Supernova Erupts in M101


— As of November 10th: Down to visual magnitude 12.5, deep orange color, and getting ever lower after sunset.

— As of September 15th, the supernova was still holding at its peak of magnitude 10.0 where it had been for a week, though now with slight signs that it's beginning to fade; see up-to-date light curve. The supernova is easy in a 6-inch scope despite moonlight, though its galaxy is invisible in a bright sky. A window of moonless observing time starts opening up again right after dark on September 16th or 17th. Although it looks just like any star, it's thousands of times more distant that any other that's visible in amateur telescopes from northern latitudes.

— The supernova was up to magnitude 13.8 on the American evening of August 25th, one day after discovery, and 12.4 on the evening of the 27th. By the evening of the 29th it was up to 11.5 and easier to spot than the galaxy itself in moderately light-polluted skies. On the evening of the 30th, S&T's Tony Flanders put it at 11.2. It held By the evening of September 5th it was magnitude 10.2. It was holding steady at its peak magnitude of 10.0 from about September 9th through 15th.


Good news for those of you who missed out on June's supernova in the Whirlpool Galaxy, M51: You can slew just across to the other side of the Big Dipper's handle to track another stellar explosion.

Supernova in M101, August 22-24
This one's located in the face-on spiral M101, sometimes called the Pinwheel Galaxy. It was discovered on August 24th at magnitude 17.2 by the Palomar Transient Factory (PTF), an automated supernova search being conducted with the 1.2-m Oschin Schmidt Telescope at Palomar Observatory in southern California.

Since the same telescope saw nothing at the same location one day earlier (limiting magnitude = 20.6), the stellar explosion must have been caught mere hours after its onset. According to PTF participant Andy Howell (University of California, Santa Barbara), never before has a Type Ia supernova been discovered so early in its brightening. "As soon as I saw the discovery image I knew we were onto something big," he says.

Designated SN 2011fe (though dubbed "PTF 11kly" initially), the supernova brightened rapidly. It had already climbed to 13.8 by 20h Universal Time on August 25th, as noted by Krisztián Sárneczky at Konkoly Observatory in Hungary. Spectra taken earlier that day at Lick Observatory show very broad, blueshifted absorption lines from ionized calcium and silicon blasting outward at 14,500 to 16,500 km per second — and no hydrogen lines. These are characteristics of a Type Ia supernova: the complete thermonuclear destruction of a carbon-oxygen white dwarf star that had been collecting mass in a binary system.

The supernova was up to magnitude 13.8 on the American evening of the 25th and 12.4 on the evening of the 27th. S&T's Alan MacRobert estimated it at 11.5 on the American evening of the 29th (August 30.1 UT) using a 12.5-inch scope at 75× and an AAVSO comparison-star chart. It was holding steady at its peak magnitude of 10.0 from about September 9th through 15th.

Supernova in M101
Peter Nugent / Palomar Transient Factory
The early detection, combined with the relative closeness of M101 (23 million light-years), makes this a spectacular find for professional researchers. A normal Type Ia supernova at this distance should reach magnitude 10.0 at its peak, if none of its light is absorbed by interstellar matter in M101. That's well within visual reach in a 4-inch telescope — and much brighter than the galaxy appears visually! In a light-polluted sky you'll be using the supernova to find the galaxy rather than vice versa.

If you haven't yet tracked down this evolving fireball, do it soon. The Dipper's handle is getting lower after dark, and moonlight has been returning to the evening sky since September 3rd.

Relatively bright at 8th magnitude but large and diffuse, M101 sits north of the last two stars in the Big Dipper's handle, forming a roughly equilateral triangle with them 6° on a side. The supernova is located about 4.4 arcminutes south (and a bit west) of M101's center at right ascension 14h 03m 05.8s, declination +54° 16′ 25″.

Here's the American Association of Variable Star Observers' Special Alert that went out August 24th with a link to comparison-star charts and other observing info.

Here's a light curve of magnitude measurements (visual, R, V, and B) that the AAVSO has received.

You can create and print out comparison-star charts at various scales, depths and orientations using the AAVSO's chart-making utility. Enter the star name SN 2011fe.

See also the AAVSO's Supernova 2011fe web page.

11 thoughts on “Supernova Erupts in M101

  1. EM Jackson

    I can’t bve sure but would like to know if it is possible that last night 8-24 to early 8-25 I waqs looking up in the general direction of this super nova and witnessed a bright flash not like a shooting star but a flash with a short stubby tail pointed downward. Could that have been the super nova I saw flash? Thank you for any help.

  2. Navneeth

    EM Jackson,
    You can see from the slides from Palomar that the SN had already appeared by the night of the 23rd. (Sorry to burst your bubble.)


    P.S.: Would the webmaster consider making the comments section threaded?

  3. Ernie Ostuno

    I observed the supernova at 0415 UTC on September 6th with a 13.1 inch Dobsonian. Using the AAVSO finder charts I estimated it at around 10.2 magnitude, easily brighter than the core of M101. Also got a nice look at Comet Garradd. Hopefully the supernova will still be fairly bright when the moon is out of the way again next week.

  4. AstroDr.Mike (AstroDoc)

    I was able to clearly see SN 2011fe in M101 using mounted 16 x 60mm Pentax binoculars on Saturday night 9/3/11. The observation was confirmed by another highly experienced observer using mounted 17 x 70mm Fujinon binoculars. We estimated the supernova at between magnitude 10.1 and 10.3 using nearby field stars. The supernova was very bright in my C-14 the same night. This is a binocular supernova!

  5. Steven Christenson

    I photographed the supernova on the evening of September 22, 2011 from a not particularly dark sky. If the brightness has indeed peaked it certainly doesn’t seem like it’s fading away very quickly!

    The supernova is easily brighter than the M101 core. While my images are less than stellar, it was exciting to see both the galaxy and the supernova quite clearly.

    Using World Wide Telescope for a "before" image, it is easy to see the supernova.

    It will be interesting to image it more in the coming weeks to see how it changes (and, of course to improve my technique).

    Your comments and questions are welcomed.

  6. Pingback: Pro-Am Collaboration Yields Stunning Images

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