4U 1700-37 is one of the stronger binary X-ray sources

X-ray binary

X-ray binaries are a class of binary stars that are luminous in X-rays.The X-rays are produced by matter falling from one component, called the donor to the other component, called the accretor, which is compact: a white dwarf, neutron star, or black hole.The infalling matter releases...

 in the sky.
It was discovered by the Uhuru

Uhuru (satellite)

Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...

 satellite.
The "4U" designation refers to the Fourth (and final) Uhuru catalog.
It is associated with a bright (6.53 V magnitude) supergiant Of star HD 153919, which is orbited by an accreting compact object that must be either a neutron star

Neutron star

A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

 or a black hole

Black hole

A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

.
The X-ray source is eclipsed by the star every ~3.4 days, but no pulsations have yet been observed.
The source is one of the ten brightest persistent X-ray sources in the 10-100 keV hard X-ray energy region.
External links

• SIMBAD http://en.wikipedia.org/w/index.php?title=4U_1700-37&action=submit