Hiroko Niikura

Constraints on PBH with densecadence HSC observation of M31
Masahiro Takada (Kavli IPMU)
Collaborators: M. Chiba (Tohoku), M. Ishigaki, K. Hayashi, S. More,
Hiroko Niikura, N. Yasuda (Kavli IPMU), T. Sumi (Osaka), R.
Lupton (Princeton), S. Miyazaki, M. Tanaka, F. Yoshida (NAOJ)

Andromeda Galaxy (M31)• In the northernhemisphere (notaccessible from DES,LSST)• Large spiral galaxy• HSC FoV ~ entire M31• ~770kpc (𝜇~24.4),
reachable distance(not too far)!

Primordial Black Hole (PBH)
Capela et al. 13

100FIRAS
Femtolensing
Capture by NSs in GCs,
this work
Star Formation

10 2
WPBH /WDM• Dark matter needed• Can be formed in the earlyuniverse• One of viable candidates ofCDM (based on a minimum
assumption, from Standard
Model particles in principle)• Progenitor of LIGO GW
binary BHs? (Sasaki,Suyama, Tanaka &Yokoyama, PRL 2016; Bird
te al. 16)

EROS+MACHO

10 4

Hawking
WMAP3

10 6

10 8 15
10MPBH ⇠ 1024 g ⇠ MH @ T ⇠ 1010 GeV1020

10251030

BH mass, g10351040

probing PBHs with lensing• If PBHs are (a part of)dark matter, theyshould exist in
between the Earth andM31 (huge volume!)• PBHs causemicrolensing
magnification on starsin M31• Lensing can probe
invisible• HSC can monitor allstars in the bulge anddisk regions of M31

PBH microlensing on M31 star
M31 halo• Lensed image can’t be resolved
with optical resolution (~10-8arcsec) ⇒ only light curve is asignal• So huge volume• MW/M31 halo ~ 1012Msun (weassumed NFW models)• PBH has a peculiar velocity of~200km/s

MW halo
PBH

Paczynski 86

PBH microlensing on M31 star
Cumulative optical depth of PBH microlensing for a single star in M3110 5⌧

10 610 7Assumed

MPBH = 10
10 8101

8⌦PBH
M ,=1
⌦DM102103

dL [kpc]

If we observe ~106 stars at one time, one star atleast should be micro-lensed if PBHs are DM

PBH microlensing event rate
Event rate [events/star/hour/hour]dL ✓EtE ⇠⇠ 34 minvPBH

10 310 4✓

MPBH
10 8 M◆1/2 ✓dL100 kpc

10 10 M
10 9 M

10 5

10 8 M◆✓vPBH200 km/s◆ 1⌦PBH=1⌦DM

10 61010 7 M

710 8
10 9 2106min

10 160min

100101102t̂ [hours] (time scale of ML light curve)

Event rate per unit obs. time and per a given timescale oflight curve for a single star in M31

Hiroko Niikura
HSC dense-cadence observation of M31 (PI Takada)

Got this idea from conversation with Hitoshi
and Masahiro Kawasaki
90sec exposure each (r-band)~35sec readout~190 exposures
No dithering
one clear night (seeing~0.5-0.6’’)
Also used g-data (fromChallenges: Pixel lensing
Fluxes from multiple stars are overlapped at each position

dense star region
Upper left: reference image (0.5’’)
Upper right: target image (0.8’’)
Lower: difference image

Accurate PSF and astrometry
measurements needed.
HSC pipeline works!

21.5

22.0 green: 2min cadence

diff- PSF

mag

diff

23.0
23.5
24.0
24.5
25.0

sum counttarget

time

Ref.

22.5

90
80
70
60
50
40
30
20
10
00

5000

10000
15000
time [sec]

20000

25000

20000

25000

Flare star (M star)
A factor of 10
brightened

05000

10000
15000
time [sec]22magAn entire star disappears for~10min, with a 3hrs interval~10min232425~3hrs

26
27

05000

10000
15000
time [sec]WD – brown dwarf binary
20000

25000

time

So far… no promising candidate :<CCD edge

CCD defect15000

counts

10000

CCD defect

5000
05000

0

5000

10000

15000

20000

25000

1000
500
0500
1000
1500
2000
2500
3000

CCD edge

05000

10000

15000

20000

25000

time [sec]4000

Moving object

2000

counts• ~10,000 candidates• In the end, based on visual inspection• Impose the conditions (fitting to a model
microlensing light curve, …)• No secure candidate of PBH lensing• PS: no contact binary of OB stars

countstime [sec]

0
2000
4000
6000

0

5000

10000

15000

time [sec]

20000

25000
12

Constraint on the PBH abundance
efficiency of detecting microlensing of astar in a given magnitude under ourobservation conditions; estimated using
the simulated microlensing light curves

104

22mag

number counts of source stars in M31

103

23mag

102

26mag

µ [/arcmin2 ]

24mag
25mag

green: HSC peaks
blue: HST stars

101
100
10 110 2
10 32624

2220r[mag]1816summary• HSC is very powerful: ~1min exposure reaches
25-26mag depth for a point source• Image difference technique (already integratedin the standard HSC pipeline)• Tightest upper bound on the PBH abundance:tighter than Kepler 2yrs data & now no allowed
window of PBH mass
• New opportunity for time-domain astronomy with
HSC before LSST: GW counterpart, supernovae,….

HSC hunt of Planet Nine
Fumi Yoshida (PI), MT, Mike Brown, Masaomi Tanaka …

24-26mag