The Bright X-Ray Source in NGC 3413 (original) (raw)
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The ULX source X-3 in NGC 4258: a search for its X-ray and optical properties
Monthly Notices of the Royal Astronomical Society, 2020
We present the results of a search for the nature of ultraluminous X-ray source (ULX) X-3 in the nearby galaxy NGC 4258. We use archival data from XMM–Newton, Chandra, NuSTAR, and Hubble Space Telescope (HST) observations. Total X-ray data were analysed to find that the model parameters of the system are indicative of a stellar-mass black hole, ∼10 M⊙, as the central compact object. Furthermore, analyses of the optical data from HST reveal two optical candidates at 90 per cent confidence level within an error radius of 0.28 arcsec. Assuming the optical emission is dominated by the donor star, both of these candidates are found to have spectral types that lie between B3 and F1 with absolute magnitudes of MV ≈ −6.4. Moreover, the age and mass estimates for the candidates are found to be 10 and 18 Myr and 13 and 20 M⊙, respectively.
X-Ray Spectral and Optical Properties of a Ulx in NGC 4258 (M106)
The Astrophysical Journal, 2016
We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L X ∼ 2 × 10 39 erg s −1 in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST/Advanced Camera for Surveys (ACS), three optical sources have been identified as counterpart candidates within the 1σ error radius of 0 .3. The brightest one has an absolute magnitude of M V ≈ −7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M V ≈ −5.8 and −5.3 mag. The possible spectral types of the candidates from brightest to dimmest were determined as B6−A5, B0−A7, and B2−A3, respectively. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10 − 15M indicating that the compact source is most likely a stellar-mass black hole.
The ultraluminous X-ray sources NGC 1313 X-1 and X-2
Advances in Space Research, 2006
We present a detailed analysis of XMM archival data of two Ultraluminous X-ray Sources (ULXs) in the nearby spiral galaxy NGC 1313: NGC 1313 X-1 and X-2. The spectral continuum of these sources was modeled with a soft thermal component plus a power-law. If the soft component originates from an accretion disk, the inferred mass of the compact remnant is > ∼ 100M ⊙ , making it an Intermediate Mass Black Hole (IMBH). A detailed analysis of the residuals of the XMM EPIC-pn spectrum shows some evidence for the presence of an Oxygen emission line in NGC 1313 X-1. The simultaneous presence of an excess in emission, although at a much reduced significance level, at different energies in the X-ray spectra of NGC 1313 X-1 and X-2 is suggestive of typical emission lines from young supernova remnants. An optical counterpart for NGC 1313 X-2 was also identified. On an ESO 3.6 m image, the Chandra error box embraces a R ∼ 23 mag stellar-like object and excludes a previously proposed optical counterpart.
Optical studies of ultra-luminous X-ray sources in nearby galaxies
2005
Optical studies of ultra-luminous X-ray sources is an essential step in understanding the nature of these enigmatic sources, and in this paper we report our studies of five ULXs in NGC4559, NGC5194, NGC1313 and NGC628 observed with the Hubble Space Telescope and the 6.4 Magellan/Baade telescope. The ULX in NGC4559 is identified with four blue and red supergiants within a 0farcs20\farcs20farcs2 error circle, in a star forming region that is younger than 107.410^{7.4}107.4 years. ULX-3 in NGC5194 is located on the rim of a star cluster with a few faint stars within the 0farcs30\farcs30farcs3 error circle, though the secondary in this system is expected to be a low mass ($0.3M_\odot$) star below detection limits given its two hour period. ULX-5 in NGC5194 is located on a spiral arm with seven objects within the 0farcs80\farcs80farcs8 error circle, which can be improved with future observations. Both ULXs in NGC5194 are in regions younger than 107.810^{7.8}107.8 years. The ULXs in NGC1313 and NGC628 was observed with the Baade telescope....
The Astrophysical Journal, 2015
We present XMM-Newton and NuSTAR observations of two ultraluminous X-ray sources in the nearby galaxy IC 342. The observations were carried out in two epochs separated by ∼ 7 days, with each having an approximate exposure time of 40 ks (XMM-Newton) and ∼100 ks (NuSTAR). We observe little spectral or flux variability above 1 keV between epochs, with unabsorbed 0.3-30 keV luminosities being 1.04 +0.08 −0.06 × 10 40 erg s −1 for IC 342 X-1 and 7.40 ± 0.20 × 10 39 erg s −1 for IC 342 X-2. IC 342 X-2 shows a highly variable component prominent below 1 keV that cannot be explained by blackbody or thermal plasma emission. With the broad bandpass of these observations we can demonstrate conclusively for the first time that both objects have a clear spectral turnover above ∼8 keV. Neither source is consistent with a black hole binary in a low/hard state, and a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum can be ruled out. While the overall continuum shape appears similar for both, IC 342 X-1 shows a soft blackbody-like excess between 1-2 keV which can be interpreted as resulting from a thin accretion disk with T in ∼ 0.3 keV, or from an optically thick outflow, while IC 342 X-2 lacks this excess component. The broadband spectrum of IC 342 X-1 suggests that if the source is powered by an accretion disk, then it must have a significantly shallower temperature profile relative to a thin Shakura & Sunyaev disk and possibly consistent with slim and/or advection dominated disks.
XMM‐Newton Archival Study of the Ultraluminous X‐Ray Population in Nearby Galaxies
The Astrophysical Journal, 2006
We present the results of an archival XMM-Newton study of the bright X-ray point sources (L X > 10 38 erg s −1 ) in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, searching for a soft-hard state dichotomy similar to that known for Galactic X-ray binaries and testing the specific predictions of the IMBH hypothesis. To this end, we searched for "low-state" objects, which we defined as objects within our sample which had a spectrum well fit by a simple absorbed power law, and "high-state" objects, which we defined as objects better fit by a combined blackbody and a power law. Assuming that "low-state" objects accrete at approximately 10% of the Eddington luminosity and that "high-state" objects accrete near the Eddington luminosity we further divided our sample of sources into low and high state ULX sources. We classify 16 sources as low-state ULXs and 26 objects as high-state ULXs. As in Galactic black hole systems, the spectral indices, Γ, of the lowstate objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures for the high state is 0.1-1 keV, with the most luminous systems tending toward the lowest temperatures. We therefore divide our high-state ULXs into candidate IMBHs (with blackbody temperatures of approximately 0.1 keV) and candidate stellar mass BHs (with blackbody temperatures of approximately 1.0 keV). A subset of the candidate stellar mass BHs have spectra that are well-fit by a Comptonization model, a property similar of Galactic BHs radiating in the "very-high" state near the Eddington limit.
XMM-Newton Observations of Luminous Sources in Nearby Galaxies NGC 4395, NGC 4736, and NGC 4258
The Astronomical Journal, 2013
We present results from a study of the non-nuclear discrete sources in a sample of three nearby spiral galaxies (NGC 4395, NGC 4736, and NGC 4258) based on XMM-Newton archival data supplemented with Chandra data for spectral and timing analyses. A total of 75 X-ray sources has been detected within the D 25 regions of the target galaxies. The large collecting area of XMM-Newton makes the statistics sufficient to obtain spectral fitting for 16 (about 20%) of these sources. Compiling the extensive archival exposures available, we were able to obtain the detailed spectral shapes of diverse classes of point sources. We have also studied temporal properties of these luminous sources. 11 of them are found to show short-term (less than 80 ks) variation while 8 of them show long-term variation within factors of ∼ 2 to 5 during a time interval of ∼ 2 to 12 years. Timing analysis provides strong evidence that most of these sources are accreting X-ray binary (XRB) systems. One source that has properties different than others was suspected to be a Supernova Remnant (SNR), and our follow-up optical observation confirmed it. Our results indicate that sources within the three nearby galaxies are showing a variety of source populations, including several Ultraluminous X-Ray Sources (ULXs), X-ray binaries (XRBs), transients together with a Super Soft Source (SSS) and a background Active Galactic Nucleus (AGN) candidate.
The Ultraluminous X‐Ray Source NGC 1313 X‐2 (MS 0317.7−6647) and Its Environment
The Astrophysical Journal, 2004
We present new optical and Chandra observations of the field containing the ultraluminous X-ray source NGC 1313 X-2. On an ESO 3.6 m image, the Chandra error box embraces an R ¼ 21:6 pointlike object and excludes a previously proposed optical counterpart. The resulting X-ray/optical flux ratio of NGC 1313 X-2 is $500. The value of f X =f opt , the X-ray variability history, and the spectral distribution derived from a reanalysis of the ROSAT, ASCA, and XMM-Newton data indicate a luminous X-ray binary in NGC 1313 as a likely explanation for NGC 1313 X-2. If the X-ray soft component observed in the XMM-Newton EPIC spectrum originates from an accretion disk, the inferred mass of the compact remnant is %100 M , making it an intermediate-mass black hole. The derived optical luminosity (L % 10 5 L) is consistent with that of a %15-20 M companion. The properties of the environment of NGC 1313 X-2 are briefly discussed.
X‐Ray and Optical Variability of the Ultraluminous X‐Ray Source NGC 1313 X‐2
The Astrophysical Journal, 2007
We present an analysis of recent XMM-Newton and HST archive data of the ultraluminous X-ray source NGC 1313 X-2. Quasi-simultaneous observations taken with XMM-Newton, HST and VLT allow us to study both the X-ray light curve and its correlation with the optical emission of the two proposed ULX counterparts. At the end of December 2003 the source experienced a short, but intense flare, reaching a maximum luminosity of ∼ 10 40 erg/s. At the same time, the optical flux of both the suggested counterparts did not show pronounced variations (30%). Assuming that the ULX emission is isotropic and taking X-ray reprocessing into account, the optical data for one of the proposed counterparts are consistent with it being an early type, main sequence star of ∼ 10 − 18M ⊙ losing matter through Roche-lobe overflow onto a ∼ 120M ⊙ black hole at an orbital separation corresponding to a period of ∼ 2 days.
X‐Ray Emission from the Nucleus of the Dwarf Elliptical Galaxy NGC 3226
The Astrophysical Journal, 2001
We present the first high resolution X-ray image of the dwarf elliptical galaxy NGC 3226. The data were obtained during an observation of the nearby Seyfert Galaxy NGC 3227 using the Chandra X-ray Observatory. We detect a point X-ray source spatially consistent with the optical nucleus of NGC 3226 and a recently-detected, compact, flat-spectrum, radio source. The X-ray spectrum can be measured up to ∼10 keV and is consistent with a power law with a photon index 1.7 Γ 2.2, or thermal bremmstrahlung emission with 4 kT 10 keV. In both cases the luminosity in the 2-10 keV band ≃ 10 40 h −1 75 erg s −1 . We find marginal evidence that the nucleus varies within the observation. These characteristics support evidence from other wavebands that NGC 3226 harbors a low-luminosity, active nucleus. We also comment on two previously-unknown, fainter X-ray sources 15 arcsec from the nucleus of NGC 3226. Their proximity to the nucleus (with projected distances 1.3h −1 75 kpc) suggests both are within NGC 3226, and thus have luminosities (∼few×10 38 -few×10 39 erg s −1 ) consistent with black-hole binary systems.