On the nature of the

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On the nature of the Long-duration radio
transients
Eran Ofek CALTECH
Collaborators B. Breslauer, A. Gal-Yam, D.
Frail, S.R. Kulkarni, P. Chandra, M. Kasliwal,
E. Waxman, N. Gehrels
Einstein Fellows symposium October 2009
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Talk Layout
A new class Long-duration radio
transients
Summary of observational facts
What are they? Speculations
New observations
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Bower et al. (2007)
944 epochs, 1/week, for 22 years _at_ 5GHz
7 transients, fluxes 0.3-1.7mJy
Time scale lt 1 week, gt20 min
Optical counterparts ggt27.6, Rgt26.5, Kgt18
No X-ray in ROSAT
Galactic latitude b37o
Circular polarization lt30
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Long-duration radio transients
Lack of counterparts
Ofek et al. 2009
Kgt20.4 mag
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A Search for Radio transients
The FIRST-NVSS survey
Levinson et al. (2002) Gal-Yam et al. (2006)
Comparison of the NVSS and FIRST radio surveys
Area 2500 sq. deg
Flux limit 6mJy _at_ 1.4 GHz
1 transient candidates (SN in NGC4216)
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Yet, some more
Kida et al. (2008)
6 bright (gt1 Jy) transients detected by the Nasu
Pulsar Observatory, No localization Similar time
scales (lt1 day)
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Long-duration radio transients
Rates
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Long-duration radio transients
Log N Log S
Ofek et al. 2009
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Long-duration radio transients
Surface density of progenitors
7 events within 8 in Bower et al. (2007)
If catastrophic
If repeaters
rate
Number of progenitors in the Universe gt4x1016
Sky surface density Sgt60 deg-2 (_at_95 CL)
_at_ b37o
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Progenitors Extragalactic?
Ovaldsen et al. (2007)
analytic
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Progenitors? - Galactic
Many 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
High velocities _at_ birth
Large scale height
Abundant at high Galactic latitudes
Large energy reservoir rotational,
magnetic, accretion
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Ofek 09, Ofek et al. 09
Isolated-old NSs?
All
Birth rate
Init. Vel. Dist.
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Isolated-old NSs?
Distance distribution at the direction of the
Bower et al. field
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Ofek et al. 2009
Energetics NSs?
Repetition time scale
Mean luminosity 1025 erg s-1
Total energy 1043 erg
Magnetic 1041 erg
Rotational 1044 erg
NSs Energy reservoir
Accretion 1045 erg
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Isolated-old NSs?
Fireball model Incoherent synchrotron radiation
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Isolated-old NSs?
Fireball model Incoherent synchrotron radiation
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Ofek et al., in prep.
New observations
30 VLA hours (August 2008)
Target 150 fields at low Galactic latitude
11 epochs
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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 i24 for one source - no XRT
source within 2 days
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Predictions
If 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