Public Alerts from a DECam Deep Drilling Survey

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List of Co-Investigators

Melissa L. Graham (U. Washington), Peter E. Nugent, Daniel A. Goldstein, Alex Kim (LBNL), Gautham Narayan, Monika Soraisam, Yue Shen (U. Illinois), Rachel Street (Las Cumbres), Francisco Förster (U. Chile), Federica Bianco, John Gizis(U. Delaware), Stephen Smartt, Ken Smith (QUB), Abhijit Saha Thomas Matheson, Chien-Hsiu Lee, Kathy Vivas (NOIRLab), Will Clarkson (U. Michigan-Dearborn), Armin Rest (STScI), Dillon Brout (SAO), Márcio Catelan (Pontificia U. Católica de Chile), Saurabh W. Jha (Rutgers), Lifan Wang (Texas A&M), Antonella Palmese (FermiLab), John Moustakas (Siena College), Mark Sullivan (U. Southampton), Christopher Lidman (ANU), Roy Williams (ROE), Cosimo Inserra (Cardiff), Eric Bellm, Mario Jurić, Christopher Phillips, Thomas Kennedy, Keaton J. Bell, Meredith L. Rawls, J. Bryce Kalmbach, Hayden Smotherman, Siegfried Eggl (U. Washington).

We announce that the public DECam Deep Drilling Program is being run at the Blanco 4m telescope at Cerro Tololo-Inter-American Observatory as part of the DECam Alliance for Transients (DECAT), a consortium of time-domain DECam programs that have pooled their time and are scheduled for every ~3rd night from March 18 through June 10 (with pending partnership extensions through July). The DDF observational sequences described below will (weather permitting) occur every DECAT night, and will have flexible start times to enable co-scheduling with other DECAT programs.

The images have no proprietary period, and are available through the NOIRLab Astro Data Archive under proposal ID 2021A-0113. Difference image analysis will be done in real time at NERSC, on both the single exposures and the nightly deep stacks. Public alerts will be streamed to all alert brokers that receive public ZTF alerts, including ANTARES, Lasair, and ALeRCE. All are welcomed and encouraged to do science with these data products.

Extragalactic – Three pointings in the COSMOS deep fields: COSMOS-1 (150.0,+3.1), COSMOS-2 (149.22,+1.75), and COSMOS-3 (150.78,+1.75). Every DECAT night, three ~0.5 hour sequences will be done; some nights these will be back-to-back, and some nights they will be separated in time by up to a couple of hours. Each sequence cycles through the fields, obtaining a series of images in the g, r, and i filters with exposure times of 60, 86, and 130 seconds, respectively. In total, each field will be imaged five times in each filter, for a total of 15 photometric observations per night (45 for sources in the ~5% overlap region; no dithering). The 5-sigma limiting magnitudes will be r~23.5 mag (single exposure) and r~24.5 mag (nightly stack).

Galactic – One pointing in the Galactic bulge which we are calling “DECaPS East” (18:03:34 -29:32:02; l=1.462 b=-3.681). Every DECAT night, two ~0.3 hour sequences will be done; some nights these will be back-to-back, and some nights they will be separated in time by up to a couple of hours. Each sequence will cycle through the g, r, i, and z filters three times with exposure times of 96, 50, 30, and 30 seconds, respectively. In total, the field will be imaged six times in each filter, for a total of 24 photometric observations per night. The 5-sigma limiting magnitudes will be, at most, r~23.5 mag (single exposure) and r~24.5 mag (nightly stack) – but potentially shallower in such a crowded field.

See also the related TNS AstroNote: AstroNote 2021-104 | Transient Name Server

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Hi Melissa, and other Co-I,

Thank you for this opportunity!

Concerning public alerts for alert brokers already connected to ZTF (Fink in my case), where can we find connection information and alert schema? And will it be transmitted via Kafka streams as it is currently done for ZTF?

Thanks,
Julien

The Pitt-Google Broker would also be interested in connecting to the alert stream to continue and broaden our testing and starting providing publicly useful interfaces.

Wonderful, @JulienPeloton and @mwv. As I understand it, you will be able to use your existing UW connections and listen to new decat_ topics (once the streaming starts, which should be soon). E.g., decat_YYYYMMDD_propID. The proposal ID for the deep drilling fields is 2021A-0113.

The schema have been put here: GitHub - rknop/decat_schema

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Thank you @MelissaGraham for this information!

Do we already know the expected rate of alerts per night (or per exposure)? It looks quite deep!

Not sure about total alert volumes just yet – the pipelines team is doing some final work on the real/bogus, and doing some distribution tests now, so we should have an idea soon (but you’re right, with the very deep very crowded fields there will be ‘a lot’).