For every newly released LVK (LIGO/Virgo/KAGRA) GW Public Alert, we create Aitoff-projection skymaps showing the localizations, with all known public TNS transients that lie within the 50/90/99% credibility regions, over-plotted.
For each real (not mock) event we provide a map and an accompanying object list that shows all TNS transients with discovery date BEFORE the GW event time (i.e. these are not potential counterparts), and also a map showing the transients discovered AFTER the event time. The maps display with different markers the unclassified/non-SN transients (ATs) and classified supernovae according to the main subtypes of: SN Ia, SN II, SN I (which include Ib/c/n...) and SLSN; and with a breakup of the numbers to the different credibility regions. The title of each map includes the (super)event name, the alert type and the time of the event; followed by the discovery date range of the shown transients In the second line.
We limit the number of the transients with discovery date BEFORE the GW event time to 500, as an arbitrary "manageable" number of transients to relate to, and the BEFORE timespan is chosen to be one of: 1,3 or 6 months, according to when this limiting amount is surpassed. The maps and lists are being updated on an hourly basis during a period of 14/7 days for high/low-significance events (see below), respectively, after the GW event time. This update policy will be revisited according to the needs that will arise.
All maps and the corresponding transient lists are downloadable as PNG/CSV/JSON files, and it is also possible to download the whole zip file of the event, which includes the original json of the alert and the localization Healpix FITS file that we are creating from the skymap keyword of the json.
The main LVK GW page currently includes two tabs, the default one lists the active O4 run events, the second one -- O1-3 -- lists TNS information on past events from the previous runs (2015-2020).
We enable filtering of the events by their attributed significance, to include either High, Low or All (the default being High - to show the significant events). Following the documented Alert Threshold descriptions, significant GW alerts are defined such that the false-alarm-rate (FAR) < 3.9e-7 Hz (one per month) for CBC (Compact Binary Coalescence) sources, or FAR < 3.2e-8 Hz (one per year) for unmodeled burst signals that do not have a CBC signature.
The maximum time lag from the release of a real GW alert to its appearance on the TNS is expected to be of the order of 15 min. Both the maps and the json files display the most recent Alert Type that was processed (Preliminary, Initial, Update...). If a Retraction alert is issued for an event that was already processed, the event will remain in the list, shown as RETRACTED.
From the release time of this AstroNote all real incoming O4 events will be processed and displayed (upon recommencing of the O4 run scheduled for the end of this month), whereas up to this point we have populated the 39 real events from Jan 2024 (4 significant events, 35 low-significance), and additionally the significant events for which there is an indication of a NS being involved - a total of 6 events, all from 2023.
Please do not hesitate to contact us if you have any questions or comments, in person or via the TNS contact page.
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