TY - JOUR
T1 - Radio and optical follow-up observations of a uniform radio transient search
T2 - Implications for gamma-ray bursts and supernovae
AU - Gal-Yam, Avishay
AU - Ofek, Eran O.
AU - Poznanski, Dovi
AU - Levinson, Amir
AU - Waxman, Eli
AU - Frail, Dale A.
AU - Soderberg, Alicia M.
AU - Nakar, Ehud
AU - Li, Weidong
AU - Filippenko, Alexei V.
PY - 2006/3/1
Y1 - 2006/3/1
N2 - We present the first full characterization of the transient radio sky via radio and optical follow-up observations of all the possible radio transients we have discovered in a survey covering ≈1/17 of the sky. The two confirmed radio transients turn out to be an optically obscured radio supernova (SN) in the nearby galaxy NGC 4216, the first such event to be discovered by a wide-field radio survey, and a source not associated with a bright host galaxy. We speculate that this second source may be a flare from a peculiar radio-loud AGN, or a burst from an unusual Galactic compact object, but its nature merits further study. We place an upper limit of 65 radio transients above 6 mJy over the entire sky (95% confidence level). The implications are as follows. First, we derive a limit on the typical beaming of GRBs; we find fb -1 ≳ 60, ∼5 times higher than our earlier results [f b-1 ≡ (θjet2/2) -1]. Second, our results impose an upper limit on the rate of events that eject ≳1051 ergs in unconfined relativistic ejecta, whether or not accompanied by detectable emission in wavebands other than the radio. Our estimated rate, n ≤ 1000 yr-1 Gpc-1, is about 2 orders of magnitude smaller than the rate of core-collapse SNe (and Type Ib/c events in particular), indicating that only a minority of such events eject significant amounts of relativistic material, which are required by fireball models of long-soft GRBs. Finally, we show that wider and/or deeper radio variability surveys are expected to detect numerous orphan radio GRB after-glows and illustrate the great potential of new radio instruments to revolutionize the study of nearby SNe.
AB - We present the first full characterization of the transient radio sky via radio and optical follow-up observations of all the possible radio transients we have discovered in a survey covering ≈1/17 of the sky. The two confirmed radio transients turn out to be an optically obscured radio supernova (SN) in the nearby galaxy NGC 4216, the first such event to be discovered by a wide-field radio survey, and a source not associated with a bright host galaxy. We speculate that this second source may be a flare from a peculiar radio-loud AGN, or a burst from an unusual Galactic compact object, but its nature merits further study. We place an upper limit of 65 radio transients above 6 mJy over the entire sky (95% confidence level). The implications are as follows. First, we derive a limit on the typical beaming of GRBs; we find fb -1 ≳ 60, ∼5 times higher than our earlier results [f b-1 ≡ (θjet2/2) -1]. Second, our results impose an upper limit on the rate of events that eject ≳1051 ergs in unconfined relativistic ejecta, whether or not accompanied by detectable emission in wavebands other than the radio. Our estimated rate, n ≤ 1000 yr-1 Gpc-1, is about 2 orders of magnitude smaller than the rate of core-collapse SNe (and Type Ib/c events in particular), indicating that only a minority of such events eject significant amounts of relativistic material, which are required by fireball models of long-soft GRBs. Finally, we show that wider and/or deeper radio variability surveys are expected to detect numerous orphan radio GRB after-glows and illustrate the great potential of new radio instruments to revolutionize the study of nearby SNe.
KW - Gamma rays: bursts
KW - Supernovae: general
UR - http://www.scopus.com/inward/record.url?scp=33645000378&partnerID=8YFLogxK
U2 - 10.1086/499157
DO - 10.1086/499157
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
AN - SCOPUS:33645000378
SN - 0004-637X
VL - 639
SP - 331
EP - 339
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1 I
ER -