1,077 research outputs found
The luminous late-time emission of the type Ic supernova iPTF15dtg - evidence for powering from a magnetar?
iPTF15dtg is a Type Ic supernova (SN) showing a broad light curve around
maximum light, consistent with massive ejecta if we assume a
radioactive-powering scenario. We study the late-time light curve of iPTF15dtg,
which turned out to be extraordinarily luminous for a stripped-envelope (SE)
SN. We compare the observed light curves to those of other SE SNe and also with
models for the Co decay. We analyze and compare the spectra to nebular
spectra of other SE SNe. We build a bolometric light curve and fit it with
different models, including powering by radioactivity, magnetar powering, as
well as a combination of the two. Between 150 d and 750 d past explosion,
iPTF15dtg's luminosity declined by merely two magnitudes instead of the six
magnitudes expected from Co decay. This is the first
spectroscopically-regular SE SN showing this behavior. The model with both
radioactivity and magnetar powering provides the best fit to the light curve
and appears to be the more realistic powering mechanism. An alternative
mechanism might be CSM interaction. However, the spectra of iPTF15dtg are very
similar to those of other SE SNe, and do not show signs of strong CSM
interaction. iPTF15dtg is the first spectroscopically-regular SE SN whose light
curve displays such clear signs of a magnetar contributing to the powering of
the late time light curve. Given this result, the mass of the ejecta needs to
be revised to a lower value, and therefore the progenitor mass could be
significantly lower than the previously estimated 35 .Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
Passive noise control oriented design of aircraft headrests
Two Passive Noise Control (PNC) concepts were numerically evaluated in terms of their impact on the Sound Pressure Level (SPL) perceived by passengers of an aircraft flight.
A concept was based on the shape optimization of the headrests, whereas the second one was based on the adoption of a high absorbing material, i.e. a nanofiber textile, to improve the acoustic performances of the headrests.
To this aim, an aircraft seat was modelled with the Boundary Element Method (BEM) and loaded with a spherical distribution of monopole sources surrounding the seat. Different configurations of headrest shape and covering textiles were then compared in terms of the SPL calculated at passengers’ ears.
The work shows how an acoustic-oriented design of the aircraft headrests could achieve an average SPL reduction for passengers up to 3 dBA
Topological Devil's staircase in atomic two-leg ladders
We show that a hierarchy of topological phases in one dimension - a topological Devil's staircase - can emerge at fractional filling fractions in interacting systems, whose single-particle band structure describes a topological or a crystalline topological insulator. Focusing on a specific example in the BDI class, we present a field-theoretical argument based on bosonization that indicates how the system, as a function of the filling fraction, hosts a series of density waves. Subsequently, based on a numerical investigation of the low-lying energy spectrum, Wilczek-Zee phases, and entanglement spectra, we show that they are symmetry protected topological phases. In sharp contrast to the non-interacting limit, these topological density waves do not follow the bulk-edge correspondence, as their edge modes are gapped. We then discuss how these results are immediately applicable to models in the AIII class, and to crystalline topological insulators protected by inversion symmetry. Our findings are immediately relevant to cold atom experiments with alkaline-earth atoms in optical lattices, where the band structure properties we exploit have been recently realized
A new generation photodetector for astroparticle physics: the VSiPMT
The VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design we
proposed for a revolutionary photon detector. The main idea is to replace the
classical dynode chain of a PMT with a SiPM (G-APD), the latter acting as an
electron detector and amplifier. The aim is to match the large sensitive area
of a photocathode with the performance of the SiPM technology. The VSiPMT has
many attractive features. In particular, a low power consumption and an
excellent photon counting capability. To prove the feasibility of the idea we
first tested the performance of a special non-windowed SiPM by Hamamatsu (MPPC)
as electron detector and current amplifier. Thanks to this result Hamamatsu
realized two VSiPMT industrial prototypes. In this work, we present the results
of a full characterization of the VSiPMT prototype
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
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