1,609 research outputs found
Supernova Shock Breakout from a Red Supergiant
Massive stars undergo a violent death when the supply of nuclear fuel in
their cores is exhausted, resulting in a catastrophic "core-collapse"
supernova. Such events are usually only detected at least a few days after the
star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy
Evolution Explorer space telescope reveal a radiative precursor from the
supernova shock before the shock reached the surface of the star and show the
initial expansion of the star at the beginning of the explosion. Theoretical
models of the ultraviolet light curve confirm that the progenitor was a red
supergiant, as expected for this type of supernova. These observations provide
a way to probe the physics of core-collapse supernovae and the internal
structures of their progenitor starsComment: Science, in press. 32 pages, 7 figure
A Relativistic Type Ibc Supernova Without a Detected Gamma-ray Burst
Long duration gamma-ray bursts (GRBs) mark the explosive death of some
massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They
are distinguished by the production of an energetic and collimated relativistic
outflow powered by a central engine (an accreting black hole or neutron star).
Observationally, this outflow is manifested in the pulse of gamma-rays and a
long-lived radio afterglow. To date, central engine-driven SNe have been
discovered exclusively through their gamma-ray emission, yet it is expected
that a larger population goes undetected due to limited satellite sensitivity
or beaming of the collimated emission away from our line-of-sight. In this
framework, the recovery of undetected GRBs may be possible through radio
searches for SNe Ibc with relativistic outflows. Here we report the discovery
of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb,
which requires a substantial relativistic outflow powered by a central engine.
The lack of a coincident GRB makes SN 2009bb the first engine-driven SN
discovered without a detected gamma-ray signal. A comparison with our extensive
radio survey of SNe Ibc reveals that the fraction harboring central engines is
low, ~1 percent, measured independently from, but consistent with, the inferred
rate of nearby GRBs. Our study demonstrates that upcoming optical and radio
surveys will soon rival gamma-ray satellites in pinpointing the nearest
engine-driven SNe. A similar result for a different supernova is reported
independently.Comment: To appear in Nature on Jan 28 2010. Embargoed for discussion in the
press until 13:00 US Eastern Time on Jan 27 (Accepted version, 27 pages,
Manuscript and Suppl. Info.
Nephropathy in Pparg-null mice highlights PPARγ systemic activities in metabolism and in the immune system.
Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-dependent transcription factor involved in many aspects of metabolism, immune response, and development. Total-body deletion of the two Pparg alleles provoked generalized lipoatrophy along with severe type 2 diabetes. Herein, we explore the appearance and development of structural and functional alterations of the kidney, comparing Pparg null-mice to their littermate controls (carrying Pparg floxed alleles). We show that renal hypertrophy and functional alterations with increased glucosuria and albuminuria are already present in 3 weeks-old Pparg null-mice. Renal insufficiency with decreased creatinine clearance progress at 7 weeks of age, with the advance of the type 2 diabetes. At 52 weeks of age, these alterations are accompanied by signs of fibrosis and mesangial expansion. More intriguingly, aged Pparg null-mice concomitantly present an anti-phospholipid syndrome (APS), characterized by the late appearance of microthrombi and a mesangioproliferative pattern of glomerular injury, associated with significant plasmatic levels of anti-β2- glycoprotein1 antibodies and renal deposition of IgG, IgM, and C3. Thus, in line with the role of PPARγ in metabolic homeostasis, Pparg null-mice first represent a potent model for studying the initiation and the development of diabetic nephropathy. Second, and in relation with the important PPARγ activity in inflammation and in immune system, these mice also highlight a new role for PPARγ signaling in the promotion of APS, a syndrome whose pathogenesis is poorly known and whose current treatment is limited to prevention of thrombosis events
SN 2010ay is a Luminous and Broad-lined Type Ic Supernova within a Low-metallicity Host Galaxy
We report on our serendipitous pre-discovery detection and detailed follow-up
of the broad-lined Type Ic supernova (SN) 2010ay at z = 0.067 imaged by the
Pan-STARRS1 3pi survey just ~4 days after explosion. The SN had a peak
luminosity, M_R ~ -20.2 mag, significantly more luminous than known GRB-SNe and
one of the most luminous SNe Ib/c ever discovered. The absorption velocity of
SN 2010ay is v_Si ~ 19,000 km/s at ~40 days after explosion, 2-5 times higher
than other broad-lined SNe and similar to the GRB-SN 2010bh at comparable
epochs. Moreover, the velocity declines ~2 times slower than other SNe Ic-BL
and GRB-SNe. Assuming that the optical emission is powered by radioactive
decay, the peak magnitude implies the synthesis of an unusually large mass of
56 Ni, M_Ni = 0.9 M_solar. Modeling of the light-curve points to a total ejecta
mass, M_ej ~ 4.7 M_sol, and total kinetic energy, E_K ~ 11x10^51 ergs. The
ratio of M_Ni to M_ej is ~2 times as large for SN 2010ay as typical GRB-SNe and
may suggest an additional energy reservoir. The metallicity (log(O/H)_PP04 + 12
= 8.19) of the explosion site within the host galaxy places SN 2010ay in the
low-metallicity regime populated by GRB-SNe, and ~0.5(0.2) dex lower than that
typically measured for the host environments of normal (broad-lined) Ic
supernovae. We constrain any gamma-ray emission with E_gamma < 6x10^{48} erg
(25-150 keV) and our deep radio follow-up observations with the Expanded Very
Large Array rule out relativistic ejecta with energy, E > 10^48 erg. We
therefore rule out the association of a relativistic outflow like those which
accompanied SN 1998bw and traditional long-duration GRBs, but place
less-stringent constraints on a weak afterglow like that seen from XRF 060218.
These observations challenge the importance of progenitor metallicity for the
production of a GRB, and suggest that other parameters also play a key role.Comment: 19 pages, 10 figures, V3 has revisions following referee's report;
more information at
http://www.cfa.harvard.edu/~nsanders/papers/2010ay/summary.htm
An Intermediate Luminosity Transient in NGC300: The Eruption of a Dust-Enshrouded Massive Star
[abridged] We present multi-epoch high-resolution optical spectroscopy,
UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an
intermediate luminosity optical transient recently discovered in the nearby
galaxy NGC300. We find that the transient (NGC300 OT2008-1) has a peak absolute
magnitude of M_bol~-11.8 mag, intermediate between novae and supernovae, and
similar to the recent events M85 OT2006-1 and SN2008S. Our high-resolution
spectra, the first for this event, are dominated by intermediate velocity
(~200-1000 km/s) hydrogen Balmer lines and CaII emission and absorption lines
that point to a complex circumstellar environment, reminiscent of the yellow
hypergiant IRC+10420. In particular, we detect broad CaII H&K absorption with
an asymmetric red wing extending to ~1000 km/s, indicative of gas infall onto a
massive and relatively compact star (blue supergiant or Wolf-Rayet star); an
extended red supergiant progenitor is unlikely. The origin of the inflowing gas
may be a previous ejection from the progenitor or the wind of a massive binary
companion. The low luminosity, intermediate velocities, and overall similarity
to a known eruptive star indicate that the event did not result in a complete
disruption of the progenitor. We identify the progenitor in archival Spitzer
observations, with deep upper limits from Hubble data. The spectral energy
distribution points to a dust-enshrouded star with a luminosity of about 6x10^4
L_sun, indicative of a ~10-20 M_sun progenitor (or binary system). This
conclusion is in good agreement with our interpretation of the outburst and
circumstellar properties. The lack of significant extinction in the transient
spectrum indicates that the dust surrounding the progenitor was cleared by the
outburst.Comment: Submitted to ApJ; emulateapj style; 39 pages; 26 figure
The Optical SN 2012bz Associated with the Long GRB 120422A
The association of Type Ic SNe with long-duration GRBs is well established.
We endeavor, through accurate ground-based observational campaigns, to
characterize these SNe at increasingly high redshifts. We obtained a series of
optical photometric and spectroscopic observations of the Type Ic SN2012bz
associated with the Swift long-duration GRB120422A (z=0.283) using the 3.6-m
TNG and the 8.2-m VLT telescopes. The peak times of the light curves of
SN2012bz in various optical filters differ, with the B-band and i'-band light
curves reaching maximum at ~9 and ~23 rest-frame days, respectively. The
bolometric light curve has been derived from individual bands photometric
measurements, but no correction for the unknown contribution in the
near-infrared (probably around 10-15%) has been applied. Therefore, the present
light curve should be considered as a lower limit to the actual UV-optical-IR
bolometric light curve. This pseudo-bolometric curve reaches its maximum (Mbol
= -18.56 +/- 0.06) at 13 +/- 1 rest-frame days; it is similar in shape and
luminosity to the bolometric light curves of the SNe associated with z<0.2 GRBs
and more luminous than those of SNe associated with XRFs. A comparison with the
model generated for the bolometric light curve of SN2003dh suggests that
SN2012bz produced only about 15% less 56Ni than SN2003dh, about 0.35 Msol.
Similarly the VLT spectra of SN2012bz, after correction for Galactic extinction
and for the contribution of the host galaxy, suggest comparable explosion
parameters with those observed in SN2003dh (EK~3.5 x 10^52 erg, Mej~7 Msol) and
a similar progenitor mass (~25-40 Msol). GRB120422A is consistent with the
Epeak-Eiso and the EX,iso-Egamma,iso-E_peak relations. GRB120422A/SN2012bz
shows the GRB-SN connection at the highest redshift so far accurately monitored
both photometrically and spectroscopically.Comment: 7 pages, 6 figures, 2 tables, accepted for publication in Astronomy &
Astrophysic
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