OUTBURST OF 15-BOOTIDS METEOR SHOWER

     P. Jenniskens, SETI Institute and NASA Ames Research Center, and Esko Lyytinen, Finland, report activity of the 15-Bootids (IAU shower 923, code FBO) between April 21d22h01m and April 22d00h13m UTC, 2019, corresponding to solar longitude 31.24 to 31.34 deg. (J2000). Six 15-Bootids were detected by low-light video cameras of the CAMS BeNeLux network, coordinated by C. Johannink, during routine observations from 19h50m to 03h15m UTC that night, all between 22h01m and 00h12m UTC. Confirmation comes from the United Arab Emirates Astronomical Camera Network, operated by M. Odeh of the International Astronomical Center in Abu Dhabi, which observed from 16h19m to 01h14m UTC. Four 15-Bootids were detected, all between 23h00m and 00h13m UTC (c.f., April 22 radiant map displayed at http://cams.seti.org/FDL/). 
    The shower's geocentric radiant is centered on R.A. = 213.7 +/- 0.2 deg., Decl. = +11.3 +/- 0.2 deg, with geocentric speed 27.7+/- 0.3 km/s. The meteoroids moved in a prograde long-period comet orbit with orbital elements q = 0.634 +/- 0.004 AU, e = 0.975 +/- 0.038, i = 19.8 +/- 0.5 deg., w = 254.2 +/- 0.5 deg., and Node = 31.3 +/- 0.2 deg. (J2000). The shower was first recognized from activity out of a compact radiant in 2011?2014, when 9 meteors were detected by different meteor networks between 30.86 and 31.01 deg. solar longitude, five of which occurred in 2013 (c.f., Jenniskens et al. 2016, Icarus 266, 384).
    Calculations of the planetary perturbations of a 1-revolution dust trail in this orbit (assuming ejection in 1260 AD) confirm that the dust trail was within 0.001 AU from Earth's orbit in 2013, crossing Earth's orbit at 30.98 deg. solar longitude. The shower may also have been active in 1965, 1972, 1995, and 2003. The next encounter is predicted not until 2027 (centered on 30.66 deg. solar longitude). 
    The orbital elements bear some resemblance to those of the bright comet C/539 W1, with parabolic elements q = 0.16 +/- 0.15 AU, i = 19 +/- 6 deg., w = 246 +/- 40 deg., and Node = 33 +/- 20 deg. (c.f. Hasegawa, 1979, PASJ 31, 257). The broad 2-h duration of the shower, presumably requiring somewhat higher ejection velocities, is consistent with a relatively large comet. The comet may be on its way back to the inner solar system.