Tomo-e Gozen High-Cadence Transient Survey
Tomoki Morokuma (Univ. of Tokyo, IoA; tmorokuma@ioa.s.u-tokyo.ac.jp),
Nozomu Tominaga (Konan Univ.), Masaomi Tanaka (Tohoku Univ.), Keiichi
Maeda (Kyoto Univ.), Shigeyuki Sako, Ryou Ohsawa (Univ. of Tokyo, IoA),
Tomo-e Gozen SN WG members

New Parameter Space: High Cadence Transient Surveys
Northern Sky Transient Survey w/ Tomo-e Gozen
Survey DesignSurvey Statistics
Summary

105cm Kiso Schmidt Telescope@Nagano, Kiso
105 cm Schmidt telescope (4th largest Schmidt in the world)
since 1974
open-use ==> collaboration basis (2018-)

Tomo-e Gozen High-Cadence Transient Survey

Seimei UM 2020

2020/08/17-19

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Tomo-e Gozen April 2019 completed
84 CMOS sensors
low dark current, readout noise
operated in room temp. (no cooler)effective area: 20 deg2 (9 deg in diameter)
1k x 2k ~ 22.4 x 39.7 arcmin2
no filter (gri, Ha, … sometimes)
2 fps readout (nominal): up to ~200 Hz

Tomo-e Gozen High-Cadence Transient Survey

蔀関月作, 「巴御前出陣図」,東京国立博物館,©Image: TNM Image Archives

Seimei UM 2020

2020/08/17-193

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High-Cadence
Transient Survey
Seimei
UM2020 systematic searches,
2020/08/17-19

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“Moment” of Supernova Explosion
Supernova Shock Breakout
beforeafterdayshours

shock breakout©Univ. of Tokyo
Tomo-e Gozen High-Cadence Transient Survey

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2020/08/17-19

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Very Early Phases of Core-Collapse Supernovae
Discovered by Victor Buso@Argentine, 16-inch telescope
SN 2016gkg@NGC 613
Bersten+2018, Nature

possible detection with Gaia (Garnavich+2016, Rubin+2016)
serendipitous detections with Swift/XRT (SN 2008D; Soderberg+2008), GALEX (Schawinski+2008)
almost no detailed follow-ups for previous detections because of low S/N (high-z), discovery
latency, insufficient follow-up time (large telescopes) <== overcome by Tomo-e + Seimei obs.
Tomo-e Gozen High-Cadence Transient Survey

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2020/08/17-19

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Northern Sky Transient Survey w/ Tomo-e Gozen
7,000 deg2 - 2 hr cadence - 18 mag depth 2019 (initial phase)
7,000 deg2 - one visit - 18 mag depth
2020- (now)==> 2,000 deg2 - 0.5 hr cadence - 18 mag depth
no filter: effectively g+r bands
1 visit
6 sec exposure: [0.5 sec exposure] x 12 ==> ~18-19 mag~60 deg2 w/ 2x2 (or 2x3) dithering to fill the gaps between sensors
cadence: ~2 hours ==> ~0.5 hours (around midnight)
survey area: ~7,000 deg2 / 2 hrs ==> ~2,000 deg2 / 0.5 hrs
survey planning: Pedroso, Ikeda, TM+ et al. in prep.
recent (2020 winter) changes:
2-hour cadence in a night ==> one-visit all-sky, then 0.5-hour cadencenear-future changes:
reference for image subtraction: [PS1/r] ==> [Tomo-e]achieve better subtraction around bright nearby galaxies
24 contiguous frames instead of 12?
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Tomo-e Gozen High-Cadence Transient Survey

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2020/08/17-19

Transient Survey PowerYasuda+2019

Tomo-e Gozen
higher cadenceTomo-e Gozen High-Cadence Transient Survey

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Data Products
after image subtraction:
Subtracted images relative to PS1 r-band
CNN (Hamasaki 2020, master thesis/Konan U.)==> automatic alert for bright transients
Coadded good-seeing Tomo-e data will be used in a few months.
better subtraction
photometry@subtracted images
photometry of Tomo-e-detected transients
photometry of other known (reported to TNS) transients
almost the same search for GW EM counterparts (Niino+ in prep.)
before image subtraction for variable stars etc.
Photometry for all the detected sources, calibrated relative to PS1light curves for all the sources will be available.
blazar variability study (Morita, 2020, master thesis/U. of Tokyo)
motion detection
NEO searchDiscovery of 8 NEOs incl. 2019 FA
size: ~8m (http://www.ioa.s.u-tokyo.ac.jp/kisohp/NEWS/2019FA/2019FA.html)

We are preparing a dedicated server to store the products and release
them with limited access. Contact us if you are interested in it.
Tomo-e Gozen High-Cadence Transient Survey

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2020/08/17-19

9Transients in Transient Name Server (TNS)
Dec > -3 deg & 2019/04/06 - 2019/12/31 (discovery date@TNS)~1,600 transients reported to TNS#(Tomo-e Obs, deeper than discovery magnitude) > 0
247 transients
279 transients
337 transients-50
TNS discovery date

Example: SN 2019dwy (SN Ic)

13t [days]

Tomo-e discovery(2nd detection), MJD=58585.71 (12 days before TNS
discoery), ~18 mag

subTNS discovery
MJD=58597.41
17.2 mag (ASAS-SN)

Tomo-eref
Tomo-e Gozen High-Cadence Transient Survey

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2020/08/17-19

10Target Handling System: web I/Flink to SDSS (if available)link to SDSS, PS1, TNS, MPChecker

link to visibility plot (IAC)

link to Tomo-e Gozen fits

light curve in magnitude unit
(light curve in linear scale below)

Tomo-e Gozen High-Cadence Transient Survey

image cutout
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Proposed Observations for Seimei/KOOLS-IFU
expectation: ~15 candidates per semester w/ ~> 1 mag day-1(up to 150 Mpc)
“flash spectroscopy” (<1 day after Tomo-e discovery)~4 objects (among ~15) per semester
more (~4 more times) follow-up w/ Seimei/KOOLS-IFU
Discoveries, identification, & characterization of a few rapidly evolving transients

Other Follow-ups
multi-band light curves
automated follow-up w/ MITSuME(w/ K. Murata et al.)Tomo-e Gozen survey: bright enoughFigure 4 domestic
The first telescopes
supernova discoveredfor OISTER
Tomo-e Gozen.
This supernova
was spediscovery==> follow-up
within thescopicallyobserved with Seimei/KOOLS-IFU
samenight

Gemini-N/GMOS and identified as a Typez = 0.025. From left to right, 6-second Te Gozen discovery image, PS1 reference imFigure 3 Light curves of rapid transients withsubtracted image (Tomo-e−PS1), and follo
planned epochs of KOOLS-IFU spectroscopy. @Our Seimei
proposal (fromKanata/HOWPolIC Tanaka+2016)-band image.
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Tomo-e Gozen High-Cadence Transient Survey

Seimei UM 2020

2020/08/17-19

Summary
Let’s catch supernovae (and other transient phenomena) in early-phase (rightafter explosions).
Tomo-e Gozen was completed in April 2019.
Northern Sky Transient Survey has been started since Nov. 2018 w/ partiallycompleted Tomo-e Gozen.
full operation w/ completed Tomo-e Gozen started in Oct. 2019.
7,000 deg / 2 hours, 18 mag depth ==> 2,000 deg2 / 0.5 hours, 18 mag depth
almost all-sky data are taken at least once during a night.
All the northern sky regions (Dec>0) have been observed at least once.
survey planning w/ statistical approach (Joao, Ikeda, TM, et al. in prep.)
additionally consider weather conditions (avoid cloudy region and choose clearsky region)
Development of automatic data reduction pipeline & website I/F are almost done.
Machine-learning technique (CNN) to pick up only real sources developed.
Automatic alerts (to MITSuME & Seimei) in near-future?
quick follow-up observations w/ Seimei, Kanata, etc. (OISTER), Gemini, etc.
“flash” spectroscopy w/ KOOLS-IFU
fully utilize “2 Hz” data to search for more rapid transients in future
see our pilot study in Richmond+2020
Please contact us (Morokuma, Ohsawa, or Sako) if you are interested in thesurvey, data, Tomo-eetc.Gozen High-Cadence Transient Survey
13Seimei UM 2020
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