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NGC 1365 Ultraluminous X-ray sources
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Title: The XMM-Newton long look of NGC 1365: lack of a high/soft state in its ultraluminous X-ray sources
Authors: Roberto Soria (MSSL-UCL), Guido Risaliti (Harvard CfA & INAF Arcetri), Martin Elvis (Harvard CfA), Giuseppina Fabbiano (Harvard CfA), Stefano Bianchi (Univ. Roma 3), Zdenka Kuncic (Sydney Uni)

Based on our long (~ 300 ks) 2007 XMM-Newton observation of the Seyfert galaxy NGC 1365, we report here on the spectral and timing behaviour of two ultraluminous X-ray sources, which had previously reached isotropic X-ray luminosities L_X ~ 4 x 10^{40} erg/s (0.3-10 keV band). In 2007, they were in a lower state (L_X ~ 5 x 10^{39} erg/s, and L_X ~ 1.5 x 10^{39} erg/s for X1 and X2, respectively). Their X-ray spectra were dominated by power-laws with photon indices Gamma ~ 1.8 and Gamma ~ 1.2, respectively. Thus, their spectra were similar to those at their outburst peaks. Both sources have been seen to vary by a factor of 20 in luminosity over the years, but their spectra are always dominated by a hard power-law; unlike most stellar-mass BHs, they have never been found in a canonical high/soft state dominated by a standard disk. The lack of a canonical high/soft state seems to be a common feature of ULXs. We speculate that the different kind of donor star and/or a persistently super-Eddington accretion rate during their outbursts may prevent accretion flows in ULXs from settling into steady standard disks.

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RE: NGC 1365
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Title: Extremely massive young clusters in NGC1365
Authors: E. Galliano, D. Alloin, E. Pantin, G.L. Granato, P. Delva, L. Silva, P.O. Lagage, P. Panuzzo

In a previous work, three bright MIR/radio sources were discovered in the nuclear region of NGC1365. We here confirm that these sources are young and massive "embedded" clusters, and derive their parameters, such as extinction, age and mass. Using ISAAC and VISIR at the VLT we obtained NIR and MIR maps and LR spectra. The dataset is first interpreted by comparing the observations with images and spectra of the close-by young cluster R136 in the LMC and then by using model predictions for both the nebular emission lines and the spectral energy distribution of the sources. We produce maps of the region containing the three sources in the R, J, Ks, L' bands and at 12.8micro. We also provide spectra in K, L and N. The spectral energy distribution of the three sources rises with wavelength. Emission lines from ionised hydrogen and molecular hydrogen are detected, as well as PAH emission. Conspicuous [NeII]12.8 line is also present, while neither the [ArIII] 8.9 nor the [SIV] 10.4 lines are detected. This provides a stringent constraint on the age of the sources: they are relatively evolved young clusters (6-8 Myr). Owing to their ionising photon rates and ages, they must be extremely massive clusters (around 10^7 solar masses). Their MIR spectral energy distribution suggests the presence of two components: (1) an optically thin component, with a continuum comparable to that of R136, and (2) an optically thick component which might be related to subsequent or on-going episodes of star formation. These sources are good candidates for evolving according to a bi-modal hydrodynamical regime, in which matter is trapped at the centre of a compact and massive cluster.

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Chandra Sees Remarkable Eclipse of Black Hole
Chandra observations of the galaxy NGC 1365 have captured a remarkable eclipse of the supermassive black hole at its centre. A dense cloud of gas passed in front of the black hole, which blocked high-energy X-rays from material close to the black hole. This serendipitous alignment allowed astronomers to measure the size of the disk of material around the black hole, a relatively tiny structure on galactic scales. The Chandra image (shown in the inset) contains a bright X-ray source in the middle, which reveals the position of the supermassive black hole. An optical view of the galaxy from the European Space Observatory's Very Large Telescope shows the context of the Chandra data.

ngc1365
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Credit: X-ray: NASA/CXC/CfA/INAF/Risaliti Optical: ESO/VLT

Position (J2000): RA 03h 33m 36.40s | Dec -36 08' 25.00

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