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  • 1. Botticella, M. T.
    et al.
    Cappellaro, E.
    Greggio, L.
    Pignata, G.
    Della Valle, M.
    Grado, A.
    Limatola, L.
    Baruffolo, A.
    Benetti, S.
    Bufano, F.
    Capaccioli, M.
    Cascone, E.
    Covone, G.
    De Cicco, D.
    Falocco, Serena
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Haeussler, B.
    Harutyunyan, V.
    Jarvis, M.
    Marchetti, L.
    Napolitano, N. R.
    Paolillo, M.
    Pastorello, A.
    Radovich, M.
    Schipani, P.
    Tomasella, L.
    Turatto, M.
    Vaccari, M.
    Supernova rates from the SUDARE VST-omegacam search II. Rates in a galaxy sample2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 598, article id A50Article in journal (Refereed)
    Abstract [en]

    Aims. This is the second paper of a series in which we present measurements of the supernova (SN) rates from the SUDARE survey. The aim of this survey is to constrain the core collapse (CC) and Type Ia SN progenitors by analysing the dependence of their explosion rate on the properties of the parent stellar population averaging over a population of galaxies with different ages in a cosmic volume and in a galaxy sample. In this paper, we study the trend of the SN rates with the intrinsic colours, the star formation activity and the masses of the parent galaxies. To constrain the SN progenitors we compare the observed rates with model predictions assuming four progenitor models for SNe Ia with different distribution functions of the time intervals between the formation of the progenitor and the explosion, and a mass range of 8-40 M for CC SN progenitors. Methods. We considered a galaxy sample of approximately 130 000 galaxies and a SN sample of approximately 50 events. The wealth of photometric information for our galaxy sample allows us to apply the spectral energy distribution (SED) fitting technique to estimate the intrinsic rest frame colours, the stellar mass and star formation rate (SFR) for each galaxy in the sample. The galaxies have been separated into star-forming and quiescent galaxies, exploiting both the rest frame U-V vs. V-J colour-colour diagram and the best fit values of the specific star formation rate (sSFR) from the SED fitting. Results. We found that the SN Ia rate per unit mass is higher by a factor of six in the star-forming galaxies with respect to the passive galaxies, identified as such both on the U-V vs. V-J colour-colour diagram and for their sSFR. The SN Ia rate per unit mass is also higher in the less massive galaxies that are also younger. These results suggest a distribution of the delay times (DTD) less populated at long delay times than at short delays. The CC SN rate per unit mass is proportional to both the sSFR and the galaxy mass, confirming that the CC SN progenitors explode soon after the end of the star formation activity. The trends of the Type Ia and CC SN rates as a function of the sSFR and the galaxy mass that we observed from SUDARE data are in agreement with literature results at different redshifts suggesting that the ability of the stellar populations to produce SN events does not vary with cosmic time. The expected number of SNe Ia is in agreement with that observed for all four DTD models considered both in passive and star-forming galaxies so we can not discriminate between different progenitor scenarios. The expected number of CC SNe is higher than that observed, suggesting a higher limit for the minimum progenitor mass. However, at least part of this discrepancy between expected and observed number of CC SNe may reflect a fluctuation due to the relatively poor statistics. We also compare the expected and observed trends of the SN Ia rate with the intrinsic U-J colour of the parent galaxy, assumed to be a tracer of the age distribution. While the slope of the relation between the SN Ia rate and the U-J colour in star-forming galaxies can be well-reproduced by all four DTD models considered, only the steepest of them is able to account for the rates and colour in star-forming and passive galaxies with the same value of the SN Ia production efficiency. The agreement between model predictions and data could be found for the other DTD models, but with a productivity of SN Ia higher in passive galaxies compared to star-forming galaxies.

  • 2.
    Falocco, Serena
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Nandi, Sumana
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    A (likely) X-ray jet from NGC6217 observed by XMM-Newton2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, no 2, p. 2280-2288Article in journal (Refereed)
    Abstract [en]

    NGC6217 is a nearby spiral galaxy with a starburst region near its centre. Evidence for a low-luminosity Active Galactic Nucleus (AGN) in its core has also been found in optical spectra. Intriguingly, X-ray observations by ROSAT revealed three knots aligned with the galaxy centre, resembling a jet structure. This paper presents a study of XMM-Newton observations made to assess the hypothesis of a jet emitted from the centre of NGC6217. The XMM data confirm the knots found with ROSAT and our spectral analysis shows that they have similar spectral properties with a hard photon index Gamma similar to 1.7. The core of NGC6217 is well fitted by a model with an AGN and a starburst component, where the AGN contributes at most 46 per cent of the total flux. The candidate jet has an apparent length similar to 15 kpc and a luminosity of similar to 5 x 10(38) erg s(-1). It stands out by being hosted by a spiral galaxy, since jets are more widely associated with ellipticals. To explain the jet launching mechanism we consider the hypothesis of an advection dominated accretion flow with a low accretion rate. The candidate jet emitted from NGC6217 is intriguing since it represents a challenge to the current knowledge of the connection between AGN, jets and host galaxies.

  • 3.
    Falocco, Serena
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Paolillo, M.
    Comastri, A.
    Carrera, F. J.
    Ranalli, P.
    Iwasawa, K.
    Georgantopoulos, I.
    Vignali, C.
    Gilli, R.
    The XMM deep survey in the CDF-S X. X-ray variability of bright sources2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 608, article id A32Article in journal (Refereed)
    Abstract [en]

    Aims. We aim to study the variability properties of bright hard X-ray selected active galactic nuclei (AGN) in the redshift range between 0.3 and 1.6 detected in the Chandra Deep Field South (XMM-CDFS) by a long (similar to 3 Ms) XMM observation.& para;& para;Methods. Taking advantage of the good count statistics in the XMM CDFS, we search for flux and spectral variability using the hardness ratio (HR) techniques. We also investigate the spectral variability of different spectral components (photon index of the power law, column density of the local absorber, and reflection intensity). The spectra were merged in six epochs (defined as adjacent observations) and in high and low flux states to understand whether the flux transitions are accompanied by spectral changes.& para;& para;Results. The flux variability is significant in all the sources investigated. The HRs in general are not as variable as the fluxes, in line with previous results on deep fields. Only one source displays a variable HR, anti-correlated with the flux (source 337). The spectral analysis in the available epochs confirms the steeper when brighter trend consistent with Comptonisation models only in this source at 99% confidence level. Finding this trend in one out of seven unabsorbed sources is consistent, within the statistical limits, with the 15% of unabsorbed AGN in previous deep surveys. No significant variability in the column densities, nor in the Compton reflection component, has been detected across the epochs considered. The high and low states display in general different normalisations but consistent spectral properties.& para;& para;Conclusions. X-ray flux fluctuations are ubiquitous in AGN, though in some cases the data quality does not allow for their detection. In general, the significant flux variations are not associated with spectral variability: photon index and column densities are not significantly variable in nine out of the ten AGN over long timescales (from three to six and a half years). Photon index variability is found only in one source (which is steeper when brighter) out of seven unabsorbed AGN. The percentage of spectrally variable objects is consistent, within the limited statistics of sources studied here, with previous deep samples.

  • 4.
    Larsson, Josefin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    D'Ammando, F.
    Univ Bologna, Dipartimento Fis & Astron, Via Gobetti 93-2, I-40129 Bologna, Italy.;Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Falocco, Serena
    KTH, School of Engineering Sciences (SCI), Physics.
    Giroletti, M.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Orienti, M.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Piconcelli, E.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Rome, Italy..
    Righini, S.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 1, p. 43-55Article in journal (Refereed)
    Abstract [en]

    A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an similar to 80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio-gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.

  • 5. Liu, Zhu
    et al.
    Yuan, Weimin
    Lu, Youjun
    Carrera, Francisco J.
    Falocco, Serena
    KTH, School of Engineering Sciences (SCI), Physics. Oskar Klein Ctr, Sweden.
    Dong, Xiao-Bo
    Dependence of the broad Fe K alpha line on the physical parameters of AGN2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 463, no 1, p. 684-695Article in journal (Refereed)
    Abstract [en]

    In this paper, the dependence of the broad Fe K alpha line on the physical parameters of AGN, such as the black hole mass M-BH, accretion rate (equivalently represented by Eddington ratio lambda(Edd)) and optical classification is investigated by applying the X-ray spectra stacking method to a large sample of AGN which have well measured optical parameters. A broad-line feature is detected (> 3 sigma) in the stacked spectra of the high lambda(Edd) sub-sample (log lambda(Edd) > -0.9). The profile of the broad line can be well fitted with relativistic broad-line model, with the line energy consistent with highly ionized Fe K alpha line (i.e. Fe xxvi). A model consisting of multiple narrow lines cannot be ruled out, however. We found hints that the Fe K line becomes broader as the lambda(Edd) increases. No broad-line feature is shown in the sub-sample of broad-line Seyfert 1 (BLS1) galaxies and in the full sample, while a broad line might be present, though at low significance, in the sub-sample of narrow-line Seyfert 1 (NLS1) galaxies. We find no strong dependence of the broad line on black hole masses. Our results indicate that the detection/properties of the broad Fe K alpha line may strongly depend on lambda(Edd), which can be explained if the ionization state and/or truncation radius of the accretion disc changes with lambda(Edd). The non-detection of the broad line in the BLS1 sub-sample can be explained if the average equivalent width of the relativistic Fe K alpha line is weak or/and the fraction of sources with relativistic Fe K alpha line is small in BLS1 galaxies.

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