-
C C Thöne,
A de Ugarte Postigo,
C L Fryer,
K L Page,
J Gorosabel,
M A Aloy,
D A Perley,
C Kouveliotou,
H T Janka,
P Mimica, [......],
K Bundy,
C Choi,
H Jeong,
H Korhonen,
P Kubànek,
J Lim,
A Moskvitin,
T Muñoz-Darias,
S Pak,
I Parrish
[show abstract]
[hide abstract]
ABSTRACT: Long γ-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its γ-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy.
Nature 12/2011; 480(7375):72-4. · 36.28 Impact Factor
-
D N Burrows,
J A Kennea,
G Ghisellini,
V Mangano,
B Zhang,
K L Page,
M Eracleous,
P Romano,
T Sakamoto,
A D Falcone, [......],
L A Antonelli,
S D Barthelmy,
G Cusumano,
P Giommi,
A Melandri,
M Perri,
J L Racusin,
B Sbarufatti, M H Siegel,
N Gehrels
[show abstract]
[hide abstract]
ABSTRACT: Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.
Nature 08/2011; 476(7361):421-4. · 36.28 Impact Factor
-
C. C. Thöne,
A. de Ugarte Postigo,
C. L. Fryer,
K. L. Page,
J. Gorosabel,
M. A. Aloy,
D. A. Perley,
C. Kouveliotou,
H. -T. Janka,
P. Mimica, [......],
K. Bundy,
C. Choi,
H. Jeong,
H. Korhonen,
P. Kubanek,
J. Lim,
A. Moskvitin,
T. Muñoz-Darias,
S. Pak,
I. Parrish
[show abstract]
[hide abstract]
ABSTRACT: Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive
stellar deaths, usually as- sociated with supernovae (Woosley et al. 2006).
They release ultra-relativistic jets producing non-thermal emission through
synchrotron radiation as they interact with the surrounding medium (Zhang et
al. 2004). Here we report observations of the peculiar GRB 101225A (the
"Christmas burst"). Its gamma-ray emission was exceptionally long and followed
by a bright X-ray transient with a hot thermal component and an unusual optical
counterpart. During the first 10 days, the optical emission evolved as an
expanding, cooling blackbody after which an additional component, consistent
with a faint supernova, emerged. We determine its distance to 1.6 Gpc by
fitting the spectral-energy distribution and light curve of the optical
emission with a GRB-supernova template. Deep optical observations may have
revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium
star-neutron star merger that underwent a common envelope phase expelling its
hydrogen envelope. The resulting explosion created a GRB-like jet which gets
thermalized by interacting with the dense, previously ejected material and thus
creating the observed black-body, until finally the emission from the supernova
dominated. An alternative explanation is a minor body falling onto a neutron
star in the Galaxy (Campana et al. 2011).
05/2011;
-
D. N. Burrows,
J. A. Kennea,
G. Ghisellini,
V. Mangano,
B Zhang,
K. L. Page,
M. Eracleous,
P. Romano,
T Sakamoto,
A. D. Falcone, [......],
S. D. Barthelmy,
G. Cusumano,
P. Giommi,
F. E. Marshall,
A. Melandri,
M. Perri,
J. L. Racusin,
B. Sbarufatti, M. H. Siegel,
N. Gehrels
[show abstract]
[hide abstract]
ABSTRACT: Massive black holes are believed to reside at the centres of most galaxies.
They can be- come detectable by accretion of matter, either continuously from a
large gas reservoir or impulsively from the tidal disruption of a passing star,
and conversion of the gravitational energy of the infalling matter to light.
Continuous accretion drives Active Galactic Nuclei (AGN), which are known to be
variable but have never been observed to turn on or off. Tidal disruption of
stars by dormant massive black holes has been inferred indirectly but the on-
set of a tidal disruption event has never been observed. Here we report the
first discovery of the onset of a relativistic accretion-powered jet in the new
extragalactic transient, Swift J164449.3+573451. The behaviour of this new
source differs from both theoretical models of tidal disruption events and
observations of the jet-dominated AGN known as blazars. These differences may
stem from transient effects associated with the onset of a powerful jet. Such
an event in the massive black hole at the centre of our Milky Way galaxy could
strongly ionize the upper atmosphere of the Earth, if beamed towards us.
04/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present Swift UV/Optical Telescope (UVOT) imaging of the galaxies M81 and
Holmberg IX. We combine UVOT imaging in three near ultraviolet (NUV) filters
(uvw2: 1928 {\AA}, uvm2: 2246 {\AA}, and uvw1: 2600 {\AA}) with ground based
optical imaging from the Sloan Digital Sky Survey to constrain the stellar
populations of both galaxies. Our analysis consists of three different methods.
First we use the NUV imaging to identify UV star forming knots and then perform
SED modeling on the UV/optical photometry of these sources. Second, we measure
surface brightness profiles of the disk of M81 in the NUV and optical. Last we
use SED fitting of individual pixels to map the properties of the two galaxies.
In agreement with earlier studies we find evidence for a burst in star
formation in both galaxies starting ~200 Myr ago coincident with the suggested
time of an M81-M82 interaction. In line with theories of its origin as a tidal
dwarf we find that the luminosity weighted age of Holmberg IX is a few hundred
million years. Both galaxies are best fit by a Milky Way dust extinction law
with a prominent 2175 {\AA} bump. In addition, we describe a stacked median
filter technique for modeling the diffuse background light within a galaxy, and
a Markov chain method for cleaning segment maps generated by SExtractor.
04/2011;
-
S. R. Oates,
M. J. Page,
P. Schady,
M. De Pasquale,
P. A. Evans,
K. L. Page,
M. M. Chester,
P. A. Curran,
T. S. Koch,
N. P. M. Kuin,
P. W. A. Roming, M. H. Siegel,
S. Zane,
J. A. Nousek
[show abstract]
[hide abstract]
ABSTRACT: We present the systematic analysis of the Ultraviolet/Optical Telescope (UVOT) and X-ray Telescope (XRT) light curves for a sample of 26 Swift gamma-ray bursts (GRBs). By comparing the optical/UV and X-ray light curves, we found that they are remarkably different during the first 500 s after the Burst Alert Telescope trigger, while they become more similar during the middle phase of the afterglow, i.e. between 2000 and 20 000 s.If we take literally the average properties of the sample, we find that the mean temporal indices observed in the optical/UV and X-rays after 500 s are consistent with a forward-shock scenario, under the assumptions that electrons are in the slow cooling regime, the external medium is of constant density and the synchrotron cooling frequency is situated between the optical/UV and X-ray observing bands. While this scenario describes well the averaged observed properties, some individual GRB afterglows require different or additional assumptions, such as the presence of late energy injection.We show that a chromatic break (a break in the X-ray light curve that is not seen in the optical) is present in the afterglows of three GRBs and demonstrate evidence for chromatic breaks in a further four GRBs. The average properties of these breaks cannot be explained in terms of the passage of the synchrotron cooling frequency through the observed bands, nor a simple change in the external density. It is difficult to reconcile chromatic breaks in terms of a single component outflow and instead, more complex jet structure or additional emission components are required.
Monthly Notices of the Royal Astronomical Society 03/2011; 412(1):561 - 579. · 4.90 Impact Factor
-
F. E. Marshall,
L. A. Antonelli,
D. N. Burrows,
S. Covino,
M. de Pasquale,
P. A. Evans,
D. Fugazza,
S. T. Holland,
E. W. Liang,
P. T. O'Brien,
S. R. Oates,
J. P. Osborne,
C. Pagani,
T. Sakamoto, M. H. Siegel,
X. F. Wu,
and B. Zhang
[show abstract]
[hide abstract]
ABSTRACT: GRB 100418A is a long gamma-ray burst (GRB) at redshift z = 0.6235 discovered with the Swift Gamma-ray Burst Explorer with unusual optical and X-ray light curves. After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least ~7 × 103 s after the trigger, peak at ~5 × 104 s, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in GRB afterglows. Observations with Rapid Eye Mount during a gap in the Swift coverage indicate a bright optical flare at ~2.5 × 104 s. The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the jet of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is ≥102 times the 1051 erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis jet model would require the intrinsic T 90 for the GRB jet viewed on-axis to be very short, ~10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs. The non-detection of a jet break up to t ~ 2 × 106 s indicates a jet half-opening angle of at least ~14°, and a relatively high-collimation-corrected jet energy of E jet ≥ 1052 erg.
The Astrophysical Journal 01/2011; 727(2):132. · 6.02 Impact Factor
-
S. R. Oates,
M. J. Page,
P. Schady,
M. De Pasquale,
P. A. Evans,
K. L. Page,
M. M. Chester,
P. A. Curran,
T. S. Koch,
N. P. M. Kuin,
P. W. A. Roming, M. H. Siegel,
S. Zane,
J. A. Nousek
[show abstract]
[hide abstract]
ABSTRACT: We present the systematic analysis of the UVOT and XRT light curves for a sample of 26 Swift Gamma-Ray Bursts (GRBs). By comparing the optical/UV and X-ray light curves, we found that they are remarkably different during the first 500s after the BAT trigger, while they become more similar during the middle phase of the afterglow, i.e. between 2000s and 20000s. If we take literally the average properties of the sample, we find that the mean temporal indices observed in the optical/UV and X-rays after 500s are consistent with a forward-shock scenario, under the assumptions that electrons are in the slow cooling regime, the external medium is of constant density and the synchrotron cooling frequency is situated between the optical/UV and X-ray observing bands. While this scenario describes well the averaged observed properties, some individual GRB afterglows require different or additional assumptions, such as the presence of late energy injection. We show that a chromatic break (a break in the X-ray light curve that is not seen in the optical) is present in the afterglows of 3 GRBs and demonstrate evidence for chromatic breaks in a further 4 GRBs. The average properties of these breaks cannot be explained in terms of the passage of the synchrotron cooling frequency through the observed bands, nor a simple change in the external density. It is difficult to reconcile chromatic breaks in terms of a single component outflow and instead, more complex jet structure or additional emission components are required. Comment: 20 pages, 5 figures and 4 tables. Accepted for publication by MNRAS
10/2010;
-
S. B. Pandey,
C. A. Swenson,
D. A. Perley,
C. Guidorzi,
K. Wiersema,
D. Malesani,
C. Akerlof,
M. C. B. Ashley,
D. Bersier,
Z. Cano, [......],
J. M. Rex, M. H. Siegel,
R. J. Smith,
I. A. Steele,
G. Stratta,
N. R. Tanvir,
D. Weights,
S. A. Yost,
F. Yuan,
and W. Zheng
[show abstract]
[hide abstract]
ABSTRACT: The optical-infrared afterglow of the Large Area Telescope (LAT)-detected long-duration burst, GRB 090902B, has been observed by several instruments. The earliest detection by ROTSE-IIIa occurred 80 minutes after detection by the Gamma-ray Burst Monitor instrument on board the Fermi Gamma-Ray Space Telescope, revealing a bright afterglow and a decay slope suggestive of a reverse shock origin. Subsequent optical-IR observations followed the light curve for 6.5 days. The temporal and spectral behavior at optical-infrared frequencies is consistent with synchrotron fireball model predictions; the cooling break lies between optical and XRT frequencies ~1.9 days after the burst. The inferred electron energy index is p = 1.8 ± 0.2, which would however imply an X-ray decay slope flatter than observed. The XRT and LAT data have similar spectral indices and the observed steeper value of the LAT temporal index is marginally consistent with the predicted temporal decay in the radiative regime of the forward shock model. Absence of a jet break during the first 6 days implies a collimation-corrected γ-ray energy E γ > 2.2 × 1052 erg, one of the highest ever seen in a long-duration gamma-ray bursts. More events combining GeV photon emission with multiwavelength observations will be required to constrain the nature of the central engine powering these energetic explosions and to explore the correlations between energetic quanta and afterglow emission.
The Astrophysical Journal 04/2010; 714(1):799. · 6.02 Impact Factor
-
E. A. Hoversten,
C. Gronwall,
D. E. Vanden Berk,
T. S. Koch,
A. A. Breeveld,
P. A. Curran,
D. A. Hinshaw,
F. E. Marshall,
P. W. A. Roming, M. H. Siegel,
M. Still
[show abstract]
[hide abstract]
ABSTRACT: Deep Swift UV/Optical Telescope (UVOT) imaging of the Chandra Deep Field
South is used to measure galaxy number counts in three near ultraviolet (NUV)
filters (uvw2: 1928 A, uvm2: 2246 A, uvw1: 2600 A) and the u band (3645 A).
UVOT observations cover the break in the slope of the NUV number counts with
greater precision than the number counts by the Hubble Space Telescope (HST)
Space Telescope Imaging Spectrograph (STIS) and the Galaxy Evolution Explorer
(GALEX), spanning a range from 21 < m_AB < 25. Number counts models confirm
earlier investigations in favoring models with an evolving galaxy luminosity
function.
09/2009;
-
GRB Coordinates Network. 12641:1.
-
GCN Report. 327:1.
-
GRB Coordinates Network. 10651:1.
-
GRB Coordinates Network. 13012:1.
-
The Astronomer's Telegram. 3613:1.
-
GRB Coordinates Network. 12660:1.
-
P ~A Evans,
S ~D Barthelmy,
D ~N Burrows,
J ~A Kennea,
F ~E Marshall,
K ~L Page,
D ~M Palmer,
A Rowlinson, M ~H Siegel,
T ~N Ukwatta,
L Vetere
GRB Coordinates Network. 9386:1.
-
GRB Coordinates Network. 12727:1.
-
M ~C Stroh,
P ~A Evans,
J ~M Gelbord,
O Godet,
C Gronwall,
C Guidorzi,
S ~T Holland,
E ~A Hoversten,
C ~B Markwardt,
P ~T O'Brien,
J ~P Osborne,
K ~L Page, M ~H Siegel
GRB Coordinates Network. 11055:1.
-
H ~A Krimm,
S ~D Barthelmy,
P ~A Evans,
N Gehrels,
C ~B Markwardt,
K ~L Page,
D ~M Palmer,
A Rowlinson,
T Sakamoto, M ~H Siegel,
M ~A Stark,
T ~N Ukwatta,
L Vetere
GRB Coordinates Network. 9621:1.
