DISCOVERY OF A 115 DAY ORBITAL PERIOD IN THE ULTRALUMINOUS X-RAY SOURCE NGC 5408 X-1

Journal Article · Tue Dec 01 04:00:00 EST 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/706/2/L210· OSTI ID:21385099

We report the detection of a 115 day periodicity in Swift/X-Ray Telescope monitoring data from the ultraluminous X-ray source (ULX) NGC 5408 X-1. Our ongoing campaign samples its X-ray flux approximately twice weekly and has now achieved a temporal baseline of approx 485 days. Periodogram analysis reveals a significant periodicity with a period of 115.5 +- 4 days. The modulation is detected with a significance of 3.2 x 10{sup -4}. The fractional modulation amplitude decreases with increasing energy, ranging from 0.13 +- 0.02 above 1 keV to 0.24 +- 0.02 below 1 keV. The shape of the profile evolves as well, becoming less sharply peaked at higher energies. The periodogram analysis is consistent with a periodic process, however, continued monitoring is required to confirm the coherent nature of the modulation. Spectral analysis indicates that NGC 5408 X-1 can reach 0.3-10 keV luminosities of approx 2 x 10{sup 40} erg s{sup -1}. We suggest that, like the 62 day period of the ULX in M82 (X41.4+60), the periodicity detected in NGC 5408 X-1 represents the orbital period of the black hole binary containing the ULX. If this is true then the secondary can only be a giant or supergiant star.

• OSTI ID: 21385099
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 2 Vol. 706; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ENERGY RANGE
GALAXIES
GIANT STARS
KEV RANGE
KEV RANGE 01-10
LUMINOSITY
OPTICAL PROPERTIES
OSCILLATIONS
PERIODICITY
PHYSICAL PROPERTIES
STARS
SUPERGIANT STARS
TELESCOPES
VARIATIONS
X-RAY GALAXIES