Chandra observations of the Crab-like supernova remnant G21.5-0.9 reveal a compact central core and spectral variations indicative of synchrotron burn-off of higher energy electrons in the inner nebula. The central core is slightly extended, perhaps indicating the presence of an inner wind-shock nebula surrounding the pulsar. No pulsations are observed from the central region, yielding an upper limit of approximately 40% for the pulsed fraction. A faint outer shell may be the first evidence of the expanding ejecta and blast wave formed in the initial explosion, indicating a composite nature for G21.5-0.9.

No abstract

No abstract

X rays in the energy band 0.2–3.0 keV have been detected coming from both polar regions of Jupiter. The observations were made in 1979 and 1981 by using the imaging proportional counter and high resolution imaging detectors on the Einstein X ray astronomy satellite. The measured flux density of ∼6×10−4cm−2s−1 at earth corresponds to an X ray luminosity of ∼4×109 W in the 0.2‐ to 3.0‐keV energy band. The energy spectrum of the X rays is extremely soft and can be characterized by a power law with an exponent of ∼2.3. Detector energy resolution is insufficient to distinguish a soft line spectrum from a continuum. However, the shape of the response and the observed X ray power indicate that the source of this auroral emission is not electron bremsstrahlung as on the earth, but is most probably line emission from O and S ions with energies between 0.03 and 4.0 MeV/nucleon precipitating from the outer boundary of the Io plasma torus at L ∼ 8.

The young pulsar PSR B0540-69 was one of the first targets observed with the Chandra X-Ray Observatory. The high angular resolution of Chandra allows us to resolve the compact nebula surrounding the pulsar. We have determined a position for PSR B0540-69 of R.A. = 05 h 40 m 11 s .221, decl. = −69 • 19 ′ 54 ′′ .98 (J2000) with a 1σ radial uncertainty of 0.7 ′′ . Combining our measurements of the pulsar period with previous measurements covering a span of 12 years, we derive a braking index of 2.08. The spectrum of the pulsed emission is consistent with a power-law with a photon index of 1.83 ± 0.13. The compact nebula has a softer spectrum with a photon index of 1.85-2.26.