Supernova in M82 Fades and Reddens Supernova 2014J in M82 has faded but, more than six weeks after it exploded, is still in view at about magnitude 12. On January 21st a group of astronomy students spotted a supernova in M82, the famous nearby irregular galaxy in Ursa Major. It peaked at V magnitude 10.5 during the first week of February, and as of March 10th it was still visible in amateur scopes about magnitude 12. Follow the ongoing preliminary light curve provided by the American Association of Variable Star Observers (AAVSO). As can be seen there, the supernova is turning redder. Spectra showed it to be a Type Ia supernova — an exploded white dwarf — with debris originally expanding at up to 20,000 kilometres per second. It is significantly dimmed and reddened by dust in M82 along our line of sight. By one estimate, it would be two magnitudes brighter if we were seeing it in the clear. Update: A February 27th news release from Berkeley: Closest supernova in decades is also a little weird. And from the Space Telescope Science Institute: Hubble Monitors Supernova in Nearby Galaxy M82. Supernova in Messier 82 Before and after. The supernova image, taken remotely by Ernesto Guido, Nick Howes, and Martino Nicolini on January 22.3, saw the exploded star at unfiltered CCD magnitude 11.3. M82 is a near neighbour as galaxies go, at a distance of 11 or 12 million light-years. Its a favourite for amateur astronomers and researchers alike with its thick dust bands, sprays of hydrogen gas, and bright centre undergoing massive star formation. The supernova is not in the central star-forming region but off to one side, 58 arcseconds to the west-southwest. Remarkably, the supernova went undiscovered for nearly a week as it brightened. Prediscovery unfiltered CCD images by Koichi Itagaki of Yamagata, Japan, show nothing at its location to as faint as magnitude 17.0 through January 14.5. But it was magnitude 14.4 on January 15.6, 13.9 on January 16th, 13.3 on January 17th, 12.2 on January 19th, and 11.9 on January 20th. (Images.) So the actual explosion occurred (from Earths viewpoint) late on January 14th or early on the 15th Universal Time. Where to Look M82 is high in the northeast after dark (for observers at mid-northern latitudes) and higher through much of the night. Heres a comparison-star chart from the AAVSO. On the chart north is up, east is left, and the field is ½° wide; star magnitudes are given to the nearest tenth with the decimal point omitted. The galaxy shows up as an elongated swarm of faint dots. (If you want other parameters, you can make your own chart using the AAVSO Variable Star Plotter; for star name enter SN 2014J.) Heres the preliminary light curve with photometry shown in the B, V, and R bands (blue, visual, and red light) as well as eyeball magnitude estimates (shown black). Heres a wide-field view of M81 and M82 including the supernova, for a broader perspective. On the AAVSO discussion thread for SN 2014J, Chris Stephan of Wooster, Ohio, said on January 31st, One thing that I noticed at the telescope is that the comp[arison] stars are pinpoint. There seems like a slight nebulosity around the SN. Ill bet this is from all the galactic dust in M82, and the billions of stars in it that seem so close [to it] from our distance. Has anyone else noticed this? Others say theyve noticed this too and that it has interfered with their visual magnitude estimates. A Flukey Find The first people to recognize the supernova were a group of students — Ben Cooke, Tom Wright, Matthew Wilde and Guy Pollack, assisted by teaching fellow Stephen J. Fossey — taking a quick image at the University of London Observatory (within the London city limits!) on the evening of January 21st at 19:20 UT. The discovery was a fluke, says a university press release, —a 10-minute telescope workshop for undergraduate students that led to a global scramble to acquire confirming images and spectra. The weather was closing in, with increasing cloud, Fossey says. So instead of the planned practical astronomy class, I gave the students an introductory demonstration of how to use the CCD camera on one of the observatory’s automated 0.35-meter telescopes. The students chose M82, a bright and photogenic galaxy, as their target, as it was in one of the shrinking patches of clear sky. While adjusting the telescope’s position, Fossey noticed a star overlaid on the galaxy which he did not recognise from previous observations. They inspected online archive images of the galaxy, and it became apparent that there was indeed a new starlike object in M82. With clouds closing in, they switched to taking a rapid series of 1- and 2-minute exposures through different colour filters to check that the object persisted, and to be able to measure its brightness and colour. The original press release, and a BBC story repeating it, claimed that this is the nearest supernova since Supernova 1987A in the Large Magellanic Cloud. In fact, SN 1993J in M81 was at essentially the same distance within the uncertainties, and two subsequent supernovae, SN 2004am and SN 2008iz (an obscured radio supernova), occurred within M82 itself. However, this is said to be the nearest Type Ia supernova since 1972. Thats the kind that is so valuable for measuring the size and expansion rate of the universe. Despite the dimming and reddening, astronomers hope that SN 2014J will provide new details about exactly what happens in these standard-candle explosions. Supernova in Another Messier Galaxy Meanwhile a fainter supernova, SN 2014L, appeared in M99 in Coma Berenices. It was discovered at about magnitude 17.2 on January 26th (information and images), peaked at about 14.4 around February 8th, and was back down to 15.3 as of February 23rd. M99 is a spiral galaxy about 50 million light-years away in the Virgo Cluster, four times as far as M82. It has hosted three previous known supernovae (1967H, 1972Q, and 1986I) and the odd lesser outburst PTF .
Posted on: Tue, 11 Mar 2014 08:14:29 +0000
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