Search

Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds1,2. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated3. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839–10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10−13s s−1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star.

Context. Despite about a decade of observations, very little is known about the optical and infrared (IR) emission properties of the soft gamma-ray repeaters (SGRs) and of the anomalous X-ray pulsars (AXPs), the magnetar candidates, and about the physical processes which drive their emission at these wavelengths. This is mainly due to the limited number of identifications achieved so far, five in total, and to the sparse spectral coverage obtained from multi-band optical/IR photometry.

Aims. XTE J1810-197 is the first transient anomalous X-ray pulsar ever discovered. Its highly variable X-ray flux allowed us to study the timing and spectral emission properties of a magnetar candidate over a flux range of about two orders of magnitude.

In December 2004, the soft gamma-ray repeater SGR 1806-20 emitted the most powerful giant flare ever observed. This probably involved a large-scale rearrangement of the magnetosphere leading to observable variations in the properties of its X-ray emission. Here we present the results of the first Suzakuobservation of SGR 1806-20, together with almost simultaneous observations with XMM-Newtonand INTEGRAL. The source seems to have reached a state characterized by a flux close to the pre-flare level and by a relatively soft spectrum. Despite this, SGR 1806-20  also remained quite active after the giant flare, allowing us to study several short bursts observed by Suzakuin the 1–100 keV range. We discuss the broad-band spectral properties of SGR 1806-20, covering both persistent and bursting emission, in the context of the magnetar model, and consider its recent theoretical developments.

Aims.Previous studies of the X-ray flux and spectral properties of 1RXS J170849-400910 showed a possible correlation with the spin glitches that occurred in 1999 and 2001. However, due to the sparseness of spectral measurements and the paucity of detected glitches, no firm conclusion could be drawn.

Aims.We report on a multi-band high-energy observing campaign aimed at studying the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910, one of the magnetar candidates.

Context.Recent radio observations have unveiled the existence of a number of radio pulsars with spin-down derived magnetic fields in the magnetar range. However, their observational properties appear to be more similar to those of the classical radio pulsars than to the magnetars's ones.

Convincing evidence of long-term variations in the emission properties of the anomalous X-ray pulsar 1RXS J170849.0–400910 has been gathered in the past few years. In particular, and following the pulsar glitches of 1999 and 2001, XMM-Newtonwitnessed a decline in 2003 of the X-ray flux accompanied by a definite spectral softening. This suggested the existence of a correlation between the luminosity and the spectral hardness in this source, similar to what was seen in the soft γ-repeater SGR 1806–20. Here we report on new Chandraand Swiftobservations of 1RXS J170849.0–400910 performed in 2004 and 2005, respectively. These observations confirm and strengthen the proposed correlation. The trend appears to have now reversed: the flux has increased and the spectrum is now harder. We briefly discuss the consequences of these observations for the twisted magnetosphere scenario for anomalous X-ray pulsars.

XMM-Newtonobserved the soft gamma repeater SGR 1806–20  about two months after its 2004 December 27 giant flare. A comparison with the previous observations taken with the same instrument in 2003–2004 shows that the pulsed fraction and the spin-down rate have significantly decreased and that the spectrum slightly softened. These changes may indicate a global reconfiguration of the neutron star magnetosphere. The spectral analysis confirms that the presence of a blackbody component in addition to the power-law is required. Since this additional component is consistent with being constant with respect to the earlier observations, we explore the possibility of describing the long-term spectral evolution as only due to the power-law variations. In this case, the slope of the power-law does not significantly change and the spectral softening following the giant flare is caused by the increase of the relative contribution of the blackbody over the power-law component.

We report the results of a recent (July 2004) XMM-NewtonTarget of Opportunity observation of the Anomalous X-ray Pulsar 1E 1048.1–5937 together with a detailed re-analysis of previous observations carried out in 2000 and 2003. In July 2004 the source had a 2–10 keV flux of 6.2 $\times$10-12erg cm-2s-1and a pulsed fraction PF= 0.68. Comparison of the three data sets shows the presence of an anti-correlation between flux and pulsed fraction, implying that previous estimates of the source energetics based on the assumption of a large and constant pulsed fraction might be significantly underestimated. The source spectrum is well described by a power law plus blackbody model (kT~ 0.63 keV, photon index Γ~ 2.7–3.5) or, alternatively, by the sum of two blackbodies of which the hotter is Comptonized by relativistic electrons. In this case the temperatures are $kT{_1}$~ 0.2–0.3 keV and $kT{_2}$~ 0.4–0.5 keV and the emitting area of the cooler component is consistent with the whole neutron star surface. The long-term luminosity variation of a factor $\ga$2 is accompanied by relatively small variations in the spectral shape. Phase-resolved spectroscopy indicates a harder spectrum together with the pulse maximum. No spectral features have been detected with 4σlimits on the equivalent width in the range ~10–220 eV, depending on line energy and width.

The sky region including the Chandra position of SGR 1806–20 was monitored in the IR band during 2004, following its increased high energy bursting activity. Observations were performed using NAOS-CONICA, the adaptive optics IR camera mounted on Yepun VLT, which provided images of unprecedented quality (FWHMbetter than 0$\farcs$1). After the 2004 December 27th giant flare, the source position has been nailed by VLA observations of its radio counterpart, reducing the positional uncertainty to 0$\farcs$04. Using IR data from our monitoring campaign, we discovered the likely IR counterpart to SGR 1806–20 based on positional coincidence with the Chandra and VLA uncertainty regions and flux variability of a factor of about 2 correlated with that at higher energies. We compare our findings with other isolated neutron star classes thought to be related, at some level, with SGRs.

We report on observations aimed at searching for flux variations from the proposed IR counterpart of the Anomalous X-ray Pulsar (AXP) XTE J1810-197. These data, obtained in March 2004 with the adaptive optics camera NAOS-CONICA at the ESO VLT, show that the candidate proposed by Israel et al. ([CITE], ApJ, 603, L97) was fainter by $\Delta H=0.7\pm0.2$and $\Delta K_{\rm s}=0.5\pm0.1$with respect to October 2003, confirming it as the IR counterpart of XTE J1810-197. We also report on an XMM-Newton observation carried out the day before the VLT observations. The 0.5-10 keV absorbed flux of the source was $2.2\times10^{-11}$erg cm-2s-1, which is less by a factor of about two compared to the previous XMM-Newton observation on September 2003. Therefore, we conclude that a similar flux decrease took place in the X-ray and IR bands. We briefly discuss these results in the framework of the proposed mechanism(s) responsible for the IR variable emission of AXPs.

We report on a spectral and timing analysis of BeppoSAX data of the 13.6 s period transient X-ray pulsar EXO 053109-6609.2. Observations were carried out in March 1997 and October 1998, catching the source during a high and a low emission state, respectively. Correspondingly, the X-ray luminosity is found at a level of $ 4.2 \times 10^{37}~\rm erg\,s^{-1}$and $1.5\times 10^{36}~\rm erg\,s^{-1}$in the two states. In the high state the X-ray emission in the energy range 1–100 keV is well fitted by an absorbed power-law with photon index $ \Gamma\sim 1.7$plus a blackbody component with a characteristic temperature of ~3.5 keV. Moreover, we find evidence of iron emission at ~6.8 keV, a typical feature in this class of sources but never seen before in the EXO 053109-6609.2 spectrum. In the low state an absorbed power-law with $\Gamma\sim 0.4$is sufficient to fit the 1–10 keV data. During BeppoSAX observations EXO 053109-6609.2 display variations of the pulse profile with the X-ray flux: it showed single peaked and double peaked profiles in the low and high state, respectively. Based on these two observations we infer a spin-up period derivative of -(1.14 ±0.08) $\times$$10^{-10}~{\rm ss}^{-1}$. By comparing these with other period measurements reported in the literature we find an alternating spin-up and spin-down behaviour that correlates well with the X-ray luminosity.

Diffuse radio emission was detected around the soft gamma-ray repeater SGR 1806-20  after its 2004 powerful giant flare. We study the possible extended X-ray emission at small scales around SGR 1806-20, in two observations by the High Resolution Camera Spectrometer (HRC-S) on board of the Chandra X-ray Observatory: in 2005, 115 days after the giant flare, and in 2013, during quiescence. We compare the radial profiles extracted from data images and PSF simulations, carefully considering various issues related to the uncertain calibration of the HRC PSF at sub-arcsecond scales. We do not see statistically significant excesses pointing to an extended emission on scales of arcseconds. As a consequence, SGR 1806-20 is compatible with being point-like in X-rays, months after the giant flare, as well as in quiescence.

Context. We report on near-infrared (IR) observations of the three anomalous X-ray pulsars XTE?J1810?197, 1RXS?J1708?4009, and 1E?1841?045, and the soft gamma-ray repeater SGR?1900+14, taken with the ESO-VLT, the Gemini, and the CFHT telescopes.Aims. This work aims at identifying and/or confirming the IR?counterparts of these magnetars, as well as at measuring their possible IR?variability.Methods. To perform photometry of objects as faint as Ks?20, we used data taken with the largest telescopes, equipped with the most advanced IR detectors and in most of the cases with adaptive optics devices. The latter are critical for achieving the sharp spatial accuracy required to pinpoint faint objects in crowded fields.Results. We confirm with high confidence identification of the IR?counterpart to XTE?J1810?197?and its IR?variability. For 1E?1841?045? and SGR?1900+14, we propose two candidate IR counterparts based on the detection of IR?variability. For 1RXS?J1708?4009, we show that none of the potential counterparts within the source X-ray error circle can as yet be convincingly associated with this AXP.Conclusions. The IR?variability of the AXP XTE?J1810?197? does not follow the same monotonic decrease in its post-outburst X-ray emission. Instead, the IR?variability appears more like the one observed in radio band, although simultaneous IR?and radio observations are crucial for any conclusion in this respect. For 1E?1841?045? and SGR?1900+14, follow-up observations are needed to confirm our proposed candidates with higher confidence.

In December 2004, the soft gamma-ray repeater SGR?1806-20?emitted the most powerful giant flare ever observed. This probably involved a large-scale rearrangement of the magnetosphere leading to observable variations in the properties of its X-ray emission. Here we present the results of the first Suzaku?observation of SGR?1806-20, together with almost simultaneous observations with XMM-Newton?and INTEGRAL. The source seems to have reached a state characterized by a flux close to the pre-flare level and by a relatively soft spectrum. Despite this, SGR?1806-20? also remained quite active after the giant flare, allowing us to study several short bursts observed by Suzaku?in the 1?100?keV range. We discuss the broad-band spectral properties of SGR?1806-20, covering both persistent and bursting emission, in the context of the magnetar model, and consider its recent theoretical developments.

In this paper, the dynamics of primary production in the Daly River in tropical Australia are investigated. We used the diurnal-curve method for both oxygen and pH to calculate photosynthesis and respiration rates as indicators of whole-river productivity. The Daly River has maximum discharges during the summer, monsoonal season. Flow during the dry season is maintained by groundwater discharge via springs. The study investigated how primary production and respiration evolve during the period of low flow in the river (April?November). The relationship between primary production and the availability of light and nutrients enabled the role of these factors to be assessed in a clear, oligotrophic tropical river. The measured rate of photosynthesis was broadly consistent with the estimated mass of chlorophyll associated with the main primary producers in the river (phytoplankton, epibenthic algae, macroalgae, macrophytes). A significant result of the analysis is that during the time that plant biomass re-established after recession of the flows, net primary production proved to be ~4% of the rate of photosynthesis. This result and the observed low-nutrient concentrations in the river suggest a tight coupling between photosynthetic fixation of carbon and the microbial degradation of photosynthetic products comprising plant material and exudates.

The reproductive characteristics of T. procerum in three lagoons in the Mediterranean south-east of South Australia were used to investigate the role of water regime in the often heterogeneous and patchy distribution of aquatic vegetation. A theoretical explanation for these patterns, based on sexual reproduction vis-a-vis seedling establishment, is proposed. Owing to the unpredictable nature of seed dispersal and the narrow range of suitable conditions for germination and establishment that result from fluctuating and variable water levels, establishment events are spatially and temporally dynamic. These features may be important for maintaining species distribution, species survival and habitat diversity. Population resilience through genetically heterogeneous stands is another outcome. The implications of sexual reproduction by clonal plants are discussed, as is the need to maintain the conditions that plants need to flower, germinate and become established. The unpredictable nature of establishment events makes them difficult to manage. Regulation and pondageldrainage may be having a profound effect on the survival of many aquatic plant species owing to their inability to regenerate under such conditions.

The response of B. arthrophylla and T. procerum in pot experiments to depth and depth changes provided insight into how plants survive fluctuating water levels. At 0 cm depth, most biomass was placed below ground, which can be interpreted as the placement of resource-acquiring tissues (roots, rhizomes) in resource (nutrients, space) -supplying environments. At 50 and 100 cm, the placement of biomass into shoots recognized the need for a higher supply of above-ground resources (light, inorganic carbon, oxygen). However, the responses of the two species to flooding or exposure differed. Rhizome storage supported an increase in the number and height of B. arthrophylla stems when flooded by 50 cm but this species was unable to counteract submergence to 100 cm without the critical loss of root mass. The slow turnover rate of the cuticularized B. arthrophylla stems indicates that biomass needs to be allocated above water as well as above ground. Other responses indicated that this species may be better suited to seasonally fluctuating rather than permanent water levels. T. procerum dealt with water level changes via morphological plasticity. Along with the rapid growth and turnover of the spongy leaves, its shoot and total mass were maintained primarily from resources in the tubers.

A compact scanning microscope that uses a semiconductor laser both to illuminate a specimen and to detect the signal reflected from it is described. It is demonstrated that the spatial filtering performed by the laser detector ensures confocal operation. Two detection regimes, one employing a laser power monitor and the other using the diode junction voltage as a signal, are compared.

A total of 349 adult red drum (Sciaenops ocellata) were collected from the coastal marsh below Hopedale in southeastern Louisiana, between October, 1967 and October, 1968. A total of 286 fish (82%) contained identifiable food items which were analyzed as to frequency of occurrence and percent of total volume. The main food items in order of occurrence were fish, shrimp, and crabs. Blue crabs, mud crabs, and penaeid shrimp were the crustaceans most frequently eaten, and at least 14 different species of fish were utilized to some degree. Food habits varied substantially from season to season. Fish was the main food item during winter and spring months. Crustaceans, crabs and shrimp combined comprised the bulk of the diet during the summer and fall months. Only slight differences in food habits were detected due to size or sex. Gonadal examination of eight adults indicated that spawning took place between September and December. The length-weight relationship and seasonal condition values were determined. Red drum of a given standard length were generally heavier than previously reported. Condition values from this study represented fish in overall good condition.

Context.With two consecutive outbursts recorded in four months (October 2008 and January 2009), and a possible third outburst in 2007, 1E 1547.0-5408 is one of the most active transient anomalous X-ray pulsars known so far.