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

Talk Layout

Summary of observational facts

New observations

What are they? Speculations…

A new class: Long-duration radio transients

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%

Long-duration radio transientsLack of counterparts

Ofe

k e

t al. 2

00

9

K>20.4 mag

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)

Yet, some more…Kida et al. (2008)…

6 bright (>1 Jy) transients detected by theNasu Pulsar Observatory,No localizationSimilar time scales (~<1 day)

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

Long-duration radio transientsLog N – Log S

Ofe

k e

t al. 2

00

9

nSSN )(

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

Progenitors – Extragalactic?O

vald

sen e

t al. (

20

07

)

analytic

Progenitors? - GalacticMany Galactic progenitors are ruled out:Flare stars, X-ray binaries, pulsars, magnetars,Evaporating BHs, microlensing,Floating planets,solar flares reflected from asteroids…

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

Isolated-old NSs?Ofek 09, Ofek et al. 09

All

Birth rateInit. Vel. Dist.

Isolated-old NSs?Distance distribution at the direction of the Bower et al. field

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

Isolated-old NSs?Fireball model – Incoherent synchrotron radiation

1

1~/

Hzs rge105~

day5.0~

5

1118

GHz

eB

syn

UU

L

t

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

New observations

30 VLA hours (August 2008)

Target: 150 fields at low Galactic latitude 11 epochs

Ofek et al., in prep.

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

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

End