Fermi LAT observes gamma rays from a huge thermonuclear explosion in space

May 5, 2015

Huge natural thermonuclear explosions, so called stellar novae, are observed in binary systems consisting of a dense compact white dwarf circling a star. The Fermi LAT has for the first time ever detected gamma-ray emission from such an event. This observation indicates particle acceleration in the shock wave produced by the nova explosion to at least GeV energies.

Huge natural thermonuclear explosions, so called stellar novae, are observed in binary systems consisting of a dense compact white dwarf circling a star. The white dwarf accretes hydrogen-rich material from the massive star onto its surface due to its strong gravity. Eventually, this surface material becomes dense and hot enough to trigger an explosive thermonuclear fusion reaction. The energy released in this process is typically 10^45 erg, corresponding to the energy the sun produces in about 10000 years. V407 Cygni is such a binary star system in which a red giant star transfers mass to its white dwarf companion. On March 10, 2010, Japanese observers found a huge increase in the optical brightness of V407 Cyg, indicating a nova outburst. A similar event had been observed in this system over 70 years ago in 1936.

The Fermi LAT team with significant contributions from KIPAC researcher Rolf Buehler has found a related transient gamma-ray source in the LAT data. Gamma-ray emission has been detected from this source in the time period between between March 12, 2010 and March 16, 2010 with high significance. It is also spatially coincident with the location of V407 Cyg. Given the proximity of the detection in space and time to the nova explosion, it is extremely likely that the gamma
rays originate from this event. It is the first time ever that high-energy gamma rays are observed from a stellar nova. The
observation indicates particle acceleration in the shock wave produced by the nova explosion to at least GeV energies. An astronomers telegram has been sent by the LAT team to notify the astrophysical community of this event and to encourage follow-up observations throughout the electromagnetic spectrum. A more detailed analysis of the Fermi LAT data is currently in progress and will be the topic of a forthcoming publication.