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04-12-2009
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Aql X-1 in outburst

Submitter: Valeriu Tudose
Description: Aql X-1 is an X-ray binary system comprising a neutron star and a main sequence star. The compact object is accreting matter from the companion via an accretion disc. Matter is ejected from the system in the form of a relatively narrow outflow called jet.

Aql X-1 exhibits outbursts about once a year, during which the X-ray and optical emissions suddenly increase and, the paradigm says, blobs of matter are launched into interstellar space at near relativistic speeds, forming a more powerful jet.

Generally speaking, the jets can be best observed at radio wavelengths. Unfortunately they are usually very faint, close to the sensitivity limits of radio telescopes. Thus the outbursts offer some of the best opportunities to try to detect them.

In November, Aql X-1 has been very active again. The European VLBI Network (EVN) observed the system at 5 GHz for about 4.5 h. The resulting radio map is shown above. Although Aql X-1 has been detected at radio frequencies during previous outbursts, this is the first time that a high-resolution (mas scale) image of the system has been captured. More interestingly, a marginally significant extended emission component is apparent towards the south-east. This could be the first direct evidence for the presence of a jet in Aql X-1.

ATel 2317
Copyright: V. Tudose, Z. Paragi
 
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