The Puzzling Negative Orbit-Period Derivative of the Low-Mass X-Ray Binary 4U 1820-30 in NGC 6624
arXiv:1409.4767 · doi:10.1088/0004-637X/795/2/116
Abstract
4U 1820-30 is a low-mass X-ray binary near the center of the globular cluster NGC 6624 consisting of, at least, one neutron star and one helium white dwarf. Analyzing 16 years of data from the Rossi X-ray Timing Explorer (RXTE) allows us to measure its orbital period and its time derivative with unprecedented accuracy to be P = 685.01197 +- 0.00003 s and dP/dt /P = -5.3 +- 0.3x10^-8 yr^-1. Hence, we confirm that the period derivative is significantly negative at the >17 sigma level, contrary to theoretical expectations for an isolated X-ray binary. We discuss possible scenarios that could explain this discrepancy, and conclude that the center of NGC 6624 most likely contains large amounts of non-luminous matter such as dark remnants. We also discuss the possibility of an IMBH inside NGC 6624, or that a dark remnant close to 4U 1820-30 causes the observed shift.
19 pages, 9 figures, ApJ; replaced to conform with published version (minor changes)
References in corpus (4)
- Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
- Gemini and Hubble Space Telescope Evidence for an Intermediate Mass Black Hole in omega Centauri
- Surface Brightness Profiles of Galactic Globular Clusters from Hubble Space Telescope Images
- Dependence of the orbital modulation of X-rays from 4U 1820-303 on the accretion rate
Cited by in corpus (10)
- Evidence for an intermediate-mass black hole in the globular cluster NGC 6624
- Mass models of NGC 6624 without an intermediate-mass black hole
- ALMA observations of 4U 1728-34 and 4U 1820-30: first detection of neutron star X-ray binaries at 300 GHz
- Orbital Evolution of Neutron-Star -- White-Dwarf Binaries by Roche-Lobe Overflow and Gravitational Wave Radiation
- Neutron Stars in X-ray Binaries and their Environments
- Eclipse Timings of the LMXB XTE J1710-281 : Discovery of a third orbital period glitch
- A Circumbinary Disk Scenario For The Negative Orbital-Period Derivative Of The Ultracompact X-ray Binary 4u1820-303
- Evolution of binaries with compact objects in globular clusters
- Updated Orbital Ephemeris and Detection of Superhump Modulation in X-ray Band for the Ultra-Compact Low Mass X-ray Binary 4U 1820-30
- Ultra-compact X-ray Binaries: A Review