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Register a new userA time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RX J0822-4300
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RX J0822-4300 is the Central Compact Object associated with the Puppis A supernova remnant. Previous X-ray observations suggested RX J0822-4300 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 0.8 keV 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 RX J0822-4300. 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 ~0.80 keV in 2001 to ~0.73 keV in 2009--2010. 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 disk. 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.
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We have observed the HI distribution in an area 40 x 40 around the neutron star candidate RX J0822-4300, which is located in the supernova remnant Puppis A. The observations of the 21 cm line were obtained with the Australia Telescope Compact Array (ATCA) and were combined with single dish data from the Southern Galactic Plane Survey. The spatial resolution is 90, and the velocity resolution, 1 km/s . A sensitivity of ~ 0.7 K was achieved. The results revealed a double lobed feature of reduced emission at +16 km/s, centered on the central compact object (CCO), and aligned with an HI hole blueshifted by 13 km/s. The HI depressions have probably been created by the sweeping up of ~ 2 solar masses. The alignement between the lobes and the optical expansion centre of Puppis A suggests that the CCO could be ejecting two opposite jets. The velocity at which the two lobes are best defined allowed us to confirm that the distance to Puppis A is 2.2 kpc, based on a systemic velocity of +16 km/s. The hydrogen column density computed using this systemic velocity is consistent with estimates from models for X-ray spectra, thus reinforcing our conclusion that the kinematic distance is 2.2 k pc.
We present the discovery of a strongly phase-variable absorption feature in the X-ray spectrum of the nearby, thermally-emitting, isolated neutron star RX J0720.4-3125. The absorption line was detected performing detailed phase-resolved spectroscopy in 20 XMM-Newton observations, covering the period May 2000 - September 2012. The feature has an energy of ~750eV, an equivalent width of ~30eV, and it is significantly detected for only ~20% of the pulsar rotation. The absorption feature appears to be stable over the timespan covered by the observations. Given its strong dependence on the pulsar rotational phase and its narrow width, a plausible interpretation is in terms of resonant proton cyclotron absorption/scattering in a confined magnetic structure very close to the neutron star surface. The inferred field in such a magnetic loop is B_loop ~ 2 x 10^{14} G, a factor of ~7 higher than the surface dipolar magnetic field.
We present an improved proper motion measurement of the central compact object RX J0822-4300, located in the supernova remnant Puppis A. By employing a new data set taken in February 2019 by the High Resolution Camera aboard the Chandra X-ray Observatory, we approximately double the available temporal baseline for our analysis to slightly more than 19 years (7000 days). We correct for the astrometric inaccuracy of Chandra using calibrator stars with known optical positions that are detected in all observations. Thereby, we obtain absolute positions of RX J0822-4300 accurate to around $0.1^{primeprime}$ and from these a new best estimate for its total proper motion of $mu_{rm tot}= (80.4 pm 7.7),rm{mas,yr}^{-1}$. For a remnant distance of 2 kpc, this corresponds to a projected kick velocity of $(763 pm 73), rm{km,s}^{-1}$ at a position angle of $phi_0 = (247.8 pm 4.4)^{circ}$. The proper motion measurement of RX J0822-4300 is used for discussing the kinematic age of Puppis A.
We report on a deep radio search for a pulsar wind nebula associated with the radio-quiet neutron star RX J0822-4300 in the supernova remnant Puppis A. The well-determined properties of Puppis A allow us to constrain the size of any nebula to less than 30 arcsec; however we find no evidence for such a source on any spatial scale up to 30 arcmin. These non-detections result in an upper limit on the radio luminosity of any pulsar-powered nebula which is three orders of magnitude below what would be expected if RX J0822-4300 was an energetic young radio pulsar beaming away from us, and cast doubt on a recent claim of X-ray pulsations from this source. The lack of a radio nebula leads us to conclude that RX J0822-4300 has properties very different from most young radio pulsars, and that it represents a distinct population which may be as numerous, or even more so, than radio pulsars.
In the present paper an alternative theoretical interpretation to the generally assumed thermal emission models of the observed X-ray spectrum of isolated pulsar RX J0420.0-5022 is presented. It is well known that the distribution function of relativistic particles is one-dimensional at the pulsar surface. However, cyclotron instability causes an appearance of transverse momenta of relativistic electrons, which as a result, start to radiate in the synchrotron regime. On the basis of the Vlasovs kinetic equation we study the process of the quasi-linear diffusion (QLD) developed by means of the cyclotron instability. This mechanism provides generation of optical and X-ray emission on the light cylinder lengthscales. The analysis of the three archival XMM-Newton observations of RX J0420.0-5022 is performed. Considering a different approach of the synchrotron emission theory, the spectral energy distribution is obtained that is in a good agreement with the observational data. A fit to the X-ray spectrum is performed using both the present synchrotron emission model spectrum absorbed by cold interstellar matter and generally assumed absorbed black-body model.
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