Spectral variability in Swift and Chandra observations of the Ultraluminous source NGC 55 ULX1

Abstract

NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only marginal hints of a limited number of dips in the light curve, previously reported to occur in this source, although the uncertainties due to the low counting statistics of the data are large. The Chandra and Swift spectra showed clearly spectral variability which resembles those observed in other ULXs. We can account for this spectral variability in terms of changes in both the normalization and intrinsic column density of a two-components model consisting of a blackbody (for the soft component) and a multicolour accretion disc (for the hard component). We discuss the possibility that strong outflows ejected by the disc are in part responsible for such spectral changes.

arXiv comment9 pages, 6 figure; accepted to be published on MNRAS

References in corpus (48)

• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• The Swift X-ray Telescope
• Massive Black Holes as Population III Remnants
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• Ultraluminous X-Ray Sources in External Galaxies
• The formation of massive black holes through collision runaway in dense young star clusters
• The Nature of Accreting Black Holes in Nearby Galaxy Nuclei
• On The Maximum Mass of Stellar Black Holes
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• An Intermediate-mass Black Hole of Over 500 Solar Masses in the Galaxy ESO 243-49
• The Ultraluminous State
• Global Structure of Three Distinct Accretion Flows and Outflows around Black Holes through Two-Dimensional Radiation-Magnetohydrodynamic Simulations
• Ultraluminous X-ray Sources in the Chandra and XMM-Newton Era
• XMM-Newton observations of the brightest Ultraluminous X-ray sources
• Global Radiation-Magnetohydrodynamic Simulations of Black Hole Accretion Flow and Outflow: Unified Model of Three States
• Distances to Nearby Galaxies in Sculptor
• A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source
• A 400 solar mass black hole in the Ultraluminous X-ray source M82 X-1 accreting close to its Eddington limit
• Slim Disk Model for Ultra-Luminous X-Ray Sources
• The ultraluminous X-ray sources NGC 1313 X-1 and X-2: a broadband study with NuSTAR and XMM-Newton
• Puzzling accretion onto a black hole in the ultraluminous X-ray source M101 ULX-1
• Low metallicity natal environments and black hole masses in Ultraluminous X-ray Sources
• The most extreme ultraluminous X-ray sources: evidence for intermediate-mass black holes?
• Spectral variability of ultraluminous X-ray sources
• X-ray Variability and Hardness of ESO 243-49 HLX-1: Clear Evidence for Spectral State Transitions
• Comptonization in Super-Eddington Accretion Flow and Growth Timescale of Supermassive Black Holes
• Quasi-Periodic Variability in NGC 5408 X-1
• Low metallicity and ultra-luminous X-ray sources in the Cartwheel galaxy
• Challenging times: a re-analysis of NGC 5408 X-1
• Broad absorption features in wind-dominated ULXs?
• A Systematic Study of Variability in a Sample of Ultraluminous X-ray Sources
• Spectral States and Evolution of Ultraluminous X-ray Sources
• The missing link: a low mass X-ray binary in M31 seen as an ultraluminous X-ray source
• Why Is Supercritical Disk Accretion Feasible?
• X-ray spectral evolution in M33 X-8
• X-ray spectral states and metallicity in the ultraluminous X-ray sources NGC 1313 X-1 and X-2
• A dipping black-hole X-ray binary candidate in NGC 55
• X-ray Outflows and Super-Eddington Accretion in the Ultraluminous X-ray Source Holmberg IX X-1
• Ultra Luminous X-ray Sources: a deeper insight into their spectral evolution
• Chandra and Swift Follow-up Observations of the Intermediate Mass Black Hole in ESO243-49
• Radiation Hydrodynamic Instability in Plane-Parallel, Super-Eddington Atmosphere: A Mechanism for Clump Formation
• A long-term X-ray monitoring of the ultraluminous X-ray source NGC 5408 X-1 with Swift reveals the presence of dips but no orbital period
• Searching for Massive Outflows in Holmberg IX X-1 and NGC 1313 X-1: The Iron K Band
• A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1
• X-ray study of HLX1: intermediate-mass black hole or foreground neutron star?
• Discovery of a Highly Variable Dipping Ultraluminous X-ray source in M94
• Patchy Accretion Disks in Ultraluminous X-ray Sources
• A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1 - II. Constraints from photometry

Cited by in corpus (16)

• Ultraluminous X-Ray Sources
• Discovery of a 2.8 s pulsar in a 2 d orbit High-Mass X-ray Binary powering the Ultraluminous X-ray source ULX-7 in M51
• Ultraluminous X-ray sources
• From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link
• Diagnosing the accretion flow in ultraluminous X-ray sources using soft X-ray atomic features
• XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows
• Long-term X-ray spectral evolution of Ultraluminous X-ray sources: implications on the accretion flow geometry and the nature of the accretor
• The rare X-ray flaring activity of the Ultraluminous X-ray source NGC 4559 X7
• The chameleon on the branches: spectral state transition and dips in NGC 247 ULX-1
• Unveiling the disc structure in ultraluminous X-ray source NGC 55 ULX-1
• On the nature of the ultraluminous X-ray source Holmberg II X-1
• Transient X-ray source population in the Magellanic-type galaxy NGC 55
• A transient ultraluminous X-ray source in NGC 55
• XMM-Newton multi-year campaign on NGC 55 ULX-1: Resolving the wind and its variability with RGS
• Ultraluminous X-ray sources in the group-centric elliptical galaxy NGC 5813
• Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55 ULX1