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Session 16 - Radio Pulsars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[16.08] An X-ray Synchrotron Nebula Associated with the Radio Pulsar PSR B1853+01 in the Supernova Remnant W44

I. Harrus, J. P. Hughes (SAO)

We present results of a study using ASCA X-ray data from the vicinity of the radio pulsar PSR B1853+01 located within the supernova remnant (SNR) W44. PSR B1853+01 is a 267 ms pulsar, which to date has only been detected in the radio band. Previous observations at soft X-ray energies (e.g., ROSAT HRI) have failed to detect any significant X-ray emission (pulsed or unpulsed) from the pulsar. In addition, no high energy tail was seen in the Ginga spectrum of W44 leading to a 3\sigma upper limit of 3.6\times 10^-12ergs cm^-2 s^-1 for the 2--10 keV flux of a Crab-like power-law component contributing to the spectrum of W44.

Over the 0.5--5 keV band, the ASCA data show soft thermal (kT\sim 0.5 keV) emission from W44 with a morphology very similar to that observed before by Einstein and ROSAT. In the high energy band (5--10 keV) the SNR for the most part is not visible and instead an unresolved source coincident with the position of PSR B1853+01 is evident. The observed ASCA spectra are consistent with a power-law origin (photon index \sim 3.5) for the X-ray emission from this source at a flux level below the Ginga upper limit. The maximum allowed size for the source is determined directly from the ASCA data (<5^\prime), while the minimum size is determined indirectly from the nondetection of a point source in the ROSAT HRI data (>1.5^\prime). We also report on our timing analysis, which failed to detect pulsations from the X-ray source at the pulsar's period.

Based on these lines of evidence, we suggest that the new hard source in W44 represents the X-ray synchrotron nebula surrounding PSR B1853+01, rather than the beamed output of the pulsar itself. The ratio of the nebula's X-ray luminosity to the spin-down energy loss of the pulsar is consistent with that of other known plerions, lending further support to our interpretation. This is the first indirect detection in the X-ray band of the pulsar associated with W44.

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