Supernova Remnant Age Research Articles

A Spatial and Spectral Study of Nonthermal Filaments in Historical Supernova Remnants: Observational Results withChandra

The outer shells of young supernova remnants (SNRs) are the most plausible acceleration sites of high-energy electrons with the diffusive shock acceleration (DSA) mechanism. We studied spatial and spectral properties close to the shock fronts in four historical SNRs (Cas A, Kepler's remnant, Tycho's remnant, and RCW 86) with excellent spatial resolution of Chandra. In all of the SNRs, hard X-ray emissions were found on the rims of the SNRs, which concentrate in very narrow regions (so-called filaments); apparent scale widths on the upstream side are below or on the order of the point-spread function of Chandra, while they are 05-40'' (0.01-0.4 pc) on the downstream side with most reliable distances. The spectra of these filaments can be fitted with both thermal and nonthermal (power law and SRCUT) models. The former requires unrealistic high temperature (2 keV) and low abundances (1 solar) for emission from young SNRs and may be thus unlikely. The latter reproduces the spectra with best-fit photon indices of 2.1-3.8, or roll-off frequencies of (0.1-28) × 1017 Hz, which reminds us of the synchrotron emission from electrons accelerated via DSA. We consider various physical parameters as functions of the SNR age, including the previous results on SN 1006; the filament width on the downstream side increases with the SNR age, and the spectrum becomes softer, keeping a nonthermal feature. It was also found that a function, that is, the roll-off frequency divided by the square of the scale width on the downstream side, shows negative correlation with the age, which might provide us some information on the DSA theory.

On the transition of the adiabatic supernova remnant to the radiative stage in a nonuniform interstellar medium

Methods for estimation of different reference times which appear in the description of transition of a strong adiabatic shock into the radiative era are reviewed. The need for consideration of an additional transition subphase in between the end of the adiabatic era and the beginning of the radiative “pressure-driven snowplow” stage for a shock running in the uniform or nonuniform medium is emphasized. This could be of importance in particular for studying of the interaction of supernova remnants (SNRs) with molecular clouds and therefore for understanding the processes of the cosmic ray production in such systems. The duration of this subphase – about 70% of SNR age at its beginning – is almost independent of the density gradient for media with increasing density and is longer for higher supernova explosion energy and for smaller density in the place of explosion. It is shown as well that if the density of the ambient medium decreases then the cooling processes could differ from the commonly accepted scenario of the “thin dense radiative shell” formation. This property should be studied in the future because it is important for models of nonspherical SNRs which could be only partially radiative.

Influence of an Internal Magnetar on Supernova Remnant Expansion

Most of the proposed associations between magnetars and supernova remnants suffer from age problems. Usually, supernova remnant ages are determined using some approximation for the Sedov-Taylor supernova phase, which yields a relation between radius and age for a fixed energy of the explosion (generally assumed to be ~1051 ergs). Those ages do not generally agree with the characteristic ages of the (proposed) associated magnetars. We show in this work that a faster expansion results when the energy injected into the supernova remnant by magnetar spin-down is taken into account, thus helping to improve the matches between characteristic ages and supernova remnant ages. However, the magnetar velocities inferred from observations would make some associations inviable if correct. Since characteristic ages may not be good age estimators after all, their influence on the likelihood of the association may not be as important. In this work, we perform simple numerical simulations of supernova remnant expansion with internal magnetars and apply them to the observed sample of objects. A short initial spin period, thought to be important for the very generation of the magnetic field, is shown to be quite relevant to the modified expansion of the remnant. We finally analyze all proposed associations on a case-by-case basis, addressing the likelihood of each one, according to this perspective. We consider a larger explosion energy and reassess the characteristic age issue, and conclude that ~50% of the associations can be real, provided that soft gamma repeaters and anomalous X-ray pulsars are magnetars.

A Multiwavelength Search for a Counterpart of the Brightest Unidentified Gamma‐Ray Source 3EG J2020+4017 (2CG 078+2)

In search of the counterpart to the brightest unidentified gamma-ray source, 3EG J2020+4017 (2CG 078+2), we report on new X-ray and radio observations of the gamma Cygni field with the Chandra X-Ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data. With Chandra it became possible for the first time to measure the position of the putative gamma-ray counterpart, RX J2020.2+4026, with subarcsecond accuracy and to deduce its X-ray spectral characteristics. These observations demonstrate that RX J2020.2+4026 is associated with a K field star and therefore is unlikely to be the counterpart of the bright gamma-ray source 2CG 078+2 in the SNR G78.2+2.1 as had been previously suggested. The Chandra observation detected 37 additional X-ray sources, which were correlated with catalogs of optical and infrared data. Subsequent GBT radio observations covered the complete 99% EGRET likelihood contour of 3EG J2020+4017 with a sensitivity limit of L(sub 820) approximately 0.1 mJy kpc(exp 2), which is lower than most of the recent deep radio search limits. If there is a pulsar operating in 3EG J2020+40 17, this sensitivity limit suggests that either the pulsar does not produce significant amounts of radio emission or that its geometry is such that the radio beam does not intersect with the line of sight. Finally, reanalysis of archival ROSAT data leads to a flux upper limit of fx(0.1 - 2.4 keV) less than 1.8 x 10(exp -13) ergs s(exp -1) cm(exp -2) for a putative pointlike X-ray source located within the 68% confidence contour of 3EG J2020+4017. Adopting the supernova remnant age of 5400 yr and assuming a spin-down to X-ray energy conversion factor of 10(exp 14), this upper limit constrains the parameters of a putative neutron star as a counterpart for 3EG J2020+4017 to be P is approximately greater than 160 (d 1.5 kpc)(exp -1) ms, P is approximately greater than 5 x 10(exp -13) ((d 1.5 kpc)(exp -1)) s s(exp -1), and B (perpendicular) is approximately greater than 9 x 10(exp l2) )(d 1.5 kpc)(exp -1)) G.

Supernova Remnants in the Magellanic Clouds. IV. X‐Ray Emission from the Largest Supernova Remnant in the Large Magellanic Cloud

We present the first X-ray detection of SNR 0450-70.9, the largest known supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical images and high-dispersion spectra, and radio continuum maps. Optical images of SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments along the eastern and western rims and within the shell interior. The interior filaments have higher [S II]/Hα ratios and form an apparent inner shell morphology. The X-ray emission region is smaller than the full extent of the optical shell, with the brightest X-ray emission found within the small interior shell and on the western rim of the large shell. The expansion velocity of the small shell is ~220 km s-1, while that of the large shell is ~120 km s-1. The radio image shows central brightening and a fairly flat radio spectral index over the SNR. However, no point X-ray or radio source corresponding to a pulsar is detected, and the X-ray emission is predominantly thermal. Therefore, these phenomena can be most reasonably explained in terms of the advanced age of the large SNR. Using hydrodynamic models combined with a nonequilibrium ionization model for thermal X-ray emission, we derived a lower limit on the SNR age of ~45,000 yr, well into the later stages of SNR evolution. Despite this, the temperature and density derived from spectral fits to the X-ray emission indicate that the remnant is still overpressured and thus that the development is largely driven by hot gas in the SNR interior.

Limits on diffusive shock acceleration in supernova remnants in the presence of cosmic-ray streaming instability and wave dissipation

The instability in the cosmic-ray precursor of a supernova shock moving in interstellar medium is studied. The level of magnetohydrodynamic turbulence in this region determines the maximum energy of particles accelerated by the diffusive shock acceleration mechanism. The high efficiency of cosmic ray acceleration is accepted, and the consideration is not limited by the case of weak turbulence. It is assumed that Kolmogorov type nonlinear wave interactions together with the ion-neutral collisions restrict the amplitude of random magnetic field. As a result, the maximum energy of accelerated particles strongly depends on the age of supernova remnant. The maximum energy can be as high as $\sim10^{17}Z$ eV in young supernova remnants and falls down to about $\sim10^{10}Z$ eV at the end of Sedov stage. Thus the standard estimate of maximum particle energy based on the Bohm limit calculated for the interstellar magnetic field strength is not justified in this case. This finding may explain why the supernova remnants with the age more than a few thousand years are not prominent sources of very high energy gamma-rays.

The Pulsar Wind Nebula Torus of PSR J0538+2817 and the Origin of Pulsar Velocities

We find evidence for a faint wind nebula surrounding PSR J0538+2817 in Chandra X-Ray Observatory ACIS imaging. This object is particularly interesting, as the pulsar spin-down age is largest for any such X-ray pulsar wind nebula (PWN). If interpreted as an equatorial torus, the PWN supports the claimed association with the S147 supernova remnant and implies good alignment between the pulsar spin and space velocity. Comparison of the supernova remnant age, X-ray cooling age, and characteristic age suggests a birth spin period of ≳130 ms. In turn, if we accept as causal the alignment of the linear and angular momenta, this places strong constraints on the origin of the "kick" at the neutron star birth.

New Constraints on the Energetics, Progenitor Mass, and Age of the Supernova Remnant G292.0+1.8 Containing PSR J1124−5916

We present spatially resolved spectroscopy of the supernova remnant (SNR) G292.0+1.8 with the Chandra X-ray observatory. This SNR contains the 135 ms pulsar, J1124-5916. We apply non-equilibrium ionization (NEI) models to the data. By comparing the derived abundances with those predicted from nucleosynthesis models, we estimate a progenitor mass of 30-40 solar masses. We also derive the intrinsic parameters of the supernova explosion such as its energy, the age of the SNR, the blast wave velocity, and the swept-up mass. In the Sedov interpretation, our estimated SNR age of 2,600 years is close to the pulsar's characteristic age of 2,900 years. This confirms the pulsar/SNR association and relaxes the need for the pulsar to have a non-canonical value for the braking index, a large period at birth or a large transverse velocity. We discuss the properties of the pulsar wind nebula (PWN) in the light of the Kennel and Coroniti model and estimate the pulsar wind magnetization parameter. We also report the first evidence for steepening of the power law spectral index with increasing radius from the pulsar.

Stromgren zones of supernovae

The minimum emission measures observed in the directions toward pulsars or supernova remnants are inversely proportional to the pulsar or supernova remnant ages. It is concluded that the ionized gas in the vicinities of a number of pulsars and supernova remnants was formed during the first 1000 years after supernova explosions.

Magnetar Spin-Down.

We examine the effects of a relativistic wind on the spin-down of a neutron star and apply our results to the study of soft gamma repeaters (SGRs), which are thought to be neutron stars with magnetic fields greater than 1014 G. We derive a spin-down formula that includes torques from both dipole radiation and episodic or continuous particle winds. We find that if SGR 1806-20 puts out a continuous particle wind of 1037 ergs s-1, then the pulsar age is consistent with that of the supernova remnant, but the derived surface dipole magnetic field is only 3x1013 G, in the range of normal radio pulsars. If instead the particle wind flows are episodic with small duty cycle, then the observed period derivatives imply magnetar-strength fields, while still allowing characteristic ages within a factor of 2 of the estimated supernova remnant age. Close monitoring of the periods of SGRs will allow us to establish or place limits on the wind duty cycle and thus the magnetic field and age of the neutron star.

The optical counterpart to the luminous X-ray supernova remnant in NGC 6946

view Abstract Citations (33) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Counterpart to the Luminous X-Ray Supernova Remnant in NGC 6946 Blair, William P. ; Fesen, Robert A. Abstract We identify a high surface brightness optical supernova remnant (SNR) in NGC 6946 that is coincident with a bright soft X-ray point source detected in a ROSAT PSPC image of this galaxy (Schlegel 1994). Optical CCD/interference filter images and spectra show the object to have an observed Hα flux of 1.9 x 10^-14^ ergs cm^-2^ s^-1^, corresponding to an intrinsic Hα luminosity of 2 x 10^38^ (d/5.1 Mpc)^2^ ergs s^- 1^. A moderate-resolution optical spectrum shows normal SNR line emissions, with no high velocities (V <400 km s^-1^) or relative line strengths indicative of enriched heavy element abundances. This suggests a relatively old SNR, a conclusion supported by the presence of an emission nebula at its position on photographic plates dating back to at least 1921. With both an optical line flux and soft X-ray flux exceeding those of other luminous extragalactic SNRs, this object may have an optical luminosity near the maximum limit for SNRs. Assuming current flux levels, we estimate the SNR's age to be <= 3500 yr and suggest its unusual luminosity is due to both its expansion into dense surroundings and a relatively low column density along our line of sight. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/187285 Bibcode: 1994ApJ...424L.103B Keywords: Balmer Series; Data Reduction; H Alpha Line; Light (Visible Radiation); Optical Emission Spectroscopy; Supernova Remnants; X Ray Sources; Charge Coupled Devices; Line Of Sight; Luminosity; Photographic Plates; Rosat Mission; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6946; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (6) NED (1) HEASARC (1)