Searcharxiv⌕ Search

arXiv subjects

S. Ciroi

Publications and source records attributed to S. Ciroi.

At least 55 records · Page 3Linked to original sources
arXiv2018

MAGNUM survey: A MUSE-Chandra resolved view on ionized outflows and photoionization in the Seyfert galaxy NGC 1365

Ionized outflows, revealed by broad asymmetric wings of the [OIII] line, are commonly observed in AGN but the low intrinsic spatial resolution of observations has generally prevented a detailed characterization of their properties. The MAGNUM survey aims at overcoming these limitations by focusing on the nearest AGN, including NGC 1365, a nearby Seyfert galaxy (D~17 Mpc), hosting a low-luminosity AGN (Lbol ~ 2x10^43 erg/s). We want to obtain a detailed picture of the ionized gas in the central ~5 kpc of NGC 1365 in terms of physical properties, kinematics, and ionization mechanisms. We also aim to characterize the warm ionized outflow as a function of distance from the nucleus and its relation with the nuclear X-ray wind. We employed VLT/MUSE optical integral field spectroscopic observations to investigate the warm ionized gas and Chandra ACIS-S X-ray data for the hot highly-ionized phase. We obtained flux, kinematic, and diagnostic maps of the optical emission lines, which we used to disentangle outflows from disk motions and measure the gas properties down to a spatial resolution of ~70 pc. [OIII] emission mostly traces an AGN-ionized kpc-scale biconical outflow with velocities up to ~200 km/s. Hα emission traces instead star formation in a circumnuclear ring and along the bar, where we detect non-circular motions. Soft X-rays are mostly due to thermal emission from the star-forming regions, but we could isolate the AGN photoionized component which matches the [OIII] emission. The mass outflow rate of the extended ionized outflow matches that of the nuclear X-ray wind and then decreases with radius. However, the hard X-ray emission from the circumnuclear ring suggests that star formation might contribute to the outflow. The integrated mass outflow rate, kinetic energy rate, and outflow velocity are broadly consistent with the typical relations observed in more luminous AGN.

astro-ph.GA↗
arXiv2018

Velocity-resolved reverberation mapping of five bright Seyfert 1 galaxies

We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one AGN (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-Hbeta reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hbeta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity dependent Hbeta lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.

astro-ph.GA↗
arXiv2018

Optical observations of "hot" novae returning to quiescence

We have monitored the return to quiescence of novae previously observed in outburst as supersoft X-ray sources, with optical photometry of the intermediate polar (IP) V4743 Sgr and candidate IP V2491 Cyg, and optical spectroscopy of these two and seven other systems. Our sample includes classical and recurrent novae, short period (few hours), intermediate period (1-2 days) and long period (symbiotic) binaries. The light curves of V4743 Sgr and V2491 Cyg present clear periodic modulations. For V4743 Sgr, the modulation occurs with the beat of the rotational and orbital periods. If the period measured for V2491 Cyg is also the beat of these two periods, the orbital one should be almost 17 hours. The recurrent nova T Pyx already shows fragmentation of the nebular shell less than 3 years after the outburst. While this nova still had strong [OIII] at this post-outburst epoch, these lines had already faded after 3 to 7 years in all the others. We did not find any difference in the ratio of equivalent widths of high ionization/excitation lines to that of the Hbeta line in novae with short and long orbital period, indicating that irradiation does not trigger high mass transfer rate from secondaries with small orbital separation. An important difference between the spectra of RS Oph and V3890 Sgr and those of many symbiotic persistent supersoft sources is the absence of forbidden coronal lines. With the X-rays turn-off, we interpret this as an indication that mass transfer in symbiotics recurrent novae is intermittent.

astro-ph.SR↗
arXiv2018

Supersoft X-ray sources identified with Be binaries in the Magellanic Clouds

We investigated four luminous supersoft X-ray sources (SSS) in the Magellanic Clouds suspected to have optical counterparts of Be spectral type. If the origin of the X-rays is in a very hot atmosphere heated by hydrogen burning in accreted envelopes of white dwarfs (WDs), like in the majority of SSS, these objects are close binaries, with very massive WD primaries. Using the South African Large Telescope (SALT), we obtained the first optical spectra of the proposed optical counterparts of two candidate Be stars associated with SUZAKU J0105-72 and XMMU J010147.5-715550, respectively a transient and a recurrent SSS, and confirmed the proposed Be classification and Small Magellanic Clouds membership. We also obtained new optical spectra of two other Be stars proposed as optical counterparts of the transient SSS XMMU J052016.0-692505 and MAXI-J0158-744. The optical spectra with double peaked emission line profiles, are typical of Be stars and present characteristics similar to many high mass X-ray binaries with excretion disks, truncated by the tidal interaction with a compact object. The presence of a massive WD that sporadically ignites nuclear burning, accreting only at certain orbital or evolutionary phases, explains the supersoft X-ray flares. We measured equivalent widths and distances between lines' peaks, and investigated the variability of the prominent emission lines' profiles. The excretion disks seem to be small in size, and are likely to be differentially rotating. We discuss possible future observations and the relevance of these objects as a new class of type Ia supernovae progenitors.

astro-ph.SR↗
arXiv2018

What we learn from the X-ray grating spectra of Nova SMC 2016

Nova SMC 2016 has been the most luminous nova known in the direction of the Magellanic Clouds. It turned into a very luminous supersoft X-ray source between day 16 and 28 after the optical maximum. We observed it with Chandra, the HRC-S camera and the Low Energy Transmission Grating (LETG) on 2016 November and 2017 January (days 39 and 88 after optical maximum), and with XMM-Newton on 2016 December (day 75). We detected the compact white dwarf (WD) spectrum as a luminous supersoft X-ray continuum with deep absorption features of carbon, nitrogen, magnesium, calcium, probably argon and sulfur on day 39, and oxygen, nitrogen and carbon on days 75 and 88. The spectral features attributed to the WD atmosphere are all blue-shifted, by about 1800 km/s on day 39 and up to 2100 km/s in the following observations. Spectral lines attributed to low ionization potential transitions in the interstellar medium are also observed. Assuming the distance of the Small Magellanic Cloud, the bolometric luminosity exceeded Eddington level for at least three months. A preliminary analysis with atmospheric models indicates effective temperature around 700,000 K on day 39, peaking at the later dates in the 850,000-900,000 K range, as expected for a 1.25 m(sol) WD. We suggest a possible classification as an oxygen-neon WD, but more precise modeling is needed to accurately determine the abundances. The X-ray light curves show large, aperiodic ux variability, not associated with spectral variability. We detected red noise, but did not find periodic or quasi-periodic modulations.

astro-ph.HE↗
arXiv2018

The flat-spectrum radio quasar 3C 345 from the high to the low emission state

We report simultaneous observations at different energy bands in radio, optical, UV, X-rays and $γ$ rays of the flat-spectrum radio-quasar 3C 345. We built the light curve of the source at different frequencies from 2008, the beginning of the \textit{Fermi} all-sky survey, to 2016, using new data and public archives. In particular we obtained several optical spectra, to study the behavior of emission lines and the continuum in different activity states and to derive the black hole mass. 3C 345 showed two flaring episodes in 2009, which occurred simultaneously in $γ$ ray, optical/UV and X-rays, and were later followed in radio. The source shows an inverse Compton dominated spectral energy distribution, which moved from higher to lower frequencies from the high to the low state. The reverberation of emission lines during one outburst event allowed us to constrain the location of production of $γ$ rays very close to the broad-line region, and possibly in the jet-base. We report the observation of an increased accretion after the outburst, possibly induced by the decrease of magnetic field intensity with respect to the low state.

astro-ph.HE↗
arXiv2018

Radio-emitting narrow-line Seyfert 1 galaxies in the JVLA perspective

We report the first results of a survey on 74 narrow-line Seyfert 1 galaxies (NLS1s) carried out in 2015 with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A-configuration. So far, this is the largest survey aimed to image the radio continuum of NLS1s. We produced radio maps in order to compare the general properties of three different samples of objects: radio-quiet NLS1s (RQNLS1s), steep-spectrum radio-loud NLS1s (S-NLS1s), and flat-spectrum radio-loud NLS1s (F-NLS1s). We find that the three classes correspond to different radio morphologies, with F-NLS1s being more compact, and RQNLS1s often showing diffuse emission on kpc scales. We also find that F-NLS1s might be low-luminosity and possibly young blazars, and that S-NLS1s are part of the parent population of F-NLS1s. Dedicated studies to RQNLS1s are needed in order to fully understand their role in the unification pictures.

astro-ph.GA↗
arXiv2017

An orientation-based unification of young jetted AGN: the case of 3C 286

In recent years, the old paradigm according to which only high-mass black holes can launch powerful relativistic jets in active galactic nuclei (AGN) has begun to crumble. The discovery of $γ$-rays coming from narrow-line Seyfert 1 galaxies (NLS1s), usually considered young and growing AGN harboring a central black hole with mass typically lower than 10$^8$ M$_\odot$, indicated that also these low-mass AGN can produce powerful relativistic jets. The search for parent population of $γ$-ray emitting NLS1s revealed their connection with compact steep-spectrum sources (CSS). In this proceeding we present a review of the current knowledge of these sources, we present the new important case of 3C 286, classified here for the fist time as NLS1, and we finally provide a tentative orientation based unification of NLS1s and CSS sources.

astro-ph.GA↗
arXiv2017

High resolution spectroscopy of the extended narrow-line region of IC 5063 and NGC 7212

We studied the properties of the gas of the extended narrow line region (ENLR) of two Seyfert 2 galaxies: IC 5063 and NGC 7212. We analysed high resolution spectra to investigate how the main properties of this region depend on the gas velocity. We divided the emission lines in velocity bins and we calculated several line ratios. Diagnostic diagrams and SUMA composite models (photo-ionization + shocks), show that in both galaxies there might be evidence of shocks significantly contributing in the gas ionization at high |V|, even though photo-ionization from the active nucleus remains the main ionization mechanism. In IC 5063 the ionization parameter depends on V and its trend might be explained assuming an hollow bi-conical shape for the ENLR, with one of the edges aligned with the galaxy disk. On the other hand, NGC 7212 does not show any kind of dependence. The models show that solar O/H relative abundances reproduce the observed spectra in all the analysed regions. They also revealed an high fragmentation of the gas clouds, suggesting that the complex kinematics observed in these two objects might be caused by interaction between the ISM and high velocity components, such as jets.

astro-ph.GA↗
arXiv2017

Kiloparsec-scale emission in the narrow-line Seyfert 1 galaxy Mrk 783

We present the first results of a radio survey of 79 narrow-line Seyfert 1 (NLS1) carried out with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A configuration aimed at studying the radio properties of these sources. We report the detection of extended emission in one object: Mrk 783. This is intriguing, since the radio-loudness parameter R of this object is close to the threshold between radio-quiet and radio-loud active galactic nuclei (AGN). The galaxy is one of the few NLS1 showing such an extended emission at z < 0.1. The radio emission is divided in a compact core component and an extended component, observed on both sides of the nucleus and extending from 14 kpc south-east to 12 kpc north-west. There is no sign of a collimated jet, and the shape of the extended component is similar to those of some Seyfert galaxies. The properties of the emission are compatible with a relic produced by the intermittent activity cycle of the AGN.

astro-ph.GA↗
arXiv2016

A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey

We revisited the spectroscopic characteristics of narrow-line Seyfert 1 galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7) public archive. We confirm that NLS1s are mostly characterized by Balmer lines with Lorentzian profiles, lower black hole masses and higher Eddington ratios than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common properties. Strong Fe II emission does not seem to be a distinctive property of NLS1s, as low values of Fe II/H$β$ are equally observed in these AGNs. Our data indicate that Fe II and Ca II kinematics are consistent with the one of H$β$. On the contrary, O I $λ$8446 seems to be systematically narrower and it is likely emitted by gas of the broad-line region more distant from the ionizing source and showing different physical properties. Finally, almost all NLS1s of our sample show radial motions of the narrow-line region highly-ionised gas. The mechanism responsible for this effect is not yet clear, but there are hints that very fast outflows require high continuum luminosities (> $10^{44}$ erg/s) or high Eddington ratios (log(L$_{\rm bol}$/L$_{\rm Edd}$) > -0.1).

astro-ph.GA↗
arXiv2016

V4743 Sgr, a magnetic nova?

Two XMM Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed shortly after it returned to quiescence, 2 and 3.5 years after the explosion. The X-ray light curves revealed a modulation with a frequency of ~0.75 mHz, indicating that V4743 Sgr is most probably an intermediate polar (IP). The X-ray spectra have characteristics in common with known IPs, with a hard thermal plasma component that can be fitted only assuming a partially covering absorber. In 2004 the X-ray spectrum had also a supersoft blackbody-like component, whose temperature was close to that of the white dwarf (WD) in the supersoft X-ray phase following the outburst, but with flux by at least two orders of magnitude lower. In quiescent IPs, a soft X-ray flux component originates at times in the polar regions irradiated by an accretion column, but the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible origin different from accretion. We suggest that it may have been due to an atmospheric temperature gradient on the WD surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. An optical spectrum obtained with SALT 11.5 years after the outburst showed a prominent He II 4686A line and the Bowen blend, which reveal a very hot region, but with peak temperature shifted to the ultraviolet (UV) range. V4743 Sgr is the third post-outburst nova and IP candidate showing a low-luminosity supersoft component in the X-ray flux a few years after the outburst.

astro-ph.SR↗
arXiv2016

[O III] line properties in two samples of radio-emitting narrow-line Seyfert 1 galaxies

The [O III] $λλ$ 4959,5007 lines are a useful proxy to test the kinematic of the narrow-line region (NLR) in active galactic nuclei (AGN). In AGN, and particularly in narrow-line Seyfert 1 galaxies (NLS1s) these lines often show few peculiar features, such as blue wings, often interpreted as outflowing component, and a shift $-$ typically toward lower wavelengths $-$ of the whole spectroscopic feature in some exceptional sources, the so-called blue outliers, which are often associated to strong winds. We investigated the incidence of these peculiarities in two samples of radio-emitting NLS1s, one radio-loud and one radio-quiet. We also studied a few correlations between the observational properties of the [O III] lines and those of the AGN. Our aim was to understand the difference between radio-quiet and radio-loud NLS1s, which may in turn provide useful information on the jet formation mechanism. We find that the NLR gas is much more perturbed in radio-loud than in radio-quiet NLS1s. In particular the NLR dynamics in $γ$-ray emitting NLS1s appears to be highly disturbed, and this might be a consequence of interaction with the relativistic jet. The less frequently perturbed NLR in radio-quiet NLS1s suggests instead that these sources likely do not harbor a fully developed relativistic jet. Nonetheless blue-outliers in radio-quiet NLS1s are observed, and we interpret them as a product of strong winds.

astro-ph.GA↗
arXiv2016

Unveiling the parent population of beamed narrow-line Seyfert 1s

Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN) recently identified as a new class of $γ$-ray sources. The high energy emission is explained by the presence of a relativistic jet observed at small angles, just like in the case of blazars. When the latter are observed at larger angles they appear as radio-galaxies, but an analogue parent population for beamed NLS1s has not yet been determined. In this work we analyze this problem by studying the physical properties of three different samples of parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s, and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In our approach, we first derived black hole mass and Eddington ratio from the optical spectra, then we investigated the interaction between the jet and the narrow-line region from the [O III] $λλ$4959,5007 lines. Finally, the radio luminosity function allowed us to compare their jet luminosity and hence determine the relations between the samples.

astro-ph.GA↗
arXiv2016

Unveiling the submerged part of the iceberg: radio-loud narrow-line Seyfert 1s with SKA

Narrow-line Seyfert 1 galaxies (NLS1) are active galactic nuclei (AGN) known to have small masses of the central black hole and high accretion rates. NLS1s are generally radio-quiet, but a small part of them (about 7\%) are radio-loud. The recent discovery of powerful relativistic jets in radio-loud NLS1s (RLNLS1s), emitting at high-energy $γ$-rays, opened intriguing questions. The observed luminosity of the jet is generally weak, smaller than blazars, although when rescaled for the mass of the central black hole, it becomes of the same order of magnitude of the latter. The weak luminosity, and hence observed flux, resulted in a small number of known RLNLS1. From a recent survey of RLNLS1s, it was found that only 8 out of 42 sources had radio flux density at 1.4 GHz greater than 100 mJy, while 21 out of 42 had flux density smaller than 10 mJy. In addition, given the strong variability at all wavelengths, with present-day facilities RLNLS1s can often only be detected during high activity periods. The Square Kilometer Array (SKA), with its superior sensitivity, will break this limit, allowing us to unveil a relatively unknown population of jetted AGN. We present the results of a study aimed at evaluating the scenario that could emerge after the advent of SKA.

astro-ph.GA↗
arXiv2015

Exploring the parent population of beamed NLS1s: from the black hole to the jet

The aim of this work is to understand the nature of the parent population of beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical properties of three parent candidates samples: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s and disk-hosted radio-galaxies. In particular, we focused on the black hole mass and Eddington ratio distribution and on the interactions between the jet and the narrow-line region.

astro-ph.GA↗
arXiv2015

Multiwavelength survey of a sample of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

We report on a multiwavelength survey of a sample of 42 flat-spectrum radio-loud narrow-line Seyfert 1 galaxies (RLNLS1s). This is the largest known sample of this type of active galactic nucleus (AGN) to date. We found that 17% of sources were detected at high-energy gamma rays (E>100 MeV), and 90% at X-rays (0.3-10 keV). The masses of the central black holes are in the range $\sim 10^{6-8}M_{\odot}$, smaller than the values of blazars. The disk luminosities are about 1-49% of the Eddington value, with one outlier at 0.3%, comparable with the luminosities observed in flat-spectrum radio quasars (FSRQs). The jet powers are $\sim 10^{42-46}$ erg s$^{-1}$, comparable with BL Lac Objects, yet relatively smaller than FSRQs. However, once renormalized by the mass of the central black hole, the jet powers of RLNLS1s, BL Lacs, and FSRQs are consistent each other, indicating the scalability of the jets. We found episodes of extreme variability at high energies on time scales of hours. In some cases, dramatic spectral and flux changes are interpreted as the interplay between the relativistic jet and the accretion disk. We conclude that, despite the distinct observational properties, the central engines of RLNLS1s are similar to those of blazars.

astro-ph.HE↗