Stars as Laboratories for Fundamental Physics - MPP Theory Group

Anomalous Stellar Energy Losses Bounded by Observations 57
ROSAT. X-rays have been observed from a number of compact sources
in supernova remnants and from several isolated pulsars. However,
with the limited spectral resolution of these instruments it is difficult
to extract the actual thermal surface emission because there can be
significant nonthermal x-ray emission from the magnetosphere.
There are three candidates in the 10 3 yr age category (3C58, the
Crab pulsar, RCW 103) from which x-rays have been observed by the
Einstein Observatory (Tab. 2.4). However, ROSAT did not detect a
compact source in RCW 103; only an upper flux limit has been reported
(Tab. 2.4). The Crab pulsar is x-ray bright mostly from nonthermal
emission so that ROSAT could only establish an upper limit on
its surface temperature. The remaining Einstein source 3C58 probably
should also be interpreted as an upper limit on thermal surface emission.
These upper limits are in agreement with the standard cooling
curves of Nomoto and Tsuruta (1987) shown in Fig. 2.15.
The Einstein data point for the Vela pulsar at an age of about
10 4 yr is somewhat low, a fact which has given rise to the speculation
that “exotic” cooling effects may be operating such as neutrino emission
by virtue of a meson condensate. However, a blackbody spectral fit to
the ROSAT observations yields a much higher temperature (Tab. 2.4,
Fig. 2.15. Surface temperature (observed at infinity) of a neutron star with
baryon mass 1.4 M ⊙ (gravitational mass 1.3 M ⊙ ) according to Nomoto and
Tsuruta (1987). The solid line is for an equation of state of intermediate
stiffness (model FP), the dotted line for a stiff (PS), and the dashed line for
a soft model (BPS). All “nonstandard” effects were ignored. The measurements
of Tab. 2.4 are also shown.