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