118 research outputs found
Modern meson--exchange potential and superfluid neutron star crust matter
In this work we study properties of neutron star crusts, where matter is
expected to consist of nuclei surrounded by superfluid neutrons and a
homogeneous background of relativistic electrons. The nuclei are disposed in a
Coulomb lattice, and it is believed that the structure of the lattice
influences considerably the specific heat of the neutronic matter inside the
crust of a neutron star. Using a modern meson--exchange potential in the
framework of a local--density approximation we calculate the neutronic specific
heat accounting for various shapes of the Coulomb lattice, from spherical to
non--spherical nuclear shapes. We find that a realistic nucleon--nucleon
potential leads to a significant increase in the neutronic specific heat with
respect to that obtained assuming a uniform neutron distribution. The increase
is largest for the non--spherical phase of the crust. These results may have
consequences for the thermal history of young neutron stars.Comment: Revtex, 5 pages, 4 figures included as uuencoded p
Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies
Superluminous supernovae (SLSNe) are very bright explosions that were only
discovered recently and that show a preference for occurring in faint dwarf
galaxies. Understanding why stellar evolution yields different types of stellar
explosions in these environments is fundamental in order to both uncover the
elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In
this paper, we present the first results of our project to study SUperluminous
Supernova Host galaxIES, focusing on the sample for which we have obtained
spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50% in
our sample) occur in a class of galaxies that is known as Extreme Emission Line
Galaxies (EELGs). The probability of this happening by chance is negligible and
we therefore conclude that the extreme environmental conditions and the SLSN
phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more
massive, more metal-rich galaxies with softer radiation fields. Therefore, if
SLSNe-II constitute a uniform class, their progenitor systems are likely
different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average,
not found in as extreme environments as H-poor SLSNe. We propose that H-poor
SLSNe result from the very first stars exploding in a starburst, even earlier
than GRBs. This might indicate a bottom-light initial mass function in these
systems. SLSNe present a novel method of selecting candidate EELGs independent
of their luminosity.Comment: Published version, matches proofs. Accepted 2015 February 13. 23
pages, 8 figures, 4 tables. Minor changes with respect to previous versio
Superfluidity in beta-stable neutron star matter
In this work we present results for pairing gaps in --stable neutron
star matter with electrons and muons using a relativistic
Dirac--Brueckner--Hartree--Fock approach, starting with modern meson--exchange
models for the nucleon--nucleon interaction. Results are given for
superconducting protons and and neutron superfluids. A
comparison is made with recent non--relativistic calculations and the
implications for neutron star cooling are discussed.Comment: 7 pages, RevTex latex style, 3 figs include
The economics of free: freemium games, branding and the impatience economy
The gaming industry has seen dramatic change and expansion with the emergence of ‘casual’ games that promote shorter periods of game play. Free to download, but structured around micro-payments, these games raise the complex relationship between game design and commercial strategies. Although offering a free gameplay experience in line with open access philosophies, these games also create systems that offer control over the temporal dynamics of that experience to monetise player attention and inattention. This article will examine three ‘freemium’ games, Snoopy Street Fair, The Simpsons’ Tapped Out and Dragonvale, to explore how they combine established branding strategies with gameplay methods that monetise player impatience. In examining these games, this article will ultimately indicate the need for game studies to interrogate the intersection between commercial motivations and game design 2 and a broader need for media and cultural studies to consider the social, cultural, economic and political implications of impatience
The Type Ib SN 1999dn: One Year of Photometric and Spectroscopic Monitoring
Extensive optical and near-infrared (NIR) observations of the type Ib
supernova 1999dn are presented, covering the first year after explosion. These
new data turn this object, already considered a prototypical SNIb, into one of
the best observed objects of its class. The light curve of SN 1999dn is mostly
similar in shape to that of other SNeIb but with a moderately faint peak
M_V=-17.2 mag). From the bolometric light curve and ejecta expansion
velocities, we estimate that about 0.11 Msun of 56Ni were produced during the
explosion and that the total ejecta mass was 4-6 Msun with a kinetic energy of
at least 5x10^{51} erg. The spectra of SN 1999dn at various epochs are similar
to those of other Stripped Envelope (SE) SNe showing clear presence of H at
early epochs. The high explosion energy and ejected mass, along with the small
flux ratio [CaII]/[OI] measured in the nebular spectrum, together with the lack
of signatures of dust formation and the relatively high-metallicity environment
point toward a single massive progenitor (M_ZAMS>=23-25 Msun) for SN 1999dn.Comment: 15 pages, 11 figures. MNRAS accepted; This version matches the
published on
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
SN 2020kyg and the rates of faint Iax Supernovae from ATLAS
We present multi-wavelength follow-up observations of the ATLAS discovered faint Iax supernova SN 2020kyg that peaked at an absolute magnitude of Mg ≈ −14.9 ± 0.2, making it another member of the faint Iax supernova population. The bolometric light curve requires only ≈7 × 10−3 M⊙ of radioactive 56Ni, with an ejected mass of Mej ∼ 0.4 M⊙ and a low kinetic energy of E ≈ 0.05 ± 0.02 × 1051 erg. We construct a homogeneous volume-limited sample of 902 transients observed by ATLAS within 100 Mpc during a 3.5 year span. Using this sample, we constrain the rates of faint Iax (Mr ≳ −16) events within 60 Mpc at of the SN Ia rate. The overall Iax rate, at of the Ia rate, is dominated by the low-luminosity events, with luminous SNe Iax (Mr ≲ −17.5) like 2002cx and 2005hk accounting for only of the Ia rate (a 2σ upper limit of approximately 3%). We favour the hybrid CONe WD + He star progenitor channel involving a failed deflagration of a near Chandrasekhar mass white dwarf, expected to leave a bound remnant and a surviving secondary companion, as a candidate explanation for faint Iax explosions. This scenario requires short delay times, consistent with the observed environments of SNe Iax. Furthermore, binary population synthesis calculations have suggested rates of of the SN Ia rate for this channel, consistent with our rate estimates
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