Speaker
Description
4U 1556-60 is an X-ray binary that was discovered more than 50 years ago as a persistent X-ray source. However, very little was known about it, including fundamental properties such as its distance, whether the accreting compact object was a black hole or neutron star, and its orbital period. Recently, Gaia Data Release 3 has provided a parallax for the optical counterpart of 4U 1556-60, placing it only 700 pc away and making it one of the closest X-ray binaries known to date. Motivated by this new distance, we have re-investigated 4U 1556-60 using both old and new data, and found that this X-ray binary might be quite unusual and intriguing. Our conclusion is that 4U 1556-60 is most likely to be a very faint ultracompact neutron star X-ray binary at 700 pc. Interestingly, there appears to be residual hydrogen in the accretion disk, it has never been observed to undergo a thermonuclear burst, and furthermore it has a radio upper limit that makes it one of the weakest X-ray binary jets known to date. These results and others have provided a fresh perspective on 4U 1556-60, and motivate future follow up work to better understand its properties as a very nearby and possibly rare class of X-ray binary.
| Talk category | NOVA Network 3 |
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