[Pafgbt] pulsar search metric

[Paul Demorest]

Ok.. maybe some of the PALFA planning documents would be helpful?

http://www.naic.edu/alfa/pulsar/

-Paul

On Tue, 2 Mar 2010, Rick Fisher wrote:

> Hi Paul,
>
> Thanks for the run down on sensitivity.  Right now I'm thinking very 
> primitively about things like how far apart to form the beams and what the 
> effects of lower sensitivity of outer beams might be.  My intuition is that a 
> 1 dB or even 0.5 dB degradation in outer beam aperture efficiency hurts 
> pretty significantly in terms of new pulsar count, but I'd like to quantify 
> this.  Scattering, duty cycle, etc. are backend design issues that we'll need 
> to deal with separately.  I have the ATNF pulsar catalog from which I can 
> generate a log(N) - log(S) relationship, and I'll see how far I can go with 
> that.
>
> Rick
>
> On Tue, 2 Mar 2010, Paul Demorest wrote:
>
>> 
>> The usual pulsar sensitivity expression (for a single beam/pointing) is
>> 
>> S_min = (# sigma) * (T_sys/G) / sqrt(2*BW*t_int) * sqrt(W/(P-W))
>> 
>> (see for example the Lorimer and Kramer book.. this eqn is probably given 
>> in lots of other places as well)
>> 
>> Most of these are just the standard factors.. T_sys needs to include both 
>> recvr temp and galactic BG sky temp.  P is the pulse period and W is the 
>> pulse width.  W is really the only complicated thing, it's usually taken as 
>> a quadrature sum of several terms:
>> 
>> W^2 = W_psr^2 + W_dm^2 + W_inst^2 + W_scat^2
>> 
>> W_psr is the intrinsic pulse width, typically assumed to be 5-10% of P for 
>> survey planning purposes.  MSPs tend to have a higher duty cycle than slow 
>> PSRs.
>> 
>> W_dm is the dm smearing, which depends on the frequency resolution, and is 
>> equal to 8.3us*DM*chan_bw(MHz)/RF(GHz)^3.
>> 
>> W_inst is the instrumental time resolution.
>> 
>> W_scat is ISM scatter broadening.. usually ignored except in special cases 
>> like galactic center searches.
>> 
>> The sensitivty ends up being a function of pulse period and dispersion 
>> measure.  To compare searches involving different numbers of beams, fields 
>> of view, etc, this should probably be converted to telescope time needed to 
>> cover a certain area to a certain sensitivty or something along those 
>> lines.
>> 
>> I don't know of a standard way of bringing other factors like data storage 
>> and computation requirements into a single metric.  Here are a couple SKA 
>> memos that may or may not be useful:
>> 
>> http: //www.skatelescope.org/PDF/memos/105_Memo_Smits.pdf
>> http: //www.skatelescope.org/PDF/memos/97_Memo_Cordes_REVISED.pdf
>> 
>> -Paul
>> 
>> On Mon, 1 Mar 2010, Walter Brisken wrote:
>> 
>>>
>>>  http://xxx.lanl.gov/abs/astro-ph/0304364
>>>
>>>  This paper discusses searches for "fast transients", i.e., single pulses.
>>>  Possibly not exactly what you want, but I believe it could be generalized
>>>  easily for the case of periodic sources.
>>>
>>>  On Mon, 1 Mar 2010, Rick Fisher wrote:
>>> 
>>> >  I've been tinkering with metrics for assessing PAF perfomance for 
>>> pulsar
>>> >  searches.  Are there any published papers or internal reports on the
>>> >  subject?
>>> > >  Rick
>> 
>> 
>