bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid denudation processes in cryptogamic communities from Maritime Antarctica subjected to human trampling
Authors: Pertierra L.R. , Lara F. , Tejedo P. , Quesada A. , Benayas J.
Published: March 2013

This study explores the impact of human trampling on moss and lichen dominated communities of Maritime Antarctica. A simulation of trampling was performed on previously unaffected plots of different terricolous cryptogamic assemblages at Byers Peninsula, Livingston Island. The communities studied were: 1) a uniform moss carpet, 2) a heterogeneous moss assemblage composed of hummocks and turfs, and 3) a fellfield lichen community. All communities analysed were extremely sensitive but different denudation processes were observed. None of the plots maintained 50% of initial coverage after 200 pedestrian transits. Even very low trampling intensity resulted in disturbance at all plots. Sensitivities of the different communities were identified in order to formulate recommendations for minimizing the trampling impacts. In our study the lichen dominated community on dry exposed soils exhibited the lowest resistance to trampling. For moss communities, lower resistance was found in peat soils with higher water content and biomass. With the current trend of increasing human presence in Antarctica, we predict that the cumulative impacts of trampling over future decades will adversely affect all types of moss and lichen communities.
Phylogeographic analysis of filterable bacteria with special reference toRhizobialesstrains that occur in cryospheric habitats
Authors: Nakai Ryosuke , Shibuya Eri , Justel Ana , Rico Eugenio , Quesada Antonio , Kobayashi Fumihisa , Iwasaka Yasunobu , Shi Guang-Yu , Amano Yuki , Iwatsuki Teruki , Naganuma Takeshi
Published: March 2013

Although the lower size limit of microorganisms was previously believed to bec. 0.2 μm, there is evidence for the existence of microorganisms that can pass through 0.2 μm-pore-size filters called ultramicrobacteria or nanobacteria. However, information on the phylogeny and biogeography of these bacteria is limited. We obtained 53 isolates of 0.2 μm-passable bacteria from 31 samples collected at 26 locations worldwide, including the Arctic Svalbard Islands, deserts, and Maritime Antarctica. Phylogenetic analysis of near full-length 16S rRNA gene sequences revealed that 18 of the 53 isolates were < 97% homologous with previously cultured isolates, representing potentially novel species. Two isolates (orderRhizobiales) (100% identical) collected from Byers Peninsula, Livingston Island in Maritime Antarctica, were closely related (99.8% similarity) to an isolate collected from intertidal sediments in East Antarctica. In addition, the sequence of this Antarctic isolate showed ≥ 97% similarity to 901 sequences derived from known isolates and samples collected at geographically disparate locations under various environmental conditions. Interestingly, among 13 sequences showing ≥ 99% similarity, ten were isolated from cryospheric habitats such as Arctic, Antarctic, and alpine environments. This implies that suchRhizobialesstrains occur in the cryospheric regions, however, their abundance and biomass may be scarce depending on the geographic location.
Ecological relationships and stoichiometry within a Maritime Antarctic watershed
Authors: Velázquez David , Ángeles Lezcano Maria , Frias Ana , Quesada Antonio
Published: March 2013

During summer, ice-free areas are common in Maritime Antarctica, and vegetation and microbial communities frequently occur in the moist parts of catchments. In this paper, we present new data and evaluate the biomass, C, N, and P content of various types of vegetation, and the water catchment of an oligotrophic lake sited at Byers Peninsula, Livingston Island, South Shetland Islands. As the main results show, the total amount of C, N, and P contained in the organisms of the watershed is 144, 0.71 and 0.018 g m-2, respectively. According to element contents, 98% of the biological C from the watershed is within mosses and microbial mats structures (79.1 and 19.0% respectively). Also, 98.7% of the N is partially distributed between moss carpets, microbial mats and lichens, 55.2, 43.5, and 3.37 x 10-7% respectively. On the other hand, 90.2% of P is within moss carpets structures. Nutrient pools in the communities of Limnopolar Lake itself are a minor component of the whole catchment.
Stability and endemicity of benthic diatom assemblages from different substrates in a maritime stream on Byers Peninsula, Livingston Island, Antarctica: the role of climate variability
Authors: Pla-Rabes Sergi , Toro Manuel , Van De Vijver Bart , Rochera Carlos , Villaescusa Juan Antonio , Camacho Antonio , Quesada Antonio
Published: March 2013

Diatom assemblages from four different substrates from a stream on Byers Peninsula were analysed during the summer. The substrate type was the main factor explaining the variability in the diatom assemblages. Sandy biofilms showed a higher diversity and a greater number of endemic species. Two main hydrological regimes were observed: 1) a hydrologically unstable period with high variability in stream flow and successive freezing and thawing periods, 2) a late summer hydrologically stable period, characterized by low stream velocity and variability. The structure of the diatom communities was different between the two hydrological periods, although the substrate modulated the difference. The diatom assemblages showed low similarity among the substrates and high dominance of endemic species during early summer. The late summer community showed high dominance of motile cosmopolitan species on all substrate types. As the length of both hydrological regimes would ultimately be driven by climatic variability, the predicted climate warming could reduce overall stream diversity. Hence, subtle changes could alter the length of both hydrological periods. The relationship between diatom species association with different substrates and hydrological regimes could be relevant for tracking past climate variability using diatom palaeorecords.
Structure of planktonic microbial communities along a trophic gradient in lakes of Byers Peninsula, South Shetland Islands
Authors: Rochera Carlos , Toro Manuel , Rico Eugenio , Fernández-Valiente Eduardo , Villaescusa Juan Antonio , Picazo Antonio , Quesada Antonio , Camacho Antonio
Published: March 2013

A systematic limnological survey of water bodies of Byers Peninsula (Livingston Island, South Shetland Islands) was carried out during the summer of 2001/02. Abundances of microbial plankton were determined which allowed a delineation of the pelagic food web structure. We also report the nutrient status of these lakes. We demonstrate the occurrence of a trophic gradient that extended from upland lakes (oligotrophic) to the coastal ones (eutrophic). The study shows that a lake's morphology regulates the relative importance of the pelagic and benthic habitats, whereas nutrient loads mainly determine its trophic status. Yet, some of the variability observed could be also a legacy of the landscape. Photosynthetic pigments analyses by high-performance liquid chromatography of the lake waters revealed a major occurrence of chlorophytes, chrysophytes and diatoms. The chlorophyllaconcentrations in lakes in the central plateau were consistently lower (< 2.5 μg l-1) than coastal sites, which were one order of magnitude higher. Numbers of both bacterioplankton and autotrophic picoplankton also increased from inland to coastal sites. However, the relative role of autotrophic picoplankton in the total phytoplankton assemblage decreased with the increase in nutrients loads. Our results show that the trophic status clearly plays a significant role in structuring the pelagic communities of these lakes despite climatic constraints.
Vertical structure of bi-layered microbial mats from Byers Peninsula, Maritime Antarctica
Authors: Rochera Carlos , Villaescusa Juan Antonio , Velázquez David , Fernández-Valiente Eduardo , Quesada Antonio , Camacho Antonio
Published: March 2013

A summer study of the vertical structure of bi-layered microbial mats was carried out on Byers Peninsula (Livingston Island, South Shetland Islands). These benthic communities had a common basic structure that consisted of two distinct layers differing in composition, morphology and colour. Our sampling focused on mats showing more layering, which thrived over moist soils and at the bottom of ponds. The photosynthetic pigments analysis performed by high-performance liquid chromatography demonstrated a major occurrence of cyanobacteria and diatoms on these mats, the former being more abundant in relative terms on the surface and composed by morphospecies grouping into orders Oscillatoriales, Nostocales and Chroococcales. The areal chlorophyll a concentrations were slightly higher in the deeper layer although not significantly. Our microscopic and chemical analyses showed that non-active biomass accumulates at the surface. Hence, the upper layers showed the sheath pigment scytonemin and higher amounts of exopolysaccharides, as a strategy to cope with environmental stress. On the other hand, the basal layer was composed of more active photosynthetic microbiota, which also revealed a more balanced stoichiometry. Here we exemplify how environmental stresses are potentially overcome by physiological mechanisms developed by microbial mats which also shape their vertical structure.
A Comparison of Patient Needs Following Two Hurricanes
Authors: Nufer Kevin E. , Wilson-Ramirez Gina
Published: March 2013

Objectives:

The New Mexico-1 Disaster Medical Assistance Team (NM-1 DMAT) has responded to more disasters due to hurricanes than disasters from any other type of event. To assess whether defined patient needs may be applied to future hurricanes, the patient needs after Hurricanes Andrew and Iniki were compared. The study question was, “Did patient medical needs differ after these hurricanes?”

Methods:

Design: Retrospective cohort review. Subjects: All patients evaluated by NM-1 DMAT following Hurricanes Andrew and Iniki. Observations: Age, past medical history, chief complaint, diagnosis, diagnostic tests, treatments, triage level, and disposition. Age was analyzed using Student's t-test, other data were analyzed using the chisquare test.

Results:

A total of 1,056 patients were evaluated. Age distributions did not differ between events. More patients had co-morbidities after Hurricane Andrew. The only difference in chief complaint was that more patients complained of “cold” symptoms following Hurricane Iniki. The only differences in diagnoses were for upper respiratory infections, which were diagnosed more often after Hurricane Iniki. There were no differences in the administration of tetanus toxoid, antibiotics, or analgesics. Patients evaluated after Hurricane Andrew had more diagnostic tests performed and a higher illness/injury acuity. The proportion of the total number of patients conveyed to a hospital did not differ.

Conclusion:

Patient needs were similar after Hurricane Andrew and Hurricane Iniki and may be applicable for predicting the needs of patients for future hurricanes.
Pulsars are cool. Seriously.
Authors: Ransom Scott M.
Published: March 2013

Ever since the first pulsar was discovered by Bell and Hewish over 40 years ago, we've known that not only are pulsars fascinating and truly exotic objects, but that we can use them as powerful tools for basic physics and astrophysics as well. Taylor and Hulse hammered these views home with their discovery and timing of the spectacular “binary pulsar” in the 1970s and 1980s. In the last two decades a host of surprises and a promise of phenomenal scientific riches in the future has come from the millisecond pulsars. As our instrumentation has become more sensitive and better suited to measuring the pulses from these objects, they've given us new tests of general relativity, fantastic probes of the interstellar medium, constraints on the physics of ultra-dense matter, new windows into binary and stellar evolution, and the promise of a direct detection of gravitational waves. These things really are cool, and there is much more we will do with them in the future.
Magnetars: neutron stars with huge magnetic storms
Authors: Rea Nanda
Published: March 2013

Among the many different classes of stellar objects, neutron stars provide a unique environment where we can test (at the same time) our understanding of matter with extreme density, temperature, and magnetic field. In particular, the properties of matter under the influence of magnetic fields and the role of electromagnetism in physical processes are key areas of research in physics. However, despite decades of research, our limited knowledge on the physics of strong magnetic fields is clear: we only need to note that the strongest steady magnetic field achieved in terrestrial labs is some millions of Gauss, only thousands of times stronger than a common refrigerator magnet. In this general context, I will review here the state of the art of our research on the most magnetic objects in the Universe, a small sample of neutron stars called magnetars. The study of the large high-energy emission, and the flares from these strongly magnetized (~ 1015 Gauss) neutron stars is providing crucial information about the physics involved at these extremes conditions, and favoring us with many unexpected surprises.
The High Time Resolution Universe surveys for pulsars and fast transients
Authors: Keith Michael J.
Published: March 2013

The High Time Resolution Universe survey for pulsars and transients is the first truly all-sky pulsar survey, taking place at the Parkes Radio Telescope in Australia and the Effelsberg Radio Telescope in Germany. Utilising multibeam receivers with custom built all-digital recorders the survey targets the fastest millisecond pulsars and radio transients on timescales of 64 μs to a few seconds. The new multibeam digital filter-bank system at has a factor of eight improvement in frequency resolution over previous Parkes multibeam surveys, allowing us to probe further into the Galactic plane for short duration signals. The survey is split into low, mid and high Galactic latitude regions. The mid-latitude portion of the southern hemisphere survey is now completed, discovering 107 previously unknown pulsars, including 26 millisecond pulsars. To date, the total number of discoveries in the combined survey is 135 and 29 MSPs These discoveries include the first magnetar to be discovered by it's radio emission, unusual low-mass binaries, gamma-ray pulsars and pulsars suitable for pulsar timing array experiments.
New results from LOFAR
Authors: Kondratiev Vladislav
Published: March 2013

The LOw Frequency Array, LOFAR, is a next generation radio telescope with its core in the Netherlands and elements distributed throughout Europe. It has exceptional collecting area and wide bandwidths at frequencies from 10 MHz up to 250 MHz. It is in exactly this frequency range where pulsars are brightest and also where they exhibit rapid changes in their emission profiles. Although LOFAR is still in the commissioning phase it is already collecting data of high quality. I will present highlights from our commissioning observations which will include: unique constraints on the site of pulsar emission, individual pulse studies, observations of millisecond pulsars, using pulsars to constrain the properties of the magneto-ionic medium and pilot pulsars surveys. I will also discuss future science projects and advances in the observing capabilities.
Pulsar searches in nearby dwarf spheroidal galaxies
Authors: Rubio-Herrera Eduardo , Maccarone Thomas
Published: March 2013

We have been undertaking a comprehensive survey for pulsars and fast radio transients in the dwarf spheroidal satellite galaxies of the Milky Way using the Green Bank Radio Telescope operating at a central frequency of 350 MHz. Our search pipeline allows the detection of periodical signals and single dispersed pulses and it is optimized to search for millisecond radio pulsars. Here we present preliminary results of the searches we have conducted in the Ursa Minoris, Draco and Leo I dwarf spheroidal satellite galaxies. Our searches have revealed no periodic signals but a few unconfirmed millisecond single pulses at various dispersion measures, possibly related to neutron stars. Detecting neutron stars in these systems can potentially help to test the existence of haloes of dark matter surrounding these systems as predicted by Dehnen & King (2006).
The decaying magnetic field of magnetars: evidence and inference
Authors: Dall'Osso Simone
Published: March 2013

Magnetic field decay in neutron stars has been a long debated subject, since the early realization that radio pulsars were likely spinning neutron stars endowed with a 1E12 G magnetic dipole. This problem has however eluded all attempts of solution so far, mostly due to the scarcity of observational indications. Here I discuss the observational evidence for decay of the dipole magnetic field in magnetar candidates (Soft Gamma Repeaters and Anomalous X-ray Pulsars) and present a quantitative study of its main properties. I show that the decaying dipole does not have enough energy to power the persistent X-ray emission of magnetars. The latter must thus directly reveal the decay of an additional, stronger field component, presumably hidden in the interior of these neutron stars. Using existing models it is possible to characterize the salient properties of this internal field component and their implications for magnetar astrophysics. Finally, I sketch preliminary considerations on evolutionary links between magnetars and other classes of neutron stars with strong dipole field that do not show magnetar-like activity.
The first radio-quiet millisecond pulsar?
Authors: Belfiore Andrea
Published: March 2013

The Fermi-LAT source 2FGL J2339.6-0532 is likely to host a millisecond pulsar in a ‘black-widow’ system. Strong indications of its nature come from gamma rays and particularly from optical and X-ray observations. However, no pulsations have been found so far neither in radio nor in gamma rays, despite deep searches. I will present here our efforts to find pulsations in Fermi-LAT data. I will describe the uncertainties in the orbital and spin parameters of the source, broadly covered in our search. I will prove the robustness of our technique on other similar systems, and through simulations. I will present the results of our search: the most likely candidates and the further constraints on the parameters of the putative pulsar. Finally, I will discuss the implications of our results and the prospects to find pulsations in this and other similar systems in the future.
Formation of the planet orbiting the millisecond pulsar J1719–1438
Authors: van Haaften L. M. , Nelemans G. , Voss R. , Jonker P. G.
Published: March 2013

In 2011, Bailes et al. reported on the discovery of a detached companion in a 131 minute orbit around PSR J1719–1438, a 173 Hz millisecond pulsar. The combination of the very low mass function and such a short orbital period is unique. The discoverers suggested that the progenitor system could be an ultracompact X-ray binary (UCXB), which is a binary with a sub-hour orbital period in which a (semi-)degenerate donor fills its Roche lobe and transfers mass to a neutron star. The standard gravitational-wave driven UCXB scenario, however, cannot produce a system like PSR J1719–1438 as it would take longer than the age of the Universe to reach an orbital period of 131 min. We investigate two modifications to the standard UCXB evolution that may resolve this discrepancy. The first involves significant heating and bloating of the donor by pulsar irradiation, and in the second modification the system loses orbital angular momentum via a fast stellar wind from the irradiated donor, additional to the losses via the usual gravitational wave radiation. In particular a donor wind is effective in accelerating orbital expansion, and even a mild wind could produce the 131 minute period within the age of the Universe. We note that UCXBs could be an important class of progenitors of solitary millisecond radio pulsars.
A peculiar thermonuclear X-ray burst from the transiently accreting neutron star SAX J1810.8–2609
Authors: Degenaar N. , Wijnands R.
Published: March 2013

We report on a thermonuclear (type-I) X-ray burst that was detected from the neutron star low-mass X-ray binary SAX J1810.8–2609 in 2007 with Swift. This event was longer (≃20 min) and more energetic (a radiated energy of Eb≃6.5×1039 erg) than other X-ray bursts observed from this source. A possible explanation for the peculiar properties is that the X-ray burst occurred during the early stage of the outburst when the neutron star was relatively cold, which allows for the accumulation of a thicker layer of fuel. We also report on a new accretion outburst of SAX J1810.8–2609 that was observed with MAXI and Swift in 2012. The outburst had a duration of ≃17 days and reached a 2–10 keV peak luminosity of ≃ 3 × 1037 (D/5.7 kpc)2 erg s−1. This is a factor >10 more luminous than the two previous outbursts observed from the source, and classifies it as a bright rather than a faint X-ray transient.
Constraining neutron star EoS from cooling stages of X-ray bursts
Authors: Poutanen Juri , Suleimanov Valery
Published: March 2013

Thermal emission during X-ray bursts is a powerful tool to determine neutron star masses and radii, if the Eddington flux and the apparent radius in the cooling tail can be measured accurately, and distances to the sources are known. We propose here an improved method of determining the basic stellar parameters using the data from the cooling phase of long, photospheric radius expansion bursts covering a large range of luminosities. For this purpose, we computed a large set of atmosphere models for burst luminosities varying by two orders of magnitude and for various chemical compositions and surface gravities. We show that the variation of the inverse square root of the apparent blackbody radius with the flux, observed during the photospheric radius expansion bursts from a number of sources at low accretion rate is entirely consistent with the theoretical expectations of the color-correction factor evolution. However, for bursts happening at higher accretion rates the observed evolution is inconsistent with theory, implying that accretion strongly disturbs the neutron star atmosphere. These findings have profound implications for the recent claims on determination of the neutron star radii and masses from such bursts. Our method allows us to determine both the Eddington flux and the ratio of the stellar apparent radius to the distance much more reliably. For 4U 1724-307, we find a lower limit on the neutron star radius of 13 km, independently of the chemical composition. These results suggest that the matter inside neutron stars is characterized by a stiff equation of state.
Merging neutron star binaries: equation of state and electrodynamics
Authors: Lai Dong
Published: March 2013

Merging neutron star (NS) binaries may be detected by ground-based gravitational wave (GW) interferometers (e.g. LIGO/VIRGO) within this decade and may also generate electromagnetic radiation detectable by wide-field, fast imaging telescopes that are coming online. The GWs can provide new constraint on the NS equation of state (including mass-radius relation and the related nuclear symmetry energy). This paper reviews various hydrodynamical and electrodynamical processes in coalescing NS binaries, with focus on the pre-merger phase.
Neutron star seismology
Authors: Andersson Nils
Published: March 2013

I will provide an overview of recent improvements in our models for vibrating neutron stars, discussing the role of composition, heat, crust elasticity and superfluidity. I will explain how the results may impact on observations, in particular related to magnetar QPOs and future gravitational-wave searches.
Magnetar X-ray emission mechanisms
Authors: Zane Silvia
Published: March 2013

Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are peculiar X-ray sources which are believed to be magnetars: ultra-magnetized neutron stars which emission is dominated by surface fields (often in excess of 1E14 G, i.e. well above the QED threshold).

Spectral analysis is an important tool in magnetar astrophysics since it can provide key information on the emission mechanisms. The first attempts at modelling the persistent (i.e. outside bursts) soft X-ray (¡10 keV) spectra of AXPs proved that a model consisting of a blackbody (kT 0.3-0.6 keV) plus a power-law (photon index 2-4) could successfully reproduce the observed emission. Moreover, INTEGRAL observations have shown that, while in quiescence, magnetars emit substantial persistent radiation also at higher energies, up to a few hundreds of keV. However, a convincing physical interpretation of the various spectral components is still missing.

In this talk I will focus on the interpretation of magnetar spectral properties during quiescence. I will summarise the present status of the art and the currents attempts to model the broadband persistent emission of magnetars (from IR to hard Xrays) within a self consistent, physical scenario.
Pulsar Timing Arrays: Status and Techniques
Authors: Hobbs George
Published: March 2013

Three pulsar timing arrays are now producing high quality data sets. As reviewed in this paper, these data sets are been processed to 1) develop a pulsar-based time standard, 2) search for errors in the solar system planetary ephemeris and 3) detect gravitational waves. It is expected that the data sets will significantly improve in the near future by combining existing observations and by using new telescopes.
Prospects for probing strong gravity with a pulsar-black hole system
Authors: Wex N. , Liu K. , Eatough R. P. , Kramer M. , Cordes J. M. , Lazio T. J. W.
Published: March 2013

The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems, utilizing present and future radio telescopes, like FAST and SKA.
PSR J1906+0746: From relativistic spin-precession to beam modeling
Authors: Desvignes Gregory , Kramer Michael , Cognard Ismaël , Kasian Laura , van Leeuwen Joeri , Stairs Ingrid , Theureau Gilles
Published: March 2013

Shortly after the discovery of PSR J1906+0746, some hints of profile variations were already interpreted as first signs of relativistic spin-precession occuring. Using observations from the Nançay, Arecibo and Green Bank Radio Observatories, we report here the measurement of pulse profile and polarimetric variations. Using the Rotating Vector Model, we show that PSR J1906+0746 is likely to be an orthogonal rotator (α ≃ 80°). Fitting our polarimetric data to a precession model, we determined the geometry of the pulsar and found a wide misalignment angle (δ = 89−44+85 deg, 95% C.L.), although the uncertainty is large. Assuming this geometry, we constructed the beam maps of both magnetic poles.
The pulsar population in Globular Clusters and in the Galaxy
Authors: Freire Paulo C. C.
Published: March 2013

In this paper, I review some of the basic properties of the pulsar population in globular clusters (GCs) and compare it with the the Galactic disk population. The neutron stars (NSs) in GCs were likely formed - and appear to continue forming - in highly symmetric supernovae (SNe), likely from accretion-induced collapse (AIC). I review the many pulsar finds and discuss some particularly well populated GCs and why they are so. I then discuss some particularly interesting objects, like millisecond pulsars (MSPs) with eccentric orbits, which were heavily perturbed by passing stars. Some of these systems, like NGC 1851A and NGC 6544B, are almost certainly the result of exchange interactions, i.e., they are witnesses to the very same processes that created the large population of MSPs in the first place. I also review briefly the problem posed by the presence of young pulsars in GCs (with a special emphasis on a sub-class of young pulsars, the super-energetic MSPs), which suggest continuing formation of NSs in low-velocity SNe. In the final section, I discuss the possibility of an analogous population in the Galaxy and highlight a particularly interesting case, PSR J1903+0327, where the primary neutron star appears to have formed with a small-velocity kick and small fractional mass loss. Systems with primary NSs formed in electron-capture SNe should constitute a distinct low-velocity Galactic population akin in many respects to the GC population. Current high-resolution surveys of the Galactic plane should be able to detect it clearly.
The extended X–ray emission around RRAT J1819–1458
Authors: Camero-Arranz A. , Rea N. , McLaughlin M.A. , Bucciantini N. , Slane P. , Gaensler B. , Torres D. , Stella L. , de Oña E. , Israel G. , Camilo F. , Possenti A.
Published: March 2013

We present new imaging and spectral analysis of the recently discovered extended X–ray emission around the high-magnetic-field rotating radio transient RRAT J1819–1458. We used two Chandra observations, taken on 2008 May 31 and 2011 May 28. The diffuse X–ray emission was detected with a significance of ~19σ in the image obtained by combining the two observations. Long-term spectral variability has not been observed. Possible scenarios for the origin of this diffuse X–ray emission, further detailed in Camero–Arranz et al. (2012), are here discussed.
Science with radio pulsar astrometry
Authors: Chatterjee Shami
Published: March 2013

High precision astrometry on radio pulsars can provide model-independent estimates of their distances and velocities. Such estimates serve to calibrate models of the Galactic electron density distribution, thereby improving distance estimates for the entire pulsar population. They can provide independent astrometric information for precision pulse timing, reducing the number of fit parameters and thus potentially improving the sensitivity of pulsar timing arrays to the gravitational wave background. Individual neutron stars also serve as laboratories for astrophysics. For example, distances to highly luminous recycled pulsars identified by the Fermi gamma ray space telescope will constrain their energetics and may serve to probe the equation of state for nuclear matter at extremes of density and pressure. Here we provide an update on ongoing astrometry programs with the Very Long Baseline Array and the scientific results from these efforts.
The complex charm of the pulsar magnetosphere
Authors: Timokhin A. N.
Published: March 2013

I give a brief overview of recent results from self-consistent modeling of electron-positrons cascades in pulsar polar caps. These results strongly suggest that the pulsar magnetosphere is a more complex system than was assumed before.
Binary pulsar B1259-63 spectrum evolution: detailed study
Authors: Dembska Marta , Kijak Jarosław , Lewadowski Wojciech
Published: March 2013

We studied the radio spectrum of PSR B1259-63 in an unique binary with Be star LS 2883 and showed that the shape of the spectrum depends on the orbital phase. We proposed a qualitative model which explains this evolution. We considered two mechanisms that might influence the observed radio emission: free-free absorption and cyclotron resonance. Recently published results have revealed a new aspect in pulsar radio spectra. There were found objects with turnover at high frequencies in spectra, called gigahertz-peaked spectra (GPS) pulsars. Most of them adjoin such interesting environments as HII regions or compact pulsar wind nebulae (PWN). Thus, it is suggested that the turnover phenomenon is associated with the environment than being related intrinsically to the radio emission mechanism. Having noticed the apparent resemblance between the B1259-63 spectrum and the GPS, we suggest that the same mechanisms should be responsible for both cases. Therefore, the case of B1259-63 can be treated as a key factor to explain the GPS phenomenon observed for the solitary pulsars with interesting environments and also another types of spectra (e.g. with break).
“An X-Raydio Switcheroo” – The detection of correlated mode changes in radio and X-ray
Authors: van Leeuwen Joeri , Hermsen Wim , Hessels Jason , Kuiper Lucien , Mitra Dipanjan , Rankin Joanna , Stappers Ben , Wright Geoff
Published: March 2013

We present high-sensitivity XMM/LOFAR observations that show for the first time that mode switching extends from radio to X-ray. In pulsar B0943+10, the known changes in radio profile and drift rate are confidently tied to simultaneous changes in X-ray emission.

In mode switching, seen in many pulsars, profile and subpulse-drift behavior change almost instantaneously. The mechanism for these drastic changes, or for the bi-stable emission behavior, is not understood; while even for the basic emission mechanism different families of theories (e.g. vacuum gap, or space-charge limited flow models) exist.

To discriminate between such models, we carried out a campaign of 42 hours of simultaneous LOFAR/XMM-Newton observations on PSR B0943+10. Through LOFAR's unparalleled low-frequency sensitivity, mode changes were pinpointed to 10-second accuracy. XMM X-ray photons were next separated by the two radio modes. We discovered large modal differences in the X-ray pulsations, flux, and spectral shapes: in the radio-bright mode, no X-ray pulsations are detected – but in the radio-quiet mode, B0943+10 is strongly pulsating in X-ray.
A new low-B magnetar: Swift J1822.3–1606
Authors: Camero-Arranz A. , Rea N. , Israel G. L. , Esposito P. , Pons J. A. , Mignani R. P. , Turolla R. , Zane S. , Burgay M. , Possenti A. , Campana S. , Enoto T. , Gehrels N. , Göğüş E. , Götz D. , Kouveliotou C. , Makishima K. , Mereghetti S. , Oates S. R.
Published: March 2013

We report on the long term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and XMM-Newton of the outburst of the newly discovered magnetar Swift J1822.3–1606 (SGR 1822-1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery (July 2011), through the first stages of its outburst decay (April 2012). Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016(2) s and a period derivative Ṗ = 8.3(2) × 10−14 ss−1, which entails an inferred dipolar surface magnetic field of B ≃ 2.7 × 1013 G at the equator. This measurement makes Swift J1822.3–1606 the second lowest magnetic field magnetar (after SGR 0418+5729; Rea et al. 2010). Following the flux and spectral evolution from the beginning of the outburst, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modeling the secular thermal evolution of Swift J1822.3–1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and crustal toroidal fields of Bp ~ 1.5 × 1014 G and Btor ~ 7 × 1014 G, respectively, and if its current age is ~550 kyr (Rea et al. 2012).
Unified description of dense matter in neutron stars and magnetars
Authors: Chamel N. , Pavlov R. L. , Mihailov L. M. , Velchev Ch. J. , Stoyanov Zh. K. , Mutafchieva Y. D. , Ivanovich M. D. , Fantina A. F. , Pearson J. M. , Goriely S.
Published: March 2013

We have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.
New timing solutions for RRATs
Authors: Cui Bingyi , Boyles Jason , McLaughlin Maura , Palliyaguru Nipuni
Published: March 2013

The rotating radio transients are sporadic pulsars which are difficult to detect through periodicity searches. By using a single-pulse search method, we can discover these sources, measure their periods, and determine timing solutions. Here we introduce our results on six RRATs based on Parkes and Green Bank Telescope (GBT) observations, along with a comparison of the spin-down properties of RRATs and normal pulsars.
Birth accelerations of neutron stars
Authors: Heras Ricardo
Published: March 2013

We suggest that neutron stars experienced at birth three related physical changes, which may originate in magneto-rotational instabilities: (i) an increase in period from the initial value P0 to the current value Ps, implying a change of rotational energy Δ Erot; (ii) an exponential decay of its magnetic field from the initial value B0 to the current surface value Bs, implying a change of radiative energy Δ Erad; and (iii) an increase of space velocity from the initial value v0 to the current value v, implying a change of kinetic energy Δ Ekin. These changes are assumed to be connected by Δ Erad + Δ Ekin = Δ Erot. This means that the radiation loss and increase of kinetic energy are both at the expense of a rotational energy loss. It is shown that this energy conversion occurs during times of order of 10−4 s if the neutron stars are born with magnetic fields in the range of 1015–1016 G and initial periods in range 1–20 ms. It is shown that the birth accelerations of neutron stars are of the order of 108g.
Neutron stars: history of the magnetic field decay
Authors: Igoshev Andrei P. , Kholtygin Alexander F.
Published: March 2013

Using the data of the ATNF pulsar catalog we study the relation connected the real age t of young neutron stars (NS) and their spin-down age τ. We suppose that this relation is independent from both initial period of the NS and its initial surface magnetic field, and that the laws of the surface magnetic field decay are similar for all NSs in the Milky Way. We further assume that the birth-rate of pulsars was constant during at least last 200 million years. With these assumptions we were able to restore the history of the magnetic field decay for the galactic NSs. We reconstruct the universal function f(t) = B(t)/B0, where B0 is the initial magnetic field and B(t) is the magnetic field of NS at the age t. The function f(t) can be fitted by a power law with power index α = −1.17.
Testing the relationship between nulling, drifting and mode-changing
Authors: Joshi Bhal Chandra
Published: March 2013

Recent observations, suggesting that subpulse drifting, pulse nulling and profile mode-changes are related phenomena, are reviewed and it is argued that these are associated with global changes in the magnetosphere. Long simultaneous multi-frequency observations are useful to test this premise as is illustrated by the preliminary results from a recent study of PSR B0031–07, B0809+74 and B2319+60. Such observations for a larger sample of pulsars will be useful to constrain recent models, invoking global changes in the pulsar magnetosphere, proposed to explain observations demonstrating association of spin-down changes with profile mode-changes.
Gamma-ray emission from pulsar binaries
Authors: Kirk John , Mochol Iwona
Published: March 2013

Pulsar winds, containing charged particles, waves and a net (phase-averaged) magnetic field, are thought to fuel the high-energy emission from several gamma-ray binaries. They terminate where the ram pressure matches that of the surroundings - which, in binaries, is provided by the wind of the companion. Before termination, pulsed emission can be produced by inverse Compton scattering of photons from the companion by particles in the waves. After termination, both the bulk kinetic energy of the particles and the Poynting flux in the waves are dissipated into an energetic particle population embedded in the surviving phase-averaged magnetic field. Pulsed emission is no longer possible, but a substantial flux of unpulsed high-energy photons can be produced. I will present results showing that the physical conditions at the termination shock can be divided into two regimes: a high density one, where current sheets in the wind are first compressed by an MHD shock and subsequently dissipate by reconnection, and a low density one, where the wind can first convert into an electromagnetic wave in the shock precursor, which then damps and merges into the wind nebula. The shocks surrounding isolated pulsars fall into the low-density category, but those around pulsars in binary systems, may transit from one regime to the other according to binary phase. The implications of the shock-structure dichotomy for these objects will be discussed.
TeV cosmic-ray electrons from millisecond pulsars
Authors: Kisaka Shota , Kawanaka Norita
Published: March 2013

Recent γ-ray observations by the Fermi Gamma-Ray Space Telescope suggest that the γ-ray millisecond pulsar (MSP) population is separated into two subclasses with respect to pair multiplicity. Here, we calculate the cosmic-ray electron/positron spectra from MSPs. Based on the assumption of equipartition in the pulsar-wind region, the typical energy of electrons/positrons ejected by an MSP with pair multiplicity of the order of unity is ~50 TeV. In this case, we find that a large peak in the 10-50 TeV energy range would be observed in the cosmic-ray electron/positron spectrum. Even if the fraction of pair-starved MSPs is 10%, a large peak would be detectable with future missions such as CALET and CTA.
A pulsar census of the Local Group
Authors: Kondratiev Vladislav , Lorimer Duncan , McLaughlin Maura , Ransom Scott
Published: March 2013

We carried out a search for pulsars in nearby galaxies with the GBT and Arecibo radio telescopes at 820 and 327 MHz, correspondingly. Currently, the Magellanic Clouds are the only galaxies except for Milky Way known to harbor radio pulsars, with a total of 20 pulsars being discovered there to date. Discovery of pulsars in other galaxies can be used to trace the history of massive star formation and would allow to probe the intermediate intergalactic medium. We selected 22 galaxies of the Local Group at high galactic latitudes, |b| > 26 deg, with most of them being dwarf spheroidals with old star population. This makes them promising targets to search for giant pulses from recycled millisecond pulsars. Both single-pulse and periodicity searches were performed for trial dispersion measures up to 1000. No extragalactic pulsars are found in half of the selected targets processed so far. I will give the overview of our targetted searches, present potential candidates and discuss the obtained results.
H-cluster stars
Authors: Lai X. Y. , Xu R. X.
Published: March 2013

The study of dense matter at ultra-high density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other. That might produce quarks grouped in clusters, although the hypothetical quark-clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality.

Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we are therefore considering here a possible kind of quark-clusters, H-clusters, that could emerge inside compact stars during their initial cooling, as the dominant components inside (the degree of freedom could then be H-clusters there). We study the stars composed of H-clusters, i.e., H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general understanding of different manifestations of compact stars, we expect further observational and experimental tests for the H-cluster stars in the future.
Profile stability and timing precision limit of millisecond pulsars
Authors: Liu Kuo
Published: March 2013

Millisecond pulsars are shown to have highly regular rotations and stable profiles, which enables the utilisation of them as accurate clocks. In this talk, I will present the latest studies on profile stability of several millisecond pulsars. I will focus on single pulse stability and its influence on the shape and phase of integrated profiles achieved on short timescales. It will be shown that the single pulse instability seems to be a source dependent issue, and they would influence differently on timing precision of the pulsar. The understanding of profile stability is essential in determining the timing precision limit and the optimal timing scheme with the future radio telescopes.
Do magnetars really exist?
Authors: Malov I. F.
Published: March 2013

It is shown that there are neither necessary nor sufficient properties to provide unambiguous evidence for including any object in the AXP/SGR class.
Global structure of the pulsar force-free magnetosphere revisited
Authors: Petrova Svetlana
Published: March 2013

A new model of the pulsar force-free magnetosphere is suggested, which includes the presence of the polar, outer and slot gaps. It is based on a new exact solution of the pulsar equation in the form of an offset monopole and the resultant split-offset monopole scheme.
X-ray properties of G308.3-1.4 and its central compact object
Authors: Seo K. A. , Hui C. Y. , Huang R. H. H. , Trepl L. , Lu T.-N. , Kong A. K. H. , Walter F. M.
Published: March 2013

We present a short Chandra observation that confirms a previous unidentified extended X-ray source, G308.3-1.4, as a new supernova remnant (SNR) in the Milky Way. Apart from identifying its SNR nature, a bright X-ray point source has also been discovered at the geometrical center. Its X-ray spectral properties are similar to those of a particular class of neutron star known as central compact objects (CCOs). On the other hand, the optical properties of this counterpart suggests it to be a late-type star. Together with the interesting ~ 1.4 hours X-ray periodicity found by Chandra, this system can possibly provide the first direct evidence of a compact binary survived in a supernova explosion.
Formation of Binary and Millisecond Pulsars: Puzzles and Possible Solutions
Authors: Shao Yong , Li Xiang-Dong
Published: March 2013

We present a systematic study of the evolution of intermediate- and low-mass X-ray binaries. Our calculations suggest that millisecond binary pulsars in wide orbits might have neutron stars born massive, or been formed through mass transfer driven by planet/brown dwarf-involved common envelope evolution.
On the glitch evolution of pulsars
Authors: Urama J. O. , Joshi B. C. , Chukwude A. E.
Published: March 2013

Observation of pulsar glitches remains a powerful tool for studying the interior of neutron stars. Many of the observed glitch properties are shown to result from the evolution of glitches in the different manifestations of neutron stars. Specifically, the type of glitches associated with the Crab and Vela pulsars are explained by this model. We are, also, able to adequately account for the absence, or very low rate, of glitches among the youngest and the very old pulsars.