科研之友
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摘要
We present a search for fast optical transients (tau similar to 0.5 hr-1 day) using repeated observations of the Pan-STARRS1 Medium-Deep Survey (PS1/MDS) fields. Our search takes advantage of the consecutive (gP1rP1) observations (16.5 minutes in each filter), by requiring detections in both bands, with non-detections on preceding and subsequent nights. We identify 19 transients brighter than 22.5 AB mag (S/N greater than or similar to 10). Of these, 11 events exhibit quiescent counterparts in the deep PS1/MDS templates that we identify as M4-M9 dwarfs at d approximate to 0.2-1.2 kpc. The remaining eight transients lack quiescent counterparts, exhibit mild but significant astrometric shifts between the g(P1) and r(P1) images, colors of (g - r)(P1) approximate to 0.5-0.8 mag, non-varying light curves, and locations near the ecliptic plane with solar elongations of about 130., which are all indicative of main-belt asteroids near the stationary point of their orbits. With identifications for all 19 transients, we place an upper limit of RFOT(tau similar to 0.5hr) less than or similar to 0.12 deg(-2) day(-1) (95% confidence level) on the sky-projected rate of extragalactic fast transients at less than or similar to 22.5 mag, a factor of 30-50 times lower than previous limits; the limit for a timescale of similar to 1 day is R-FOT less than or similar to 2.4x10(-3) deg(-2) day(-1). To convert these sky-projected rates to volumetric rates, we explore the expected peak luminosities of fast optical transients powered by various mechanisms, and find that non-relativistic events are limited to M approximate to -10 to approximate to-14 mag for a timescale of similar to 0.5 hr to similar to 1 day, while relativistic sources (e. g., gamma-ray bursts, magnetar-powered transients) can reach much larger luminosities. The resulting volumetric rates are less than or similar to 13 Mpc(-3) yr(-1) (M approximate to -10 mag), less than or similar to 0.05 Mpc(-3) yr(-1) (M approximate to -14 mag), and less than or similar to 10(-6) Mpc(-3) yr(-1) (M approximate to -24 mag), significantly above the nova, supernova, and gamma-ray burst rates, respectively, indicating that much larger surveys are required to provide meaningful constraints. Motivated by the results of our search, we discuss strategies for identifying fast optical transients in the Large Synoptic Survey Telescope main survey, and reach the optimistic conclusion that the veil of foreground contaminants can be lifted with the survey data, without the need for expensive follow-up observations.
- 出版日期2013-12-10
