HSC Transient Survey
Nozomu Tominaga(Konan Univ./Kavli IPMU)

3rd Mar 2017
マルチメッセンジャー天文学研究会

Contents• Optical transient survey• HSC transient survey
Short transients• HSC follow-up survey
Gravitational waves
Fast radio bursts

Optical transient survey

Optical transient survey~ Supenova survey

Amateur & traditional
supernova survey• Targeted nearby galaxies

Untargeted opticaltransient surveys since 1995

Rau+09Subaru/Hyper Suprime Cam• Hyper Suprime-Cam (HSC)• Diameter: 8.2m, FoV: 1.77deg2, ~900M pixels• mlim (5s) w/ 1min: 24.5(i), 23.8(z)(DECam 1min: 23.3(i), 22.5(z))

HSC

1.5deg

HST/WFCSuprime-Cam

Survey power “Etendue” oftelescopes/cameras
W

HUGE data is provided by HSC• 104 science CCD chips ~ 900M pixels• hscPipe (HSC data analysis pipeline) is available.
http://hsc.mtk.nao.ac.jp/pipedoc_e/index.html

These are required for stationary objects.
The data analysis probably takes >1 week.

How about transient surveys?
• data flow: ~4TB/night (strategy-dependent)• 200-300 exposures/nights• raw data: ~2GB/exposure• processed data: ~26GB/exposure• final data: ~36GB/epoch/field• hscPipe is designed for stationary objects.
Some modifications are required.

Subaru system
Raw data

Real-time transient
detection systemtransfer
HSC on-site system
Raw data

I stayed Subaru observatory ~1 week for the initial setup.
2012-2015

Bias, flat, WCS,absmag
Primary
reduceddata

Morokuma, NT, Tanaka, et al.
Transient server
4 nodes (64 cores)
30TB storage

Candidatecatalog[mySQL]

Image subtraction

Sourcedetection

uploadweb page
PHP, mySQL

Warping
Coadding
dithered image<1hr stacked
data

Subtraction
with template
and previous
images

Subtracted
data

Image cutout, magnitude

How can we discover transients?
-Image subtraction-

How can we discover transients?
-Image subtraction-

How can we discover transients?
-Image subtraction-

The image subtraction is powerfulwhen transients are superposed on host galaxies.

Real-time detection and quick alert+N. Okabe, T.Futamase

http://tpweb2.phys.konan-u.ac.jp/~tominaga/HSC-SN/

SN candidates -Jul 2014-

SN candidates -May 2015-

SN candidates -subtracted-

HSC follow-up survey-Gravitational wave-

天文月報2017年1月号

First detection: GW150914

36+5-4M8 and 29+4-4M8 BHs merged at 410+160-180Mpc

Unscheduled discovery ofGW150914• Signal detection

Skymap of GW150914• Sep 14, 2015, 09:50:45 (UT)
• during engineering run (ER8)• Alert announced• Sep 16, 2015 (+2days)• 2days before scheduled O1 run• False alarm rate (FAR)• <~ 1/month (alert)• < 1/100yrs (Jan 2016)• < 1/203,000yrs (Feb 2016)

LVC + 16

LV-EM follow-ups of GW150914• 25 of 63 observing teams J-GEM• Broad band tiled observation• Observation of nearby galaxies• Spectroscopic follow-up
observations• Optical: ~900deg2 (50% of LIB)
• NIR: ~70deg2 (8% of final map)
LVC + 16

See also Nissanke-san’s talkSubaru/HSC was not available

Alert
GW150914

HSC observing run

HSC is only available at >+21days after GW150914.
The visibility of GW150914 from Mauna Kea was poor.

Second detection: GW151226

14.2+8.3-3.7M8 and 7.5+2.3-2.3M8 BHs merged at 440+180-190Mpc

2015-12-27 16:28:13 (UT) (+1.6days)
GCN/LVC_INITIAL_SKYMAP
TITLE:

GCN/LVC NOTICENOTICE_DATE:Sun 27 Dec 15 16:28:13 UTNOTICE_TYPE:

LVC Initial Skymap

TRIGGER_NUM:

G211117

TRIGGER_DATE:

17382 TJD; 360 DOY; 2015/12/26 (yy/mm/dd)

TRIGGER_TIME:

13133.647758 SOD {03:38:53.647758} UTGROUP_TYPE:

1 = CBC (= compact binary coalescence)

SEARCH_TYPE:

3 = HighMass (including BH)

PIPELINE_TYPE: 4 = GSTLAL
FAR:

6.340e-09 [Hz] (one per 1825.5 days)

CHIRP_MASS:
ETA:-1.0000 [M_solar]-1.000

MAX_DIST:-1.00 [Mpc]

TRIGGER_ID:

0x0

MISC:

0x2100003

error region: ~1300deg2 (90%)

Optical WF follow-ups of GW151226• DECam 28.8deg2 (Cowperthwaite + 16 ApJL)• 3 AGNs and 1 SNIIP (i~21.7 and z~21.5)• PS1 290deg2 (Smartt+16 MNRAS)• 20 SNe from 49 OTs (i~20.5)
No plausible• iPTF 952deg2 (Cenko+16 GCN)
optical counterpart• 2 SNe from 20 OTs (R~20)• MASTER 99% of North (Lipunov+16 GCN)
• 1 PSN from 7 OTs• VST 72deg2 (Grado+16 GCN)
• Skymapper 110deg2 (Yuan+16 GCN)
• 1 OT (i~18.6)• J-GEM collaboration (Yoshida, Utsumi, NT+ 16 PASJ) Yoshida-san’s talkAvailability of Subaru/HSC
GW151226

We have no access to HSC.
Original schedule of Subaru

Availability of Subaru/HSC
GW151226

Updated schedule of Subaru

Observation summary -Subaru/HSC• Date: Jan 7 (+12days), 13, and Feb 6, 2016 (half nights)• Filter: i, z ~50sec exp. (34sec overhead)• Limiting magnitude: i~24.3mag, z~23.6mag• Survey fields: 50 pointing ~ 60deg2
Galactic plane (= high extinction)

50 pointing ~ Total time (5hr - 30min) filter exchange
Exposure +/ 1.4minoverhead/ 2 colori, z/ 2 times# of exposure
per pointing

Regions with the highest
probability were observed.
Yoshida, Utsumi, NT + 17

Candidate selection• Reference frame: Feb 6, 2016
• Science frames: Jan 7 1st, 2nd, 13, 2016
• Detection criteria:• To remove bogus and cosmic rays
• 2 detections with z on Jan 7  red color• Signal-to-noise ratio > 5 s• Elongation > 0.8 of point spread function (psf)• FWHM 0.8-1.3 of psf• Residual after psf subtraction < 3 s• To exclude minor planets• No detection with i on Jan 7 at 0.5-45arcsec• No registered minor planets at <0.5arcsec• To exclude brightening sources  short time scale• Positive sources on difference image (Jan 7 - Feb 6)

Candidates from Subaru/HSC• 1256 candidates remain and visually inspected.
16.8”x16.8”
i-band3.4”x3.4”
Reference

Jan 7 1st

Jan 7 2ndz-band

Light curve

Jan 13

Candidates from Subaru/HSC• Color-magnitude diagram in difference images
NS-BH(100Mpc)

SNIa z=0.1, 0.2, 0.3
SNIIP z=0.05, 0.1, 0.15
SNIbc z=0.05, 0.1, 0.15

NS-NS(100Mpc)
5days
9days

5days

 SN Ia at z=0.2
9days
Yoshida, Utsumi, NT + 16

Candidates from Subaru/HSC• 60 candidates are likely to be astronomicalobjects.
• 20 AGN• 40 SNe• SNe Ia at z<0.3 are dominant• No candidate for an optical counterpart ofGW151226
This is consistent with the fact that
GW151226 was a BH-BH merger at ~440Mpc.
Yoshida, Utsumi, NT + 17

If GW151226 was a nearby NS-NSor BH-NS merger,
BH+NS
50Mpc
PS1
100Mpc
NS+NS 50Mpc
100MpcJ-GEM untargeted survey
J-GEM nearby galaxy obs.

200MpcSubaru/HSC

Summary• Subaru/HSC is the most powerful instrument fortransient searches. However, we should keep in mind
that HSC is not always available and that data
analysis is quite tough.
• Realtime data analysis system works well (with sometroubles) for designed strategies, i.e., SN survey.
• Follow-up obs. with HSC is performed for GW151226.
• Time variability, color evolution, and location arekeys to identify kilonovae from other transients.