References of "Hutsemekers, Damien"
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See detailPolarization of changing-look quasars
Hutsemekers, Damien ULiege; Agis-Gonzalez, Beatriz ULiege; Marin, F. et al

in Astronomy and Astrophysics (2019), 625

If the disappearance of the broad emission lines observed in changing- look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization ... [more ▼]

If the disappearance of the broad emission lines observed in changing- look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions. Based on observations made with the William Herschel telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias and observations made with ESO Very Large Telescope at the Paranal Observatory under program ID 101.B-0209. [less ▲]

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See detailQuasar Microlensing: Revolutionizing our Understanding of Quasar Structure and Dynamics
Moustakas, Leonidas; O'Dowd, Matthew; Anguita, Timo et al

in arXiv e-prints (2019)

Microlensing by stars within distant galaxies acting as strong gravitational lenses of multiply-imaged quasars, provides a unique and direct measurement of the internal structure of the lensed quasar on ... [more ▼]

Microlensing by stars within distant galaxies acting as strong gravitational lenses of multiply-imaged quasars, provides a unique and direct measurement of the internal structure of the lensed quasar on nano-arcsecond scales. The measurement relies on the temporal variation of high-magnification caustic crossings which vary on timescales of days to years. Multiwavelength observations provide information from distinct emission regions in the quasar. Through monitoring of these strong gravitational lenses, a full tomographic view can emerge with Astronomical-Unit scale resolution. Work to date has demonstrated the potential of this technique in about a dozen systems. In the 2020s there will be orders of magnitude more systems to work with. Monitoring of lens systems for caustic-crossing events to enable triggering of multi- platform, multi-wavelength observations in the 2020s will fulfill the potential of quasar microlensing as a unique and comprehensive probe of active black hole structure and dynamics. [less ▲]

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See detailHigh resolution optical spectroscopy of the N2-rich comet C/2016 R2 (PanSTARRS)
Opitom, C.; Hutsemekers, Damien ULiege; Jehin, Emmanuel ULiege et al

in Astronomy and Astrophysics (2019), 624

Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma ... [more ▼]

Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma dominated by strong emission bands of CO[SUP]+[/SUP] and, more surprisingly, N[SUB]2[/SUB][SUP]+[/SUP]. <BR /> Aims: The strong detection of N[SUB]2[/SUB][SUP]+[/SUP] in the coma of C/2016 R2 provided an ideal opportunity to measure the [SUP]14[/SUP]N/[SUP]15[/SUP]N isotopic ratio directly from N[SUB]2[/SUB][SUP]+[/SUP] for the first time, and to estimate the N[SUB]2[/SUB]/CO ratio, which is an important diagnostic to constrain formation models of planetesimals, in addition to the more general study of coma composition. <BR /> Methods: We obtained high resolution spectra of the comet in February 2018 when it was at 2.8 au from the Sun. We used the UVES spectrograph of the European Southern Observatory Very Large Telescope, complemented with narrowband images obtained with the TRAPPIST telescopes. <BR /> Results: We detect strong emissions from the N[SUB]2[/SUB][SUP]+[/SUP] and CO[SUP]+[/SUP] ions, but also CO[SUB]2[/SUB][SUP]+[/SUP], emission lines from the CH radical, and much fainter emissions of the CN, C[SUB]2[/SUB], and C[SUB]3[/SUB] radicals that were not detected in previous observations of this comet. We do not detect OH or H[SUB]2[/SUB]O[SUP]+[/SUP], and we derive an upper limit of the H[SUB]2[/SUB]O[SUP]+[/SUP]/CO[SUP]+[/SUP] ratio of 0.4, implying that the comet has a low water abundance. We measure a N[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio of 0.06 ± 0.01. The non-detection of NH[SUB]2[/SUB] indicates that most of the nitrogen content of the comet is in N[SUB]2[/SUB]. Together with the high N[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio, this could indicate a low formation temperature of the comet or that the comet is a fragment of a large differentiated Kuiper Belt object. The CO[SUB]2[/SUB][SUP]+[/SUP]/CO[SUP]+[/SUP] ratio is 1.1 ± 0.3. We do not detect [SUP]14[/SUP]N[SUP]15[/SUP]N[SUP]+[/SUP] lines and can only put a lower limit on the [SUP]14[/SUP]N/[SUP]15[/SUP]N ratio (measured from N[SUB]2[/SUB][SUP]+[/SUP]) of about 100, which is compatible with measurements of the same isotopic ratio for NH[SUB]2[/SUB] and CN in other comets. Finally, in addition to the [OI] and [CI] forbidden lines, we detect for the first time the forbidden nitrogen lines [NI] doublet at 519.79 and 520.03 nm in the coma of a comet. [less ▲]

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See detailChanging-look quasars: a challenge for the AGN unification model
Hutsemekers, Damien ULiege

Scientific conference (2019, March 05)

Type 1 active galactic nuclei (AGNs) are characterized by both broad and narrow emission lines in their optical spectrum while type 2 AGNs only show narrow emission lines. The “unification model” suggests ... [more ▼]

Type 1 active galactic nuclei (AGNs) are characterized by both broad and narrow emission lines in their optical spectrum while type 2 AGNs only show narrow emission lines. The “unification model” suggests that type 1 and type 2 AGNs are the same objects viewed under different inclinations, the AGN core being obscured by an equatorial dusty torus in type 2 objects. A key argument in favor of the unification model was the discovery of hidden broad line regions in type 2 AGNs using spectropolarimetry. A handful of high luminosity AGNs (quasars) changing from type 1 to type 2 or vice-versa on timescales of a few years have been recently uncovered, thus challenging the unification model. To explain these spectral changes, two main scenarios have been proposed: a variation of the rate of accretion onto the supermassive black hole, or variable dust absorption due to the motion of individual clouds in a clumpy torus. Observations constraining these scenarios will be discussed, with particular emphasis on polarization measurements. [less ▲]

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See detailThe role of Active Galactic Nuclei in galaxy evolution: insights from space ultraviolet spectropolarimetry
Marin, F.; Charlot, S.; Agis-Gonzalez, Beatriz ULiege et al

in arXiv e-prints (2019)

This Astro2020 white paper summarizes the unknowns of active galactic nuclei (AGN) physics that could be unveiled thanks to a new, space-born, ultraviolet spectropolarimeter. The unique capabilities of ... [more ▼]

This Astro2020 white paper summarizes the unknowns of active galactic nuclei (AGN) physics that could be unveiled thanks to a new, space-born, ultraviolet spectropolarimeter. The unique capabilities of high energy polarimetry would help us to understand the precise mechanisms of matter and energy transfer and supermassive black holes growth, together with the impact of AGN feedback on galaxy evolution. [less ▲]

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See detailAnalytic methods for the Abel transform of exponential functions describing planetary and cometary atmospheres.
Hubert, Benoît ULiege; Munhoven, Guy ULiege; Opitom, Cyrielle et al

Poster (2018, December 11)

Remote sensing of planetary and cometary atmosphere is one of the most important source of data and knowledge of the gas layers surrounding the celestial objects of our solar system, including our own ... [more ▼]

Remote sensing of planetary and cometary atmosphere is one of the most important source of data and knowledge of the gas layers surrounding the celestial objects of our solar system, including our own planet. Most of the instruments used up to now and that will be used in a near future study the emission of radiations directly produced by the atmosphere. Under optically thin conditions, this observation method provides the local volume emission rate (VER) originating from the atmosphere, integrated along the full line of sight (l.o.s.) of the instrument. Under a spherical or cylindrical symmetry assumption, the l.o.s. integration of the VER takes the form of the Abel transform of the vertical VER profile. The simplest analytical functions representing VER profiles in real planetary and cometary atmosphere include an exponential function of the altitude (or radial distance), giving the isothermal profile for a planet and the Haser model for a coma. The Abel transform of these functions can be computed analytically using combinations of special functions. Retrieving the vertical (radial) profile of the VER does however require to invert the observed Abel transform to account for possible departures from these idealized analytical expressions, so that indefinite integrals defined from the Abel integral (which we will call indefinite Abel transforms) are needed (or numerical integrations need to be performed). In this study, we present a new method to produce a workable series development allowing accurate computation of the indefinite Abel transforms that appear in the study of optically thin emissions of planetary and cometary atmospheres. Indeed, taking the Taylor series development of the exponential function to reduce the problem to a series of indefinite Abel transforms of polynomial functions (which can be carried analytically) does not work. It leads to the computation of the difference of large, nearly equal numbers, which cannot be done accurately. Our method rather relies on an appropriate series development of the Jacobian of the Abel transform. We show that the computation can be done reliably up to near machine precision, and that accuracy control can be enforced for tailored applications. Possible applications are considered, that include the study of comas and of the upper atmosphere of Mars and the Earth [less ▲]

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See detaillnsight on quasar changing-look physics from optical polarimetry
Hutsemekers, Damien ULiege; Agis-Gonzalez, Beatriz ULiege; Sluse, Dominique ULiege et al

Conference (2018, December 11)

A handful of quasars changing from type 1 (strong broad and narrow emission lines) to type 1.9 (strong narrow lines only and dim continuum) on timescales of a few years have been recently uncovered. If ... [more ▼]

A handful of quasars changing from type 1 (strong broad and narrow emission lines) to type 1.9 (strong narrow lines only and dim continuum) on timescales of a few years have been recently uncovered. If the disappearance of the broad emission lines observed in changing-look quasars were caused by the obscuration of the quasar core through moving dust clouds in the torus, high linear polarization typical of type 2 quasars would be expected. We measured the polarization of the changing-look quasar J1011+5442 in which the broad emission lines have disappeared between 2003 and 2015. We found a polarization degree compatible with null polarization. This measurement suggests that the observed change of look is not due to a change of obscuration in a torus hiding the continuum source and the broad line region. Our results thus support the idea that the vanishing of the broad emission lines in J1011+5442 is due to an intrinsic dimming of the ionizing continuum source that is most likely caused by a rapid decrease in the rate of accretion onto the supermassive black hole. New polarization measurements have been secured for a sample of changing-look quasars. They essentially confirm our previous results. [less ▲]

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See detailTRUE2: unveiling the nature of true Seyfert 2 candidates through optical polarimetry
Agis-Gonzalez, Beatriz ULiege; Hutsemekers, Damien ULiege; Acosta Pulido, Jose et al

Poster (2018, December 10)

The so-called true Seyfert 2 candidates [1] are Seyferts galaxies whose optical spectra do not show broad lines. Yet, in the X-ray domain, they exhibit some characteristic behavior of Seyferts 1 such as ... [more ▼]

The so-called true Seyfert 2 candidates [1] are Seyferts galaxies whose optical spectra do not show broad lines. Yet, in the X-ray domain, they exhibit some characteristic behavior of Seyferts 1 such as lack of X-ray obscuration and/or short timescale variability. A true Seyfert 2 candidate will be confirmed as a true Seyfert 2 galaxy if the lack of the broad line region (BLR) emission is not only observational but physical. Since the BLR is hidden behind the circumnuclear, optically-thick, dusty torus, only polar-scattered light can probe the presence or absence of the BLR. Hence, scattering-induced polarization is the only way to probe the existence of hidden-BLRs (HBLR). [less ▲]

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See detailProbing the structure and evolution of active galactic nuclei with the ultraviolet polarimeter POLLUX aboard LUVOIR
Marin, F.; Charlot, S.; Hutsemekers, Damien ULiege et al

in SF2A-2018: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics (2018, December 01)

The ultraviolet (UV) polarization spectrum of nearby active galactic nuclei (AGN) is poorly known. The Wisconsin Ultraviolet Photo-Polarimeter Experiment and a handful of instruments on board the Hubble ... [more ▼]

The ultraviolet (UV) polarization spectrum of nearby active galactic nuclei (AGN) is poorly known. The Wisconsin Ultraviolet Photo-Polarimeter Experiment and a handful of instruments on board the Hubble Space Telescope were able to probe the near- and mid-UV polarization of nearby AGN, but the far-UV band (from 1200 Å down to the Lyman limit at 912 Å) remains completely uncharted. In addition, the linewidth resolution of previous observations was at best 1.89 Å. Such a resolution is not sufficient to probe in detail quantum mechanical effects, synchrotron and cyclotron processes, scattering by electrons and dust grains, and dichroic extinction by asymmetric dust grains. Exploring those physical processes would require a new, high-resolution, broadband polarimeter with full ultraviolet-band coverage. In this context, we discuss the AGN science case for POLLUX, a high-resolution UV spectropolarimeter, proposed for the 15-meter primary mirror option of LUVOIR (a multi-wavelength space observatory concept being developed by the Goddard Space Flight Center and proposed for the 2020 Decadal Survey Concept Study). [less ▲]

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See detailOptical linear polarization measurements of quasars obtained with the Very Large Telescope at Paranal Observatory⋆
Hutsemekers, Damien ULiege; Borguet, B.; Sluse, Dominique ULiege et al

in Astronomy and Astrophysics (2018), 620

We report 87 previously unpublished optical linear polarization measurements of 86 quasars obtained in May and October 2008, and from April to July 2015 with the FOcal Reducer and low-dispersion ... [more ▼]

We report 87 previously unpublished optical linear polarization measurements of 86 quasars obtained in May and October 2008, and from April to July 2015 with the FOcal Reducer and low-dispersion Spectrographs FORS1 and FORS2 attached to the Very Large Telescope at the Paranal Observatory. Of the 86 quasars, 37 have p ≥ 0.6%, 9 have p ≥ 2%, and 1 has p ≥ 10%. Based on observations made with the ESO VLT at the Paranal Observatory under programme ID 081.A-0023, 082.B-0029, 095.A-0600.Full Table 3 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (<A href="http://ftp://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A68">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A68</A> [less ▲]

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See detailA high resolution spetrum of comet C/2016 R2 (PanSTARRS) with the ESO VLT
Jehin, Emmanuel ULiege; Opitom, Cyrielle; Hutsemekers, Damien ULiege et al

in Bulletin of the American Astronomical Society (2018, October 01), 50

The returning long period comet C/2016 R2 (PanSTARRS) was discovered on September 7, 2016 at 6.3 au from the Sun. While it was already showing a 20" coma at this large distance (Weryk and Wainscoat 2016 ... [more ▼]

The returning long period comet C/2016 R2 (PanSTARRS) was discovered on September 7, 2016 at 6.3 au from the Sun. While it was already showing a 20" coma at this large distance (Weryk and Wainscoat 2016), it is only in December 2017 that it was found that this comet had a very unusual composition. From radio observations the comet appeared to be very rich in CO and very poor in HCN (Wierzchos and Womack 2018) and its optical spectrum was dominated by CO[SUP]+[/SUP] and more surprisingly N[SUB]2[/SUB][SUP]+[/SUP] emission bands (Cochran and McKay 2018), while most of the emission bands usually detected in the optical spectrum of comets were not detected. In order to investigate in detail its coma in the optical, we obtained a total of 6 hours of Director Discretionary Time on C/2016 R2 with UVES, the high resolution optical spectrograph of the ESO Very Large Telescope, between February 11 and 16, 2018. We used two different settings to optimally cover the whole optical spectrum (326-1060 nm) with a resolving power of 80.000. We report on those observations. We detect strong emissions of the ions CO[SUP]+[/SUP] and N[SUB]2[/SUB][SUP]+[/SUP], and also several CO[SUB]2[/SUB][SUP]+ [/SUP]bands, but no H[SUB]2[/SUB]O[SUP]+[/SUP] . We detect emission lines of the radicals CN, C[SUB]2[/SUB] and C[SUB]3[/SUB] but they are very weak. We computed from these spectra the N[SUB]2[/SUB][SUP]+[/SUP] / CO[SUP]+[/SUP] / CO[SUB]2[/SUB][SUP]+[/SUP] ratios in the coma of the comet which put some constraints on the comet formation models, and compared those values to other comets. The forbidden oxygen [OI] lines are detected, allowing to measure the ratio between the green line and the red doublet which provides a way to determine the abundance of CO and CO[SUB]2[/SUB] relative to H[SUB]2[/SUB]O. For the first time we report the detection of the nitrogen [NI] forbidden doublet at 5197.9 and 5200.2 Å in the coma of a comet, confirming the high abundance of nitrogen in this comet. Interestingly we also detect a line at 9850 Å which could be one of the carbon [CI] forbidden lines but we do not detect the other line of the doublet at 9823 Å. Because of the strong N[SUB]2[/SUB][SUP]+[/SUP] emissions, it was also a unique opportunity to measure the [SUP]14[/SUP]N/[SUP]15[/SUP]N isotopic ratio directly in N[SUB]2[/SUB], the main nitrogen reservoir in the solar nebula. [less ▲]

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See detailComet 66P/du Toit: A Near Earth Main Belt Comet?
Yang, Bin; Opitom, Cyrielle; Jehin, Emmanuel ULiege et al

in Bulletin of the American Astronomical Society (2018, October 01), 50

We obtained medium-resolution and high-resolution spectra of the near-Earth Jupiter family comet (JFC) 66P/du Toit from 300 to 2500 nm with X-shooter/VLT and UVES/VLT on 2018 July 01, 07 and 13 ... [more ▼]

We obtained medium-resolution and high-resolution spectra of the near-Earth Jupiter family comet (JFC) 66P/du Toit from 300 to 2500 nm with X-shooter/VLT and UVES/VLT on 2018 July 01, 07 and 13, respectively. In addition, we obtained a series of narrow-band images of 66P between 2018 May and July with TRAPPIST-South. Comet 66P is one of the weakly active JFCs that were identified by Fernandez & Sosa (2015) as having the highest probability of coming from the Main Belt. Our main goal is to investigate the composition of this comet via measuring the gaseous species in the UV and visible and to study its dust properties via measuring the continuum over a broad wavelength range. Additionally, we aim to measure the ortho-to-para abundance ratio of NH2 to constrain the formation conditions of this comet. I will present our spectroscopic observations as well as the photometric observations of 66P. I will discuss whether this comet shows any clear difference in terms of its volatile profile or its dust profile compared to other typical JFCs. [less ▲]

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See detailHigh resolution spectroscopy of the unusual comet C/2016 R2 (PanSTARRS)
Opitom, Cyrielle; Hutsemekers, Damien ULiege; Rousselot, Philippe et al

in EPSC Abstracts (2018, September 01), 12

We report on high spectral resolution observations of the peculiar comet C/2016 R2 (Pan-STARRS). This comet was found to have a highly unusual composition, with a very high abundance of CO, and is only ... [more ▼]

We report on high spectral resolution observations of the peculiar comet C/2016 R2 (Pan-STARRS). This comet was found to have a highly unusual composition, with a very high abundance of CO, and is only the third comet in which the N2+ ion is clearly detected. Our observations allowed us to measure the N2+/CO+/CO2+ ratios. Among other things, we also put an upper limit to the 14N/15N isotopic ratio, measured for the first time directly from N2+, and detected the [NI] lines for the first time in a comet. [less ▲]

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See detailSearch for water outgassing of (1) Ceres near its perihelion
Rousselot, Philippe; Opitom, Cyrielle; Jehin, Emmanuel ULiege et al

in EPSC Abstracts (2018, September 01), 12

(1) Ceres is the largest body in the main asteroid belt and one of the most intriguing object since the discovery of water outgassing in the infrared by the Herschel space observatory in 2014. Ceres is ... [more ▼]

(1) Ceres is the largest body in the main asteroid belt and one of the most intriguing object since the discovery of water outgassing in the infrared by the Herschel space observatory in 2014. Ceres is the current target of NASA's Dawn spacecraft. Recently, the possible influence of the local flux of solar energetic particles (SEP) on the production of a cerean exosphere and water vapor has been suggested. On the other hand the Herschel, IUE and ground-based observations seem to show a correlation between water vapor emission and Ceres heliocentric distance. We used the opportunity of both the perihelion passage of (1) Ceres in 2018 and the presence of Dawn in its vicinity (for measuring the SEP flux in real time) to check the influence of heliocentric distance on water outgassing. We searched for OH emission lines from the limb of Ceres in the near- UV. Despite a sensitivity level similar to the Herschel observations we did not detect any water outgassing. [less ▲]

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See detailVizieR Online Data Catalog: Polarization of quasars (Hutsemekers+, 2018)
Hutsemekers, Damien ULiege; Borguet, B.; Sluse, Dominique ULiege et al

Textual, factual or bibliographical database (2018)

This Table contains optical linear polarization measurements of 86 quasars obtained in May 2008, October 2008, and from April to July 2015 with the Focal Reducer and low dispersion Spectrographs FORS1 and ... [more ▼]

This Table contains optical linear polarization measurements of 86 quasars obtained in May 2008, October 2008, and from April to July 2015 with the Focal Reducer and low dispersion Spectrographs FORS1 and FORS2 attached to the Very Large Telescope at the Paranal Observatory. (1 data file). [less ▲]

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See detailTRUE2: Establishing a detectability limit on hidden broad line regions
Agis-Gonzalez, Beatriz ULiege; Hutsemekers, Damien ULiege; Acosta Pulido, Jose et al

Poster (2018, July)

True Seyfert 2 candidates are those Seyferts galaxies whose optical spectral do not show broad lines, nevertheless in the X-ray domain, they exhibit some characteristic behavior of Seyferts 1 such as lack ... [more ▼]

True Seyfert 2 candidates are those Seyferts galaxies whose optical spectral do not show broad lines, nevertheless in the X-ray domain, they exhibit some characteristic behavior of Seyferts 1 such as lack of X-ray obscuration and/or short timescale variability. A true 2 candidate will be confirmed as a true Seyfert 2 if the lack of its broad line region (BLR) is not only observational but physical. These kind of objects are thought to accrete at low Eddington rates, in agreement with theoretical models that predict that the BLR disappears below a certain critical value of accretion rate and/or luminosity. In the last decade, a significant number of true Seyfert 2s with low accretion rates has been claimed in the literature. However, some exceptions as GNS 069 or 2XMM J1231+1106 show high accretion rates, which seem to contradict the generally accepted explanation. A limit on the detection of hidden broad line regions (HBLRs) must be established in order to make sure that BLRs are not present intrinsically. Since true Seyfert 2 candidates are selected by the absence of X-ray obscuration, the most plausible explanation to cause the non-detection of a physically present HBLR would be the absence of an adequate scattering medium. Polarimetry can play a key role to answer this question. The presence of an efficient scattering region would imply a high continuum of polarization. We propose to assess what degrees of polarization are high enough to indicate the presence of a scattering medium able to act as a mirror and thus providing us with the indirect view of the HBLRs. We got new imaging polarimetry data from ISIS@WHT of 10 true 2 candidates which had not been checked in polarized light. If scattering regions are present, undeniable degrees of polarization around 1−3% should be measured. Comparing the measured continuum of polarization with simulations we will be able to estimate a decidability limit on HBLRs. Specifically, we will apply STOKES, a Monte Carlo radiative transfer code which can be used to model, predict, fit and interpret the polarization of AGN [less ▲]

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See detailVST: The First Large Survey Telescope for Optical Polarimetry
Smette, Alain; Bagnulo, Stefano; Snik, Frans et al

in VST in the Era of the Large Sky Surveys. Zenodo 1304780 (2018, June 01)

Replacing the unused ADC by a polarizing filter would transform the VST into the first large polarimetric optical survey telescope, without affecting the current capabilities of the VST+OmegaCAM system ... [more ▼]

Replacing the unused ADC by a polarizing filter would transform the VST into the first large polarimetric optical survey telescope, without affecting the current capabilities of the VST+OmegaCAM system. Scientific cases include: mapping the Milky-Way and Magellanic clouds magnetic fields, surveys of quasar polarization, identification and variability of polarized brown dwarfs, polarimetric characterization and mapping of solar-system objects (incl. the moon, comets, and asteroids), detection of polarized signal around the L4 and L5 Lagrange points, a census of magnetic white dwarfs and Herbig Ae/Be stars, etc. The design of the VST limits the technical implementation for the polarimetric unit to a single-beam system: therefore, we will develop data-driven calibration methods to achieve a sub-percent polarimetric accuracy. The proposed implementation is of low cost and requires no major development, as polarizing filters of the needed size are readily available. In particular, it does not require major modification neither of VST, nor of OmegaCAM. In fact, the currently offered capabilities of the VST+OmegaCAM are preserved as the polarizing filter can be removed from the optical beam. Would this project be accepted, efforts will be needed on the design of the polarimeter unit to optimize accuracy and execution times, on the design of the calibration plan, and on the extension of the data reduction pipeline to extract the polarization signals. [less ▲]

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See detailOptical polarimetry within the changing-look AGN scenario
Agis-Gonzalez, Beatriz ULiege; Hutsemekers, Damien ULiege; Sluse, Dominique ULiege et al

Conference (2018, April 03)

Changing-look AGN are a extraordinary type of AGN which represents a violation of the AGN unified model. Studying this class of objects in polarized light helps us to shade light on the sub-parsec AGN ... [more ▼]

Changing-look AGN are a extraordinary type of AGN which represents a violation of the AGN unified model. Studying this class of objects in polarized light helps us to shade light on the sub-parsec AGN structure and find out which additional ingredients are needed so that the unified model can describe the complex AGN taxonomy. We carried out a detailed analysis of multi-epoch observations of the Seyfert galaxy ESO 362-G18 in X- ray, UV and optical ranges. In total, 45 X-ray observations and 4 optical data sets, 2 of them in polarized light, ranging from January 2003 till March 2016. The four optical analyzed spectra reveal ESO362-G18 as a changing-look Seyfert galaxy, since two spectra are of type 1.5 and the remaining two show ESO362-G18 as a type 1.9 AGN. We have polarized measurements of one of the type 1.5 data sets and also one of the type 1.9, allowing us to compare the polarization properties in both states of a changing-look Seyfert galaxy by first time. From the X-ray data set, we found ESO362-G18 to exhibit relativistic reflection, including a detected soft time lag between continuum and reflection components, whose results support the compact nature of the X-ray emitting regions. We proved a very rapidly spinning Kerr back hole and a very high inclination of ~53o(in two ways, dependent and independent model; see Agís-González et al 2014). Thanks to this derived model, we have also detected two absorption events driven by clouds situated at torus scales. The relatively high inclination we derived is consistent with the idea that our LOS is grazing the obscuring torus (which has a typical half-opening angle of the order of 45o). If the torus is not homogeneous but clumpy, such high inclination may intercept from time to time some of the clumps of the obscuring torus, explaining the detected X-ray absorption events and possibly why ESO362-G18 exhibits changes of look from type 1 to type 2 in its optical spectra. Moreover, the X-ray luminosity keeps roughly constant along the available observation, which discard a change in the accretion rate. Therefore, we will discuss the polarized properties of this intriguing changing-look Seyfert galaxy whose change of look is probably due to absorption in our LOS. At the same time, we will also expose optical polarimetry as a diagnostic tool to disentangle the cause of changes of look. [less ▲]

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See detailA Changing-Look AGN to Be Probed by X-ray Polarimetry
Agis-Gonzalez, Beatriz ULiege; Hutsemekers, Damien ULiege; Miniutti, Giovanni

in Galaxies (2018), 6

Active galactic nuclei (AGN) produce the highest intrinsic luminosities in the Universe from within a compact region. The central engine is thought to be powered by accretion onto a supermassive black ... [more ▼]

Active galactic nuclei (AGN) produce the highest intrinsic luminosities in the Universe from within a compact region. The central engine is thought to be powered by accretion onto a supermassive black hole. A fraction of this huge release of energy influences the evolution of the host galaxy, and in particular, star formation. Thus, AGN are key astronomical sources not only because they play an important role in the evolution of the Universe, but also because they constitute a laboratory for extreme physics. However, these objects are under the resolution limit of current telescopes. Polarimetry is a unique technique capable of providing us with information on physical AGN structures. The incoming new era of X-ray polarimetry will give us the opportunity to explore the geometry and physical processes taking place in the innermost regions of the accretion disc. Here we exploit this future powerful tool in the particular case of changing-look AGN, which are key for understanding the complexity of AGN physics. [less ▲]

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