NEW X-RAY OBSERVATIONS OF THE GEMINGA PULSAR WIND NEBULA
- Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab., University Park, PA 16802 (United States)
- Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Mumbai 400005 (India)
Previous observations of the middle-aged pulsar Geminga with XMM-Newton and Chandra have shown an unusual pulsar wind nebula (PWN), with a 20'' long central (axial) tail directed opposite to the pulsar's proper motion and two 2' long, bent lateral (outer) tails. Here, we report on a deeper Chandra observation (78 ks exposure) and a few additional XMM-Newton observations of the Geminga PWN. The new Chandra observation has shown that the axial tail, which includes up to three brighter blobs, extends at least 50'' (i.e., 0.06d{sub 250} pc) from the pulsar (d{sub 250} is the distance scaled to 250 pc). It also allowed us to image the patchy outer tails and the emission in the immediate vicinity of the pulsar with high resolution. The PWN luminosity, L{sub 0.3-8{sub keV}} {approx} 3 x 10{sup 29} d {sup 2}{sub 250} erg s{sup -1}, is lower than the pulsar's magnetospheric luminosity by a factor of 10. The spectra of the PWN elements are rather hard (photon index {Gamma} {approx} 1). Comparing the two Chandra images, we found evidence of PWN variability, including possible motion of the blobs along the axial tail. The X-ray PWN is the synchrotron radiation from relativistic particles of the pulsar wind (PW); its morphology is connected with the supersonic motion of Geminga. We speculate that the outer tails are either a sky projection of the limb-brightened boundary of a shell formed in the region of contact discontinuity, where the wind bulk flow is decelerated by shear instability, or polar outflows from the pulsar bent by the ram pressure from the interstellar medium. In the former case, the axial tail may be a jet emanating along the pulsar's spin axis, perhaps aligned with the direction of motion. In the latter case, the axial tail may be the shocked PW collimated by ram pressure.
- OSTI ID:
- 21448783
- Journal Information:
- Astrophysical Journal, Vol. 715, Issue 1; Other Information: DOI: 10.1088/0004-637X/715/1/66; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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