# Are the compact objects in supernova remnants isolated neutron stars?

It seems all the central compact objects correlated with supernova remnant(SNRs) are isolated, not in binaries, right?

I find only one exception. A source is claimed to be a compact binary which correlates with SNR G308.3-1.4.ads link

My question is, generally, are the compact objects in SNR always isolated? And observationally, are the compact objects in SNRs neutron stars?

• I'm not quite clear, since you have phrased your questions as statements. Do you mean "Are the compact objects in SNR always isolated?" and "Are the compact objects in SNRs neutron stars?" – James K Nov 5 '16 at 16:09
• @james your summary is correct. – questionhang Nov 6 '16 at 1:45

## 2 Answers

All type II supernovae are associated with the core collapse of a massive star and are thought to produce some sort of compact star. Supernovae should also always produce an expanding supernova remnant. Almost all massive stars are part of multiple systems.

These three facts might lead you to believe that most, if not all, supernova remnants should contain an observable compact star in a multiple system.

There are two classes of reason why this is not the case - observational issues and physical mechanisms.

Observationally, we do not see compact multiple systems unless one of the stars is a pulsar, which requires a correct orientation to see it, or if the compact star is accreting mass from its companion. The latter requires a close binary system that thas survived the supernova. Also note that isolated black holes may exist in supernovae remnants but would be unobservable.

Physically, the supernova explosion may disrupt the binary system. Pulsars are typically travelling at hundreds of km/s thanks to the "kick" they received from their supernova. Supernova remnants are not visible for long ($\sim$ a million years or less), so pulsars that have been kicked out of a binary can still be found within the supernova remnant.

The short-lived nature of supernovae remnants also biases against finding compact, X-ray accreting binaries. Typically, the compact star's companion must evolve to either fill its Roche lobe (for a low-mass X-ray binary) or to develop high mass loss rates (for a high-mass X-ray binary). This would not normally happen within the short life of the visible supernova remnant.

So examples of observable compact binary systems in supernova remnants are rare. But there are at least two examples known in our Galaxy and several in others. The (at least) two in our Galaxy are Circinus X-1 and SS433.

• ss433 is an X-ray binary, not in a SNR, although there is a SNR nearby. – questionhang Nov 6 '16 at 14:12
• Why do you say this? Have you looked at the paper I referenced? SS433 is at the centre of the SNR W50. @questionhang – Rob Jeffries Nov 6 '16 at 16:55
• you are right. Why do not we mention SS433 is in a SNR much? W50 is not famous at all. – questionhang Nov 10 '16 at 12:33

There are plenty of hard-x-ray binaries that involve a compact object with a companion. Some should be in supernova remnants, but I don't know how many. Are you sure there is a problem?