Welcome to our wiki. If you're here, you're a member of the LIGO periodic sources analysis group or an astronomer or astrophysicist with overlapping interests. In the latter case, you may be interested in opportunities to collaborate here.

Don't wait for advanced LIGO before jumping in. It's further away than you've heard (maybe 2013-2014 for full sensitivity). But initial LIGO is running right now at full sensitivity, and it's starting to get interesting sooner than we thought. Partly this is due to theoretical developments (raising the strength of possible sources), and partly due to thinking harder about integrating knowledge from photon astronomy. Because we're just on the edge of interesting sensitivity, a concerted effort on the interaction between LIGO data analysis, photon astronomy, and theory of astrophysical sources can make a big difference in our results for the next few years. This is a great opportunity for LIGO folks, astronomers, and astrophysicists to work together and do some neat science.

LIGO can look for periodic sources better if we know more about them from photon astronomy. Our searches tend to be computationally limited, and thus searching a narrower parameter space directly increases our effective sensitivity for a fixed data set. An example is the difference between known pulsars, where we can do essentially optimal filtering, versus searching the whole sky where we lose XXX due to computational limits and false alarm statistics.

Photon astronomy sets indirect upper limits on gravitational wave emission. These provide milestones for LIGO to beat. An example is known pulsars, where we can infer the maximum quadrupole moment by assuming all the (radio or x-ray) spindown comes from gravitational radiation reaction. Direct limits on gravitational wave emission are always interesting at some level, even if they don't beat the indirect limits from photons, but it's much more interesting for LIGO to say we're beating the indirect limits. And there's always the chance we might see something, which is even more interesting.

Theoretical expectations also influence where and how LIGO looks. Obviously work on gravitational wave emission mechanisms is important; but there are other things it's useful to have guidance on like where young neutron stars are likely to be.

Finally, interpretation of LIGO results depends on emission mechanisms and previous indirect upper limits. You'll see this in the results sections of the LIGO periodic sources papers. (WE NEED A LIST.) There are a lot more in preparation; keep in mind we've been running 2-3 years from data taking to publication! Think of these results sections as a great way for your papers to get cited, and something you can point to in proposals.

We (LIGO) think of neutron stars in four categories, in contrast to the many astronomers and astrophysicists think of. It comes down to how the searches work: LIGO's data analysis has different constraints from most photon astronomy.

The rest of this section is slightly modified from an extract from the LIGO 2006 internal white paper on periodic sources.

Rapidly rotating neutron stars are the most promising sources of continuous gravitational wave signals in the LIGO frequency band. (We use the term ``neutron star'' broadly, keeping in mind that some such stars may contain quark matter or other exotica.) These stars are expected to emit gravitational radiation through a variety of mechanisms, including elastic deformations \cite{Bildsten:1998ey, Ushomirsky:2000ax, Owen:2005fn}, magnetic deformations \cite{Cutler:2002nw, Melatos:2005ez}, unstable -mode oscillations \cite{Owen:1998xg, Bildsten:1998ey, Andersson:1998qs}, and free precession \cite{Jones:2001yg}, all of which operate differently in accreting and non-accreting stars. We present a review of these emission mechanisms in \cite{S2Fstat}. The conclusion is that the most promising sources of detectable gravitational waves are non-accreting neutron stars for initial LIGO (through deformations) and accreting neutron stars for advanced LIGO (through deformations or -modes). This is because upper limits on gravitational wave emission inferred from pre-existing photon observations are more optimistic for non-accreting stars, but according to present theories accreting neutron stars are more likely to be emitting at or near those upper limits.

From the point of view of observational (photon) astronomy, our searches target four types of neutron stars: non-accreting pulsars, accreting stars (which may or may not pulse), non-pulsing non-accreting stars, and heretofore unobserved objects. For each type of object, astronomers know or infer various properties of the population and of single objects, including upper limits on gravitational wave emission which LIGO has to beat in order to claim a novel result. From our point of view, each type of object presents a distinct data analysis challenge which is directly related to how much information astronomers can provide, now and in the future. Since most of our searches are computationally limited, the sensitivity of each is directly dependent on how much information can be obtained from photon astronomers.

Known Pulsars

The Unknown

Accreting Neutron Stars

Directed Searches

Various Meetings