1,011 research outputs found
Effect of feeding different levels of corn snack waste on broiler performance
This study was conducted to investigate the effect of using corn snack waste on growth performance, carcass traits and economical efficiency of broiler chicks. Five hundred Ross 308 day-old broiler chicks were divided randomly into 20 pens. There were 25 chicks in each pen which consists of 4 treatments (4 levels of waste corn snack) with five replicates. Corn snack waste had been considered in grower and finisher periods in level 170, 300 and 500 g/Kg of diet. Usage of corn snack waste had reduced (P<0.05) feed intake and weight gain of broiler chicks. However usage of corn snack waste in broiler chick's diet in levels 170 and 350 g/Kg increased feed conversion ratio and in level 500 g/Kg, feed conversion ratio were improved (p<0.05). The usage of corn snack waste was induced by the negative effect on performance of carcass and weight thigh, but reduced breast meat weight also reduces abdominal fat, and had no effect on liver, heart, gastrointestinal tract (p<0.05).Keyword: Corn snack waste, corn by-product, broiler performance, broiler diet
Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory
We searched for thermonuclear X-ray bursts from Galactic neutron stars in all
event mode data of the Neil Gehrels Swift Observatory collected until March 31,
2018. In particular, we are interested in the intermediate-duration bursts
(shell flashes fueled by thick helium piles) with the ill-understood phenomenon
of strong flux fluctuations. Nine such bursts have been discussed in the
literature to date. Swift is particularly suitable for finding additional
examples. We find and list a total of 134 X-ray bursts; 44 are detected with
BAT only, 41 with XRT only, and 49 with both. Twenty-eight bursts involve
automatic slews. We find 12 intermediate-duration bursts, all detected in
observations involving automatic slews. Five show remarkably long
Eddington-limited phases in excess of 200 s. Five show fluctuations during the
decay phase; four of which are first discussed in the present study. We discuss
the general properties of the fluctuations, considering also 7 literature
cases. In general two types of fluctuations are observed: fast ones, with a
typical timescale of 1 s and up and downward fluctuations of up to 70%, and
slow ones, with a typical timescale of 1 min and only downward fluctuations of
up to 90%. The latter look like partial eclipses because the burst decay
remains visible in the residual emission. We revisit the interpretation of this
phenomenon in the context of the new data set and find that it has not changed
fundamentally despite the expanded data set. It is thought to be due to a
disturbance of the accretion disk by outflowing matter and photons, causing
obscuration and reflection due to Thompson scattering in an orbiting highly
ionized cloud or structure above or below the disk. We discuss in detail the
most pronounced burster SAX J1712.6-3739. One of the bursts from this source is
unusual in that it lasts longer than 5600 s, but does not appear to be a
superburst.Comment: Accepted for publication in Astronomy & Astrophysics, 29 pages, 12
figures. Version 2 has 3 bursts from IGR J17480-2446 re-identified to 2 from
Swift J174805.3-244637 and 1 from EXO 1745-24
IGR J17254-3257, a new bursting neutron star
The study of the observational properties of uncommonly long bursts from low
luminosity sources with extended decay times up to several tens of minutes is
important when investigating the transition from a hydrogen-rich bursting
regime to a pure helium regime and from helium burning to carbon burning as
predicted by current burst theories. IGR J17254-3257 is a recently discovered
X-ray burster of which only two bursts have been recorded: an ordinary short
type I X-ray burst, and a 15 min long burst. An upper limit to its distance is
estimated to about 14.5 kpc. The broad-band spectrum of the persistent emission
in the 0.3-100 keV energy band obtained using contemporaneous INTEGRAL and
XMM-Newton data indicates a bolometric flux of 1.1x10^-10 erg/cm2/s
corresponding, at the canonical distance of 8 kpc, to a luminosity about
8.4x10^35 erg/s between 0.1-100 keV, which translates to a mean accretion rate
of about 7x10^-11 solar masses per year. The low X-ray persistent luminosity of
IGR J17254-3257 seems to indicate the source may be in a state of low accretion
rate usually associated with a hard spectrum in the X-ray range. The nuclear
burning regime may be intermediate between pure He and mixed H/He burning. The
long burst is the result of the accumulation of a thick He layer, while the
short one is a prematurate H-triggered He burning burst at a slightly lower
accretion rate.Comment: 4 pages, 4 figures, 1 table; accepted for publication in A&A Letters.
1 reference (Cooper & Narayan, 2007) correcte
Evidence of heavy-element ashes in thermonuclear X-ray bursts with photospheric superexpansion
A small subset of thermonuclear X-ray bursts on neutron stars exhibit such a
strong photospheric expansion that for a few seconds the photosphere is located
at a radius r_ph >~ 1000 km. Such `superexpansions' imply a large and rapid
energy release, a feature characteristic of pure He burst models. Previous
calculations have shown that during a pure He burst, the freshly synthesized
heavy-element ashes of burning can be ejected in a strong radiative wind and
produce significant spectral absorption features. We search the burst data
catalogs and literature and find 32 superexpansion bursts. We find that these
bursts exhibit the following interesting features: (1) At least 31 are from
(candidate) ultracompact X-ray binaries in which the neutron star accretes
hydrogen-deficient fuel, suggesting that these bursts indeed ignite in a
helium-rich layer. (2) In 2 bursts we detect strong absorption edges during the
expansion phase. The edge energies and depths are consistent with the H-like or
He-like edge of iron-peak elements with abundances greater than 100 times
solar, suggesting that we are seeing the exposed ashes of nuclear burning. (3)
The superexpansion phase is always followed by a moderate expansion phase
during which r_ph ~ 30 km and the luminosity is near the Eddington limit. (4)
The decay time of the bursts, t_d, ranges from short (approximately 10 s) to
intermediate (>~ 1000 s). However, despite the large range of t_d, the duration
of the superexpansion is always a few seconds, independent of t_d. By contrast,
the duration of the moderate expansion is always of order t_d. (5) The
photospheric radii r_ph during the moderate expansion phase are much smaller
than steady state wind models predict. We show that this may be further
indication that the wind contains highly non-solar abundances of heavy
elements.Comment: Accepted for publication in Astronomy & Astrophysic
Broad-band X-ray measurements of the black hole candidate XTE J1908+094
XTE J1908+094 is an X-ray transient that went into outburst in February 2002.
After two months it reached a 2-250 keV peak flux of 1 to 2 X 10-8 erg/s/cm2.
Circumstantial evidence points to an accreting galactic black hole as the
origin of the the X-radiation: pulsations nor thermonuclear flashes were
detected that would identify a neutron star and the spectrum was unusually hard
for a neutron star at the outburst onset. We report on BeppoSAX and RXTE All
Sky Monitor observations of the broad-band spectrum of XTE J1908+094. The
spectrum is consistent with a model consisting of a Comptonization component by
a ~40 keV plasma (between 2 and 60 keV this component can be approximated by a
power law with a photon index of 1.9 to 2.1), a multicolor accretion disk
blackbody component with a temperature just below 1 keV and a broad emission
line at about 6 keV. The spectrum is heavily absorbed by cold interstellar
matter with an equivalent hydrogen column density of 2.5 X 10+22 cm-2, which
makes it difficult to study the black body component in detail. The black body
component exhibits strong evolution about 6 weeks into the outburst. Two weeks
later this is followed by a swift decay of the power law component. The
broadness of the 6 keV feature may be due to relativistic broadening or Compton
scattering of a narrow Fe-K line.Comment: Accepted for publication in Astronomy & Astrophysic
A four-year baseline Swift study of enigmatic X-ray transients located near the Galactic center
We report on continued monitoring observations of the Galactic center carried
out by the X-ray telescope aboard the Swift satellite in 2008 and 2009. This
campaign revealed activity of the five known X-ray transients AX J1745.6-2901,
CXOGC J174535.5-290124, GRS 1741-2853, XMM J174457-2850.3 and CXOGC
J174538.0-290022. All these sources are known to undergo very faint X-ray
outbursts with 2-10 keV peak luminosities of Lx,peak~1E34-1E36 erg/s, although
the two confirmed neutron star low-mass X-ray binaries AX J1745.6-2901 and GRS
1741-2853 can also become brighter (Lx,peak~1E36-1E37 erg/s). We discuss the
observed long-term lightcurves and X-ray spectra of these five enigmatic
transients. In 2008, AX J1745.6-2901 returned to quiescence following an
unusually long accretion outburst of more than 1.5 years. GRS 1741-2853 was
active in 2009 and displayed the brightest outburst ever recorded for this
source, reaching up to a 2-10 keV luminosity of Lx~1E37 (D/7.2 kpc)^2 erg/s.
This system appears to undergo recurrent accretion outbursts approximately
every 2 years. Furthermore, we find that the unclassified transient XMM
J174457-2850.3 becomes bright only during short episodes (days) and is often
found active in between quiescence (Lx~1E32 erg/s) and its maximum outburst
luminosity of Lx~1E36 erg/s. CXOGC J174535.5-290124 and CXOGC J174538.0-290022,
as well as three other very-faint X-ray transients that were detected by Swift
monitoring observations in 2006, have very low time-averaged mass-accretion
rates of ~< 2E-12 Msun/yr. Despite having obtained two years of new data in
2008 and 2009, no new X-ray transients were detected.Comment: Minor textual revisions according to referee report, accepted for
publication in A&
The effect of rotation on the stability of nuclear burning in accreting neutron stars
Hydrogen and/or helium accreted by a neutron star from a binary companion may
undergo thermonuclear fusion. At different mass accretion rates different
burning regimes are discerned. Theoretical models predict helium fusion to
proceed as a thermonuclear runaway for accretion rates below the Eddington
limit and as stable burning above this limit. Observations, however, place the
boundary close to 10% of the Eddington limit. We study the effect of
rotationally induced transport processes on the stability of helium burning.
For the first time detailed calculations of thin helium shell burning on
neutron stars are performed using a hydrodynamic stellar evolution code
including rotation and rotationally induced magnetic fields. We find that in
most cases the instabilities from the magnetic field provide the dominant
contribution to the chemical mixing, while Eddington-Sweet circulations become
important at high rotation rates. As helium is diffused to greater depths, the
stability of the burning is increased, such that the critical accretion rate
for stable helium burning is found to be lower. Combined with a higher heat
flux from the crust, as suggested by recent studies, turbulent mixing could
explain the observed critical accretion rate. Furthermore, close to this
boundary we find oscillatory burning, which previous studies have linked to mHz
QPOs. In models where we continuously lower the heat flux from the crust, the
period of the oscillations increases by up to several tens of percents, similar
to the observed frequency drift, suggesting that this drift could be caused by
the cooling of deeper layers.Comment: 11 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a Comptonised accreting ms pulsar ?
We report the discovery of a high-energy transient with the IBIS/ISGRI
detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934,
was first detected on 2nd December 2004 in the routine monitoring of the
IBIS/ISGRI 20--60 keV images. The observations were conducted during Galactic
Plane Scans, which are a key part of the INTEGRAL Core Programme observations.
After verifying the basic source behaviour, the discovery was announced on 3rd
December. The transient shows a hard Comptonised spectrum, with peak energy
release at about 20 keV and a total luminosity of ~ 0.9E36 erg/s in the 5--100
keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of
the discovery of IGR J00291+5934, a number of observations were made by other
instruments. We summarise the results of those observations and, together with
the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of
accreting X-ray millisecond pulsars.Comment: Accepted for publication as an A&A Letter 24/01/2005. 5 pages, 2
figure
Chandra and RXTE Spectra of the Burster GS 1826-238
Using simultaneous observations from Chandra and RXTE, we investigated the
LMXB GS 1826-238 with the goal of studying its spectral and timing properties.
The uninterrupted Chandra observation captured 6 bursts (RXTE saw 3 of the 6),
yielding a recurrence time of 3.54 +/- 0.03 hr. Using the proportional counter
array on board RXTE, we made a probable detection of 611 Hz burst oscillations
in the decaying phases of the bursts with an average rms signal amplitude of
4.8%. The integrated persistent emission spectrum can be described as the dual
Comptonization of ~ 0.3 keV soft photons by a plasma with kT_e ~ 20 keV and an
optical depth of about 2.6 (interpreted as emission from the accretion disk
corona), plus the Comptonization of hotter ~ 0.8 keV seed photons by a ~ 6.8
keV plasma (interpreted as emission from or near the boundary layer). We
discovered evidence for a neutral Fe K\alpha emission line, and we found
interstellar Fe L_II and Fe L_III absorption features. The burst spectrum can
be fit by fixing the disk Comptonization parameters to the persistent emission
best-fit values, and adding a blackbody. The blackbody/seed photon temperature
at the peak of the burst is ~ 1.8 keV and returns to ~ 0.8 keV over 200 s. The
blackbody radius is consistent with R_bb = 10.3-11.7 km assuming a distance of
6 kpc; however, by accounting for the fraction of the surface that is obscured
by the disk as a function of binary inclination, we determined the source
distance must actually be near 5 kpc in order for the stellar radius to lie
within the commonly assumed range of 10-12 km.Comment: Accepted for publication in ApJ; 13 pages, 6 figure
- …