2,036 research outputs found
Probing the Intergalactic Medium with Fast Radio Bursts
The recently discovered fast radio bursts (FRBs), presumably of
extra-galactic origin, have the potential to become a powerful probe of the
intergalactic medium (IGM). We point out a few such potential applications. We
provide expressions for the dispersion measure and rotation measure as a
function of redshift, and we discuss the sensitivity of these measures to the
HeII reionization and the IGM magnetic field. Finally we calculate the
microlensing effect from an isolate, extragalctic stellar-mass compact object
on the FRB spectrum. The time delays between the two lensing images will induce
constructive and destructive interference, leaving a specific imprint on the
spectra of FRBs. With a high all-sky rate, a large statistical sample of FRBs
is expected to make these applications feasible.Comment: 4 pages, 1 figure; Typos for the variable x in Eq.6 corrected;
Published in ApJ; Originally the Appendix E of arXiv:1402.4766; Separated
from the main paper upon the referee's reques
Wave-Driven Mass Loss in the Last Year of Stellar Evolution: Setting the Stage for the Most Luminous Core-Collapse Supernovae
During the late stages of stellar evolution in massive stars (C fusion and
later), the fusion luminosity in the core of the star exceeds the star's
Eddington luminosity. This can drive vigorous convective motions which in turn
excite internal gravity waves. The local wave energy flux excited by convection
is itself well above Eddington during the last few years in the life of the
star. We suggest that an interesting fraction of the energy in gravity waves
can, in some cases, convert into sound waves as the gravity waves propagate
(tunnel) towards the stellar surface. The subsequent dissipation of the sound
waves can unbind up to several of the stellar envelope. This
wave-driven mass loss can explain the existence of extremely large stellar mass
loss rates just prior to core-collapse, which are inferred via circumstellar
interaction in some core-collapse supernovae (e.g., SNe 2006gy and PTF 09uj,
and even Type IIn supernovae more generally). An outstanding question is
understanding what stellar parameters (mass, rotation, metallicity, age) are
the most susceptible to wave-driven mass loss. This depends on the precise
internal structure of massive stars and the power-spectrum of internal gravity
waves excited by stellar convection.Comment: Version accepted to MNRA
The Office of the Future: Virtual, Portable, and Global.
Virtual reality has the potential to change the way we work. We envision the future office worker to be able to work productively everywhere solely using portable standard input devices and immersive head-mounted displays. Virtual reality has the potential to enable this, by allowing users to create working environments of their choice and by relieving them from physical world limitations, such as constrained space or noisy environments. In this paper, we investigate opportunities and challenges for realizing this vision and discuss implications from recent findings of text entry in virtual reality as a core office task
Comparing and combining measurement-based and driven-dissipative entanglement stabilization
We demonstrate and contrast two approaches to the stabilization of qubit
entanglement by feedback. Our demonstration is built on a feedback platform
consisting of two superconducting qubits coupled to a cavity which are measured
by a nearly-quantum-limited measurement chain and controlled by high-speed
classical logic circuits. This platform is used to stabilize entanglement by
two nominally distinct schemes: a "passive" reservoir engineering method and an
"active" correction based on conditional parity measurements. In view of the
instrumental roles that these two feedback paradigms play in quantum
error-correction and quantum control, we directly compare them on the same
experimental setup. Further, we show that a second layer of feedback can be
added to each of these schemes, which heralds the presence of a high-fidelity
entangled state in realtime. This "nested" feedback brings about a marked
entanglement fidelity improvement without sacrificing success probability.Comment: 40 pages, 12 figure
Far-Ultraviolet to Near-Infrared Spectroscopy of A Nearby Hydrogen Poor Superluminous Supernova Gaia16apd
We report the first maximum-light far-Ultraviolet to near-infrared spectra
(1000A - 1.62um, rest) of a H-poor superluminous supernova, Gaia16apd. At
z=0.1018, it is one of the closest and the UV brightest such events, with 17.4
(AB) magnitude in Swift UV band (1928A) at -11days pre-maximum. Assuming an
exponential form, we derived the rise time of 33days and the peak bolometric
luminosity of 3x10^{44}ergs^-1. At maximum light, the estimated photospheric
temperature and velocity are 17,000K and 14,000kms^-1 respectively. The
inferred radiative and kinetic energy are roughly 1x10^{51} and 2x10^{52}erg.
Gaia16apd is extremely UV luminous, emitting 50% of its total luminosity at
1000 - 2500A. Compared to the UV spectra (normalized at 3100A) of well studied
SN1992A (Ia), SN2011fe(Ia), SN1999em (IIP) and SN1993J (IIb), it has orders of
magnitude more far-UV emission. This excess is interpreted primarily as a
result of weaker metal line blanketing due to much lower abundance of
iron-group elements in the outer ejecta. Because these elements originate
either from the natal metallicity of the star, or have been newly produced, our
observation provides direct evidence that little of these freshly synthesized
material, including 56Ni, was mixed into the outer ejecta, and the progenitor
metallicity is likely sub-solar. This disfavors Pair-Instability Supernova
(PISN) models with Helium core masses >=90Msun, where substantial 56Ni material
is produced. Higher photospheric temperature of Gaia16apd than that of normal
SNe may also contribute to the observed far-UV excess. We find some indication
that UV luminous SLSNe-I like Gaia16apd could be common. Using the UV spectra,
we show that WFIRST could detect SLSNe-I out to redshift of 8.Comment: 19 pages. Match with the version accepted in Ap
Studies of multiple stellar systems - IV. The triple-lined spectroscopic system Gliese 644
We present a radial-velocity study of the triple-lined system Gliese 644 and
derive spectroscopic elements for the inner and outer orbits with periods of
2.9655 and 627 days. We also utilize old visual data, as well as modern speckle
and adaptive optics observations, to derive a new astrometric solution for the
outer orbit. These two orbits together allow us to derive masses for each of
the three components in the system: M_A = 0.410 +/- 0.028 (6.9%), M_Ba = 0.336
+/- 0.016 (4.7%), and $M_Bb = 0.304 +/- 0.014 (4.7%) M_solar. We suggest that
the relative inclination of the two orbits is very small. Our individual masses
and spectroscopic light ratios for the three M stars in the Gliese 644 system
provide three points for the mass-luminosity relation near the bottom of the
Main Sequence, where the relation is poorly determined. These three points
agree well with theoretical models for solar metallicity and an age of 5 Gyr.
Our radial velocities for Gliese 643 and vB 8, two common-proper-motion
companions of Gliese 644, support the interpretation that all five M stars are
moving together in a physically bound group. We discuss possible scenarios for
the formation and evolution of this configuration, such as the formation of all
five stars in a sequence of fragmentation events leading directly to the
hierarchical configuration now observed, versus formation in a small N cluster
with subsequent dynamical evolution into the present hierarchical
configuration.Comment: 17 pages, 9 figures, Accepted for publication in MNRA
Spectroscopic Redshifts for Seven Lens Galaxies
We report VLT observations of 11 lensed quasars, designed to measure the
redshifts of their lens galaxies. We successfully determined the redshifts for
seven systems, five of which were previously unknown. The securely measured
redshifts for the lensing galaxies are: HE0047-1756 z=0.408; PMNJ0134-0931
z=0.766; HE0230-2130 z=0.522; HE0435-1223 z=0.455; SDSS0924+021 z=0.393;
LBQS1009-025 z=0.871; and WFIJ2033-472 z=0.658. For four additional systems
(BRI0952-0115, Q1017-207, Q1355-2257 and PMNJ1632-003) we estimate tentative
redshifts based on some features in their spectra.Comment: 8 pages, ApJ, submitte
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