A research cruise was organized on board the Italian National Research Council (CNR) R/V Urania to test the oil spill monitoring system developed during the PRogetto pilota Inquinamento Marino da ...Idrocarburi project (PRIMI, pilot project for marine oil pollution). For the first time, this system integrated in a modular way satellite oil spill detection (Observation Module) and oil spill displacement forecasting (Forecast Module) after detection. The Observation Module was based on both Synthetic Aperture RADAR (SAR) and optical satellite detection, namely SAR and Optical Modules, while the Forecast Module on Lagrangian numerical circulation models. The cruise (Aug. 6–Sep. 7, 2009) took place in the Mediterranean Sea, around Sicily, an area affected by heavy oil tanker traffic with frequent occurrence of oil spills resulting from illegal tank washing. The cruise plan was organized in order to have the ship within the SAR image frames selected for the cruise, at acquisition time. In this way, the ship could rapidly reach oil slicks detected in the images by the SAR Module, and/or eventually by the Optical Module, in order to carry out visual and instrumental inspection of the slicks. During the cruise, several oil spills were detected by the two Observation Modules and verified in situ, with the essential aid of the Forecasting Module which provided the slick position by the time the ship reached the area after the alert given by the SAR and/or optical imagery. Results confirm the good capability of oil spill SAR detection and indicate that also optical sensors are able to detect oil spills, ranging from thin films to slicks containing heavily polluted water. Also, results confirm the useful potential of oil spill forecasting models, but, on the other hand, that further work combining satellite, model and in situ data is necessary to refine the PRIMI system.
The middle-aged PSR J0357+3205 is a nearby, radio-quiet, bright gamma -ray pulsar discovered by the Fermi mission. Our previous Chandra observation revealed a huge, very peculiar structure of diffuse ...X-ray emission originating at the pulsar position and extending for >9' on the plane of the sky. To better understand the nature of such a nebula, we have studied the proper motion of the parent pulsar. We performed relative astrometry on Chandra images of the field spanning a time baseline of 2.2 yr, unveiling a significant angular displacement of the pulsar counterpart, corresponding to a proper motion of (XT65 + or - 0''.030 yr super(-1) at a position angle (PA.) of 314degrees + or - 8degrees. At a distance of ~500 pc, the space velocity of the pulsar would be of ~390 km s super(-1) assuming no inclination with respect to the plane of the sky. The direction of the pulsar proper motion is aligned very well with the main axis of the X-ray nebula (P.A. = 315degrees.5 + or - 1degrees.5), pointing to a physical, yet elusive, link between the nebula and the pulsar space velocity. No optical emission in the H alpha line is seen in a deep image collected at the Gemini telescope, which implies that the interstellar medium into which the pulsar is moving is fully ionized.
The peculiar central compact object 1E 1207.4-5209 in the G296.5+10.0 supernova remnant has been proposed to be an “ anti-magnetar” – a young neutron star born with a weak dipole field. Accretion, ...possibly of supernova fallback material, has also been invoked to explain a large surface temperature anisotropy as well as the generation of peculiar cyclotron absorption features superimposed on its thermal spectrum. Interestingly enough, a faint optical/infrared source was proposed as a possible counterpart to 1E 1207.4-5209, but later questioned, based on coarse positional coincidence. On the basis of the large offset of 1E 1207.4-5209 with respect to the center of its host supernova remnant, the source should move at mas yr super(-1). Thus, we tested the association by measuring the proper motion of the proposed optical counterpart. Using Hubble Space Telescope (HST) observations spanning 3.75 years, we computed a 3σ upper limit of 7 mas yr super(-1). Absolute astrometry on the same HST data set also places the optical source significantly off the 99% confidence Chandra position. This allows us to safely rule out the association. Using the HST data set, coupled to ground-based observations collected at the ESO/Very Large Telescope (VLT), we set the deepest limits ever obtained on the optical/infrared emission from 1E 1207.4-5209. By combining these limits with the constraints derived from X-ray timing, we rule out accretion as the source of the thermal anisotropy of the neutron star.
The puzzling X-ray source in RCW103 Luca, A; Caraveo, P A; Mereghetti, S ...
Astrophysics and space science,
04/2007, Letnik:
308, Številka:
1-4
Journal Article
Recenzirano
1E 161348-5055 (1E) is a compact object lying at the center of the 2000 year old Supernova Remnant (SNR) RCW103. Its original identification as an isolated, radio-quiet neutron star has been ...questioned in recent years by the observation of a significant long-term variability, as well as by reports of a possible periodicity at ∼6 hours. Here we report conclusive evidence for a strong (nearly 50%) periodic modulation of 1E at 6.67±0.03 hours, discovered during a long (90 ks) XMM-Newton observation performed in August 2005, when the source was in a “low state”. The source spectrum varies along the 6.67 hr cycle. No fast pulsations are seen. 1E could be a very young binary system, possibly composed of a compact object and a low-mass star in an eccentric orbit. This would be the first example of a low-mass X-ray binary (LMXB) associated with a SNR, and thus the first LMXB for which we know the precise birth date, just 2000 years ago. Alternatively, if it is an isolated neutron star, the unprecedented combination of age, period and variability may only fit in a very unusual scenario, featuring a peculiar magnetar, dramatically slowed-down over 2000 years, possibly by a supernova debris disc.
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope opened a new era for pulsar astronomy, detecting {gamma}-ray pulsations from more than 60 pulsars, {approx}40% of which are ...not seen at radio wavelengths. One of the most interesting sources discovered by LAT is PSR J0357+3205, a radio-quiet, middle-aged ({tau}{sub C} {approx} 0.5 Myr) pulsar standing out for its very low spin-down luminosity (E-dot{sub rot}{approx}6x10{sup 33} erg s{sup -1}), indeed the lowest among non-recycled {gamma}-ray pulsars. A deep X-ray observation with Chandra (0.5-10 keV), coupled with sensitive optical/infrared ground-based images of the field, allowed us to identify PSR J0357+3205 as a faint source with a soft spectrum, consistent with a purely non-thermal emission (photon index {Gamma} = 2.53 {+-} 0.25). The absorbing column (N{sub H} = 8 {+-} 4 x 10{sup 20} cm{sup -2}) is consistent with a distance of a few hundred parsecs. Moreover, the Chandra data unveiled a huge (9 arcmin long) extended feature apparently protruding from the pulsar. Its non-thermal X-ray spectrum points to synchrotron emission from energetic particles from the pulsar wind, possibly similar to other elongated X-ray tails associated with rotation-powered pulsars and explained as bow-shock pulsar wind nebulae (PWNe). However, energetic arguments as well as the peculiar morphology of the diffuse feature associated with PSR J0357+3205 make the bow-shock PWN interpretation rather challenging.
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