Impact of noise transients on low latency gravitational-wave event localization

Gravitational-wave (GW) data contains non-Gaussian noise transients called "glitches." During the third LIGO-Virgo observing run about 24% of all gravitational-wave candidates were in the vicinity of a glitch, while even more events could be affected in future observing runs due to increasing detector sensitivity. This poses a problem since glitches can affect the estimation of GW source parameters, including sky localization, which is crucial to identify an electromagnetic counterpart. This is the first of its kind study that evaluates the importance of relative glitch positioning in time with respect to a GW signal. In this paper we estimate how much sky localization is affected by a nearby glitch in low latency. We injected binary black hole (BBH), binary neutron star (BNS), and neutron star-black hole (NSBH) signals into data containing three different classes of glitches: blips, thunderstorms and fast scatterings. The impact of these glitches was assessed by estimating the number of tile pointings that a telescope would need to search over until the true sky location of an event is observed. We find that blip glitches generally do not affect the localization of our tested GW signals, however in very rare cases of a blip glitch overlap with a BBH or a NSBH signal can cause the true position of the event to lie well outside the 90% computed sky localization, severely compromising electromagnetic follow-up. Thunderstorm glitches have a noticeable impact on BBH and NSBH events, especially if there is no third interferometer. In such cases we find that the electromagnetic follow-up efforts with telescopes as large as 20 deg(2) field of view (FOV) are affected. Observing BBH and NBSH signals with three-detector network reduces the bias in sky localization caused by thunderstorm glitches, making the bias to affect only small (FOV = 1 deg(2)) telescopes. BNS events appear to be not affected by thunderstorm glitches. Fast scattering glitches have no impact on the low latency localization of BBH and BNS signals. For NSBH signals observed with two-detector network, the sky localization bias due to fast scattering glitches is significant enough to affect even large (FOV = 20 deg(2)) telescopes. Observing NSBH signals with three interferometers reduces the bias such that it impacts only small (FOV = 1 deg(2)) telescopes.