Possible science cases of transient source searches in mm/submm: gamma-ray burst orphan afterglows, and fast radio bursts 戸谷 友則 (TOTANI, Tomonori) Department of Astronomy, Univ. of Tokyo The 3rd workshop onLarge Aperture mm/submm Telescopes in the ALMA era NAOJ, Mitaka, Tokyo 2015/Mar/10
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Possible science cases of transient source searches in mm/submm:
gamma-ray burst orphan afterglows, and fast radio bursts
戸谷 友則 (TOTANI, Tomonori)
Department of Astronomy, Univ. of Tokyo
The 3rd workshop onLarge Aperture mm/submm Telescopes in the ALMA era
NAOJ, Mitaka, Tokyo 2015/Mar/10
Contents✦ orphan afterglows of gamma-ray bursts (GRBs)
✦ as a possible science case for a wide-field, large submm telescope
✦ some comments on fast radio bursts (FRBs)✦ related on the (still largely unexplored) science chance by wide field monitoring of radio sky
the Picture of (long) GRBs
GRB Jets and Orphan GRB Afterglows✦ Suggestions of jet/collimation of GRBs
✦ Too large isotropic energy > 3×1054 erg✦ Breaks in light curves of afterglows
✦ Prediction of the jet hypothesis: orphan afterglows without prompt GRBs✦ A test of GRB jet/collimation✦ no convincing detection so far
Past Radio Transients Survey at ~GHz✦ FIRST survey transient search (Thyagarajan+’11)
✦ 8444 deg2, down to 1 mJy @ 1.4 GHz✦ 1627 variable sources detected, more than half unidentified!
✦ MOST 22-yr transient object search (Bannister+’11)✦ 2776 deg2, down to 14 mJy @ 843 MHz✦ 57 highly variable and 15 transient sources✦ most of them suspected to be scintillating AGNs
Expected Event Rate in submm Wide Survey✦ ~10 deg2, 0.1 mJy (5σ) @ 2 mm by ~ month scale survey✦ LST info from Kohno-san
✦ strong orphan effect at Fν(150GHz) <~ 1 mJy ✦ Nexp/Non-axis ~ 50 at 0.1 mJy
✦ A deep and large survey by LST should be able to detect orphan afterglows!
LST FIRST
FRBs
Fast Radio Bursts: A New Transient Population at Cosmological Distances
✦ the first one event reported by Lorimer et al. (2007), confirmed by Thornton et al. (2013)✦ ~Jy level flux at GHz frequency ✦ intrinsic pulse width <~ 1 msec (observed width broadened by scattering)✦ dispersion measure indicates z ~ 0.5-1✦ ~ 104 /sky /day ~ 4×104 yr-1 Gpc-3 (z < 1, 〈z〉=0.75)✦ many proposed scenarios:
✦ SGR giant flares, delayed collapse of hyper massive NS, NS-NS mergers, WD-WD mergers, ...✦ a unique probe for ionized IGM (=missing baryon!)
Thoronton+’13
FRB search in submm/mm?✦ similar FoV of LST to Parkes
✦ a similar FRB detection rate if the sensitivity to msec burst is same?
✦ nothing known for SED of FRBs ✦ coherent emission✦ perhaps similar to pulsars?✦ still variety in radio spectrum
✦ short time delay by dispersion✦ difficult to measure DM?✦ difficult to discriminate from noise events?
✦ better angular resolution✦ ~15 min at Parkes, ~10 arcsec by LST✦ good to identify counterparts/host galaxies
some general thoughts... ✦ FRBs as a good lesson:
✦ discovery of z=0.5-1 sources first by a big radio telescope with a FoV of ~1 deg2
✦ in optical, this is similar to a search for z~1 supernovae by Subaru!✦ the bright, transient radio sky seems to be largely unexplored.
✦ Bohdan Paczynski’s words on optical astronomy ✦ "We do not know what is happening in the sky in real time, even at the bright end. This is a huge gap in astronomical research, which can be filled only with small, wide-angle instruments."
✦ "It's sort of embarrassing to the astronomical community that the brightest sky is so poorly mapped"✦ from "The Future of Small Telescopes in the New Millennium", ed. T.D. Oswalt
✦ Same can be said for radio, or even worse✦ discussion of large mm/submm telescopes after ALMA started to work!
✦ Many exciting new phenomena yet to be discovered by wide field radio surveys?