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At 17:00 UTC, on Friday the 27th of March, 2020, the third observation period (O3) of the Virgo Collaboration and the LIGO Scientific Collaboration was suspended because of the COVID-19 pandemic. This decision was taken to protect the safety of staff at the observatories. For more information and updates, please visit this link.

On Tuesday the 31st of March, 2020, following calibration measurements and various final tests, the Advanced Virgo detector - hosted by the European Gravitational Observatory (EGO, near Pisa, Italy) - was put into standby mode.

The plots that follow summarise the results achieved during the O3 run by Advanced Virgo and by the global network of gravitational-wave detectors formed by Advanced Virgo and the two Advanced LIGO detectors in the US.

Advanced Virgo sensitivity improvement during O3 and comparison with O2.

The sensitivity of Advanced Virgo during O3, its improvement over time and a comparison with the sensitivity during O2. Click here for more information

The top plot shows the Advanced Virgo sensitivity to gravitational waves versus frequency. Here, the sensitivity is given in terms of amplitude spectral density of the interferometer output noise, expressed in units of gravitational wave strain. Thus the lower the curve, the more sensitive the detector in that frequency range.

In the bottom plots the sensitivity is given in terms of the 'BNS range', i.e. the average distance at which the merger of a Binary Neutron Star system (BNS) gives a matched filter signal-to-noise ratio (SNR) of 8 in Advanced Virgo with the current sensitivity; the distance is averaged over all the possible sky localisations and binary orientations. Each neutron star in the binary system is assumed to have a mass equal to 1.4 solar masses. The BNS range is given in units of megaparsecs (millions of parsecs, in short Mpc): a parsec is equal to 3.26 light-years. The larger the BNS range, the more sensitive the detector.

The bottom left plot refers to the 2nd observation period (O2, August 2017 for Virgo); the bottom-right plot refers to the 3rd observation period (O3, April 2019-March 2020). The steady improvements are shown by the lowering of the sensitivity curve in the top plot and the corresponding increase of the BNS range in the bottom plots.

Status of Advanced Virgo during O3

The percentage of time that Advanced Virgo spent in a given state during the 3rd observation run (O3 - top plot and top pie chart), and during the two halves of O3, namely O3a (bottom left chart) and O3b (bottom right chart), separated by a 1-month break in October 2019. During an observation period the goal of Advanced Virgo is to stay in science mode (shown in green) as much as possible, a state in which the instrument is producing sensitive data of good quality. Click here for more information

However some interruptions are unavoidable: some time is spent acquiring the control of the different instrument components (called 'locking', shown in blue); or to try to improve the performance ('commissioning' phase, shown in red). Interruptions can also be due to: weekly calibrations of the detector ('calibration', shown in yellow); planned maintenance periods every Tuesday morning in coordination with the LIGO detectors ('maintenance', shown in brown); finally, all the other states (rare, shown in gray).

Daily duty cycle of Advanced Virgo during O3

The day to day percentage of time Advanced Virgo has spent in science mode during the third observation period, called O3: this quantity is referred to as the daily duty cycle. O3 started on the 1st of April, 2019 and was suspended on the 27th of March, 2020. The observation period, common to Advanced Virgo and the two Advanced LIGO detectors, was interrupted on the 1st of October, 2019 and resumed on the 1st of November, 2019. Click here for more information

This interruption allowed for an improvement of the detectors and was called a 'commissioning break'.

The O3 run was suspended on the 27th of March, 2020, about a month before the foreseen end date, due to the worldwide covid-19 pandemic.

LIGO VIRGO duty cycle during O3

The percentage of time that the global detector network formed by Advanced Virgo (labelled as V1) and the two Advanced LIGOs (at Livingston, labelled as L1, and at Hanford, labelled as H1) spent in observation mode during O3: this quantity is referred to as the network duty cycle. Click here for more information

The plot shows that 47.4% of time, the network operated with all three detectors simultaneously in science mode; 36% of the time the network had two detectors online (three possible combinations), 13.4% of the time only one detector was up; finally, just 3% of the time none of the detectors were in science mode.

O3 cumulative public alerts

The cumulative number of gravitational-wave detections and of public alerts issued by the LIGO and Virgo Collaborations during the 3rd observation period, named O3. Click here for more information

As of April, 2020, two gravitational wave events have been confirmed from the O3 public alerts: GW190425 and GW190412. The plot shows the unretracted alerts (last update April, 2020): more information can be found in GraceDB. The gray band shows the interruption in the observation period of the global network of Advanced LIGOs and Advanced Virgo in October, 2019: this period was called a 'commissioning break'.

O2, O3a, O3b cumulative public alerts

The cumulative number of gravitational wave detections and of public alerts issued by the LIGO and Virgo Collaborations during the two parts of the 3rd observation period, called O3a (1st of April, 2019 - 1st Octobert, 2019; orange solid line) and O3b (1st November, 2019 - 27th March, 2020; green dotted line). Click here for more information

The plot also shows the cumulative number of gravitational waves detected by LIGO and Virgo during the second observation run, called O2 (30th November, 2016 - 25th August, 2017; blue solid line); the two breaks during O2 (for the winter 2016 holiday and in spring, 2017) have not been counted. The vertical dashed cyan line shows when Advanced Virgo joined the two Advanced LIGOs in O2, making the network global.

During the first observation run, O1, which ran from the 12th of September, 2015, until the 19th of January, 2016, three signals, which are not shown in the plot, were detected.