6,632 research outputs found
Gamma Ray Bursts in the Era of Rapid Followup
We present a status report on the study of gamma-ray bursts (GRB) in the era
of rapid follow-up using the world's largest robotic optical telescopes - the
2-m Liverpool and Faulkes telescopes. Within the context of key unsolved issues
in GRB physics, we describe (1) our innovative software that allows real-time
automatic analysis and interpretation of GRB light curves, (2) the novel
instrumentation that allows unique types of observations (in particular, early
time polarisation measurements) and (3) the key science questions and
discoveries to which robotic observations are ideally suited, concluding with a
summary of current understanding of GRB physics provided by combining rapid
optical observations with simultaneous observations at other wavelengths.Comment: 20 pages, 12 figures; Review article accepted for publication in
Advances in Astronomy, special issue 'Robotic Astronomy (Hindawi Publishing
Corporation)
Structural and lithologic study of northern California Coast Range and Sacramento Valley, California
The author has identified the following significant results. Photgeologic examination of repetitive multispectral ERTS-1 imagery of Northern California has disclosed several systems of linear features which may be important for the interpretation of the structural history of California. They are separated from an orthogonal system of linears in the Klamath Mts. by a set of discontinuous southeast-trending linear features (the Mendocino system) which is traceable from the Pacific Coast, at Cape Mendocino, into the eastern foothills of the Sierra Nevada. Within the Sierra Nevada, the Mendocino system separates the north-trending Sierran system from a set of linears characteristic of the Modoc Plateau. With minor exception, little overlap exists among the systems which suggests a decipherable chronology and evolutionary history for the region. The San Andres system of linears appears to truncate or co-exist with most of the other systems in the northern Coast Ranges. The Mendocino system truncates the Klamath, Sierran, and Modoc systems. The Sierran system may represent fundamental and long-persisting pre-late Paleozoic zones of crustal weakness which have been reactivated from time to time. The Mendocino system was possibly developed in early Mesozoic and is important to the structural framework of Northern California
PPl 15: The First Brown Dwarf Spectroscopic Binary
PPl 15 is the first object to have been confirmed as a brown dwarf by the
lithium test (in 1995), though its inferred mass was very close to the
substellar limit. It is a member of the Pleiades open cluster. Its position in
a cluster color-magnitude diagram suggested that it might be binary, and
preliminary indications that it is a double-lined spectroscopic binary were
reported by us in 1997. Here we report on the results of a consecutive week of
Keck HIRES observations of this system, which yield its orbit. It has a period
of about 5.8 days, and an eccentricity of 0.4+/-0.05. The rotation of the stars
is slow for this class of objects. Because the system luminosity is divided
between 2 objects with a mass ratio of 0.85, this renders each of them an
incontrovertible brown dwarf, with masses between 60-70 jupiters. We show that
component B is a little redder than A by studying their wavelength-dependent
line ratios, and that this variation is compatible with the mass ratio. We
confirm that the system has lithium, but cannot support the original conclusion
that it is depleted (which would be surprising, given the new masses). This is
a system of very close objects which, if they had combined, would have produced
a low mass star. We discuss the implications of this discovery for the theories
of binary formation and formation of very low mass objects.Comment: Latex, 18 pages, 4 figures, submitted to Astron.
RISE: a fast-readout imager for exoplanet transit timing
By the precise timing of the low amplitude (0.005 - 0.02 magnitude) transits
of exoplanets around their parent star it should be possible to infer the
presence of other planetary bodies in the system down to Earth-like masses. We
describe the design and construction of RISE, a fast-readout frame transfer
camera for the Liverpool Telescope designed to carry out this experiment. The
results of our commissioning tests are described as well as the data reduction
procedure necessary. We present light curves of two objects, showing that the
desired timing and photometric accuracy can be obtained providing that
autoguiding is used to keep the target on the same detector pixel for the
entire (typically 4 hour) observing run.Comment: Published in PROC SPIE, vol 7014, 70416
The Automatic Real-Time GRB Pipeline of the 2-m Liverpool Telescope
The 2-m Liverpool Telescope (LT), owned by Liverpool John Moores University,
is located in La Palma (Canary Islands) and operates in fully robotic mode. In
2005, the LT began conducting an automatic GRB follow-up program. On receiving
an automatic GRB alert from a Gamma-Ray Observatory (Swift, INTEGRAL, HETE-II,
IPN) the LT initiates a special override mode that conducts follow-up
observations within 2-3 min of the GRB onset. This follow-up procedure begins
with an initial sequence of short (10-s) exposures acquired through an r' band
filter. These images are reduced, analyzed and interpreted automatically using
pipeline software developed by our team called "LT-TRAP" (Liverpool Telescope
Transient Rapid Analysis Pipeline); the automatic detection and successful
identification of an unknown and potentially fading optical transient triggers
a subsequent multi-color imaging sequence. In the case of a candidate brighter
than r'=15, either a polarimetric (from 2006) or a spectroscopic observation
(from 2007) will be triggered on the LT. If no candidate is identified, the
telescope continues to obtain z', r' and i' band imaging with increasingly
longer exposure times. Here we present a detailed description of the LT-TRAP
and briefly discuss the illustrative case of the afterglow of GRB 050502a,
whose automatic identification by the LT just 3 min after the GRB, led to the
acquisition of the first early-time (< 1 hr) multi-color light curve of a GRB
afterglow.Comment: PASP, accepted (8 pages, 3 figures
From Physical to Cyber: Escalating Protection for Personalized Auto Insurance
Nowadays, auto insurance companies set personalized insurance rate based on
data gathered directly from their customers' cars. In this paper, we show such
a personalized insurance mechanism -- wildly adopted by many auto insurance
companies -- is vulnerable to exploit. In particular, we demonstrate that an
adversary can leverage off-the-shelf hardware to manipulate the data to the
device that collects drivers' habits for insurance rate customization and
obtain a fraudulent insurance discount. In response to this type of attack, we
also propose a defense mechanism that escalates the protection for insurers'
data collection. The main idea of this mechanism is to augment the insurer's
data collection device with the ability to gather unforgeable data acquired
from the physical world, and then leverage these data to identify manipulated
data points. Our defense mechanism leveraged a statistical model built on
unmanipulated data and is robust to manipulation methods that are not foreseen
previously. We have implemented this defense mechanism as a proof-of-concept
prototype and tested its effectiveness in the real world. Our evaluation shows
that our defense mechanism exhibits a false positive rate of 0.032 and a false
negative rate of 0.013.Comment: Appeared in Sensys 201
High-Pressure Synthesis of a Pentazolate Salt
The pentazolates, the last all-nitrogen members of the azole series, have
been notoriously elusive for the last hundred years despite enormous efforts to
make these compounds in either gas or condensed phases. Here we report a
successful synthesis of a solid state compound consisting of isolated
pentazolate anions N5-, which is achieved by compressing and laser heating
cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The
experiment was guided by theory, which predicted the transformation of the
mixture at high pressures to a new compound, cesium pentazolate salt (CsN5).
Electron transfer from Cs atoms to N5 rings enables both aromaticity in the
pentazolates as well as ionic bonding in the CsN5 crystal. This work provides a
critical insight into the role of extreme conditions in exploring unusual
bonding routes that ultimately lead to the formation of novel high nitrogen
content species
A transit timing analysis of nine RISE light curves of the exoplanet system TrES-3
We present nine newly observed transits of TrES-3, taken as part of a transit
timing program using the RISE instrument on the Liverpool Telescope. A
Markov-Chain Monte-Carlo analysis was used to determine the planet-star radius
ratio and inclination of the system, which were found to be
Rp/Rstar=0.1664^{+0.0011}_{-0.0018} and i = 81.73^{+0.13}_{-0.04} respectively,
consistent with previous results. The central transit times and uncertainties
were also calculated, using a residual-permutation algorithm as an independent
check on the errors. A re-analysis of eight previously published TrES-3 light
curves was conducted to determine the transit times and uncertainties using
consistent techniques. Whilst the transit times were not found to be in
agreement with a linear ephemeris, giving chi^2 = 35.07 for 15 degrees of
freedom, we interpret this to be the result of systematics in the light curves
rather than a real transit timing variation. This is because the light curves
that show the largest deviation from a constant period either have relatively
little out-of-transit coverage, or have clear systematics. A new ephemeris was
calculated using the transit times, and was found to be T_c(0) = 2454632.62610
+- 0.00006 HJD and P = 1.3061864 +- 0.0000005 days. The transit times were then
used to place upper mass limits as a function of the period ratio of a
potential perturbing planet, showing that our data are sufficiently sensitive
to have probed for sub-Earth mass planets in both interior and exterior 2:1
resonances, assuming the additional planet is in an initially circular orbit.Comment: 21 pages, 4 figures, Accepted for publication in Ap
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