LFBOTs:
interacting transients at the extreme
Daniel Perley(Liverpool JMU)
HST image of AG carinae, a luminous
massive star undergoing intense mass loss

What is an FBOT?
• Transient• Optical (/UV)• Blue (thermal SED; not a GRB afterglow)• Fast (tAHM < 12 days, with rise < few days)• Luminous (Mg < ~ -17; not LBV)
• Single-peaked or first peak dominatesFast, Luminous, Blue Optical Transients
Light curves

SpectraDrout+2014 (Pan-STARRS):
t1/2 < 12 days, Mpk < -16.5
Pursiainen+2018 (DES)
Tanaka+2016 (Subaru)
Rest+2018 (K2)
Ofek+2010 (PTF)

FBOTs in Parameter Space
GRB
afterglows

Superluminous
SNeFBOTSBO
LBV /Imposter.Ia /Ca-richECSNe?

KN
Stellarmergers

4

Modified from
Kasliwal+2011

Physical Considerations• Too luminous to benonterminal• Too fast to beradioactively
powered• Too slow to bestellar shock
breakout

GRB
afterglows

Superluminous
SNeFBOT

MN
MN

~M
i~iej

M
0.1

ej
LBV /
Imposter.Ia /Ca-richECSNe?

KN
Stellarmergers

Kasliwal+2011

Fast transients from shock interaction
The natural model for a fast-rising transient is anenergetic shock (Erad ~ 1050 erg) in extended
material (R ~ vBBtpk ~ 1014-15 cm):+ very limited
nickel production
in explosion (toavoid dominatingshock signature)+ not much
extended CSM (tenuous, extended
envelope (IIb-like)

eruptive shell (Ibn-like)AT2018cow• A fast, luminous event at 60 Mpc• Persistently hot, no sign of known
supernova features; H+He late
• Luminous, fast-variable,X-rays and radio

Prentice+2018

à Requires engine and CSM
and virtually no radioactiveelements (TDE? Failed SN?)
Ho+2019

ZTF: Nearby Fast Transients in Real Time

P48

1.2m: limit ~ 20.5 mag (30s)
47 deg2 FOV

Dedicated Spectroscopic Follow-up

P60

1.8m: spec limit ~ 19 mag (1 hr)

SEDMachine47 deg2 FOVBlagorodnova+2018

Transient Demographics
GRB
afterglows

Superluminous
SNe

FBOT

MN
MN

~M
i~iej

M
0.1ej
LBV /
Imposter.Ia /Ca-richECSNe?

KN
Stellarmergers

11

ZTF Transient Demographics
ï22

Peak absolute magnitude(AB)gSN IaSN IaxSN II
SN IIbSN IInSN Ibn/Icn
SN IbcSN Ic-BLSLSN-ISLSN-II
TDE
LBV
Ca-richILRT
LFBOT
Afterglow
Kilonova
12ï20j

ï18M

Ni~

Mej

ï16M

Ni~

10.

MeL

ï1410

Rest-frame duration (days)

100

Perley+2020

ZTF Transient Demographics"FBOT"

ï22

Peak absolute magnitude
(AB)
g

SN Ia
SN IaxSN II
SN IIbSN IInSN Ibn/Icn
SN IbcSN Ic-BLSLSN-ISLSN-II
TDE
LBV
Ca-richILRT
LFBOT
Afterglow
Kilonova
13ï20j

ï18M

Ni~Mej

ï16M

Ni~

10.

MeL

ï1410

Rest-frame duration (days)

Ho+2022
Perley+2020

100

Shock-dominated II(b)ï20g• "Normal" II / IIb with particularlystrong early shock-cooling phase
and/or underluminous plateauphase• Particularly extreme
pre-SN envelope
inflation and/ormass loss

ï22

ï18

ï16

ï1410100

Ultra-Stripped Ib/c
ï22

ï20g

• Unusually fast, unusually dim
versions of Ib/c SNe, withenhanced pre-explosion mass loss
• Heavy binary stripping by acompanion; possible NS-NS
progenitors• iPTF14gqr (De+2018),
SN2019dge (Yao+2020), etc.

ï18

ï16

ï1410100

Yao+2020Ic-BL with confined CSM
ï20g• Two known FBOT-like* cases:
SN2018gep (Ho+2019, Pritchard+2021)
iPTF16asu (Whitesides+2017)• Spectroscopically normal Ic-BL atlate times with extremely luminous
early CSM interaction; no narrowlines even in 1d spectra: very
confined CSM

ï22

ï18

ï16

ï14
10100

* Other examples exist withsubdominant first peaks

Type Ibn and Icn Supernovae
ï20g• Almost all are very fast(completely different from IIn's!)• No second peak: not much 56Ni
• Luminous but rare:Ibn: ~0.3% of CCSN
Icn: ~0.03% of CCSN

ï22

ï18

ï16

ï1410100

Narrow-line SN Parameter SpaceSLSNïIIï22

Peak absolute magnitude

SN Ia
SN IaxSN II
SN IIbSN IInSN Ibn/Icn
SN IbcSN Ic-BLSLSN-ISLSN-II
TDE
LBV
Ca-rich
ILRT
LFBOT

Icn

ï20IIn

Ibn

ï18

ï16L

ï1410
Restïframe duration (d)100Ibn Light Curves

1998bw

1994I

Underluminous atlate times

Hosseinzadeh+2017

Icn Light Curves

1998bw

pcs
21
20201
9hg
p

1994I

Underluminous atlate times

Davis+2023

Ibn/Icn and progenitor origins• Fast, dense outflows and depletion of H/He arecharacteristic of a very massive star
• Low ejecta and nickel masses indicate very littlematter was expelledà Failed SN / BH-powered transients?

ZTF Transient Demographics"FBOT"

ï22

Peak absolute magnitude
(AB)
g

SN Ia
SN IaxSN II
SN IIbSN IInSN Ibn/Icn
SN IbcSN Ic-BLSLSN-ISLSN-II
TDE
LBV
Ca-richILRT
LFBOT
Afterglow
Kilonova
23

ï20j

ï18

M

Ni~Mej

ï16

M

Ni~

10.

MeL

ï14
10

Rest-frame duration (days)

Ho+2022
Perley+2020

100

ZTF Transient Demographics"FBOT"
Peak absolute magnitude (AB)SN Ia
SN IaxSN II
SN IIbSN IInSN Ibn/Icn
SN IbcSN Ic-BLSLSN-ISLSN-II
TDE
LBV
Ca-richILRT
LFBOT
Afterglow
Kilonova
24j

M

Ni~

Mej

M

Ni~

1
0.

Me

L

Rest-frame duration (days)

Ho+2022
Perley+2020

Radio-Luminous FBOTs
ï22

ï20g

• Objects similar to 18cow(7 analogues now known)• Always very luminous (Mg < -19)
• Luminous X-ray and mm/radio
counterparts (approaching GRBs)• H & He; Complex spectral evolution• Fast X-ray (& optical) variability• Very optically faint at late times• Very rare: ~10-4 CCSN rate(LFBOTs,Cow-like, etc.)

ï18

ï16

ï14
10100

SpectraEarlyLate
Ultra-broad features(No narrow features
before ~5 days)

Yao+2021

Narrow interaction(?) lines:
He and (some) H

Emergence of complex H/He features

Perley+2019

xn

201
dIIn

Relativistic SNe

Normal CCSNew

Ne

8co

Ene
rgeticSndw

200mr
f0x2028co

202

GRB Afterglows

201

Afterglows

Radio luminosity (erg/s)

GRBRe
lativisticTDE20

X-Ray luminosity (erg/s)

X-Ray and Radio

Normal CCSNe

Yao+2021

Ho+2020

X-Ray Spectroscopy & Timing
Compton hump;possible 8 keV Fe line;
possible ~ms QPOs

1

10100

Margutti+2019
Pasham+2023

Very deep limits on SN emissionnd2020x

20

20mrf

20

18

cow

Sustained high TBB and shrinking RBB
t = 3.44

t = 4.22

t = 6.56

104

AT2018cow

103

104

t = 8.81

t = 10.58

t = 14.62"noFlux density fi (µJy)

1018000 K!

3rma l"SN102
t = 16.79

t = 18.78

t = 22.16t = 26.16

t = 31.52

t = 35.24

103

040

102030Time in days (MJD-58285)

102

103

1014 cm!

102

103

104

103

104

103

104

Wavelength (Å)

Perley & Metzger 2023

0102030

Time in days (MJD-58285)

40

Perley+2019

Host Galaxies & Environment
IIIIn

IIb
Ibn

Ib/c
Icn

Ic-BL
18cow-like

Star-formation rate (M O• yr-1)

101

100

2021csp
2019hgp
2019hgp

2018cow
2018cow

10-1

10-2(4 Myr)

10-3
106

107

108
109
Stellar mass (M O• )

1010

1011

Sun+2023

Still There, Even Hotter & Smaller

At 2-4 years:
TBB ~ 105 K
RBB ~ 10 R⊙
LBB ~ 107 L⊙

Sun+2022

Key Observational Constraints••
••••
•••
•

Early ejecta velocity ~0.2c+ Minute-long,Fastest ejecta up to ~0.5c in some objects
1047 erg
44.550
Lpeak ~ 10erg/s (2 days); Erad ~ 10 erg
optical/X-Ray
flares occur
Dense (106 cm-3), confined (1017 cm) CSM
every few
LX ~ 1043 erg/s; variable on 1-day timescales
hours 1-3
months postHe-rich material with some H
explosion
Ejecta mass <~ 1 M⊙; M56Ni <~ 0.1 M⊙(next talk)Star-forming hosts (Z ~ 1/3-2/3 Solar)
Not nuclear; not in a young dense cluster
Extremely hot, luminous, optically-thick "remnant"Some Models• Massive star à NS (Prentice+2018)• Massive star à BH (Perley+2019, Margutti+2019)• Massive star à PPISN (Leung+2020)• IMBH + WD (Kuin+2019)• IMBH + MS (Perley+2019, Kremer+2019)• WD + WD (Lyutikov+2019)• BH + WR (Metzger 2022)• NS + RSG (Soker+2019)