419 research outputs found
A young girl with apparent treatment-resistant asthma treated at Bambino Gesù children's hospital
The host galaxy and late-time evolution of the Super-Luminous Supernova PTF12dam
Super-luminous supernovae of type Ic have a tendency to occur in faint host
galaxies which are likely to have low mass and low metallicity. PTF12dam is one
of the closest and best studied super-luminous explosions that has a broad and
slowly fading lightcurve similar to SN 2007bi. Here we present new photometry
and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a
detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107).
Using deep templates and image subtraction we show that the full lightcurve can
be fit with a magnetar model if escape of high-energy gamma rays is taken into
account. The full bolometric lightcurve from -53 to +399 days (with respect to
peak) cannot be fit satisfactorily with the pair-instability models. An
alternative model of interaction with a dense CSM produces a good fit to the
data although this requires a very large mass (~ 13 M_sun) of hydrogen free
CSM. The host galaxy is a compact dwarf (physical size ~ 1.9 kpc) and with M_g
= -19.33 +/- 0.10, it is the brightest nearby SLSN Ic host discovered so far.
The host is a low mass system (2.8 x 10^8 M_sun) with a star-formation rate
(5.0 M_sun/year), which implies a very high specific star-formation rate (17.9
Gyr^-1). The remarkably strong nebular lines provide detections of the [O III]
\lambda 4363 and [O II] \lambda\lambda 7320,7330 auroral lines and an accurate
oxygen abundance of 12 + log(O/H) = 8.05 +/- 0.09. We show here that they are
at the extreme end of the metallicity distribution of dwarf galaxies and
propose that low metallicity is a requirement to produce these rare and
peculiar supernovae.Comment: 20 pages, 12 figures, 8 tables, accepted for publication to MNRA
Observed Consequences of Presupernova Instability in Very Massive Stars
This chapter concentrates on the deaths of very massive stars, the events
leading up to their deaths, and how mass loss affects the resulting death. The
previous three chapters emphasized the theory of wind mass loss, eruptions, and
core collapse physics, but here we emphasize mainly the observational
properties of the resulting death throes. Mass loss through winds, eruptions,
and interacting binaries largely determines the wide variety of different types
of supernovae that are observed, as well as the circumstellar environments into
which the supernova blast waves expand. Connecting these observed properties of
the explosions to the initial masses of their progenitor stars is, however, an
enduring challenge and is especially difficult for very massive stars.
Superluminous supernovae, pair instability supernovae, gamma ray bursts, and
"failed" supernovae are all end fates that have been proposed for very massive
stars, but the range of initial masses or other conditions leading to each of
these (if they actually occur) are still very certain. Extrapolating to infer
the role of very massive stars in the early universe is essentially
unencumbered by observational constraints and still quite dicey.Comment: 39 pages, 5 figures, to appear as chapter in the book "Very Massive
Stars in the Local Universe", ed. J. Vin
Early ultraviolet emission in the Type Ia supernova LSQ12gdj: No evidence for ongoing shock interaction
We present photospheric-phase observations of LSQ12gdj, a slowly-declining,
UV-bright Type Ia supernova. Classified well before maximum light, LSQ12gdj has
extinction-corrected absolute magnitude , and pre-maximum
spectroscopic evolution similar to SN 1991T and the super-Chandrasekhar-mass SN
2007if. We use ultraviolet photometry from Swift, ground-based optical
photometry, and corrections from a near-infrared photometric template to
construct the bolometric (1600-23800 \AA) light curve out to 45 days past
-band maximum light. We estimate that LSQ12gdj produced
of Ni, with an ejected mass near or slightly above the
Chandrasekhar mass. As much as 27% of the flux at the earliest observed phases,
and 17% at maximum light, is emitted bluewards of 3300 \AA. The absence of
excess luminosity at late times, the cutoff of the spectral energy distribution
bluewards of 3000 \AA, and the absence of narrow line emission and strong Na I
D absorption all argue against a significant contribution from ongoing shock
interaction. However, up to 10% of LSQ12gdj's luminosity near maximum light
could be produced by the release of trapped radiation, including kinetic energy
thermalized during a brief interaction with a compact, hydrogen-poor envelope
(radius cm) shortly after explosion; such an envelope arises
generically in double-degenerate merger scenarios.Comment: 18 pages, 10 figures, accepted to MNRAS; v2 accepted version. Spectra
available on WISEReP (http://www.weizmann.ac.il/astrophysics/wiserep/).
Natural-system photometry and bolometric light curve available as online
tables in MNRAS versio
Massive stars exploding in a He-rich circumstellar medium. VI. Observations of two distant Type Ibn supernova candidates discovered by La Silla-QUEST
We present optical observations of the peculiar stripped-envelope supernovae
(SNe) LSQ12btw and LSQ13ccw discovered by the La Silla-QUEST survey. LSQ12btw
reaches an absolute peak magnitude of M(g) = -19.3 +- 0.2, and shows an
asymmetric light curve. Stringent prediscovery limits constrain its rise time
to maximum light to less than 4 days, with a slower post-peak luminosity
decline, similar to that experienced by the prototypical SN~Ibn 2006jc.
LSQ13ccw is somewhat different: while it also exhibits a very fast rise to
maximum, it reaches a fainter absolute peak magnitude (M(g) = -18.4 +- 0.2),
and experiences an extremely rapid post-peak decline similar to that observed
in the peculiar SN~Ib 2002bj. A stringent prediscovery limit and an early
marginal detection of LSQ13ccw allow us to determine the explosion time with an
uncertainty of 1 day. The spectra of LSQ12btw show the typical narrow He~I
emission lines characterising Type Ibn SNe, suggesting that the SN ejecta are
interacting with He-rich circumstellar material. The He I lines in the spectra
of LSQ13ccw exhibit weak narrow emissions superposed on broad components. An
unresolved Halpha line is also detected, suggesting a tentative Type Ibn/IIn
classification. As for other SNe~Ibn, we argue that LSQ12btw and LSQ13ccw
likely result from the explosions of Wolf-Rayet stars that experienced
instability phases prior to core collapse. We inspect the host galaxies of SNe
Ibn, and we show that all of them but one are hosted in spiral galaxies, likely
in environments spanning a wide metallicity range.Comment: 15 pages, 9 figures, 4 tables. Accepted by MNRA
The supernova CSS121015:004244+132827: a clue for understanding super-luminous supernovae
We present optical photometry and spectra of the super luminous type II/IIn
supernova CSS121015:004244+132827 (z=0.2868) spanning epochs from -30 days
(rest frame) to more than 200 days after maximum. CSS121015 is one of the more
luminous supernova ever found and one of the best observed. The photometric
evolution is characterized by a relatively fast rise to maximum (~40 days in
the SN rest frame), and by a linear post-maximum decline. The light curve shows
no sign of a break to an exponential tail. A broad Halpha is first detected at
~ +40 days (rest-frame). Narrow, barely-resolved Balmer and [O III] 5007 A
lines, with decreasing strength, are visible along the entire spectral
evolution. The spectra are very similar to other super luminous supernovae
(SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes
considered a type Ia interacting with H-rich CSM. The spectra are also similar
to a subsample of H-deficient SLSNe. We propose that the properties of
CSS121015 are consistent with the interaction of the ejecta with a massive,
extended, opaque shell, lost by the progenitor decades before the final
explosion, although a magnetar powered model cannot be excluded. Based on the
similarity of CSS121015 with other SLSNe (with and without H), we suggest that
the shocked-shell scenario should be seriously considered as a plausible model
for both types of SLSN.Comment: 17 pages, 10 figures and 5 tables. In press to MNRAS. This version
matches the accepted one. Main conclusions are unchange
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