On the nature of the Long-duration radio transients
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On the nature of theLong-duration radio transients
Eran Ofek
CALTECHCollaborators:
B. Breslauer, A. Gal-Yam, D. Frail, S.R. Kulkarni, P. Chandra, M. Kasliwal, E. Waxman, N. Gehrels
Einstein Fellows symposiumOctober 2009
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Talk Layout
Summary of observational facts
New observations
What are they? Speculations…
A new class: Long-duration radio transients
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Bower et al. (2007)
944 epochs, 1/week, for 22 years @ 5GHz
7 transients, fluxes: 0.3-1.7mJy
Time scale < 1 week, >20 min
Optical counterparts: g>27.6, R>26.5, K>18
No X-ray in ROSAT
Galactic latitude: b~37o
Circular polarization <30%
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Long-duration radio transientsLack of counterparts
Ofe
k e
t al. 2
00
9
K>20.4 mag
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A Search forRadio transients
Comparison of the NVSS and FIRST radiosurveys
Area: ~2500 sq. deg
Flux limit: 6mJy @ 1.4 GHz
Levinson et al. (2002)Gal-Yam et al. (2006)
The FIRST-NVSS survey
1 transient candidates (SN in NGC4216)
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Yet, some more…Kida et al. (2008)…
6 bright (>1 Jy) transients detected by theNasu Pulsar Observatory,No localizationSimilar time scales (~<1 day)
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Long-duration radio transientsRates
1214.1
12
1
590,290330,20037.05
12
1
64.1
yrdeg002.0~
deg5.0
540
)%95(@deg5.0
1.1
-JyGHz
durmJyGHz
durmJyGHz
R
yrday
tR
CLyrday
tR
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Long-duration radio transientsLog N – Log S
Ofe
k e
t al. 2
00
9
nSSN )(
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Long-duration radio transientsSurface density of progenitors
7 events within ~8’ in Bower et al. (2007)
Sky surface density>60 deg-2 (@95% CL)
If repeaters If catastrophic
Number of progenitorsin the Universe
>4x1016
@ b~37o
rate
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Progenitors – Extragalactic?O
vald
sen e
t al. (
20
07
)
analytic
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Progenitors? - GalacticMany Galactic progenitors are ruled out:Flare stars, X-ray binaries, pulsars, magnetars,Evaporating BHs, microlensing,Floating planets,solar flares reflected from asteroids…
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Isolated-old NSs?
Large population in the Galaxy: 108-109
Large energy reservoir: rotational, magnetic, accretion
High velocities @ birth
Large scale height
Abundant at high Galactic latitudes
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Isolated-old NSs?Ofek 09, Ofek et al. 09
All
Birth rateInit. Vel. Dist.
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Isolated-old NSs?Distance distribution at the direction of the Bower et al. field
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Energetics – NSs?Ofek et al. 2009
ergday
t
Hzkpc
d
mJy
SE durflare
5.01011102
10
2
32
yrR
tb
1
22 500deg102.0
Repetition time scale:
Mean luminosity: 1025 erg s-1
Total energy: 1043 erg Magnetic: ~1041 erg
Rotational: ~1044 erg
Accretion: ~1045 erg
NSs Energy reservoir
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Isolated-old NSs?Fireball model – Incoherent synchrotron radiation
1
1~/
Hzs rge105~
day5.0~
5
1118
GHz
eB
syn
UU
L
t
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Isolated-old NSs?Fireball model – Incoherent synchrotron radiation
1
1~/
Hzs rge105~
day5.0~
5
1118
GHz
eB
syn
UU
L
t
Hz 102
K104
cm 103
cm 106
66
G 17
11s
11
35
10
e
B
e
T
n
R
B
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New observations
30 VLA hours (August 2008)
Target: 150 fields at low Galactic latitude 11 epochs
Ofek et al., in prep.
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New observations
30 VLA hours (August 2008)
Target: 150 fields at low Galactic latitude 11 epochs
Followup: VLA + Swift/XRT + P60/P200/Keck
Excpectation: ~1 event, detect: 0 (above 2 mJy)Several fainter events still under investigation.For 3 most promising - no optical counterparts i~24+ for one source - no XRT source within 2 days
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PredictionsIf transients are NSs…
Repetition time scale ~ 3 month
Spectral slope – syn. Self absorption
More abundance towards the Galactic center,but details depends on flux limit and distance
Pulsations? – search for pulsars at 5 GHz
Linear polarization, if incoherent syn. radiation
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End