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[show abstract]
[hide abstract]
ABSTRACT: We present extensive radio and millimeter observations of the unusually
bright GRB 130427A at z=0.340, spanning 0.67 to 12 days after the burst. Taken
in conjunction with detailed multi-band UV, optical, NIR, and X-ray
observations we find that the broad-band afterglow emission is composed of
distinct reverse shock and forward shock contributions. The reverse shock
emission dominates in the radio/millimeter and at <0.1 days in the
UV/optical/NIR, while the forward shock emission dominates in the X-rays and at
>0.1 days in the UV/optical/NIR. We further find that the optical and X-ray
data require a Wind circumburst environment, pointing to a massive star
progenitor. Using the combined forward and reverse shock emission we find that
the parameters of the burst are an isotropic kinetic energy of E_Kiso~2e53 erg,
a mass loss rate of Mdot~3e-8 Msun/yr (for a wind velocity of 1,000 km/s), and
a Lorentz factor at the deceleration time of Gamma(200s)~130. Due to the low
density and large isotropic energy, the absence of a jet break to ~15 days
places only a weak constraint on the opening angle of theta_j>2.5 deg, and
therefore a total energy of E_gamma+E_K>1.2e51 erg, similar to other GRBs. The
reverse shock emission is detectable in this burst due to the low circumburst
density, which leads to a slow cooling shock. We speculate that this is a
required property for the detectability of reverse shocks in the radio and
millimeter bands. Following on GRB 130427A as a benchmark event, observations
of future GRBs with the exquisite sensitivity of VLA and ALMA, coupled with
detailed modeling of the reverse and forward shock contributions will test this
hypothesis.
05/2013;
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N. E. Sanders,
A. M. Soderberg,
R. J. Foley,
R. Chornock,
D. Milisavljevic, R. Margutti,
M. R. Drout,
M. Moe,
E. Berger,
W. R. Brown, [......],
L. Chomiuk,
A. S. Friedman,
R. P. Kirshner,
G. H. Marion,
J. L. Tonry,
W. S. Burgett,
K. C. Chambers,
K. W. Hodapp,
R. P. Kudritzki,
P. A. Price
[show abstract]
[hide abstract]
ABSTRACT: We report on our discovery and observations of the Pan-STARRS1 supernova (SN)
PS1-12sk, a transient with properties that indicate atypical star formation in
its host galaxy cluster or pose a challenge to popular progenitor system models
for this class of explosion. The optical spectra of PS1-12sk classify it as a
Type Ibn SN (c.f. SN 2006jc), dominated by intermediate-width (3x10^3 km/s) and
time variable He I emission. Our multi-wavelength monitoring establishes the
rise time dt = 9-23 days and shows an NUV-NIR SED with temperature > 17x10^3 K
and a peak rise magnitude of Mz = -18.9 mag. SN Ibn spectroscopic properties
are commonly interpreted as the signature of a massive star (17 - 100 M_sun)
explosion within a He-enriched circumstellar medium. However, unlike previous
Type Ibn supernovae, PS1-12sk is associated with an elliptical brightest
cluster galaxy, CGCG 208-042 (z = 0.054) in cluster RXC J0844.9+4258. The
expected probability of an event like PS1-12sk in such environments is low
given the measured infrequency of core-collapse SNe in red sequence galaxies
compounded by the low volumetric rate of SN Ibn. Furthermore, we find no
evidence of star formation at the explosion site to sensitive limits (Sigma
Halpha < 2x10^-3 M_sun/yr/kpc^2). We therefore discuss white dwarf binary
systems as a possible progenitor channel for SNe Ibn. We conclude that PS1-12sk
represents either a fortuitous and statistically unlikely discovery, evidence
for a top-heavy IMF in galaxy cluster cooling flow filaments, or the first clue
suggesting an alternate progenitor channel for Type Ibn SNe.
03/2013;
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[show abstract]
[hide abstract]
ABSTRACT: We present continued multi-frequency radio observations of the relativistic
tidal disruption event Sw1644+57 extending to dt~600 d. The data were obtained
with the JVLA and AMI Large Array. We combine these data with public Swift/XRT
and Chandra X-ray observations over the same time-frame to show that the jet
has undergone a dramatic transition starting at ~500 d, with a sharp decline in
the X-ray flux by about a factor of 170 on a timescale of dt/t<0.2. The rapid
decline rules out a forward shock origin (direct or reprocessing) for the X-ray
emission at <500 d, and instead points to internal dissipation in the inner
jet. On the other hand, our radio data uniquely demonstrate that the low X-ray
flux measured by Chandra at ~610 d is consistent with emission from the forward
shock. Furthermore, the Chandra data are inconsistent with thermal emission
from the accretion disk itself since the expected temperature of 30-60 eV and
inner radius of 2-10 R_s cannot accommodate the observed flux level or the
detected emission at >1 keV. We associate the rapid decline with a turn off of
the relativistic jet when the mass accretion rate dropped below Mdot_Edd~0.006
Msun/yr (for a 3x10^6 Msun black hole and order unity efficiency) indicating
that the peak accretion rate was about 330 Mdot_Edd, and the total accreted
mass by 500 d is about 0.15 Msun. From the radio data we further find
significant flattening in the integrated energy of the forward shock at >250 d
with E_j,iso~2x10^54 erg (E_j~10^52$ erg for a jet opening angle, theta_j=0.1)
following a rise by about a factor of 15 at 30-250 d. Projecting forward, we
predict that the emission in the radio and X-ray bands will evolve in tandem
with similar decline rates.
12/2012;
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Ian Czekala,
E. Berger,
R. Chornock,
A. Pastorello,
G. H. Marion, R. Margutti,
M. T. Botticella,
P. Challis,
M. Ergon,
S. Smartt,
J. Sollerman,
J. Vinkó,
J. C. Wheeler
[show abstract]
[hide abstract]
ABSTRACT: We present observations of the unusual optical transient SN 2010U, including
spectra taken 1.03 days to 15.3 days after maximum light that identify it as a
fast and luminous Fe II type nova. Our multi-band light curve traces the fast
decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U
in the top 0.5% of the most luminous novae ever observed. We find typical
ejecta velocities of approximately 1100 km/s and that SN 2010U shares many
spectral and photometric characteristics with two other fast and luminous Fe II
type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme
luminosity of this nova, the maximum magnitude vs. rate of decline relationship
indicates a massive white dwarf progenitor with a low pre-outburst accretion
rate. However, this prediction is in conflict with emerging theories of nova
populations, which predict that luminous novae from massive white dwarfs should
preferentially exhibit an alternate spectral type (He/N) near maximum light.
10/2012;
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B. A. Zauderer,
E. Berger, R. Margutti,
A. J. Levan,
F. Olivares,
D. A. Perley,
W. Fong,
A. Horesh,
A. C. Updike,
J. Greiner,
N. R. Tanvir,
T. Laskar,
R. Chornock,
A. M. Soderberg,
K. M. Menten,
E. Nakar,
J. Carpenter,
P. Chandra
[show abstract]
[hide abstract]
ABSTRACT: We present X-ray, optical, near-infrared, and radio observations of GRBs
110709B and 111215A, as well as optical and near-IR observations of their host
galaxies. The combination of X-ray detections and deep optical/near-infrared
limits establish both bursts as "dark". Sub-arcsecond positions enabled by
radio detections lead to robust host galaxy associations, with optical
detections that indicate z < 4 (110709B) and 1.8 < z < 2.7 (111215A). Using the
radio and X-ray data for each burst we find that GRB 110709B requires A_V > 5.3
mag and GRB 111215A requires A_V > 8.5 mag (z=2), among the largest extinction
values inferred for dark bursts to-date. The two bursts also exhibit large
neutral hydrogen column densities (N_H > 10^22/cm^2; z=2) as inferred from
their X-ray spectra, in agreement with the trend for dark GRBs. Finally, we
find that for both bursts the afterglow emission is best explained by a
collimated outflow with a total beaming-corrected energy of E_gamma+E_K ~ 7-9 x
10^51 erg (z=2) expanding into a wind medium with a high density (n~100-350
cm^-3 at 10^17 cm). While the energy release is typical of long GRBs, the
inferred density may be indicative of larger mass loss rates for GRB
progenitors in dusty (and hence metal rich) environments. This study
establishes the critical role of radio observations in determining the origin
and properties of dark GRBs. Observations with the JVLA and ALMA will provide a
sample with sub-arcsecond positions and robust host associations that will help
shed light on obscured star formation and the role of metallicity in GRB
progenitors.
09/2012;
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D. Milisavljevic, R. Margutti,
A. M. Soderberg,
G. Pignata,
L. Chomiuk,
R. Fesen,
F. Bufano,
N. E. Sanders,
J. T. Parrent,
S. Parker, [......],
S. Chakraborti,
E. M. Levesque,
A. MacFadyen,
C. Drescher,
G. Bock,
P. Marples,
J. P. Anderson,
S. Benetti,
D. Reichart,
K. Ivarsen
[show abstract]
[hide abstract]
ABSTRACT: We present X-ray, UV/optical, and radio observations of the
stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least
luminous SNe IIb or Ib observed to date. Our observations begin with a
discovery within 1 day of explosion and span several months afterward. Early
optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that
subside rapidly and are replaced by Type Ib-like He-rich features on the
timescale of one week. High-cadence monitoring of this transition suggests that
absorption attributable to a high velocity (> 12,000 km/s) H-rich shell is not
rare in Type Ib events. Radio observations imply a shock velocity of v = 0.13c
and a progenitor star mass-loss rate of 1.4 x 10^{-5} Msun yr^{-1} (assuming
wind velocity v_w=10^3 km/s). This is consistent with independent constraints
from deep X-ray observations with Swift-XRT and Chandra. Overall, the
multi-wavelength properties of SN 2011ei are consistent with the explosion of a
lower-mass (3-4 Msun), compact (R* <= 1x10^{11} cm), He core star. The star
retained a thin hydrogen envelope at the time of explosion, and was embedded in
an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We
conclude that SN 2011ei's rapid spectral metamorphosis is indicative of
time-dependent classifications that bias estimates of explosion rates for Type
IIb and Ib objects, and that important information about a progenitor star's
evolutionary state and mass-loss immediately prior to SN explosion can be
inferred from timely multi-wavelength observations.
07/2012;
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E. Berger,
R. Chornock,
R. Lunnan,
R. Foley,
I. Czekala,
A. Rest,
C. Leibler,
A. M. Soderberg,
K. Roth,
G. Narayan, [......],
W. S. Burgett,
J. N. Heasley,
N. Kaiser,
R. -P. Kudritzki,
E. A. Magnier,
M. McCrum,
P. A. Price,
K. Smith,
J. L. Tonry,
R. J. Wainscoat
[show abstract]
[hide abstract]
ABSTRACT: We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and
Gemini spectroscopy of an ultra-luminous supernova (ULSN; dubbed PS1-11bam) at
a redshift of z=1.566 with a peak brightness of M_UV=-22.3 mag. PS1-11bam is
one of the highest redshift spectroscopically-confirmed SNe known to date. The
spectrum is characterized by broad absorption features typical of previous
ULSNe (e.g., CII, SiIII), and by strong and narrow MgII and FeII absorption
lines from the interstellar medium (ISM) of the host galaxy, confirmed by an
[OII]3727 emission line at the same redshift. The equivalent widths of the
FeII2600 and MgII2803 lines are in the top quartile of the quasar intervening
absorption system distribution, but are weaker than those of gamma-ray burst
intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy
in pre-explosion Pan-STARRS1 data and find that its UV spectral energy
distribution is best fit with a young stellar population age of tau~15-45 Myr
and a stellar mass of M \sim (1.1-2.6)x10^9 M_sun (for Z=0.05-1 Z_sun). The
star formation rate inferred from the UV continuum and [OII]3727 emission line
is ~10 M_sun/yr, higher than in any previous ULSN host. PS1-11bam provides the
first direct demonstration that ULSNe can serve as probes of the interstellar
medium in distant galaxies. At the present, the depth and red sensitivity of
PS1 are uniquely suited to finding such events at cosmologically interesting
redshifts (z~1-2); the future combination of LSST and 30-m class telescopes
promises to extend this technique to z~4.
06/2012;
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R. Margutti,
A. M. Soderberg,
L. Chomiuk,
R. Chevalier,
K. Hurley,
D. Milisavljevic,
R. J. Foley,
J. P. Hughes,
P. Slane,
C. Fransson, [......],
T. Murakami,
M. Ohno,
D. M. Palmer,
A. B. Sanin,
R. Starr,
D. Svinkin,
T. Takahashi,
M. Tashiro,
Y. Terada,
K. Yamaoka
[show abstract]
[hide abstract]
ABSTRACT: We present a generalized analytic formalism for the inverse Compton X-ray emission from hydrogen-poor supernovae and apply this framework to SN 2011fe using Swift X-Ray Telescope (XRT), UVOT, and Chandra observations. We characterize the optical properties of SN 2011fe in the Swift bands and find them to be broadly consistent with a "normal" SN Ia, however, no X-ray source is detected by either XRT or Chandra. We constrain the progenitor system mass-loss rate \dot{M}< 2\times 10^{-9}\ {M_{\odot }}\ yr^{-1} (3σ c.l.) for wind velocity vw = 100 km s-1. Our result rules out symbiotic binary progenitors for SN 2011fe and argues against Roche lobe overflowing subgiants and main-sequence secondary stars if >~ 1% of the transferred mass is lost at the Lagrangian points. Regardless of the density profile, the X-ray non-detections are suggestive of a clean environment (n CSM < 150 cm-3) for 2 × 1015 <~ R <~ 5 × 1016 cm around the progenitor site. This is either consistent with the bulk of material being confined within the binary system or with a significant delay between mass loss and supernova explosion. We furthermore combine X-ray and radio limits from Chomiuk et al. to constrain the post-shock energy density in magnetic fields. Finally, we searched for the shock breakout pulse using gamma-ray observations from theInterplanetary Network and find no compelling evidence for a supernova-associated burst. Based on the compact radius of the progenitor star we estimate that the shock breakout pulse was likely not detectable by current satellites.
The Astrophysical Journal 06/2012; 751(2). · 6.02 Impact Factor
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R. Margutti,
E. Berger,
W. Fong,
B. A. Zauderer,
S. B. Cenko,
J. Greiner,
A. M. Soderberg,
A. Cucchiara,
A. Rossi,
S. Klose,
S. Schmidl,
D. Milisavljevic,
N. Sanders
[show abstract]
[hide abstract]
ABSTRACT: We present multi-wavelength observations of the afterglow of the short
GRB111117A, and follow-up observations of its host galaxy. From rapid optical
and radio observations we place limits of r \gtrsim 25.5 mag at \deltat \approx
0.55 d and F_nu(5.8 GHz) < 18 \muJy at \deltat \approx 0.50 d, respectively.
However, using a Chandra observation at t~3.0 d we locate the absolute position
of the X-ray afterglow to an accuracy of 0.22" (1 sigma), a factor of about 6
times better than the Swift-XRT position. This allows us to robustly identify
the host galaxy and to locate the burst at a projected offset of 1.25 +/- 0.20"
from the host centroid. Using optical and near-IR observations of the host
galaxy we determine a photometric redshift of z=1.3 (+0.3,-0.2), one of the
highest for any short GRB, and leading to a projected physical offset for the
burst of 10.5 +/- 1.7 kpc, typical of previous short GRBs. At this redshift,
the isotropic gamma-ray energy is E_{gamma,iso} \approx 3\times10^51 erg
(rest-frame 23-2300 keV) with a peak energy of E_{pk} \approx 850-2300 keV
(rest-frame). In conjunction with the isotropic X-ray energy, GRB111117A
appears to follow our recently-reported E_x,iso-E_gamma,iso-E_pk universal
scaling. Using the X-ray data along with the optical and radio non-detections
we find that for a blastwave kinetic energy of E_{K,iso} \approx E_{gamma,iso},
the circumburst density is n_0 \sim 3x10^(-4)-1 cm^-3 (for a range of
epsilon_B=0.001-0.1). Similarly, from the non-detection of a break in the X-ray
light curve at t<3 d, we infer a minimum opening angle for the outflow of
theta_j> 3-10 degrees (depending on the circumburst density). We conclude that
Chandra observations of short GRBs are effective at determining precise
positions and robust host galaxy associations in the absence of optical and
radio detections.
05/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The comprehensive statistical analysis of Swift X-ray light-curves,
collecting data from six years of operation, revealed the existence of a
universal scaling among the isotropic energy emitted in the rest frame 10-10^4
keV energy band during the prompt emission (E_{gamma,iso}), the peak of the
prompt emission energy spectrum (E_{pk}), and the X-ray energy emitted in the
0.3-10 keV observed energy band (E_{X,iso}). In this paper we show that this
three-parameter correlation is robust and does not depend on our definition of
E_{X,iso}. It is shared by long, short, and low-energetic GRBs, differently
from the well-known E_{gamma,iso}-E_{pk} correlation. We speculate that the
ultimate physical property that regulates the GRB properties is the outflow
Lorentz factor.
03/2012;
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R. Margutti,
E. Zaninoni,
M. G. Bernardini,
G. Chincarini,
F. Pasotti,
C. Guidorzi,
L. Angelini,
D. N. Burrows,
M. Capalbi,
P. A. Evans, [......],
A. Moretti,
J. Nousek,
J. P. Osborne,
K. L. Page,
M. Perri,
J. Racusin,
P. Romano,
B. Sbarufatti,
S. Stafford,
M. Stamatikos
[show abstract]
[hide abstract]
ABSTRACT: We present a comprehensive statistical analysis of Swift X-ray light-curves
of Gamma-Ray Bursts (GRBs) collecting data from more than 650 GRBs discovered
by Swift and other facilities. The unprecedented sample size allows us to
constrain the REST FRAME X-ray properties of GRBs from a statistical
perspective, with particular reference to intrinsic time scales and the
energetics of the different light-curve phases in a common rest-frame 0.3-30
keV energy band. Temporal variability episodes are also studied and their
properties constrained. Two fundamental questions drive this effort: i) Does
the X-ray emission retain any kind of "memory"of the prompt gamma-ray phase?
ii) Where is the dividing line between long and short GRB X-ray properties? We
show that short GRBs decay faster, are less luminous and less energetic than
long GRBs in the X-rays, but are interestingly characterized by similar
intrinsic absorption. We furthermore reveal the existence of a number of
statistically significant relations that link the X-ray to prompt gamma-ray
parameters in long GRBs; short GRBs are outliers of the majority of these
2-parameter relations. However and more importantly, we report on the existence
of a universal 3-parameter scaling that links the X-ray and the gamma-ray
energy to the prompt spectral peak energy of BOTH long and short GRBs:
E_{X,iso}\propto E_{gamma,iso}^{1.00\pm 0.06}/E_{pk}^{0.60\pm 0.10}.
03/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We calculate the average power density spectra (PDS) of 244 long gamma-ray
bursts detected with the Swift Burst Alert Telescope in the 15-150 keV band
from January 2005 to August 2011. For the first time we derived the average PDS
in the source rest frame of 97 GRBs with known redshift. For 49 of them an
average PDS was also obtained in a common source-frame energy band to account
for the dependence of time profiles on energy. Previous results obtained on
BATSE GRBs with unknown redshift showed that the average spectrum in the
25-2000 keV band could be modelled with a power-law with a 5/3 index over
nearly two decades of frequency with a break at ~1 Hz. Depending on the
normalisation and on the subset of GRBs considered, our results show analogous
to steeper slopes (between 1.7 and 2.0) of the power-law. However, no clear
evidence for the break at ~1 Hz was found, although the softer energy band of
BAT compared with BATSE might account for that. We instead find a break at
lower frequency corresponding to a typical source rest frame characteristic
time of a few seconds. We furthermore find no significant differences between
observer and source rest frames. Notably, no distinctive PDS features are found
for GRBs with different intrinsic properties of the prompt emission either.
Finally, the average PDS of GRBs at higher redshifts shows possibly shallower
power-law indices than that of low-z GRBs. It is not clear whether this is due
to an evolution with z of the average PDS.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of a large sample of gamma-ray burst (GRB) X-ray
light curves in the rest frame to characterise their intrinsic properties in
the context of different theoretical scenarios. We determine the morphology,
time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT
\emph{without} flaring activity. We furthermore provide a one-to-one comparison
to the properties of GRBs \emph{with} X-ray flares. We find that the steep
decay morphology and its connection with X-ray flares favour a scenario in
which a central engine origin. We show that this scenario can also account for
the shallow decay phase, provided that the GRB progenitor star has a
self-similar structure with a constant envelope-to-core mass ratio $\sim
0.02-0.03$. However, difficulties arise for very long duration
($t_p\gtrsim10^4$ s) shallow phases. Alternatively, a spinning-down magnetar
whose emitted power refreshes the forward shock can quantitatively account for
the shallow decay properties. In particular we demonstrate that this model can
account for the plateau luminosity vs. end time anticorrelation.
12/2011;
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[show abstract]
[hide abstract]
ABSTRACT: SN2011it has been recently classified as a broad-line type-Ic supernova
(Tomasella, CBET 2938). A Swift-ToO was executed to observe the field of
SN2011it starting from 2011-12-08T00:22:48 UT, with the primary aim to
constrain the off-axis X-ray emission from the SN. No X-ray source is
detected at the optical position of the transient with a 3 sigma upper
limit of 2.4d-3 cts/s in the 0.3-10 keV energy band (total exposure= 8.3
ks).
The Astronomer's Telegram. 11/2011; 3804:1.
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B A Zauderer,
E Berger,
A M Soderberg,
A Loeb,
R Narayan,
D A Frail,
G R Petitpas,
A Brunthaler,
R Chornock,
J M Carpenter, [......],
N H Volgenau,
T L Culverhouse,
M F Bietenholz,
M P Rupen,
W Max-Moerbeck,
A C S Readhead,
J Richards,
M Shepherd,
S Storm,
C L H Hull
[show abstract]
[hide abstract]
ABSTRACT: Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z ≈ 6.
Nature 08/2011; 476(7361):425-8. · 36.28 Impact Factor
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Alicia M. Soderberg, R. Margutti,
B. A. Zauderer,
M. Krauss,
B. Katz,
L. Chomiuk,
J. A. Dittmann,
E. Nakar,
T. Sakamoto,
N. Kawai, [......],
A. Copete,
V. Connaughton,
M. Briggs,
C. Meegan,
A. von Kienlin,
X. Zhang,
A. Rau,
S. Golenetskii,
E. Mazets,
T. Cline
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery and detailed monitoring of X-ray emission associated
with the Type IIb SN 2011dh using data from the Swift and Chandra satellites,
placing it among the best studied X-ray supernovae to date. We further present
millimeter and radio data obtained with the SMA, CARMA, and EVLA during the
first three weeks after explosion. Combining these observations with early
optical photometry, we show that the panchromatic dataset is well-described by
non-thermal synchrotron emission (radio/mm) with inverse Compton scattering
(X-ray) of a thermal population of optical photons. In this scenario, the shock
partition fractions deviate from equipartition by a factor, (e_e/e_B) ~ 30. We
derive the properties of the shockwave and the circumstellar environment and
find a shock velocity, v~0.1c, and a progenitor mass loss rate of ~6e-5
M_sun/yr. These properties are consistent with the sub-class of Type IIb SNe
characterized by compact progenitors (Type cIIb) and dissimilar from those with
extended progenitors (Type eIIb). Furthermore, we consider the early optical
emission in the context of a cooling envelope model to estimate a progenitor
radius of ~1e+11 cm, in line with the expectations for a Type cIIb SN.
Together, these diagnostics are difficult to reconcile with the extended radius
of the putative yellow supergiant progenitor star identified in archival HST
observations, unless the stellar density profile is unusual. Finally, we
searched for the high energy shock breakout pulse using X-ray and gamma-ray
observations obtained during the purported explosion date range. Based on the
compact radius of the progenitor, we estimate that the breakout pulse was
detectable with current instruments but likely missed due to their limited
temporal/spatial coverage. [Abridged]
07/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present the first systematic study of X-ray flare candidates in short
gamma-ray bursts (SGRBs) exploiting the large 6-year Swift database with the
aim to constrain the physical nature of such fluctuations. We find that flare
candidates appear in different types of SGRB host galaxy environments and show
no clear correlation with the X-ray afterglow lifetime; flare candidates are
detected both in SGRBs with a bright extended emission in the soft gamma-rays
and in SGRBs which do not show such component. We furthermore show that SGRB
X-ray flare candidates only partially share the set of observational properties
of long GRB (LGRB) flares. In particular,the main parameter driving the
duration evolution of X-ray variability episodes in both classes is found to be
the elapsed time from the explosion, with very limited dependence on the
different progenitors, environments, central engine life-times, prompt
variability time-scales and energy budgets. On the contrary, SGRB flare
candidates significantly differ from LGRB flares in terms of peak luminosity,
isotropic energy, flare-to-prompt luminosity ratio and relative variability
flux. However, these differences disappear when the central engine time-scales
and energy budget are accounted for, suggesting that (i) flare candidates and
prompt pulses in SGRBs likely have a common origin; (ii) similar dissipation
and/or emission mechanisms are responsible for the prompt and flare emission in
long and short GRBs, with SGRBs being less energetic albeit faster evolving
versions of the long class. Finally, we show that in strict analogy to the SGRB
prompt emission, flares candidates fall off the lag-luminosity relation defined
by LGRBs, thus strengthening the SGRB flare-prompt pulse connection.
07/2011;
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B. A. Zauderer,
E. Berger,
A. M. Soderberg,
A Loeb,
R. Narayan,
D. A. Frail,
G. R. Petitpas,
A. Brunthaler,
R. Chornock,
J. M. Carpenter, [......],
N. H. Volgenau,
T. L. Culverhouse,
M. F. Bietenholz,
M. P. Rupen,
W. Max-Moerbeck,
A. C. S. Readhead,
J. Richards,
M. Shepherd,
S. Storm,
C. L. H. Hull
[show abstract]
[hide abstract]
ABSTRACT: Active galactic nuclei (AGN), powered by long-term accretion onto central
supermassive black holes, produce relativistic jets with lifetimes of greater
than one million yr that preclude observations at birth. Transient accretion
onto a supermassive black hole, for example through the tidal disruption of a
stray star, may therefore offer a unique opportunity to observe and study the
birth of a relativistic jet. On 2011 March 25, the Swift {\gamma}-ray satellite
discovered an unusual transient source (Swift J164449.3+573451) potentially
representing such an event. Here we present the discovery of a luminous radio
transient associated with Swift J164449.3+573451, and an extensive set of
observations spanning centimeter to millimeter wavelengths and covering the
first month of evolution. These observations lead to a positional coincidence
with the nucleus of an inactive galaxy, and provide direct evidence for a
newly-formed relativistic outflow, launched by transient accretion onto a
million solar mass black hole. While a relativistic outflow was not predicted
in this scenario, we show that the tidal disruption of a star naturally
explains the high-energy properties, radio luminosity, and the inferred rate of
such events. The weaker beaming in the radio compared to {\gamma}-rays/X-rays,
suggests that radio searches may uncover similar events out to redshifts of z ~
6.
06/2011;
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Z. Cano,
D. Bersier,
C. Guidorzi,
S Kobayashi,
A. J. Levan,
N. R. Tanvir,
K. Wiersema,
P. D'Avanzo,
A. S. Fruchter,
P. Garnavich, [......], R. Margutti,
P. A. Mazzali,
A. Melandri,
C. G. Mundell,
P. E. Nugent,
E. Pian,
R. J. Smith,
I. Steele,
R. A. M. J. Wijers,
S. E. Woosley
[show abstract]
[hide abstract]
ABSTRACT: We present ground-based and HST optical and infrared observations of XRF
100316D / SN 2010bh. It is seen that the optical light curves of SN 2010bh
evolve at a faster rate than the archetype GRB-SN 1998bw, but at a similar rate
to SN 2006aj, a supernova that was spectroscopically linked with XRF 060218,
and at a similar rate to non-GRB associated type Ic SN 1994I. We estimate the
rest-frame extinction of this event from our optical data to be E(B-V)=0.18 +/-
0.08 mag. We find the V-band absolute magnitude of SN 2010bh to be M_{V}=-18.62
+/- 0.08, which is the faintest peak V-band magnitude observed to-date for a
spectroscopically-confirmed GRB-SNe. When we investigate the origin of the flux
at t-t_{o}=0.598 days, it is shown that the light is not synchrotron in origin,
but is likely coming from the supernova shock break-out. We then use our
optical and infrared data to create a quasi-bolometric light curve of SN 2010bh
which we model with a simple analytical formula. The results of our modeling
imply that SN 2010bh synthesized a nickel mass of M_{Ni} \approx 0.10 M_{sun},
ejected M_{ej} \approx 2.2 M_{sun} and has an explosion energy of E_{k} \approx
1.4 x 10^{52} erg. Finally, for a sample 22 GRB-SNe we check for a correlation
between the stretch factors and luminosity factors in the R band and conclude
that no statistically-significant correlation exists.
04/2011;
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Z. Cano,
D. Bersier,
C. Guidorzi, R. Margutti,
K.M Svensson,
S. Kobayashi,
A. Melandri,
K. Wiersema,
A. Pozanenko,
A.J. van der Horst, [......],
R.L.C. Starling,
I. Steele,
R. Strom,
N. R. Tanvir,
Y. Tsapras,
Y. Urata,
A. Volnova,
A. Volvach,
R. A. M. J. Wijers,
S. E. Woosley
Monthly Notices of the Royal Astronomical Society 01/2011; 413(1):669. · 4.90 Impact Factor
