146. · 5.53 Impact Factor
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M. De Pasquale, P. Schady,
N. P. M. Kuin,
M. J. Page,
P. A. Curran,
S. Zane,
S. R. Oates,
S. T. Holland,
A. A. Breeveld,
E. A. Hoversten, [......],
T. Kamae,
H. Katagiri,
J. Kataoka,
N. Kawai,
M. Kerr,
R. M. Kippen,
J. Knodlseder,
D. Kocevski,
M. Kuss,
others
[show abstract]
[hide abstract]
ABSTRACT: We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the gamma-ray burst outflow, poorly known in short bursts. We discuss internal and external shock models for the broadband energy emission of this object.
Astrophysical Journal Letters. 01/2010; 709(2):L146-L151.
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J. P. U. Fynbo,
P. Jakobsson,
J. X. Prochaska,
D. Malesani,
C. Ledoux,
A. de Ugarte Postigo,
M. Nardini,
P. M. Vreeswijk,
K. Wiersema,
J. Hjorth, [......],
E. Rol, P. Schady,
R. L. C. Starling,
N. R. Tanvir,
D. J. Watson,
D. Xu,
T. Augusteijn,
F. Grundahl,
J. Telting,
and P.-O. Quirion
[show abstract]
[hide abstract]
ABSTRACT: We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Lyα covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., γ-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher γ-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope βOX < 0.5, is 14% in group (1), 38% in group (2), and >39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the most dusty sight lines. This should be taken into account when determining, e.g., the redshift or metallicity distribution of GRBs and when using GRBs as a probe of star formation. Finally, we characterize GRB absorption systems as a class and compare them to QSO absorption systems, in particular the damped Lyα absorbers (DLAs). On average GRB absorbers are characterized by significantly stronger EWs for H I as well as for both low and high ionization metal lines than what is seen in intervening QSO absorbers. However, the distribution of line strengths is very broad and several GRB absorbers have lines with EWs well within the range spanned by QSO-DLAs. Based on the 33 z > 2 bursts in the sample, we place a 95% confidence upper limit of 7.5% on the mean escape fraction of ionizing photons from star-forming galaxies.
The Astrophysical Journal Supplement Series 11/2009; 185(2):526. · 13.46 Impact Factor
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R. Margutti,
F. Genet,
J. Granot,
R. Barniol Duran,
C. Guidorzi,
G. Chincarini,
J Mao, P. Schady,
T Sakamoto,
A. A. Miller, [......],
P. A. Evans,
J. P. U. Fynbo,
D. Malesani,
A. Moretti,
F. Pasotti,
D. Starr,
D. N. Burrows,
S. D. Barthelmy,
P. W. A. Roming,
N. Gehrels
[show abstract]
[hide abstract]
ABSTRACT: Swift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt tail emission and constitutes the first manifestation of what is later to give rise to the shallow decay phase. Contemporaneous optical observations reveal a rapid evolution of the injection frequency of a fast cooling synchrotron spectrum through the optical band, which disfavours the afterglow onset (start of the forward shock emission along our line of sight when the outflow is decelerated) as the origin of the observed re-brightening. We investigate alternative scenarios and find that the observations are consistent with the predictions for a narrow jet viewed off-axis. The high on-axis energy budget implied by this interpretation suggests different physical origins of the prompt and (late) afterglow emission. Strong spectral softening takes place from the prompt to the steep decay phase: we track the evolution of the spectral peak energy from the gamma-rays to the X-rays and highlight the problems of the high latitude and adiabatic cooling interpretations. Notably, a softening of both the high and low spectral slopes with time is also observed. We discuss the low on-axis radiative efficiency of GRB081028 comparing its properties against a sample of Swift long GRBs with secure E_gamma,iso measurements. Comment: 22 pages, 11 figures; MNRAS accepted
10/2009;
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[show abstract]
[hide abstract]
ABSTRACT: In this paper we present the results from the analysis of a sample of 28 gamma-ray burst (GRB) afterglow spectral energy distributions, spanning the X-ray through to near-infrared wavelengths. This is the largest sample of GRB afterglow spectral energy distributions thus far studied, providing a strong handle on the optical depth distribution of soft X-ray absorption and dust-extinction systems in GRB host galaxies. We detect an absorption system within the GRB host galaxy in 79% of the sample, and an extinction system in 71% of the sample, and find the Small Magellanic Cloud (SMC) extinction law to provide an acceptable fit to the host galaxy extinction profile for the majority of cases, consistent with previous findings. The range in the soft X-ray absorption to dust-extinction ratio, N_{H,X}/Av, in GRB host galaxies spans almost two orders of magnitude, and the typical ratios are significantly larger than those of the Magellanic Clouds or Milky Way. Although dust destruction could be a cause, at least in part, for the large N_{H,X}/Av ratios, the good fit provided by the SMC extinction law for the majority of our sample suggests that there is an abundance of small dust grains in the GRB environment, which we would expect to have been destroyed if dust destruction were responsible for the large N_{H,X}/Av ratios. Instead, our analysis suggests that the distribution of N_{H,X}/Av in GRB host galaxies may be mostly intrinsic to these galaxies, and this is further substantiated by evidence for a strong negative correlation between N_{H,X}/Av and metallicity for a subsample of GRB hosts with known metallicity. Furthermore, we find the N_{H,X}/Av ratio and metallicity for this subsample of GRBs to be comparable to the relation found in other more metal-rich galaxies. Comment: 23 pages, 10 figures, accepted for publication in MNRAS
10/2009;
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M. De Pasquale, P. Schady,
N. P. M. Kuin,
M. J. Page,
P. A. Curran,
S. Zane,
S. R. Oates,
S. T. Holland,
A. A. Breeveld,
E. A. Hoversten,
G. Chincarini,
D. Grupe,
Fermi/LAT,
Fermi/GBM collaborations. Minor changes in the authorlist
[show abstract]
[hide abstract]
ABSTRACT: We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the GRB outflow, poorly known in short bursts. We discuss internal shock and external shock models for the broadband energy emission of this object. Comment: Comments: Submitted to ApJ Letters. Contact Authors: Massimiliano De Pasquale (mdp@mssl.ucl.ac.uk), Mathew Page (mjp@mssl.ucl.ac.uk), Kenji Toma (toma@astro.psu.edu), Veronique Pelassa (pelassa@lpta.in2p3.fr). Minor change in the authorlist
10/2009;
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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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J. P. U. Fynbo,
P. Jakobsson,
J. X. Prochaska,
D. Malesani,
C. Ledoux,
A. de Ugarte Postigo,
M Nardini,
P. M. Vreeswijk,
K. Wiersema,
J. Hjorth, [......],
E. Rol, P. Schady,
R. Starling,
N. Tanvir,
D. J. Watson,
D Xu,
T. Augusteijn,
F. Grundahl,
J. Telting,
P. -O. Quirion
[show abstract]
[hide abstract]
ABSTRACT: (Abridged). We present a sample of 77 optical afterglows (OAs) of Swift detected GRBs for which spectroscopic follow-up observations have been secured. We provide linelists and equivalent widths for all detected lines redward of Ly-alpha. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray selected sample of Swift bursts with optimal conditions for ground-based follow up from the period March 2005 to September 2008; 146 bursts fulfill our sample criteria. We derive the redshift distribution for this sample and conclude that less than 19% of Swift bursts are at z>7. We compare the high energy properties for three sub-samples of bursts in the sample: i) bursts with redshifts measured from OA spectroscopy, ii) bursts with detected OA, but no OA-based redshift, and iii) bursts with no detection of the OA. The bursts in group i) have significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fraction of dark bursts is 14% in group i), 38% in group ii) and > 39% in group iii). From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the most dusty sight-lines. Finally, we characterize GRB absorption systems as a class and compare them to QSO absorption systems, in particular DLAs. On average GRB absorbers are characterized by significantly stronger EWs for HI as well as for both low and high ionization metal lines than what is seen in intervening QSO absorbers. Based on the z>2 bursts in the sample we place a 95% confidence upper limit of 7.5% on the mean escape fraction of ionizing photons from star-forming galaxies. Comment: 175 pages, 14 figures. Accepted for publication in ApJS. A full resolution version of the paper can be found here: http://www.astro.ku.dk/~jfynbo/grb_lowres.pdf
07/2009;
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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;
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S. R. Oates,
M. J. Page, P. Schady,
M. De Pasquale,
T. S. Koch,
A. A. Breeveld,
P. J. Brown,
M. M. Chester,
S. T. Holland,
E. A. Hoversten,
N. P. M. Kuin,
F. E. Marshall,
P. W. A. Roming,
M. Still,
D. E. Vanden Berk,
S. Zane,
J. A. Nousek
[show abstract]
[hide abstract]
ABSTRACT: We present the first statistical analysis of 27 Ultraviolet Optical Telescope (UVOT) optical/ultraviolet light curves of gamma-ray burst (GRB) afterglows. We have found, through analysis of the light curves in the observer's frame, that a significant fraction rise in the first 500 s after the GRB trigger, all light curves decay after 500 s, typically as a power law with a relatively narrow distribution of decay indices, and the brightest optical afterglows tend to decay the quickest. We find that the rise could be either produced physically by the start of the forward shock, when the jet begins to plough into the external medium, or geometrically where an off-axis observer sees a rising light curve as an increasing amount of emission enters the observers line of sight, which occurs as the jet slows. We find that at 99.8 per cent confidence, there is a correlation, in the observed frame, between the apparent magnitude of the light curves at 400 s and the rate of decay after 500 s. However, in the rest frame, a Spearman rank test shows only a weak correlation of low statistical significance between luminosity and decay rate. A correlation should be expected if the afterglows were produced by off-axis jets, suggesting that the jet is viewed from within the half-opening angle θ or within a core of a uniform energy density θc. We also produced logarithmic luminosity distributions for three rest-frame epochs. We find no evidence for bimodality in any of the distributions. Finally, we compare our sample of UVOT light curves with the X-ray Telescope (XRT) light-curve canonical model. The range in decay indices seen in UVOT light curves at any epoch is most similar to the range in decay of the shallow decay segment of the XRT canonical model. However, in the XRT canonical model, there is no indication of the rising behaviour observed in the UVOT light curves.
Monthly Notices of the Royal Astronomical Society 04/2009; 395(1):490 - 503. · 4.90 Impact Factor
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N. P. M. Kuin,
W. Landsman,
M. J. Page, P. Schady,
M. Still,
A. A. Breeveld,
M. De Pasquale,
P. W. A. Roming,
P. J. Brown,
M. Carter, [......],
E. A. Hoversten,
S. Hunsberger,
T. Kennedy,
S. Koch,
H. Lamoureux,
F. E. Marshall,
S. R. Oates,
A. Parsons,
D. M. Palmer,
P. J. Smith
[show abstract]
[hide abstract]
ABSTRACT: We present the earliest ultraviolet (UV) spectrum of a gamma-ray burst (GRB) as observed with the Swift Ultra-Violet/Optical Telescope (UVOT). The GRB 081203A spectrum was observed for 50 s with the UV-grism starting 251 s after the Swift-Burst-Alert-Telescope (BAT) trigger. During this time, the GRB was ≈13.4 mag (u filter) and was still rising to its peak optical brightness. In the UV-grism spectrum, we find a damped Lyα line, Lyβ and the Lyman continuum break at a redshift z= 2.05 ± 0.01. A model fit to the Lyman absorption implies a gas column density of log NH i= 22.0 ± 0.1 cm−2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (v≈ 14 mag) with moderate redshift (0.5 < z < 3.5) the UVOT is able to provide redshifts, and probe for damped Lyα absorbers within 4–6 min from the time of the Swift-BAT trigger.
Monthly Notices of the Royal Astronomical Society Letters 04/2009; 395(1):L21 - L24.
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Matthew McQuinn,
Joshua S. Bloom,
Jonathan Grindlay,
David Band,
S. D. Barthelmy,
E. Berger,
A Corsi,
S. Covino,
G. J. Fishman,
Steven R. Furlanetto, [......],
A. S. Kutyrev,
Abraham Loeb,
S. Harvey Moseley,
Tsvi Piran,
L. Piro,
J. X. Prochaska,
R. Salvaterra, P. Schady,
A. M. Soderberg,
G. Tagliaferri
[show abstract]
[hide abstract]
ABSTRACT: The first structures in the Universe formed at z>7, at higher redshift than all currently known galaxies. Since GRBs are brighter than other cosmological sources at high redshift and exhibit simple power-law afterglow spectra that is ideal for absorption studies, they serve as powerful tools for studying the early universe. New facilities planned for the coming decade will be able to obtain a large sample of high-redshift GRBs. Such a sample would constrain the nature of the first stars, galaxies, and the reionization history of the Universe.
03/2009;
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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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M. De Pasquale,
P. Evans,
S. Oates,
M. Page,
S. Zane, P. Schady,
A. Breeveld,
S. Holland,
P. Kuin,
M. Still,
P. Roming,
P. Ward
[show abstract]
[hide abstract]
ABSTRACT: The Swift mission has discovered an intriguing feature of gamma-ray burst (GRBs) afterglows, a phase of shallow decline of the flux in the X-ray and optical light curves. This behaviour is typically attributed to energy injection into the burst ejecta. At some point this phase ends, resulting in a break in the light curve, which is commonly interpreted as the cessation of the energy injection. In a few cases, however, while breaks in the X-ray light curve are observed, optical emission continues its slow flux decline. This behaviour suggests a more complex scenario. In this paper, we present a model that invokes a double component outflow, in which narrowly collimated ejecta are responsible for the X-ray emission while a broad outflow is responsible for the optical emission. The narrow component can produce a jet break in the X-ray light curve at relatively early times, while the optical emission does not break due to its lower degree of collimation. In our model both components are subject to energy injection for the whole duration of the follow-up observations. We apply this model to GRBs with chromatic breaks, and we show how it might change the interpretation of the GRBs canonical light curve. We also study our model from a theoretical point of view, investigating the possible configurations of frequencies and the values of GRB physical parameters allowed in our model.
Monthly Notices of the Royal Astronomical Society 12/2008; 392(1):153 - 169. · 4.90 Impact Factor
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P. J. Brown,
S. T. Holland,
C. James,
P. Milne,
P. W. A. Roming,
K. O. Mason,
K. L. Page,
A. P. Beardmore,
D. Burrows,
A. Morgan, [......],
A. Breeveld,
M. de Pasquale,
S. Hunsberger,
M. Ivanushkina,
W. Landsman,
K. McGowan,
T. Poole,
S. Rosen, P. Schady,
and N. Gehrels
[show abstract]
[hide abstract]
ABSTRACT: We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN 2005am. The data were collected beginning about 4 days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near-UV light curve match well those of SN 1992A. The other UV observations constitute the first set of light curves shorter than 2500 Å and allow us to compare the light curve evolution in three UV bands. One interesting feature is that the decay in the intermediate UVM2 band is shallower than in the filters on either side and may result from the bump in the interstellar extinction curve. The UV behavior of this and other low-redshift supernovae can be used to constrain theories of progenitor evolution or to interpret optical light curves of high-redshift supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to SN 2005am's X-ray luminosity to be 6 × 1039 ergs s-1 in the 0.3-10 keV. This result is derived from 58 ks of exposure time spread out over 7 weeks beginning 4 days before the B-band maximum.
The Astrophysical Journal 12/2008; 635(2):1192. · 6.02 Impact Factor
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M. Still,
P. W. A. Roming,
K. O. Mason,
A. Blustin,
P. Boyd,
A. Breeveld,
P. Brown,
M. De Pasquale,
C. Gronwall,
S. T. Holland, [......],
H. Krimm,
T. Sakamoto,
P. Giommi,
M. R. Goad,
V. Mangano,
K. Page,
M. Perri,
D. N. Burrows,
N. Gehrels,
and J. Nousek
[show abstract]
[hide abstract]
ABSTRACT: We present observations of GRB 050318 by the Ultraviolet/Optical Telescope (UVOT) on board the Swift observatory. The data are the first detections of a gamma-ray burst (GRB) afterglow decay by the UVOT instrument, launched specifically to open a new window on these transient sources. We showcase UVOT's ability to provide multicolor photometry and the advantages of combining UVOT data with simultaneous and contemporaneous observations from the high-energy detectors on the Swift spacecraft. Multiple filters covering 1800-6000 Å reveal a red source with a spectral slope steeper than the simultaneous X-ray continuum. Spectral fits indicate that the UVOT colors are consistent with dust extinction by systems at z = 1.2037 and 1.4436, redshifts where absorption systems have been preidentified. However, the data can be most easily reproduced with models containing a foreground system of neutral gas redshifted by z = 2.8 ± 0.3. For both of the above scenarios, spectral and decay slopes are, for the most part, consistent with fireball expansion into a uniform medium, provided a cooling break occurs between the energy ranges of the UVOT and Swift's X-ray instrumentation.
The Astrophysical Journal 12/2008; 635(2):1187. · 6.02 Impact Factor
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A. Gomboc,
S. Kobayashi,
C. Guidorzi,
A. Melandri,
V. Mangano,
B. Sbarufatti,
C. G. Mundell, P. Schady,
R. J. Smith,
A. C. Updike, [......],
M. Ibrahimov,
A. Levan,
A. Monfardini,
C. J. Mottram,
P. T. O'Brien,
P. Prema,
D. K. Sahu,
I. A. Steele,
N. R. Tanvir,
and K. Wiersema
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 = 191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX = 1.290 ± 0.008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from α1 = 1.48 ± 0.06 to α2 = 0.88 ± 0.03) approximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.
The Astrophysical Journal 12/2008; 687(1):443. · 6.02 Impact Factor
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N. P. M. Kuin,
W. B. Landsman,
M. J. Page, P. Schady,
M. Still,
A. A. Breeveld,
M. De Pasquale,
P. J. Brown,
M. Carter,
C. James, [......],
S. Hunsberger,
T. Kennedy,
S. Koch,
H. Lamoureux,
F. E. Marshall,
S. R. Oates,
A. Parsons,
D Palmer,
P. Roming,
P. J. Smith
[show abstract]
[hide abstract]
ABSTRACT: We present the earliest ever ultraviolet spectrum of a gamma-ray burst (GRB) as observed with the Swift-UVOT. The GRB 081203A spectrum was observed for 50 seconds with the UV grism starting 251 seconds after the Swift-BAT trigger when the GRB was of u ~13.4 mag and still rising to its peak optical brightness. The UV grism spectrum shows a damped Ly-alpha line, Ly-beta, and the Lyman continuum break at a redshift z = 2.05 +/- 0.01. A model fit to the Lyman absorption implies log N(HI) = 22.0 +/- 0.2 cm-2, which is typical for GRB host galaxies with damped Ly-alpha absorbers. This observation of GRB 081203A demonstrates that for GRBs brighter than v ~14 mag and with 0.5 < z < 3.5 the UVOT will be able to provide redshifts, and probe for damped Ly-alpha absorbers within 4-6 minutes from the time of the Swift-BAT trigger. Comment: 4 pages, 4 figures, accepted by MNRAS letters
12/2008;
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P. W. A. Roming,
T. S. Koch,
S. R. Oates,
B. L. Porterfield,
D. E. Vanden Berk,
P. T. Boyd,
S. T. Holland,
E. A. Hoversten,
S. Immler,
F. E. Marshall, [......],
P. J. Brown,
M. M. Chester,
A. Cucchiara,
M. De Pasquale,
C. Gronwall,
S. D. Hunsberger,
N. P. M. Kuin,
W. B. Landsman, P. Schady,
and M. Still
[show abstract]
[hide abstract]
ABSTRACT: We present the first Swift Ultraviolet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog. The catalog contains data from over 64,000 independent UVOT image observations of 229 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The catalog covers GRBs occurring during the period from 2005 January 17 to 2007 June 16 and includes ~86% of the bursts detected by the Swift Burst Alert Telescope (BAT). The catalog provides detailed burst positional, temporal, and photometric information extracted from each of the UVOT images. Positions for bursts detected at the 3σ level are provided with a nominal accuracy, relative to the USNO-B1 catalog, of ~025. Photometry for each burst is given in three UV bands, three optical bands, and a "white" or open filter. Upper limits for magnitudes are reported for sources detected below 3σ. General properties of the burst sample and light curves, including the filter-dependent temporal slopes, are also provided. The majority of the UVOT light curves, for bursts detected at the 3σ level, can be fit by a single power-law, with a median temporal slope (α) of 0.96, beginning several hundred seconds after the burst trigger and ending at ~1 × 105 s. The median UVOT v-band (~5500 Å) magnitude at 2000 s for a sample of "well"-detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst, shows relatively strong correlations with both the prompt Swift BAT fluence, and the Swift X-ray flux at 11 hr after the trigger.
The Astrophysical Journal 11/2008; 690(1):163. · 6.02 Impact Factor
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P. W. A. Roming,
T. S. Koch,
S. R. Oates,
B. L. Porterfield,
D. E. Vanden Berk,
P. T. Boyd,
S. T. Holland,
E. A. Hoversten,
S. Immler,
F. E. Marshall, [......],
P. J. Brown,
M. M. Chester,
A. Cucchiara,
M. De Pasquale,
C. Gronwall,
S. D. Hunsberger,
N. P. M. Kuin,
W. B. Landsman, P. Schady,
M. Still
[show abstract]
[hide abstract]
ABSTRACT: We present the first Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog. The catalog contains data from over 64,000 independent UVOT image observations of 229 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The catalog covers GRBs occurring during the period from 2005 Jan 17 to 2007 Jun 16 and includes ~86% of the bursts detected by the Swift Burst Alert Telescope (BAT). The catalog provides detailed burst positional, temporal, and photometric information extracted from each of the UVOT images. Positions for bursts detected at the 3-sigma-level are provided with a nominal accuracy, relative to the USNO-B1 catalog, of ~0.25 arcseconds. Photometry for each burst is given in three UV bands, three optical bands, and a 'white' or open filter. Upper limits for magnitudes are reported for sources detected below 3-sigma. General properties of the burst sample and light curves, including the filter-dependent temporal slopes, are also provided. The majority of the UVOT light curves, for bursts detected at the 3-sigma-level, can be fit by a single power-law, with a median temporal slope (alpha) of 0.96, beginning several hundred seconds after the burst trigger and ending at ~1x10^5 s. The median UVOT v-band (~5500 Angstroms) magnitude at 2000 s for a sample of "well" detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst, shows relatively strong correlations with both the prompt Swift BAT fluence, and the Swift X-ray flux at 11 hours after the trigger.
10/2008;
