446 research outputs found
Repeatability of the European Standardized Method for Measuring Sound Reflection and Sound Insulation of Noise Barriers
The EN 1793-5 and EN 1793-6 standards have been in use for many years as a method for measuring the intrinsic characteristics of noise barriers installed along highways and railways. They require a sound source and a grid of microphones, to be placed near the barrier and in free field conditions, according to predetermined distances. In principle, small errors in positioning the sound source and microphone grid may affect the results obtained. An international round-robin test was carried out in 2012 to evaluate the repeatability and reproducibility of the method, but until now no studies have been carried out to evaluate and compare the repeatability of laboratory versus in-place measurements performed with the same equipment and its variance when an imperfect positioning of sound source and microphones is taken into account. In the present work, multiple series of sound reflection index and sound insulation index measurements performed on noise barriers of the same kind installed in the laboratory or along a highway are presented. The measurements were repeated in different ways: (1) in the laboratory, leaving the source and microphones unmoved to assess the repeatability of the results and of the measurement system under controlled conditions; (2) in the laboratory, repositioning for each measurement the source and microphone grid to assess the robustness of the method under real conditions but in a controlled environment; (3) in situ, along a highway open to traffic, repositioning for each measurement the source and microphone grid to assess the repeatability of the method under real conditions in a critical environment. In both reflection index and sound insulation index measurements, the standard deviation on single-number ratings in all cases examined is well below the value presented in EN 1793-5 and EN 1793-6, which was obtained from statistical analysis of the international round-robin test performed a dozen years ago, suggesting that expert operators with state-of-the art equipment can achieve much better results now
A Low-Cost System for Quick Measurements on Noise Barriers in Situ
This paper describes the development of a low-cost device for measuring the acoustic intrinsic characteristics of noise barriers. The system is based on the Teensy 4.1 microcontroller combined with a few other components. The measurements are carried out using a vertical linear microphone antenna housing 6 microphones and a lightweight loudspeaker, wireless connected to the main unit. Both the main system unit and the amplified loudspeaker are powered from normal 5 V USB battery packs, which are easily rechargeable and interchangeable. The system measures 6 impulse responses using an MLS signal and performs a series of calculations and frequency analyses to characterize the device under test, following a simplified version of the European standards EN 1793-5 and EN 1793-6 (commonly referred to as the âAdrienne methodâ). One measurement takes few minutes, obtaining results comparable to those obtained with the Adrienne method, which requires a more complicated and heavy measuring equipment and is much more expensive and time consuming
Do long-duration GRBs follow star formation?
We compare the luminosity function and rate inferred from the BATSE long
bursts peak flux distribution with those inferred from the Swift peak flux
distribution. We find that both the BATSE and the Swift peak fluxes can be
fitted by the same luminosity function and the two samples are compatible with
a population that follows the star formation rate. The estimated local long GRB
rate (without beaming corrections) varies by a factor of five from 0.05
Gpc^(-3)yr^(-1) for a rate function that has a large fraction of high redshift
bursts to 0.27 Gpc^(-3)yr^(-1) for a rate function that has many local ones. We
then turn to compare the BeppoSax/HETE2 and the Swift observed redshift
distributions and compare them with the predictions of the luminosity function
found. We find that the discrepancy between the BeppoSax/HETE2 and Swift
observed redshift distributions is only partially explained by the different
thresholds of the detectors and it may indicate strong selection effects. After
trying different forms of the star formation rate (SFR) we find that the
observed Swift redshift distribution, with more observed high redshift bursts
than expected, is inconsistent with a GRB rate that simply follows current
models for the SFR. We show that this can be explained by GRB evolution beyond
the SFR (more high redshift bursts). Alternatively this can also arise if the
luminosity function evolves and earlier bursts were more luminous or if strong
selection effects affect the redshift determination.Comment: 15 pages, 8 figures, accepted for publication in JCA
A New Frequency-Luminosity Relation for Long GRBs?
We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts
(GRBs). We fitted the PDS with a simple power-law and extracted the exponent of
the power-law (alpha) and the noise-crossing threshold frequency (f_th). We
find that the distribution of the extracted alpha peaks around -1.4 and that of
f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known
redshifts, we show that the redshift-corrected threshold frequency is
positively correlated with the isotropic peak luminosity. The correlation
coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the Magnetar Candidate 1E 1048.1-5937
We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.Comment: 24 pages, 4 figures, submitted to the Astrophysical Journa
Prospects for multi-messenger extended emission from core-collapse supernovae in the Local Universe
Multi-messenger emissions from SN1987A and GW170817/GRB170817A suggest a
Universe rife with multi-messenger transients associated with black holes and
neutron stars. For LIGO-Virgo, soon to be joined by KAGRA, these observations
promise unprecedented opportunities to probe the central engines of
core-collapse supernovae (CC-SNe) and gamma-ray bursts. Compared to neutron
stars, central engines powered by black hole-disk or torus systems may be of
particular interest to multi-messenger observations by the relatively large
energy reservoir of angular momentum, up to 29\% of total mass in the
Kerr metric. These central engines are expected from relatively massive stellar
progenitors and compact binary coalescence involving a neutron star. We review
prospects of multi-messenger emission by catalytic conversion of by a
non-axisymmetric disk or torus. Observational support for this radiation
process is found in a recent identification of in Extended Emission to GW170817 at a significance of
4.2\, concurrent with GRB170817A. A prospect on similar emissions from
nearby CC-SNe justifies the need for all-sky blind searches of long duration
bursts by heterogeneous computing.Comment: 96 pages, 20 figure
Constraining duty cycles through a Bayesian technique
The duty cycle (DC) of astrophysical sources is generally defined as the
fraction of time during which the sources are active. However, DCs are
generally not provided with statistical uncertainties, since the standard
approach is to perform Monte Carlo bootstrap simulations to evaluate them,
which can be quite time consuming for a large sample of sources. As an
alternative, considerably less time-consuming approach, we derived the
theoretical expectation value for the DC and its error for sources whose state
is one of two possible, mutually exclusive states, inactive (off) or flaring
(on), as based on a finite set of independent observational data points.
Following a Bayesian approach, we derived the analytical expression for the
posterior, the conjugated distribution adopted as prior, and the expectation
value and variance. We applied our method to the specific case of the
inactivity duty cycle (IDC) for supergiant fast X-ray transients. We also
studied IDC as a function of the number of observations in the sample. Finally,
we compare the results with the theoretical expectations. We found excellent
agreement with our findings based on the standard bootstrap method. Our
Bayesian treatment can be applied to all sets of independent observations of
two-state sources, such as active galactic nuclei, X-ray binaries, etc. In
addition to being far less time consuming than bootstrap methods, the
additional strength of this approach becomes obvious when considering a
well-populated class of sources () for which the prior can
be fully characterized by fitting the distribution of the observed DCs for all
sources in the class, so that, through the prior, one can further constrain the
DC of a new source by exploiting the information acquired on the DC
distribution derived from the other sources. [Abridged]Comment: Accepted for publication in Astronomy and Astrophysics. 4 pages, 2
figures, 1 table. Supporting material at
http://www.ifc.inaf.it/~romano/Sfxts/IDCSims/index.htm
Autocorrelation analysis of GRBMâBeppo-SAX burst data
An autocorrelation function (ACF) analysis was performed on 17 gamma-ray bursts with known redshift, using data from the GRBM on board Beppo-SAX. When corrected from the cosmic time dilation effect, the ACFs show a bimodal distribution at about half-maximum, in agreement with a previous study based on BATSE and Konus burst data. Although the results show more dispersion, the separation between the two classes is highly significant
Broad band turbulent spectra in gamma-ray burst light curves
Broad band power density spectra offer a window to understanding turbulent
behavior in the emission mechanism and, at the highest frequencies, in the
putative inner engines powering long GRBs. We describe a chirp search method
which steps aside Fourier analysis for signal detection in the Poisson
noise-dominated 2 kHz sampled BeppoSAX light curves. An efficient numerical
implementation is described in operations, where is the
number of chirp templates and is the length of the light curve time series,
suited for embarrassingly parallel processing. For detection of individual
chirps of duration s, the method is one order of magnitude more
sensitive in SNR than Fourier analysis. The Fourier-chirp spectra of GRB 010408
and GRB 970816 show a continuation of the spectral slope up to 1 kHz of
turbulence identified in low frequency Fourier analysis. The same continuation
is observed in an ensemble averaged spectrum of 40 bright long GRBs. An outlook
on a similar analysis of upcoming gravitational wave data is included
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