Discovery of a transient X-ray source Suzaku J1305-4930 in NGC 4945

Abstract

We report the serendipitous discovery of a transient X-ray source, Suzaku J1305$-$4930, $\sim$3 kpc southwest of the nucleus of the Seyfert 2 galaxy NGC 4945. Among the seven Suzaku observations of NGC 4945 from 2005 to 2011, Suzaku J1305$-$4930 was detected four times in July and August in 2010. The X-ray spectra are better approximated with a multi-color disk model than a power-law model. At the first detection on 2010 July 4--5, its X-ray luminosity was $(8.9_{-0.4}^{+0.2})\times 10^{38}$ erg s${}^{-1}$ and the temperature at the inner-disk radius ($k{T}_{\mathrm{in}}$) was $1.12\pm 0.04$ keV. At the last detection with Suzaku on 2010 August 4--5, the luminosity decreased to $(2.2_{-0.8}^{+0.3})\times 10^{38}$ erg s${}^{-1}$ and $k{T}_{\mathrm{in}}$ was $0.62\pm 0.07$ keV. The source was not detected on 2011 January 29, about six months after the first detection, with a luminosity upper limit of $2.4\times 10^{38}$ erg s${}^{-1}$. We also find an absorption feature which is similar to that reported in Cyg X-1. Assuming the standard disk, we suggest that Suzaku J1305$-$4930 consists of a black hole with a mass of $\sim$10 $M_{\odot }$. The relation between the disk luminosity and $k{T}_{\mathrm{in}}$ is not reproduced with the standard model of a constant inner radius but is better approximated with a slim-disk model.

arXiv comment17 pages, 10 figures

References in corpus (24)

• Modelling the behaviour of accretion flows in X-ray binaries
• Cosmicflows-2: The Data
• Hard X-ray Detector (HXD) on Board Suzaku
• Monte-Carlo Simulator and Ancillary Response Generator of Suzaku XRT/XIS System for Spatially Extended Source Analysis
• Multi-Temperature Blackbody Spectrum of a Thin Accretion Disk around a Kerr Black Hole: Model Computations and Comparison with Observations
• Reproducibility of Non-X-ray Background for the X-ray Imaging Spectrometer aboard Suzaku
• In-Orbit Performance of the Hard X-ray Detector on board Suzaku
• Resolved atomic lines reveal outflows in two ultraluminous X-ray sources
• The Three Spectral Regimes Found in the Stellar Black Hole XTE J1550--564 in its High/Soft State
• The Distribution of H2O Maser Emission in the Nucleus of NGC 4945
• Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State
• Observational Evidence for Strong Disk Comptonization in GRO J1655-40
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• XMM-Newton Observations of Ultraluminous X-Ray Sources in Nearby Galaxies
• High-resolution X-ray imaging and spectroscopy of the core of NGC 4945 with XMM-Newton and Chandra
• The X-ray reflector in NGC 4945: a time and space resolved portrait
• Simultaneous Chandra and RXTE observations of the nearby bright Seyfert 2 galaxy NGC4945
• Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945
• Chandra X-Ray Spectroscopy of the Focused Wind in the Cygnus X-1 System. II. The Nondip Spectrum in the Low/Hard State - Modulations with Orbital Phase
• Atomic and Molecular Gas in the Starburst Galaxy NGC4945
• X-Ray Sources in the Star Forming Galaxies NGC 4194 and NGC 7541
• Super-Eddington Accretion in the Ultraluminous X-ray Source NGC1313 X-2: An Ephemeral Feast
• Discovery of a bright transient ultraluminous X-ray source Suzaku J1305-4931 in NGC 4945
• Long-term Spectral Variability of the Ultra-luminous X-ray source Holmberg IX X--1

Cited by in corpus (4)

• Extragalactic fast X-ray transient candidates discovered by Chandra (2000-2014)
• Extragalactic FXT Candidates Discovered by Chandra (2014-2022)
• A new sample of transient ultraluminous X-ray sources serendipitously discovered by Swift/XRT
• Comparing the Space Densities of Millisecond-Spin Magnetars and Fast X-Ray Transients