The calibration team, which proposes to dither DARM with four pairs (suspensions, pcal) of lines per IFO from below 20 Hz up to above 2 kHz, has asked what frequencies to avoid, in order not to interfere with future targeted searches in aLIGO data for known pulsars. 

Unfortunately (or fortunately, depending on your perspective), the band to avoid at low frequencies is substantial, depending on how far away from a known pulsar one tries to stay. If one stays at least 1 Hz away from every pulsar for which the spindown limit can be beaten at its spin frequency (* see below) or twice its spin frequency, then here are the bands that are safe in that respect:

Non-vetoed bands for veto half-band = 1.000000 (one or two times pulsar frequency)
    33.42-  37.32 Hz (   3.91 Hz)
    42.88-  49.58 Hz (   6.71 Hz)
    51.59-  54.69 Hz (   3.11 Hz)
    57.22-  58.30 Hz (   1.09 Hz)
    60.31-  60.93 Hz (   0.63 Hz)
    62.94-  63.12 Hz (   0.19 Hz)
    65.13-  81.32 Hz (  16.20 Hz)
    83.33-  87.10 Hz (   3.78 Hz)
    89.11- 122.87 Hz (  33.77 Hz)
   124.88- 159.80 Hz (  34.93 Hz)
   161.81- 172.68 Hz (  10.88 Hz)
   174.69- 201.79 Hz (  27.11 Hz)
   203.80- 320.61 Hz ( 116.82 Hz)
   322.62- 346.37 Hz (  23.76 Hz)
   348.38-2000.00 Hz (1651.63 Hz)

In other words, there is no safe frequency below 33.42 Hz. The above bands are defined by vetoing 0.01-Hz bands within 1 Hz of a pulsar with a spindown limit (based on energy conservation) that is higher than the sensitivity obtainable with a 1-year coherent integration of full-aLIGO-sensitivity H1 and L1 IFOs (using the zero-detuned high-power strain noise curve).

Traditionally, targeted searches have looked at only twice the known spin frequency of the star under the assumption that the gravitational waves come from a quadrupole deformation (non-zero ellipticity). In at least one alternative scenario, however, one could detect GWs at the spin frequency itself, and future targeted searches will consider both 1*F and 2*F. How to define the spindown limit for a 1*F emission is not as straightforward, though, as for 2*F emission. In deriving the safe bands above, I have simply taken the spindown limit to be the same as for 2*F. From one perspective, that assumption is absurdly optimistic because we expect the 1*F emission to be weaker than 2*F, but from the perspective of attributing the entire spindown of the star to 1*F emission, the 1*F spindown spidwn limit should be even higher than the 2*F limit.

Given my uneasiness about how seriously to take the 1*F spindown limits, here are the corresponding safe bands when only 2*F emission is considered:

Non-vetoed bands for veto half-band = 1.000000 (two times pulsar frequency)
    33.42-  37.32 Hz (   3.91 Hz)
    42.88-  49.58 Hz (   6.71 Hz)
    51.59-  54.69 Hz (   3.11 Hz)
    57.22-  58.30 Hz (   1.09 Hz)
    60.31-  63.12 Hz (   2.82 Hz)
    65.13-  81.32 Hz (  16.20 Hz)
    83.33-  87.10 Hz (   3.78 Hz)
    89.11- 122.87 Hz (  33.77 Hz)
   124.88- 320.61 Hz ( 195.74 Hz)
   322.62- 346.37 Hz (  23.76 Hz)
   348.38-2000.00 Hz (1651.63 Hz)

Attached are plain text files and plots corresponding to veto-half-bands of 0.01 Hz, 0.10 Hz, 0.50 Hz and 1.00 Hz, along with the Matlab script used to produce them. The spindown limits were computed using parameters taken from the Australia Telescope National Facility (ATNF) pulsar catalog, using all pulsars with a rotation frequency of at least 5 Hz and with measured frequencies (Hz), non-zero measured frequency derivatives (Hz/s), distances (kpc) and epochs (MJD). See the Matlab script for details. The pulsar frequencies used here take into account the spindown and epoch of its measurement and apply to July 1, 2015.

The default veto half-band of 1 Hz used above may be too conservative, but the worry is that upconversion from a strong dither may pollute the frequency where the pulsar sits. The iLIGO Crab pulsar upper limits were appreciably degraded by their nearness to 60 Hz (several tenths of a Hz away) and motors, etc. running just below 60 Hz. Fortunately the Crab has spun down a little further from 60 Hz since the end of aLIGO, with an expected 2*F of 59.3 Hz next July (not including Doppler modulations of +/-6 mHz and a 2nd-order spindown correction of +30 mHz). 

These veto bands have been derived on the assumption that dither frequencies chosen now will be used throughout the first several observing runs. If, on the other hand, the low dither frequencies were to be used only temporarily, one could rerun the Matlab script with a different assumed noise curve and perhaps a shorter assumed observation time, e.g., 3 months for O1, and find other safe bands. 

Attachments:
* Four sets of plots showing pulsar veto bands of 0.01, 0.10, 0.50 and 1.0 Hz half-widths, where magenta bands mark pulsars with an accessible 1*F spindown limit, green bands mark pulsars with an accessible 2*F spindown limit, and black bands mark pulsars where a 1*F or 2*F spindown limit is not accessible. The blue curve shows the 1-year 2-IFO sensitivity for the zero-detuned, high-power configuration.
* Four text files with details on spindown-accessible pulsars and the resulting non-vetoed safe bands
* pulsar_gaps.m - script to generate plots and text files
* contiguous.m - utility script downloaded from Mathworks
* Text file with ATNF catalog output read in by the Matlab script