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RE: NGC 1365
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Title: NGC 1365: A low column density state unveiling a low ionisation disk wind
Author: V. Braito, J.N. Reeves, J. Gofford, E. Nardini, D. Porquet, G. Risaliti

We present the time-resolved spectral analysis of the XMM-Newton data of NGC 1365, collected during one XMM-Newton observation, which caught this "changing-look" AGN in a high flux state characterised also by a low column density (NH~10^22 cm -2) of the X-ray absorber. During this observation the low energy photoelectric cut-off is at about ~1 keV and the primary continuum can be investigated with the XMM-Newton-RGS data, which show strong spectral variability that can be explained as a variable low NH, which decreased from NH~10^23 cm -2 to 10^22 cm -2 in a 100 ks time-scale. The spectral analysis of the last segment of the observation revealed the presence of several absorption features that can be associated with an ionised (log \xi~2 erg cm s-1) outflowing wind (vout~2000 km s-1). We detected for the first time a possible P-Cygni profile of the Mg\,\textsc{xii} Ly line associated with this mildly ionised absorber indicative of a wide angle outflowing wind. We suggest that this wind is a low ionisation zone of the highly ionised wind present in NGC 1365, which is responsible for the iron K absorption lines and is located within the variable X-ray absorber. At the end of the observation, we detected a strong absorption line at E~0.76 keV most likely associated with a lower ionisation zone of the absorber (log \xi~0.2 erg cm s-1, NH~10^22 cm -2), which suggests that the variable absorber in NGC 1365 could be a low ionisation zone of the disk wind.

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PGC 13179
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NGC 6362 (also ESO 358-17, IRAS 03317-3618, MCG -6-8-26 and PGC 13179) is a magnitude +10.3 barred spiral galaxy located 56.2 ± 2.6 million light-years away in the constellation Fornax.
The galaxy was discovered by Scottish astronomer James Dunlop using a homemade 9-foot 22.86 cm (9 inch) f/12 speculum Newtonian reflector at Paramatta, New South Wales, Australia, on the 2nd September 1826.

Right Ascension 03h 33m 36.4s, Declination -36° 08' 25"

Supernovae 2012fr, 2001du, 1983V, and 1957C were observed in NGC 1365.
In February 2013, observations using the NuSTAR satellite have found out that the central supermassive black hole of NGC 1365, measured to be about 2 million solar masses in mass, is spinning at almost the speed of light

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Title: NuSTAR and XMM-Newton Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk
Author: D. J. Walton, G. Risaliti, F. A. Harrison, A. C. Fabian, J. M. Miller, P. Arevalo, D. R. Ballantyne, S. E. Boggs, L. W. Brenneman, F. E. Christensen, W. W. Craig, M. Elvis, F. Fuerst, P. Gandhi, B. W. Grefenstette, C. J. Hailey, E. Kara, B. Luo, K. K. Madsen, A. Marinucci, G. Matt, M. L. Parker, C. S. Reynolds, E. Rivers, R. R. Ross, D. Stern, W. W. Zhang

We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations of the Seyfert galaxy NGC 1365. These exhibit an extreme level of spectral variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for the first time. Despite the diverse range of absorption states, each of the observations displays the same characteristic signatures of relativistic reflection from the inner accretion disk. Through time-resolved spectroscopy we find that the strength of the relativistic iron line and the Compton reflection hump relative to the intrinsic continuum are well correlated, as expected if they are two aspects of the same broadband reflection spectrum. We apply self-consistent disk reflection models to these time-resolved spectra in order to constrain the inner disk parameters, allowing for variable, partially covering absorption to account for the vastly different absorption states observed. Each of the four observations is treated independently to test the consistency of the results obtained for the black hole spin and the disk inclination, which should not vary on observable timescales. We find both the spin and the inclination determined from the reflection spectrum to be consistent, confirming NGC 1365 hosts a rapidly rotating black hole; in all cases the dimensionless spin parameter is constrained to be a* > 0.97 (at 90% statistical confidence or better).

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Title: Cold dust in giant barred galaxy NGC1365
Authors: F. S. Tabatabaei, A. Weiss, F. Combes, C. Henkel, K. M. Menten, R. Beck, A. Kovács, R. Guesten

Observations of galaxies at sub-millimetre wavelengths, where the emission is mainly due to cold dust, are required to constrain the dust physical properties and provide important insight on the gas content of galaxies. We mapped NGC1365 at 870µm with LABOCA, the Large APEX Bolometer Camera, allowing us to probe the central mass concentration as well as the rate at which the gas flows to the center. We obtained the dust physical properties both globally and locally for different locations in the galaxy. A 20 K modified black body represents about 98% of the total dust content of the galaxy, the rest can be represented by a warmer dust component of 40 K. The bar exhibits an east-west asymmetry in the dust distribution: The eastern bar is heavier than the western bar by more than a factor of 4. Integrating the dust SED, we derive a total infrared (IR) luminosity of 9.8 x 10^{10} L_{\odot} leading to a dust-enshrouded star formation rate of ~16.7 solar masses per year in NGC1365. We derive the gas mass from the measurements of the dust emission resulting in a CO-to-H2 conversion factor of X_{CO}~1.2x10^{20} mol cm^{-2} (K km s^{-1})^{-1} in the central disk including the bar. Taking into account the metallicity variation, the central gas mass concentration is only ~20% at R<40" (3.6 kpc). On the other hand, the time-scale with which the gas flows into the center, ~300 Myr, is rather short. This indicates that the current central mass in NGC1365 is evolving fast due to the strong bar.

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Title: A rapidly spinning supermassive black hole at the centre of NGC 1365
Authors: G. Risaliti, F. A. Harrison, K. K. Madsen, D. J. Walton, S. E. Boggs, F. E. Christensen, W. W. Craig, B. W. Grefenstette, C. J. Hailey, E. Nardini, Daniel Stern, W. W. Zhang

Broad X-ray emission lines from neutral and partially ionised iron observed in active galaxies have been interpreted as fluorescence produced by the reflection of hard X-rays off the inner edge of an accretion disk. In this model, line broadening and distortion result from rapid rotation and relativistic effects near the black hole, the line shape being sensitive to its spin. Alternative models in which the distortions result from absorption by intervening structures provide an equally good description of the data, and there has been no general agreement on which is correct. Recent claims that the black hole (2E6 solar masses) at the centre of the galaxy NGC 1365 is rotating at close to its maximum possible speed rest on the assumption of relativistic reflection. Here we report X-ray observations of NGC 1365 that reveal the relativistic disk features through broadened Fe line emission and an associated Compton scattering excess of 10-30 keV. Using temporal and spectral analyses, we disentangle continuum changes due to time-variable absorption from reflection, which we find arises from a region within 2.5 gravitational radii of the rapidly spinning black hole. Absorption-dominated models that do not include relativistic disk reflection can be ruled out both statistically and on physical grounds.

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First glimpse of a black hole's spin

Astronomers have measured the rate of spin of a supermassive black hole for the first time - and it is big.
Measurements undertaken with two space-based X-ray telescopes imaged the black hole at the centre of galaxy NGC 1365.

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Title: An Examination of the Spectral Variability in NGC 1365 with Suzaku
Authors: L. W. Brenneman (1), G. Risaliti (1 and 2), M. Elvis (1), E. Nardini (1) ((1) Harvard-Smithsonian Center for Astrophysics, (2) INAF - Arcetri)

We present jointly analysed data from three deep Suzaku observations of NGC 1365. These high signal-to-noise spectra enable us to examine the nature of this variable, obscured AGN in unprecedented detail on timescales ranging from hours to years. We find that, in addition to the power-law continuum and absorption from ionised gas seen in most AGN, inner disk reflection and variable absorption from neutral gas within the Broad Emission Line Region are both necessary components in all three observations. We confirm the clumpy nature of the cold absorbing gas, though we note that occultations of the inner disk and corona are much more pronounced in the high-flux state (2008) than in the low-flux state (2010) of the source. The onset and duration of the "dips" in the X-ray light curve in 2010 are both significantly longer than in 2008, however, indicating that either the distance to the gas from the black hole is larger, or that the nature of the gas has changed between epochs. We also note significant variations in the power-law flux over timescales similar to the cold absorber, both within and between the three observations. The warm absorber does not vary significantly within observations, but does show variations in column density of a factor of more than 10 on timescales less than 2 weeks that seem unrelated to the changes in the continuum, reflection or cold absorber. By assuming a uniform iron abundance for the reflection and absorption, we have also established that an iron abundance of roughly 3.5 times the solar value is sufficient to model the broad-band spectrum without invoking an additional partial-covering absorber. Such a measurement is consistent with previous published constraints from the 2008 Suzaku observation alone, and with results from other Seyfert AGN in the literature.

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An Elegant Galaxy in an Unusual Light

A new image taken with the powerful HAWK-I camera on ESO's Very Large Telescope at Paranal Observatory in Chile shows the beautiful barred spiral galaxy NGC 1365 in infrared light. NGC 1365 is a member of the Fornax cluster of galaxies, and lies about 60 million light-years from Earth.
NGC 1365 is one of the best known and most studied barred spiral galaxies and is sometimes nicknamed the Great Barred Spiral Galaxy because of its strikingly perfect form, with the straight bar and two very prominent outer spiral arms. Closer to the centre there is also a second spiral structure and the whole galaxy is laced with delicate dust lanes.

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Title: "Comets" orbiting a black hole
Authors: R. Maiolino, G. Risaliti, M. Salvati, P. Pietrini, G. Torricelli-Ciamponi, M. Elvis, G. Fabbiano, V. Braito, J. Reeves

We use a long (300 ksec), continuous Suzaku X-ray observation of the active nucleus in NGC1365 to investigate the structure of the circumnuclear BLR clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n=10^11 cm^-3) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10^13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognise observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionisation models; we discuss the possible solutions to this discrepancy.

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