RXTE observations of the dipping low-mass X-ray binary 4U 1624-49

Abstract

We analyse ~ 360 ks of archival data from the Rossi X-Ray Timing Explorer (RXTE) of the 21 hr orbital period dipping low-mass X-ray binary 4U 1624-49. We find that outside the dips the tracks in the colour-colour and hardness-intensity diagrams (CDs and HIDs) are reminiscent of those of atoll sources in the middle and upper parts of the banana branch. The tracks show secular shifts up to ~ 10%. We study the power spectrum of 4U 1624-49 as a function of the position in the CD. This is the first time power spectra of this source are presented. No quasi-periodic oscillations (QPOs) are found. The power spectra are dominated by very low frequency noise (VLFN), characteristic for atoll sources in the banana state, and band limited noise (BLN) which is not reliably detected but may, uncharacteristically, strengthen and increase in frequency with spectral hardness. The VLFN fits to a power law, which becomes steeper when the source moves to the harder part of the CD. We conclude that 4U 1624-49 is an atoll source which in our observations is in the upper banana branch. Combining this with the high (0.5-0.7 L_Edd) luminosity, the long-term flux stability of the source as seen with the RXTE All-Sky Monitor (ASM), and with the fact that it is an X-ray dip source, we conclude that 4U 1624-49 is most likely a GX atoll source such as GX 3+1 and GX 9+9, but seen edge on.

8 pages, 5 figures, 2 tables, accepted for publication in A&A. This version: a few typos corrected

References in corpus (4)

• The atoll source states of 4U 1608-52
• On the Correlated Spectral and Timing Properties of 4U 1636-53: an Atoll Source at High Accretion Rates
• Peculiar spectral and power spectral behaviour of the LMXB GX 13+1
• The complete Z-diagram of LMC X-2

Cited by in corpus (6)

• Low Mass X-ray Binaries: The Effects of the Magnetic Braking Prescription
• Using the X-ray Dust Scattering Halo of 4U 1624-490 to determine distance and dust distributions
• The accretion disk corona and disk atmosphere of 4U 1624-490 as viewed by the Chandra-HETGS
• A possible signature of Lense-Thirring precession in dipping and eclipsing neutron-star low-mass X-ray binaries
• Constraining the geometry of the dipping atoll 4U 1624-49 with X-ray spectroscopy and polarimetry
• Constraining Progenitors of Observed LMXBs Using CARB Magnetic Braking