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MAXI Reveals Previously Unknown Brilliant X-Ray Explosion

26/10/2010

A team of astronomers have published their observations of an object that has began emitting high energy X-rays. This object, which was previously hidden within out Milky Way galaxy, was observed to be emitting from the constellation Centaurus (right ascension: 14h 09m 02.40s; declination: -61.3° 21′ 2.26″).

The object, a binary system, was revealed recently when an instrument on the International Space Station named MAXI (Monitor of All-Sky X-ray Image) on the Exposed Facility of the Japanese Experiment Module “Kibo”, which literally caught it in the act of erupting with a massive blast of X-rays known as an X-ray nova. The MAXI mission team quickly alerted astronomers worldwide to the discovery of the new X-ray source at 2:00 a.m. EDT on Wednesday, 20 October 2010, and NASA’s Swift Observatory quickly conducted an urgent “target-of-opportunity” observation nine hours later, which allowed for the location of the X-ray nova to be measured accurately.

The BAT hard X-ray transient monitor confirms the detection of MAXI J1409-619 in the 15-50 keV band.  Analysis of archival images at the XRT position shows that the source was first detected two days earlier on the 18th of October, 2010.

Just what is this stellar x-ray ‘nova’ explosion? X-ray novae are believed to be short-lived events, with an initial bright burst that falls off over a period of weeks or months. Their source is generally understood to be material falling into a black hole or accreting onto a neutron star.

The collaboration between the Swift XRT and MAXI  have allowed researchers to quickly and accurately identify this new object. MAXI and Swift’s abilities are uniquely complementary, and in this case have provided a discovery that would not have been possible without combining the knowledge obtained from both.

The Swift detection confirmed the possible presence of the previously unknown luminous X-ray source, which was designated (all be it rather unforgettably!): ‘MAXI J1409-619’.

Based on the shape of the light curve, the characteristics of the X-ray spectrum (both the flux and the “hard” X-ray photon index), the location close to the Galactic plane combined with the presence of an IR counterpart close to the XRT error circle, MAXI J1409-619 may be a good Soft X-ray Transient (SFXT) candidate.

The Swift observation suggests that this source is probably a neutron star or a black hole with a massive companion star, located at a distance of a few tens of thousands of light years from Earth in the Milky Way. The contribution of Swift’s X-ray Telescope to this discovery is that it can swing into position rapidly to focus on a particular point in the sky and it can image the sky with high sensitivity and high spatial resolution.

MAXI has established its capability to discover X-ray novae over great cosmic distances. It therefore comes as no surprise that the MAXI team has been commissioned to further conduct coordinated observations with NASA satellites to reveal the exact identity of this source.

References:

  • Patterson, J. (1984) The Evolution Of Cataclysmic & Low-Mass X-ray Binaries (LMXBs). Astrophysical Journal Supplement Series, (ISSN 0067-0049) 54 (1) pp. 443-493.
  • Hellier, C. (2001) Catacysmic Variable Stars. London: Springer Press.
  • Schwarz, G.J et al., (2007) Swift X-ray Observations Of Classical Novae. The Astrophysical Journal, 663 pp.505-515.
  • Kennea, J.A. et al., (2011) Swift Observations Of MAXI J1659–152: A Compact Binary With A Black Hole Accretor. The Astrophysical Journal, 736 (1) pp.65-74.

Further Reading:

  • Hellier, C. (2001) Catacysmic Variable Stars, London: Springer Press.
  • Madrid, J.P et al., (2006) Discovery of Thirteen Novae Candidates in M87. The Astrophysical Journal, 654 pp.41-44.
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