arXiv subjects

Jacco Vink

Publications and source records attributed to Jacco Vink.

At least 163 records · Page 9Linked to original sources

arXiv2004

Long-term variability in the X-ray emission of RX J0720.4-3125

We detect a gradual, long-term change in the shape of the X-ray spectrum of the isolated neutron star RX J0720.4-3125, such that the spectrum of the source can no longer be described as a blackbody spectrum. The change is accompanied by an energy-dependent change in the pulse profile. If the X-ray emission is influenced by the magnetic field of the pulsar, these changes in spectral shape may point to precession of the neutron star.

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arXiv2003

Revealing the obscured supernova remnant Kes 32 with Chandra

I report here on the analysis and interpretation of a Chandra observation of the supernova remnant Kes 32. Kes 32 is rather weak in X-rays due to a large interstellar absorption, which is found to be ~4E22 cm^-2, larger than previously reported. Spectral analysis indicates that the ionization age of this object is very young, with n_e t ~ 4E9 cm^-3s, and a temperature of kT_e ~ 1 keV. The X-ray emission peaks at a smaller radius than in the radio. The low ionization age suggests that Kes 32 is a young remnant. However, a young age is in contradiction with the relatively large apparent size, which indicates an age of several thousand years, instead of a few hundred years. This problem is discussed in connection with Kes 32's unknown distance and its possible association with the Norma galactic arm.

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arXiv2003

A Review of X-ray Observations of Supernova Remnants

I present a review of X-ray observations of supernova remnants with an emphasis on shell-type remnants. The topics discussed are the observation of fresh nucleosynthesis products, shock heating and cosmic ray acceleration.

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arXiv2003

X- and Gamma-ray Studies of Cas A: Exposing Core Collapse to the Core

In this review of X-ray and gamma-ray observations of Cas A, evidence is discussed that Cas A was a Type Ib supernova of a Wolf-Rayet star with a main sequence mass between 22-25 Msun, that exploded after stellar wind loss had reduced its mass to ~6 Msun. The observed kinematics and the high Ti-44 yield indicate that the supernova explosion was probably assymetric, with a kinetic energy of ~2x10^51 erg.

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arXiv2003

Shocks and Particle Acceleration in Supernova Remnants: Observational Features

The last ten years a number of observational advances have substantially increased our knowledge of shock phenomena in supernova remnants. This progress has mainly been made possible by the recent improvements in X-ray and Gamma-ray instrumentation. It has become clear that some shell-type supernova remnants, e.g. SN 1006, have X-ray emission dominated by synchrotron radiation, proving that electrons are accelerated up to 100 TeV. This is still an order of magnitude below 3E15 eV, at which energy the ion cosmic ray spectrum at earth shows a spectral break. So one of the major goals is to prove that supernova remnants are capable of accelerating ions at least up that energy. Here I review the evidence that ions and electrons are accelerated up to energies ~100 TeV in supernova remnants, and, in addition, the recent progress that has been made in understanding the physics of collisionless shock fronts and the magnetic fields inside supernova remnants.

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arXiv2003

Slow Temperature Equilibration Behind the Shock Front of SN 1006

We report on the observation of OVII Doppler line broadening in a compact knot at the edge of SN 1006 detected with the Reflective Grating Spectrometer on board XMM-Newton. The observed line width of sigma = 3.4+/-0.5 eV at a line energy of 574 eV indicates an oxygen temperature of kT = 528+/-150 keV. Combined with the observed electron temperature of 1.5 keV the observed broadening is direct evidence for temperature non-equilibration in high Mach number shocks, and slow subsequent equilibration. The OVII line emission allows an accurate determination of the ionization state of the plasma, which is characterized by a relatively high forbidden line contribution, indicating log(n_e t) ~ 9.2.

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arXiv2002

On the magnetic fields and particle acceleration in Cas A

We investigate the non-thermal X-ray emission from Cas A. For the hard X-ray continuum we test the model proposed by Laming, which invokes bremsstrahlung from electrons accelerated by lower hybrid plasma waves. The justification for this model comes from our determination of a lower limit to the average magnetic field of B > 0.5 mG, which suggest that most of the electron populations are too much affected by synchrotron losses to produce X-ray synchrotron emission. An exception is the X-ray emission from the rim surrounding Cas A, seen in Chandra continuum images. The width of this rim of 1.5" to 4", can be used to infer the magnetic field near the shock front, for which we estimate B = 0.08 - 0.16 mG, and electron energies of about 57 - 40 TeV. This is lower than the average magnetic field, but higher than what may be expected from shocked interstellar medium, suggesting a high pre-shock magnetic field, or rapid, post shock, field amplification. Combining the two magnetic field measurements we have constructed a simple two zone model. Most of the radio emission comes from inside Cas A, where the magnetic field is strong, whereas the inverse Compton emission comes from near the shock front. Only for our lower limit on the magnetic field strength near the shock front is it possible to explain the recent detection of TeV emission by HEGRA with inverse Compton, for which, in addition, we have to assume a rather high far infrared photon density that should be twice as high as our best estimate of roughly 70 cm^{-3}. Pion decay is therefore likely to be the dominant emission from Cas A at TeV energies.

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arXiv2002

The detection of the Sc-44 nuclear de-excitation lines and hard X-ray emission from Cas A

We discuss the detection of Sc-44 (product of Ti-44) in the supernova remnant Cas A with the BeppoSAX-PDS instrument, and elaborate on the nature of the hard X-ray continuum, which is not only important for correctly estimating the Sc-44 flux, but is interesting in its own right. We apply the lower hybrid wave electron acceleration model to the hard X-ray data and use upper limits on the cosmic ray injection spectrum to infer that B > 2 mG. We conclude with the prospects of observing nuclear decay lines and electron-positron annihilation in Cas A with INTEGRAL.

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arXiv2002

A synoptic spectral study of Cassiopeia-A based on XMM-Newton and BeppoSax observations

In this paper we present recent image and spectral data of Cas-A obtained with XMM-Newton and BeppoSAX. Analysis of the hard X-ray continuum does not support an interpretation of the hard X-radiation as synchrotron emission produced in the primary shock, non-thermal Bremsstrahlung is a plausible alternative. Moreover, a recent 500 kilosecond deep observation of the hard X-ray continuum by BeppoSAX has revealed the positive detection of the 44Sc nuclear decay lines at 67.9 and 78.4 keV. Appropriate modelling of the hard X-ray continuum leads to an estimate of the initial 44Ti mass of (0.8-2.5)E-4 solar masses. We also present ionisation age, temperature, abundances maps. The observed elemental abundance ratio patterns can be reconciled best with a type Ib SNe, arising from a 60 solar mass progenitor (ZAMS) with high-mass-loss. The accurate modeling of the image-resolved emission line spectra has enabled us to derive reliable Doppler velocities for the bright Si-K, S-K, and Fe-K line complexes.

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arXiv2002

Non-thermal bremsstrahlung as the dominant hard X-ray continuum emission from the supernova remnant MSH14-63 (RCW 86)

We present an analysis of the X-ray emission of the supernova remnant MSH14-63, which was partially covered by four observations with XMM-Newton. The detection of Fe K emission at 6.4 keV, and the lack of spatial correlation between hard X-ray and radio emission is evidence against a dominant X-ray synchrotron component. We argue that the hard X-ray continuum is best explained by non-thermal bremsstrahlung from a supra-thermal tail to an otherwise cool electron gas. The existence of low electron temperatures, required to explain the absence of line emission, is supported by low temperatures found in other parts of the remnant, which are as low as 0.2 keV in some regions.

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arXiv2001

XMM-Newton observations of MSH 14-63 (RCW 86)

We present an analysis of the X-ray emission of the supernova remnant MSH14-63, which was partially covered by three observations with XMM-Newton. The detection of Fe K emission at 6.4 keV, and the lack of spatial correlation between hard X-ray and radio emission is evidence against a dominant X-ray synchrotron component. We argue that the hard X-ray continuum is best explained by non-thermal bremsstrahlung from a supra-thermal tail to an otherwise cool electron gas. The existence of low electron temperatures is supported by low temperatures found in other parts of the remnant, which are as low as 0.2 keV in some regions.

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arXiv2001

Detection of the 67.9 keV and 78.4 keV lines associated with the radioactive decay of Ti-44 in Cassiopeia A

We report the detection of the Sc-44 nuclear decay lines at 67.9 keV and 78.4 keV associated with the nuclear decay of Ti-44 in Cassiopeia A. The line emission was observed by the PDS instrument on board BeppoSAX, which recently observed the supernova remnant for over 500 ks. The detection of the line emission with a flux of (2.1 +/-0.7) 10^{-5} ph/cm^2/s in each line (90% confidence) is at the 5 sigma significance level, if we can assume that the 12-300 keV continuum is adequately represented by a single power law. However, as the nature of the continuum is not clear we investigate various other possibilities. A more conservative estimate of the line flux is made by assuming that a power law continuum is at least a good approximation to the continuum emission for a narrower 30-100 keV energy range. With this limitation the measured line flux is (1.9 +/- 0.9) 10^{-5} ph/cm^2/s, with the detection still at the 3.4 sigma significance level. We suggest that together with the CGRO-COMPTEL measurement of the Ca-44 line at 1157 keV of (3.5 +/- 0.9) 10^{-5} ph/cm^2/s a flux for all three lines of (2.5 +/- 1.0) 10^{-5} ph/cm^2/s for Cas A can be adopted. This implies an initial Ti-44 mass of (0.8 - 2.5) 10^{-4} Msun.

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arXiv2000

An unresolved X-ray source inside the supernova remnant RCW 86

We report on the discovery of an unresolved X-ray source inside the supernova remnant G315.4-2.3 (RCW 86). The source is located 7' to the Southwest of the geometrical centre and may be close to the actual explosion centre of the supernova, which makes this a candidate for the stellar remnant associated with RCW 86. However, the presence of a possible optical counterpart with $V \sim 14$ at 3" from the X-ray position and evidence for long term variability means that the source is probably an active star. A better X-ray position and better X-ray spectroscopy along with an identification of the optical source are needed to exclude the X-ray source as a neutron star candidate.

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arXiv1999

The BeppoSAX X-ray spectrum of the remnant of SN 1006

We present BeppoSAX X-ray spectra of the remnant of the supernova of AD 1006, which cover a broad spectral range of 0.1-10 keV. In our analysis we concentrate on the thermal emission from the central region of the remnant. For this purpose we fitted the spectra of the whole remnant using a new version of the spectral program SPEX, which takes into account the interdependence of spectra of different regions as the result of the point spread function of the instruments. This is in particular important for separating the synchrotron emission, coming from the bright rims of the remnant, from the thermal emission from the central regions. The thermal emission appears best fitted with a combination of two spectral components with electron temperatures of about 0.7 keV and more than 3 keV. The plasma in SN 1006 appears to be very far out of ionization equilibrium (nt = 2 10^15 m^-3 s), which means that the L-shell emission of magnesium, silicon and sulphur contribute significantly to the flux below 0.5 keV. We also note the presence of Fe K line emission at 6.3+/-0.2 keV, in agreement with an origin from inner shell ionizations and excitations. We confirm that the abundances in SN 1006 are clearly non-solar. In particular silicon is very abundant. We did not find substantial variations in plasma properties over the face of the remnant, although the hotter component seems more dominant in the Northern half of the remnant.

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arXiv1999

The hard X-ray and Ti-44 emission of Cas A

We present an analysis of the BeppoSAX high X-ray energy spectrum of the supernova remnant Cassiopeia A with an observation time of 83 ks. We measure a flux upper limit of 4.1E-5 ph/cm^2/s (99.7% confidence) of the nuclear decay lines of Ti-44 at 68 keV and 78 keV that is lower and inconsistent with the flux of an accompanying line at 1157 keV measured by CGRO's Comptel. However, if the underlying X-ray continuum is lower, because the spectrum is steepening, the actual Ti-44 flux may be higher and consistent with the Comptel result, although the measured flux of (2.9 +/- 1.0)E-5 ph/cm^2/s under this assumption is still lower than the flux measured by Comptel.

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arXiv1999

A comparison of the X-ray line and continuum morphology of Cassiopeia A

We present deconvolved narrow band images of Cas A as observed by the MECS instrument on the BeppoSAX X-ray satellite. The images show that Cas A has different morphologies in the continuum and line bands. This difference points towards a synchrotron origin for part of the X-ray continuum of Cas A. Going to the hardest continuum band we find that the emission is coming predominantly from the Western region, making this the most likely location for the hard X-ray tail seen with instruments on CGRO (OSSE), BeppoSAX (PDS) and RXTE (HEXTE).

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arXiv1998

The expansion of Cassiopeia A as seen in X-rays

We have for the first time measured the overall expansion rate of the supernova remnant Cas A as seen in X-rays using ROSAT and Einstein HRI images with time differences up to almost 17 years. The overall expansion timescale of Cas A is found to be 501 plusminus 15 yr. This is significantly shorter than the timescale based on high resolution radio data. Although the results clearly indicate that Cas A is not anymore in the free expansion phase,the discrepancy between the radio and X-ray timescales cannot be easily understood. Furthermore, the expansion rate is incompatible with that predicted by a self-similar model for a supernova remnant ploughing through the wind of its progenitor.

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arXiv1998

Three Supernova Remnants observed by BeppoSAX

We present the results of three observations of shell-type supernova remnants observed by BeppoSAX. Two of the remnants (N132D and Cas A) are oxygen rich supernova remnants. They were observed during the PV phase. SN1006 was observed during A01. For SN1006 we present preliminary results on the abundance measurements based on the emission from the center of the remnant.

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