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The main part of this event took place in early-morning daylight over the UK on September 9, so was best-observed from parts of North America. Reports have suggested a high proportion of meteors were of magnitude +1 and brighter, with some well into the fireball class. The brightest so far seem to have been about magnitude -8.
As David Entwistle mentioned, it has been claimed, including by the IAU, that it was an outburst of the usually-minor September Perseid meteor shower (SPE), which peaks around September 9. No similar outburst has ever been recorded from this source, and its best Zenithal Hourly Rates are normally 5 or so, thus unnoticeable to any but dedicated meteor observers. More information on the SPE is on the September activity webpage as David said.
However, the radiant position determined from 25 video meteors caught by a camera run by the Marshall Spaceflight Center in the USA was around 03h20m RA, +43 deg Dec, while the SPE radiant position for September 9 as found by International Meteor Organization (IMO) visual and video results in recent years is closer to 04h00m RA, +47 deg Dec. In addition, regular Section contributor and video observer Enrico Stomeo near Venice in Italy has already reported a slightly different radiant position to the Marshall result, based on seven meteors he imaged on September 8/9. This was around 03h13m RA, +38 deg Dec. More importantly, Enrico was able to estimate a mean atmospheric velocity for the events he caught of 56 km/sec. This is significantly slower than the typical mean SPE velocity of 66 km/sec. No other observer has yet reported an estimated velocity for these outburst meteors, so this awaits confirmation, but if correct, and taken with the radiant position discrepancies from the known SPE position, it could suggest another, perhaps previously unknown, source was responsible instead.
Enrico mentioned a shower listed by NASA scientist Peter Jenniskens as the Epsilon Perseids. Its radiant is supposed to be active on September 9 at 03h21m RA, +39 deg Dec, with its meteors having an atmospheric velocity of around 64 km/sec, quite a good match for the position Enrico found (if not the velocity), and certainly much closer to the Marshall position than the established IMO SPE one. This radiant position was the same as that called the 'September Perseids' in the initial IAU Electronic Telegram, CBET 1501.
Another minor shower reported by Russian astronomer Alexandra Terentjeva back in 1966 may also lie nearby, the Beta Perseids. It was noted as active from September 10-27, with a radiant probably close to 02h50m RA, +42 deg Dec around September 10, and an atmospheric velocity in the range 59 to 62 km/sec. This too is quite close to the two video positions reported so far.
As for the outburst itself, another regular Section contributor Jeff Brower in British Columbia, Canada, caught it nicely with his all-sky video fireball camera, recording 13 meteors brighter than magnitude +1 between 04:12-12:26 UT on September 9. Eleven of those meteors happened between 07:26-09:21 UT, and there is a suggestion in Jeff's results alone that the peak may have been within a few minutes of 08:01 UT. The mean centre timing for all the meteors like this he recorded was 08:25 UT. The IAU reported the peak as at 08:20 UT +/- 20 mins, with activity lasting for about four hours overall away from this time. The Marshall camera's meteors were recorded between 06:20-10:30 UT.
IAU CBET 1501 also indicated no unusual visual activity was seen by experienced observer Paul Martsching in Iowa, USA from 05h-06h UT, but he caught increased rates thereafter, with many negative magnitude events, while Finnish meteoricist Esko Lyytinen was noted as having found increased radio meteor echo counts from 07:18-10:05 UT, along with our own David Entwistle.
In light of Paul Martsching's report, it's interesting that Enrico Stomeo identified meteors probably from the same radiant as early as 19:52 UT on September 8, but at a rate averaging only one every 1h40m up to 03h UT! The last two meteors he recorded from this source though were at 03:28 and 03:30 UT (his observing session ended at 03:42), which might suggest a mild increase then. Video meteor rates are not directly comparable with what a visual observer might see, so this low rate could easily have passed unnoticed visually, but it might suggest that whatever stream produced the outburst event began encountering the Earth perhaps twelve hours or more before the peak over America.
As I noted on the SPA September webpage, the month has a reputation for producing activity from this general Perseus-Auriga (and nearby) sky, activity which has been seen often only by very few people. This outburst for once was rather better-recorded, so we can hope that after further analysis, we'll have a better idea of just what produced it, and maybe why.
If anyone else was observing on September 8/9 or nights to either side, whether in the UK or elsewhere in the world, and recorded notes on meteor activity they have not submitted yet, further information would be most welcome to help the investigation along.
Alastair McBeath,
Meteor Director, Society for Popular Astronomy.
E-mail: <meteor@popastro.com> (messages under 150 kB in size only, please)
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