GOTO (telescope array)

Each GOTO system can point independently, whilst each unit telescope (UT) has a fixed orientation on the mount so all 8 must be pointed at once. Each UT's pointing is offset from the others to cover the adjacent area of sky, with a small overlap between them. This results in each GOTO system acting as a single large telescope with a very wide field of view (FoV).File:GOTO FoV.png, with an overlay showing the field of view of a single GOTO unit telescope.]]

File:GOTO Subgrid Array.svg

The UTs are ASA H400 Newtonian telescopes, each with an aperture of 400mm and a focal length of 960mm (f/2.4). Attached to each telescope is a focuser, filter wheel, and a Finger Lakes Instrumentation (FLI) ML50100 camera, based on the Onsemi KAF-50100 CCD sensor.{{Cite web |title=New KAF-50100 sensor with microlenses |url=https://www.flicamera.com/51.php |access-date=2024-01-30 |website=www.flicamera.com}} The fast focal ratio of f/2.4 and large image sensor result in a relatively large field of view, with each GOTO system having a total FoV of approximately 40 square degrees, around 200x the area of the full Moon in the sky. The fast focal ratio also means that only a small amount of time is needed to observe each area of the sky, with each visit requiring only 3 minutes of exposure time.

GOTO utilises difference imaging to identify changes of existing objects and the appearance of new transients. Images of the sky are matched to previous observations of the same region, finding the difference between these two images will show only the changes in the new image. Sources within these difference images can then be detected automatically. Using difference imaging in this way produces many thousands of candidate sources per image, the vast majority of which are artefacts of the processing and not real transients.{{Cite journal |last1=Brink |first1=Henrik |last2=Richards |first2=Joseph W. |last3=Poznanski |first3=Dovi |last4=Bloom |first4=Joshua S. |last5=Rice |first5=John |last6=Negahban |first6=Sahand |last7=Wainwright |first7=Martin |date=2013-10-21 |title=Using machine learning for discovery in synoptic survey imaging data |url=http://academic.oup.com/mnras/article/435/2/1047/1033222/Using-machine-learning-for-discovery-in-synoptic |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=435 |issue=2 |pages=1047–1060 |doi=10.1093/mnras/stt1306 |doi-access=free |issn=1365-2966|arxiv=1209.3775 }} GOTO utilises a convolutional neural network based 'real-bogus' classifier to identify which sources are likely to be real.{{Cite journal |last1=Killestein |first1=T L |last2=Lyman |first2=J |last3=Steeghs |first3=D |last4=Ackley |first4=K |last5=Dyer |first5=M J |last6=Ulaczyk |first6=K |last7=Cutter |first7=R |last8=Mong |first8=Y-L |last9=Galloway |first9=D K |last10=Dhillon |first10=V |last11=O'Brien |first11=P |last12=Ramsay |first12=G |last13=Poshyachinda |first13=S |last14=Kotak |first14=R |last15=Breton |first15=R P |date=2021-04-09 |title=Transient-optimized real-bogus classification with Bayesian convolutional neural networks – sifting the GOTO candidate stream |url=https://academic.oup.com/mnras/article/503/4/4838/6171008 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=503 |issue=4 |pages=4838–4854 |doi=10.1093/mnras/stab633 |doi-access=free |issn=0035-8711|arxiv=2102.09892 }}

In addition to follow-up of gravitational wave events, GOTO can respond to detections of gamma-ray bursts (GRBs).{{Cite journal |last1=Mong |first1=Y-L |last2=Ackley |first2=K |last3=Galloway |first3=D K |last4=Dyer |first4=M |last5=Cutter |first5=R |last6=Brown |first6=M J I |last7=Lyman |first7=J |last8=Ulaczyk |first8=K |last9=Steeghs |first9=D |last10=Dhillon |first10=V |last11=O’Brien |first11=P |last12=Ramsay |first12=G |last13=Noysena |first13=K |last14=Kotak |first14=R |last15=Breton |first15=R |date=2021-09-07 |title=Searching for Fermi GRB optical counterparts with the prototype Gravitational-wave Optical Transient Observer (GOTO) |journal=Monthly Notices of the Royal Astronomical Society |volume=507 |issue=4 |pages=5463–5476 |doi=10.1093/mnras/stab2499 |doi-access=free |issn=0035-8711|arxiv=2108.11802 }} On September 11, 2023, the Fermi Gamma-ray Space Telescope detected a gamma ray burst (GRB 230911A){{Cite web |title=GCN - Circulars - 34652 - GRB 230911A: Fermi GBM Final Real-time Localization |url=https://gcn.nasa.gov/circulars/34652 |access-date=2024-08-21 |website=gcn.nasa.gov}} and follow-up observations by GOTO discovered an optical counterpart (GOTO23akf/AT 2023shv),{{Cite web |title=AT 2023shv {{!}} Transient Name Server |url=https://www.wis-tns.org/object/2023shv |access-date=2024-08-21 |website=www.wis-tns.org}} which was later confirmed as a GRB afterglow by the Swift X-ray telescope.{{Cite journal |last1=Belkin |first1=S. |last2=Gompertz |first2=B. P. |last3=Kumar |first3=A. |last4=Ackley |first4=K. |last5=Galloway |first5=D. K. |last6=Jiménez-Ibarra |first6=F. |last7=Killestein |first7=T. L. |last8=O’Neill |first8=D. |last9=Wiersema |first9=K. |last10=Malesani |first10=D. B. |last11=Levan |first11=A. J. |last12=Lyman |first12=J. |last13=Dyer |first13=M. J. |last14=Ulaczyk |first14=K. |last15=Steeghs |first15=D. |date=2024-01-04 |title=GRB 230911A: The First Discovery of a Fermi GRB Optical Counterpart with the Gravitational-wave Optical Transient Observer (GOTO) |journal=Research Notes of the AAS |volume=8 |issue=1 |pages=6 |doi=10.3847/2515-5172/ad1876 |doi-access=free |bibcode=2024RNAAS...8....6B |issn=2515-5172}}

{{Location map+|World|places={{Location map~ | World

| label = GOTO-N

| coordinates = {{coord|28|45|36.36|N|17|52|45.54|W|}}}}

{{Location map~ | World

| label = GOTO-S

| coordinates = {{coord|31|16|24.28|S|149|3|50.83|E|}}}}|caption=Locations of GOTO-N and GOTO-S.|width=300|alt=location of GOTO-N in La Palma off the coast of Morocco and GOTO-S in eastern Australia|float=right}}GOTO's typical mode of operation when not performing a follow-up campaign is to survey the entire visible sky. As there are sites located in both the northern and southern hemispheres, the visible sky for GOTO is all areas which are visible at night from anywhere on the Earth. If both sites have good weather conditions the entire visible sky can be observed every 2–3 days.

These observations are processed using difference imaging which allows for serendipitous discovery of transients unrelated to multi-messenger events, like supernovae, tidal disruption events, and fast blue optical transients.

{{Multiple image

| image1 = Goto discovery count-20240911-en-total.svg

| image2 = Goto discovery count-20240911-en-monthly.svg

| caption1 = Total

| caption2 = Monthly

| caption_align = center

| footer = Total (line) and monthly (bar) count of transients discovered by GOTO between 2020 and September 11 2024.

| align = left

| total_width =

| direction = vertical

}}

The first phase of GOTO's development was the deployment of a prototype system located at the planned site of the northern node, consisting of four unit telescopes on a custom-built mount.{{cite journal |last1=Steeghs |first1=D |last2=Galloway |first2=D K |last3=Ackley |first3=K |last4=Dyer |first4=M J |last5=Lyman |first5=J |last6=Ulaczyk |first6=K |last7=Cutter |first7=R |last8=Mong |first8=Y-L |last9=Dhillon |first9=V |last10=O'Brien |first10=P |last11=Ramsay |first11=G |last12=Poshyachinda |first12=S |last13=Kotak |first13=R |last14=Nuttall |first14=L K |last15=Pallé |first15=E |last16=Breton |first16=R P |last17=Pollacco |first17=D |last18=Thrane |first18=E |last19=Aukkaravittayapun |first19=S |last20=Awiphan |first20=S |last21=Burhanudin |first21=U |last22=Chote |first22=P |last23=Chrimes |first23=A |last24=Daw |first24=E |last25=Duffy |first25=C |last26=Eyles-Ferris |first26=R |last27=Gompertz |first27=B |last28=Heikkilä |first28=T |last29=Irawati |first29=P |last30=Kennedy |first30=M R |last31=Killestein |first31=T |last32=Kuncarayakti |first32=H |last33=Levan |first33=A J |last34=Littlefair |first34=S |last35=Makrygianni |first35=L |last36=Marsh |first36=T |last37=Mata-Sanchez |first37=D |last38=Mattila |first38=S |last39=Maund |first39=J |last40=McCormac |first40=J |last41=Mkrtichian |first41=D |last42=Mullaney |first42=J |last43=Noysena |first43=K |last44=Patel |first44=M |last45=Rol |first45=E |last46=Sawangwit |first46=U |last47=Stanway |first47=E R |last48=Starling |first48=R |last49=Strøm |first49=P |last50=Tooke |first50=S |last51=West |first51=R |last52=White |first52=D J |last53=Wiersema |first53=K |title=The Gravitational-wave Optical Transient Observer (GOTO): prototype performance and prospects for transient science |journal=Monthly Notices of the Royal Astronomical Society |date=April 2022 |volume=511 |issue=2 |pages=2405–2422 |doi=10.1093/mnras/stac013 |doi-access=free |ref=Prototype Paper|arxiv=2110.05539 }} The prototype system was deployed during the second LIGO-Virgo Collaboration (LVC) observing run (O2), achieving first light in June 2017 with its official inauguration on July 3, 2017.

The prototype system was active during the first half of the third LVC observing run (O3a), which ran between April and October 2019.{{Cite journal |last1=Abbott |first1=R. |last2=Abe |first2=H. |last3=Acernese |first3=F. |last4=Ackley |first4=K. |last5=Adhicary |first5=S. |last6=Adhikari |first6=N. |last7=Adhikari |first7=R. X. |last8=Adkins |first8=V. K. |last9=Adya |first9=V. B. |last10=Affeldt |first10=C. |last11=Agarwal |first11=D. |last12=Agathos |first12=M. |last13=Aguiar |first13=O. D. |last14=Aiello |first14=L. |last15=Ain |first15=A. |date=2023-08-01 |title=Open Data from the Third Observing Run of LIGO, Virgo, KAGRA, and GEO |journal=The Astrophysical Journal Supplement Series |volume=267 |issue=2 |pages=29 |doi=10.3847/1538-4365/acdc9f |doi-access=free |issn=0067-0049|arxiv=2302.03676 |bibcode=2023ApJS..267...29A }} During this time GOTO was able to respond to gravitational-wave events and begin observing within one minute of alerts being received (if the source region was visible).{{Cite journal |last1=Gompertz |first1=B P |last2=Cutter |first2=R |last3=Steeghs |first3=D |last4=Galloway |first4=D K |last5=Lyman |first5=J |last6=Ulaczyk |first6=K |last7=Dyer |first7=M J |last8=Ackley |first8=K |last9=Dhillon |first9=V S |last10=O’Brien |first10=P T |last11=Ramsay |first11=G |last12=Poshyachinda |first12=S |last13=Kotak |first13=R |last14=Nuttall |first14=L |last15=Breton |first15=R P |date=2020-09-01 |title=Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-Wave Optical Transient Observer (GOTO-4) |url=https://academic.oup.com/mnras/article/497/1/726/5866841 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=497 |issue=1 |pages=726–738 |doi=10.1093/mnras/staa1845 |doi-access=free |issn=0035-8711|arxiv=2004.00025 }}

In late 2019 funding was awarded to expand the network with two full GOTO systems a duplicate site in Australia.{{Cite web |date=2020-04-05 |title=Funding Approved For GOTO Expansion |url=https://goto-observatory.org/funding-approved-for-goto-expansion/ |access-date=2024-01-25 |website=GOTO Observatory}} In 2020 the first full system of the northern node was being deployed, with the second system planned for early 2021 and the Australian site planned for later that year.{{Cite book |last1=Dyer |first1=Martin J. |last2=Steeghs |first2=Danny |last3=Galloway |first3=Duncan K. |last4=Dhillon |first4=Vik S. |last5=O'Brien |first5=Paul |last6=Ramsay |first6=Gavin |last7=Noysena |first7=Kanthanakorn |last8=Pallé |first8=Enric |last9=Kotak |first9=Rubina |last10=Breton |first10=Rene |last11=Nuttall |first11=Laura |last12=Pollacco |first12=Don |last13=Ulaczyk |first13=Krzysztof |last14=Lyman |first14=Joseph |last15=Ackley |first15=Kendall D. |chapter=The Gravitational-wave Optical Transient Observer (GOTO) |editor-first1=Heather K. |editor-first2=Jason |editor-first3=Tomonori |editor-last1=Marshall |editor-last2=Spyromilio |editor-last3=Usuda |date=2020-12-13 |title=Ground-based and Airborne Telescopes VIII |chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11445/114457G/The-Gravitational-wave-Optical-Transient-Observer-GOTO/10.1117/12.2561008.full |publisher=SPIE |volume=11445 |pages=1355–1362 |doi=10.1117/12.2561008|arxiv=2012.02685 |bibcode=2020SPIE11445E..7GD |isbn=978-1-5106-3677-4 |s2cid=216906754 |url=https://wrap.warwick.ac.uk/170742/1/WRAP-The-Gravitational-wave-Optical-Transient-Observer-GOTO-2022.pdf }}

The deployment of the second northern system was completed in August 2021{{Cite web |last=Ulaczyk |first=Krzysztof |date=2021-08-01 |title=Second GOTO system installed at Roque de Los Muchachos Observatory |url=https://goto-observatory.org/second-goto-system-installed-at-roque-de-los-muchachos-observatory/ |access-date=2024-01-25 |website=goto-observatory.org}} and, despite delays due to the 2021 volcanic eruption, the full northern node was completed in December 2021 with the upgrade of the prototype to the final hardware configuration.{{Cite web |last=Ulaczyk |first=Krzysztof |date=2021-12-08 |title=Full northern node deployed! |url=https://goto-observatory.org/full-northern-node-deployed/ |access-date=2024-01-25 |website=goto-observatory.org}}

By the end of 2022 the site for the second GOTO node (GOTO-S) had been prepared at Siding Spring Observatory (SSO) and the two domes installed.{{Cite web |last= |date=2024-01-29 |title=GOTO-South |url=https://rsaa.anu.edu.au/about/observatories/telescopes/goto-south |access-date=2024-01-29 |publisher=Australian National University |language=en}}{{Cite web |last=Ulaczyk |first=Krzysztof |date=2022-12-08 |title=New GOTO domes erected in Siding Spring Observatory |url=https://goto-observatory.org/new-goto-domes-erected-in-siding-spring-observatory/ |access-date=2024-01-25 |website=goto-observatory.org}} In May 2023 it was announced that both systems at SSO had been successfully installed.{{Cite web |last=Ulaczyk |first=Krzysztof |date=2023-05-08 |title=Two new arrays of telescopes installed at Siding Spring Observatory |url=https://goto-observatory.org/two-new-arrays-of-telescopes-installed-at-siding-spring-observatory/ |access-date=2024-01-26 |website=goto-observatory.org}}

As of April 1, 2025, data from GOTO has been used in the discovery of 2,092 astronomical transients, of which 311 have been classified as supernovae and two as tidal disruption events.{{cite web |title=TNS Transients Statistics, Skymaps and Plots {{!}} Transient Name Server |url=https://www.wis-tns.org/stats-maps |url-status=live |archive-url=https://web.archive.org/web/20250401181530/https://www.wis-tns.org/stats-maps |archive-date=1 April 2025 |access-date=1 April 2025 |website=www.wis-tns.org |publisher=International Astronomical Union |ref=IAU Statistics}}{{Cite web |title=AT 2023lli {{!}} Transient Name Server |url=https://www.wis-tns.org/object/2023lli |url-status=live |archive-url=https://web.archive.org/web/20240203002828/https://www.wis-tns.org/object/2023lli |archive-date=2024-02-03 |access-date=2024-02-03 |website=www.wis-tns.org}}{{Cite web |title=2024aegq {{!}} Transient Name Server |url=https://www.wis-tns.org/object/2024aegq |access-date=2025-01-29 |website=www.wis-tns.org}}

Kilonova Seekers is a citizen science project on the Zooniverse platform designed to assist GOTO in identifying real astrophysical transients.{{Cite web |date=2023-07-12 |title=Play 'spot the difference' to help scientists identify cosmic explosions |url=https://www.port.ac.uk/news-events-and-blogs/news/play-spot-the-difference-to-help-scientists-identify-cosmic-explosions |access-date=2025-01-31 |website=University of Portsmouth |language=en}} Volunteers are shown transient detections from GOTO, alongside a reference GOTO observation and the difference between the two, and asked whether they believe it to be a real detection. If a source reaches an 80% consensus, and has at least 8 votes, an alert is sent to the GOTO team for further investigation.{{Cite journal |last1=Killestein |first1=T L |last2=Kelsey |first2=L |last3=Wickens |first3=E |last4=Nuttall |first4=L |last5=Lyman |first5=J |last6=Krawczyk |first6=C |last7=Ackley |first7=K |last8=Dyer |first8=M J |last9=Jiménez-Ibarra |first9=F |last10=Ulaczyk |first10=K |last11=O’Neill |first11=D |last12=Kumar |first12=A |last13=Steeghs |first13=D |last14=Galloway |first14=D K |last15=Dhillon |first15=V S |date=2024-09-11 |title=Kilonova Seekers: the GOTO project for real-time citizen science in time-domain astrophysics |url=https://academic.oup.com/mnras/article/533/2/2113/7735340 |journal=Monthly Notices of the Royal Astronomical Society |volume=533 |issue=2 |pages=2113–2132 |doi=10.1093/mnras/stae1817 |doi-access=free |issn=0035-8711|hdl=2299/28414 |hdl-access=free }}

As of January 31, 2025, there have been over 2 million classifications made via Kilonova Seekers by over 3200 volunteers. In total over 158,000 possible sources have been completed as either real or bogus.{{Cite web |title=Kilonova Seekers |url=https://www.zooniverse.org/projects/tkillestein/kilonova-seekers |access-date=2025-01-31 |website=Zooniverse}}

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