A deep (100 ks) XMM-Newton observation of Geminga has shown two faint tails of diffuse X-ray emission, extending for ~$2'$ behind the pulsar, well aligned with the proper motion (PM) direction. We ...report here on a recent ~20 ks Chandra observation, which unveils a new structure, ~$25''$ long and ~$5''$ thick, starting at the pulsar position and perfectly aligned with the PM direction, with a surface brightness ~40 times higher than that of the XMM Tails. The Chandra comet-like feature has a remarkably hard spectrum (photon index ~$0.9{-}1.4$) and a luminosity of ~$5.5\times10^{28}$ erg s-1, comparable to the energetics of the larger XMM one. Geminga is thus the first neutron star to show a clear X-ray evidence of a large-scale, outer bow-shock as well as a short, inner cometary trail.
RXJ0822-4300 is the central compact object associated with the Puppis A supernova remnant. Previous X-ray observations suggested RXJ0822-4300 to be a young neutron star with a weak dipole field and a ...peculiar surface temperature distribution dominated by two antipodal spots with different temperatures and sizes. An emission line at 0.8keV was also detected. We performed a very deep (130-ks) observation with XMM-Newton, which allowed us to study in detail the phase-resolved properties of RXJ0822-4300. Our new data confirm the existence of a narrow spectral feature, best modelled as an emission line, only seen in the 'soft'-phase interval - when the cooler region is best aligned to the line of sight. Surprisingly, comparison of our recent observations to the older ones yields evidence for a variation in the emission-line component, which can be modelled as a decrease in the central energy from similar to 0.80keV in 2001 to similar to 0.73keV in 2009-10. The line could be generated via cyclotron scattering of thermal photons in an optically-thin layer of gas, or, alternatively, it could originate in low-rate accretion by a debris disc. In any case, a variation in energy, pointing to a variation of the magnetic field in the line-emitting region, cannot be easily accounted for.
Context.While waiting for new gamma-ray burst detections, the Burst Alert Telescope (BAT) onboard Swift covers each day ~50% of the sky in the hard X-ray band (“Survey data”). The large field of view ...(FOV), high sensitivity and good angular resolution make BAT a potentially powerful all-sky hard X-ray monitor, provided that mask-related systematics can be properly accounted for. Aims.We have developed and tested a complete procedure entirely based on public Swift/BAT software tools to analyse BAT Survey data, aimed at assessing the flux and spectral variability of bright sources in the 15–150 keV energy range. Methods.Detailed tests of the capabilities of our procedure were performed focusing, in particular, on the reliability of spectral measurements over the entire BAT FOV. First, we analyzed a large set of Crab observations, spread over ~7 months. Next, we studied the case of GRO J1655-40, a strongly variable source, which experienced a 9-month long outburst, beginning on February 2005. The outburst was systematically monitored with the well-calibrated PCA and HEXTE instruments onboard the RXTE mission. Due to the good BAT temporal coverage of the source, we have been able to cross-check BAT light-curves with simultaneous HEXTE ones. Results.The Crab tests have shown that our procedure recovers both the flux and the source spectral shape over the whole FOV of the BAT instrument. Moreover, by cross-checking GRO J1655-40 light-curves obtained with BAT and HEXTE, we found the spectral and flux evolution of the outburst to be in very good agreement. Using our procedure, BAT reproduces HEXTE fluxes within a 10–15% uncertainty with a $3\sigma$ sensitivity of ~20 mCrab for an on-axis source, thus establishing its ability to monitor the evolution of relatively bright hard X-rays sources.
In this Letter we study the propagation of light in the neighborhood of magnetized neutron stars. Because of the optical properties of quantum vacuum in the presence of a magnetic field, the light ...emitted by background astronomical objects is deviated, giving rise to a phenomenon of the same kind as the gravitational one. We give a quantitative estimation of this effect, and we discuss the possibility of its observation. We show that this effect could be detected by monitoring the evolution of the recently discovered double neutron star system J0737-3039.
The limited angular resolution of \gamma-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ...ones only 10% of which has been identified. Most counterparts of the identified low-latitude \gamma-ray sources are Isolated Neutron Stars (INS), both radio-loud and radio-quiet (Geminga-like) objects, which are characterised by an extremely high value of the X-ray-to-optical flux ratio f_{\rm X}/f_{\rm opt}. Therefore, the systematic X-ray and optical coverage of low-latitude unidentified \gamma-ray sources aiming at high f_{\rm X}/f_{\rm opt} sources seems one of the most promising ways to spot INS candidate counterparts. Since low latitude sources are heavily affected by the interstellar absorption at both X-ray and optical wavelengths, we have focussed on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310 and 3EG J1249-8330. These two sources, which could belong to a local galactic population, have been selected owing to their relatively good positional accuracy, spectral shape and lack of candidate extragalactic radio counterparts. Here we report on X-ray observations of the two \gamma-ray error boxes performed with XMM-Newton and on their optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2 m telescope. Less than half of the similar to 300 sources detected by the X-ray coverage have no optical counterparts. Among those, we have selected few interesting sources with f_{\rm X}/f_{\rm opt}\ge 100, which we consider promising INS candidates.
The radio-quiet neutron star 1E1207.4-5209 was the target of a 260 ks XMM-Newton observation, that yielded, as a by product, a harvest of about 200 serendipitous X-ray sources above a limiting flux ...of 2 $\times$ 10-15 erg cm-2 s-1 in the 0.3–8 keV energy range. In view of the intermediate latitude of our field ($b\simeq 10^{\circ}$), it comes as no surprise that the log N–log S distribution of our serendipitous sources is different from those measured either in the Galactic Plane or at high galactic latitudes. Here we concentrate on analyzing of the brightest sources in our sample, which unveiled a previously unknown Seyfert-2 galaxy.
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 0.''165 {+-} 0.''030 yr{sup -1} at a position angle (P.A.) of 314 Degree-Sign {+-} 8 Degree-Sign . At a distance of {approx}500 pc, the space velocity of the pulsar would be of {approx}390 km s{sup -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. = 315. Degree-Sign 5 {+-} 1. Degree-Sign 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 European Space Agency has a strong track record and plenty of ambition to propel it into its next 30 years, says Bignami. But key decisions must be made in the context of a new Europe.
Gamma-Ray Astronomy with Integral Bignami, Giovanni F.
Science (American Association for the Advancement of Science),
11/2002, Letnik:
298, Številka:
5598
Journal Article
Recenzirano
Gamma-rays received from space carry information about some of the most energetic events in the universe, such as supernovae explosions and black holes. But as Bignami explains in his Perspective, ...their detection has been a major challenge. The INTEGRAL satellite, launched recently by the European Space Agency, will use advanced technology to map gamma-ray emissions in our galaxy and beyond at unprecedented resolution.
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