413 research outputs found
Precise Timing of the X-ray Pulsar 1E 1207.4-5209: A Steady Neutron Star Weakly Magnetized at Birth
We analyze all X-ray timing data on 1E 1207.4-5209 in supernova remnant PKS
1209-51/52 gathered in 2000-2005, and find a highly stable rotation with
P=424.130451(4) ms and period derivative of (9.6 +/- 9.4)E-17 s/s. This refutes
previous claims of large timing irregularities in these data. In the dipole
spin-down formalism, the 2-sigma upper limit on period derivative implies an
energy loss rate < 1.5E32 ergs/s, surface magnetic field strength B_p < 3.5E11
G, and characteristic age tau > 24 Myr. This tau exceeds the remnant age by 3
orders of magnitude, requiring that the pulsar was born spinning at its present
period. The X-ray luminosity of 1E 1207.4-5209, L(bol) ~= 2E33 ergs/s at 2 kpc,
exceeds its spin-down energy loss, implying that L(bol) derives from residual
cooling, and perhaps partly from accretion of supernova debris. The upper limit
on B_p is small enough to favor the electron cyclotron model for at least one
of the prominent absorption lines in its soft X-ray spectrum. This is the
second demonstrable case of a pulsar born spinning slowly and with a weak
B-field, after PSR J1852+0040 in Kesteven 79.Comment: 5 pages, 2 figure, Latex, emulateapj style. Submitted to ApJ Letter
Phase Coherent Timing of RX J0806.3+1527 with ROSAT and CHANDRA
RX J0806.3+1527 is an ultra-compact, double degenerate binary with the
shortest known orbital period (321.5 s). Hakala et al. (2003) have recently
reported new optical measurements of the orbital frequency of the source which
indicate that the frequency has increased over the ~9 years since the earliest
ROSAT observations. They find two candidate solutions for the long term change
in the frequency; df/dt = 3 or 6 x 10E-16 Hz/s. Here we present the results of
a phase coherent timing study of the archival ROSAT and Chandra data for RX
J0806.3+1527 in the light of these new constraints. We find that the ROSAT --
Chandra timing data are consistent with both of the solutions reported by
Hakala et al., but that the higher df/dt = 6.1 x 10E-16 Hz/s solution is
favored at the ~97 % level. Such a large df/dt can be accomodated by an ~1 Msun
detached double degenerate system powered in the X-ray by electrical energy (Wu
et al. 2002). With such a large df/dt the system provides a unique opportunity
to explore the interaction of gravitational radiation and electromagnetic
torques on the evolution of an ultracompact binary.Comment: AASTeX preprint, 13 pages, 3 Figures. Accepted for Publication in the
Astrophysical Journal Letter
Disfuncionalidades en la regulación de los recursos hídricos en Mendoza (Argentina)
Mendoza es una provincia con un intenso aprovechamiento de las aguas mediante un modelo productivo estructurado mediante sistemas de oasis irrigados. El agua subterránea ha jugado un rol vital para expandir la frontera agrícola y mitigar los efectos nocivos en períodos de escasez. El aprovechamiento de las aguas en diversos usos está caracterizado por conflictos de intereses y disfuncionalidades que producen consecuencias contrarias al funcionamiento de un determinado sistema social. A partir de un análisis centrado en el acceso al recurso hídrico frente a los recientes balances hídricos aprobados por la Autoridad Hídrica Provincial, el trabajo problematiza sobre cómo los instrumentos de orden regulatorios en ocasiones se disocian entre sí, generando tensiones en la eficacia y eficiencia normativa. Las conclusiones brindan elementos de juicios para compatibilizar y adecuar los instrumentos de regulación vigentes, y así evitar graves distorsiones de difícil solución en la gestión hídrica.Mendoza is a province with an intense use of water through a productive model structured by irrigated oasis systems. Groundwater has played a vital role in expanding the agricultural frontier and alleviating harmful effects in times of scarcity. The use of water in various uses is characterized by conflicts of interest and dysfunctionalities that produce consequences contrary to the functioning of a given social system. Based on an analysis focused on access to water resources in the face of recent water balances approved by the Provincial Water Authority, the paper analyzes how the regulatory instruments sometimes dissociate from each other, creating tensions in efficiency and normative efficiency . The conclusions provide elements of judgments to reconcile and adapt the existing regulatory instruments, and thus avoid serious distortions that are difficult to solve in water management.Fil: Pinto, Mauricio E.. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias.Fil: Buccheri, Mauricio J.. Instituto Nacional del Agua. Centro de Economía, Legislación y Administración del Agua
Discovery of a New 89 Second X-ray Pulsar XTE J1906+09
We report on the discovery of a new pulsating X-ray source during Rossi X-ray
Timing Explorer observations of a low galactic latitude field centered at RA
(J2000) = 19 hr 05 m 43 s and Dec (J2000) = +08 deg 58 arcmin 48 arcsec.
Significant pulsations were detected by both the PCA and HEXTE instruments
aboard RXTE at a fundamental period of 89.17 +/- 0.02 seconds, with higher
harmonics also visible in the 2-10 keV power spectrum. The folded lightcurve
from the source is multiply peaked at lower energies, and changes to single
peaked morphology above ~20 keV. The phase averaged spectrum from the source is
well fit by strongly absorbed power law or thermal bremsstrahlung spectral
models of photon index 1.9 +/- 0.1 or temperature 19.5 +/- 4.6 keV,
respectively. The mean neutral hydrogen column density is approximately 10^23
cm^-2, suggesting a distance of >10 kpc to the source and a minimum 2-10 keV
X-ray luminosity of 2*10^{35} ergs s^{-1}. By comparison with other pulsars
with similar periods and luminosities, we suggest that XTE J1906+09 has a
supergiant companion with an underfilled Roche lobe. We speculate further that
one of the M stars in a peculiar M star binary system may be the companion.Comment: 14 pages, 2 figures. Accepted by ApJ Letter
Agricultural land use curbs exotic invasion but sustains native plant diversity at intermediate levels
Unveiling the processes driving exotic plant invasion represent a central issue in taking decisions aimed at constraining the loss of biodiversity and related ecosystem services. The invasion success is often linked to anthropogenic land uses and warming due to climate change. We studied the responses of native versus casual and naturalised exotic species richness to land uses and climate at the landscape level, relying on a large floristic survey undertaken in North - Eastern Italy. Both climate and land use drove exotic species richness. Our results suggest that the success of plant invasion at this scale is mainly due to warm climatic conditions and the extent of urban and agricultural land, but with different effects on casual and naturalized exotic species. The occurrence of non-linear trends showed that a small percentage of extensive agricultural land in the landscape may concurrently reduce the number of exotic plant while sustaining native plant diversity. Plant invasion could be potentially limited by land management, mainly focusing on areas with extensive agricultural land use. A more consciousness land management is more and more commonly required by local administrations. According to our results, a shift of intensive to extensive agricultural land, by implementing green infrastructures, seems to be a win\u2013win solution favouring native species while controlling the oversimplification of the flora due to plant invasion
X-ray emission from the old pulsar B0950+08
We present the timing and spectral analyses of theXMM-newton data on the
17-Myr-old, nearby radio pulsar B0950+08. This observation revealed pulsations
of the X-ray flux of the pulsar at its radio period. The pulse shape and pulsed
fraction are apparently different at lower and higher energies of the observed
0.2-10 keV energy range, which suggests that the radiation cannot be explained
by a single emission mechanism. The X-ray spectrum of the pulsar can be fitted
with a power-law model with a photon index about 1.75 and an (isotropic)
luminosity about 9.8e29 erg/s in the 0.2-10 keV. Better fits are obtained with
two-component, power-law plus thermal, models with index of 1.30 and 9.7e29
erg/s for the power-law component that presumably originates from the pulsar's
magnetosphere. The thermal component, dominating at E>0.7 keV, can be
interpreted as radiation from heated polar caps on the neutron star surface
covered with a hydrogen atmosphere. The inferred effective temperature, radius,
and bolometric luminosity of the polar caps are about 1 MK, 250 m, and 3e29
erg/s. Optical through X-ray nonthermal spectrum of the pulsar can be described
as a single power-law with index 1.3-1.4 for the two-component X-ray fit. The
ratio of the nonthermal X-ray (1-10 keV) luminosity to the nonthermal optical
(4000-9000 \AA) luminosity is within the range of 1e2-1e3 observed for younger
pulsars, which suggests that the magnetospheric X-ray and optical emissions are
powered by the same mechanism in all pulsars. An upper limit on the temperature
of the bulk of the neutron star surface, inferred from the optical and X-ray
data, is about 0.15 MK. We also analyze X-ray observations of several other old
pulsars, B2224+65, J2043+2740, B0628-28, B1813-36, B1929+10, and B0823+26.Comment: To be published in ApJ. Nonthermal optical and X-ray luminosities of
seven radio pulsars are updated and presented in a new Table. Figure 6
showing the ratios of the luminosities vs. spin-down energy is also update
X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338
Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total
of 27 thermonuclear bursts have been observed from the source with the
Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer
(RXTE). Spectroscopy of the bursts, as well as the presence of continuous burst
oscillations, suggests that all but one of the bursts are sub-Eddington. The
remaining burst has the largest peak bolometric flux of 2.64 x E^-8
erg/sec/cm^2, as well as a gap in the burst oscillations, similar to that seen
in Eddington limited bursts from other sources. Assuming this burst was
Eddington limited we obtain a source distance of about 8 kpc. All the bursts
show coherent oscillations at the 314.4 Hz spin frequency. The burst
oscillations are strongly frequency and phase locked to the persistent
pulsations. Only two bursts show evidence for frequency drift in the first few
seconds following burst onset. In both cases the initial drift corresponds to a
spin down of a few tenths of a Hz. The large oscillation amplitude during the
bursts confirms that the burst flux is modulated at the spin frequency. We
detect, for the first time, a significant first harmonic component in burst
oscillations. The ratio of countrate in the first harmonic to that in the
fundamental can be > 0.25 and is, on average, less than that of the persistent
pulsations. If the pulsations result from a single bright region on the
surface, the harmonic strength suggests the burst emission is beamed, perhaps
due to a stronger magnetic field than in non-pulsing LMXBs. Alternatively, the
harmonic content could result from a geometry with two bright regions.Comment: AASTeX, 15 pages, 4 figures. Accepted for publication in the
Astrophysical Journal Letter
Discovery of a Second Millisecond Accreting Pulsar: XTE J1751-305
We report the discovery by the RXTE PCA of a second transient accreting
millisecond pulsar, XTE J1751-305, during regular monitoring observations of
the galactic bulge region. The pulsar has a spin frequency of 435 Hz, making it
one of the fastest pulsars. The pulsations contain the signature of orbital
Doppler modulation, which implies an orbital period of 42 minutes, the shortest
orbital period of any known radio or X-ray millisecond pulsar. The mass
function, f_x = (1.278 +/- 0.003) x 10^{-6} M_sun, yields a minimum mass for
the companion of between 0.013 and 0.017 M_sun, depending on the mass of the
neutron star. No eclipses were detected. A previous X-ray outburst in June,
1998, was discovered in archival All-Sky Monitor data. Assuming mass transfer
in this binary system is driven by gravitational radiation, we constrain the
orbital inclination to be in the range 30-85 deg, and the companion mass to be
0.013-0.035 M_sun. The companion is most likely a heated helium dwarf. We also
present results from the Chandra HRC-S observations which provide the best
known position of XTE J1751-305.Comment: Astrophysical Journal Letters, Accepted, (AASTeX
X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR
Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy
at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span
reveals no significant change in its spin period. The 2 sigma upper limit on
the period derivative leads, in the dipole spin-down formalism, to an energy
loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G,
and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of
the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at
its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~
3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the
rotation-powered assumption. Instead, its high blackbody temperature,
0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~
80%, may be evidence of accretion onto a polar cap, possibly from a fallback
disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate
the light cylinder and interact with the magnetosphere while resulting torques
on the neutron star remain within the observed limits. A weak B-field is also
inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin
and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs:
the B-field, derived from a turbulent dynamo, is weaker if the NS is formed
spinning slowly, which enables it to accrete SN debris. Accretion excludes
neutron stars born with both B_p 0.1 s from radio pulsar
surveys, where B_p
40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could
explain the non-detection of a pulsar there.Comment: 8 pages, 3 figures, to appear in The Astrophysical Journa
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