5,033 research outputs found
Goals, Strategies and First Discoveries of AO327, the Arecibo All-Sky 327 MHz Drift Pulsar Survey
We report initial results from AO327, a drift survey for pulsars with the
Arecibo telescope at 327 MHz. The first phase of AO327 will cover the sky at
declinations of -1 to 28 degrees, excluding the region within 5 degrees of the
Galactic plane, where high scattering and dispersion make low-frequency surveys
sub-optimal. We record data from a 57 MHz bandwidth with 1024 channels and 125
us sampling time. The 60 s transit time through the AO327 beam means that the
survey is sensitive to very tight relativistic binaries even with no
acceleration searches. To date we have detected 44 known pulsars with periods
ranging from 3 ms to 2.21 s and discovered 24 new pulsars. The new discoveries
include three millisecond pulsars, three objects with periods of a few tens of
milliseconds typical of young as well as mildly recycled pulsars, a nuller, and
a rotating radio transient. Five of the new discoveries are in binary systems.
The second phase of AO327 will cover the sky at declinations of 28 to 38
degrees. We compare the sensitivity and search volume of AO327 to the Green
Bank North Celestial Cap survey and the GBT350 drift survey, both of which
operate at 350 MHz.Comment: Accepted for publication in Ap
Pulsar J0453+1559: A Double Neutron Star System with a Large Mass Asymmetry
To understand the nature of supernovae and neutron star (NS) formation, as
well as binary stellar evolution and their interactions, it is important to
probe the distribution of NS masses. Until now, all double NS (DNS) systems
have been measured to have a mass ratio close to unity (q 0.91). Here we
report the measurement of the individual masses of the 4.07-day binary pulsar
J0453+1559 from measurements of the rate of advance of periastron and Shapiro
delay: The mass of the pulsar is 1.559(5) and that of its companion
is 1.174(4) ; q = 0.75. If this companion is also a neutron star
(NS), as indicated by the orbital eccentricity of the system (e=0.11), then its
mass is the smallest precisely measured for any such object. The pulsar has a
spin period of 45.7 ms and a spin derivative of 1.8616(7) x; from these
we derive a characteristic age of ~ 4.1 x years and a magnetic field of
~ 2.9 x G,i.e, this pulsar was mildly recycled by accretion of matter
from the progenitor of the companion star. This suggests that it was formed
with (very approximately) its current mass. Thus NSs form with a wide range of
masses, which is important for understanding their formation in supernovae. It
is also important for the search for gravitational waves released during a
NS-NS merger: it is now evident that we should not assume all DNS systems are
symmetric
New Discoveries from the Arecibo 327 MHz Drift Pulsar Survey Radio Transient Search
We present Clusterrank, a new algorithm for identifying dispersed
astrophysical pulses. Such pulses are commonly detected from Galactic pulsars
and rotating radio transients (RRATs), which are neutron stars with sporadic
radio emission. More recently, isolated, highly dispersed pulses dubbed fast
radio bursts (FRBs) have been identified as the potential signature of an
extragalactic cataclysmic radio source distinct from pulsars and RRATs.
Clusterrank helped us discover 14 pulsars and 8 RRATs in data from the Arecibo
327 MHz Drift Pulsar Survey (AO327). The new RRATs have DMs in the range pc cm and periods in the range s. The new
pulsars have DMs in the range pc cm and periods in the
range s, and include two nullers and a mode-switching object.
We estimate an upper limit on the all-sky FRB rate of day for
bursts with a width of 10 ms and flux density mJy. The DMs of all
new discoveries are consistent with a Galactic origin. In comparing statistics
of the new RRATs with sources from the RRATalog, we find that both sets are
drawn from the same period distribution. In contrast, we find that the period
distribution of the new pulsars is different from the period distributions of
canonical pulsars in the ATNF catalog or pulsars found in AO327 data by a
periodicity search. This indicates that Clusterrank is a powerful complement to
periodicity searches and uncovers a subset of the pulsar population that has so
far been underrepresented in survey results and therefore in Galactic pulsar
population models.Comment: 41 pages, 16 figures, 4 tables, accepted by ApJ; added minor
corrections to final ApJ proo
Young Radio Pulsars in Galactic Globular Clusters
Currently three isolated radio pulsars and one binary radio pulsar with no
evidence of any previous recycling are known in 97 surveyed Galactic globular
clusters. As pointed out by Lyne et al., the presence of these pulsars cannot
be explained by core-collapse supernovae, as is commonly assumed for their
counterparts in the Galactic disk. We apply a Bayesian analysis to the results
from surveys for radio pulsars in globular clusters and find the number of
potentially observable non-recycled radio pulsars present in all clusters to be
< 3600. Accounting for beaming and retention considerations, the implied birth
rate for any formation scenario for all 97 clusters is < 0.25 pulsars per
century assuming a Maxwellian distribution of velocities with a dispersion of
10 km s^{-1}. The implied birth rates for higher velocity dispersions are
substantially higher than inferred for such pulsars in the Galactic disk. This
suggests that the velocity dispersion of young pulsars in globular clusters is
significantly lower than those of disk pulsars. These numbers may be
substantial overestimates due to the fact that the currently known sample of
young pulsars is observed only in metal-rich clusters. We propose that young
pulsars may only be formed in globular clusters with metallicities with
log[Fe/H] > -0.6. In this case, the potentially observable population of such
young pulsars is 447^{+1420}_{-399} (the error bars give the 95% confidence
interval) and their birth rate is 0.012^{+0.037}_{-0.010} pulsars per century.
The mostly likely creation scenario to explain these pulsars is the electron
capture supernova of a OMgNe white dwarf.Comment: 13 Pages, 6 Figures, 4 Tables, to appear in Ap
Pulsar J1411+2551: A Low Mass New Double Neutron Star System
In this work, we report the discovery and characterization of PSR J1411+2551,
a new binary pulsar discovered in the Arecibo 327 MHz Drift Pulsar Survey. Our
timing observations of the radio pulsar in the system span a period of about
2.5 years. This timing campaign allowed a precise measurement of its spin
period (62.4 ms) and its derivative (9.6 0.7) ; from these, we derive a characteristic age of Gyr and a
surface magnetic field strength of 2.5 G. These numbers
indicate that this pulsar was mildly recycled by accretion of matter from the
progenitor of the companion star. The system has an eccentric ()
2.61 day orbit. This eccentricity allows a highly significant measurement of
the rate of advance of periastron, . Assuming general relativity accurately models the
orbital motion, this implies a total system mass M = . The minimum companion mass is and the maximum
pulsar mass is . The large companion mass and the orbital
eccentricity suggest that PSR J1411+2551 is a double neutron star system; the
lightest known to date including the DNS merger GW 170817. Furthermore, the
relatively low orbital eccentricity and small proper motion limits suggest that
the second supernova had a relatively small associated kick; this and the low
system mass suggest that it was an ultra-stripped supernova.Comment: Accepted for publication in APJ letter
Aclimatação de mudas de bananeira 'Prata Anã' regeneradas em diferentes condições de cultivo in vitro.
A pesquisa busca avaliar o efeito de diferentes substratos na aclimatação de mudas de banana 'Prata Anã' após a etapa de enraizamento in vitro na presença e ausência de carvão ativado e após o terceiro subcultivo.bitstream/CPATC-2009-09/20520/1/bp_37.pd
Pathogenic variability of causal agent of common bean anthracnose.
The high variability of Colletotrichum lindemuthianum has resulted in continuous breakdown of resistance in commercial cultivars. Studies on the variability of C. lindemuthianum are needed to direct breeding efforts towards long-term resistance to anthracnose. The objective of this work was to investigate the pathogenic variability in isolates collected in different counties in Brazil in the last 4 years
Universal patterns in sound amplitudes of songs and music genres
We report a statistical analysis over more than eight thousand songs.
Specifically, we investigate the probability distribution of the normalized
sound amplitudes. Our findings seems to suggest a universal form of
distribution which presents a good agreement with a one-parameter stretched
Gaussian. We also argue that this parameter can give information on music
complexity, and consequently it goes towards classifying songs as well as music
genres. Additionally, we present statistical evidences that correlation aspects
of the songs are directly related with the non-Gaussian nature of their sound
amplitude distributions.Comment: Accepted for publication as a Brief Report in Physical Review
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