<figure><img src="image_1.png" /></figure>

# First X-Ray Polarimetric View of a Low-luminosity Active Galactic Nucleus: The Case of NGC 2110

Sudip Chakraborty¹, Ajay Ratheesh²,³, Daniele Tagliacozzo⁴, Philip Kaaret⁵, Jakub Podgorny⁶, Frédéric Marin⁷, Francesco Tombesi⁸,⁹,¹⁰, Steven R. Ehlert⁵, Chien-Ting J. Chen¹, Dawoon E. Kim², Ioannis Liodakis¹¹, Francesco Ursini⁴, Riccardo Middei⁹,¹², Alessandro Di Marco², Fabio La Monaca²,⁸, Srimanta Banerjee¹³, Keigo Fukumura¹⁴, W. Peter Maksym⁵, Romana Mikušincová², Rodrigo Nemmen¹⁵,¹⁶, Pierre-Olivier Petrucci¹⁷, Paolo Soffitta², Jiří Svoboda⁶, and Wenda Zhang¹⁸

¹ Science and Technology Institute, Universities Space and Research Association, Huntsville, AL 35805, USA; schakraborty2@usra.edu

² INAF Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma, Italy

³ Physical Research Laboratory, Thaltej, Ahmedabad, Gujarat 380009, India

⁴ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy

⁵ NASA Marshall Space Flight Center, Huntsville, AL 35812, USA

⁶ Astronomical Institute of the Czech Academy of Sciences, Boční II 1401, CZ-14131 Prague, Czech Republic

⁷ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, 11 rue de l'université, 67000 Strasbourg, France

⁸ Physics Department, Tor Vergata University of Rome, Via della Ricerca Scientifica 1, 00133 Rome, Italy

⁹ INAF—Astronomical Observatory of Rome, Via Frascati 33, 00040 Monte Porzio Catone, Italy

¹⁰ INFN—Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy

¹¹ Institute of Astrophysics, Foundation for Research and Technology-Hellas, GR-70013 Heraklion, Greece

¹² Space Science Data Center, Agenzia Spaziale Italiana, Via del Politecnico snc, 00133 Roma, Italy

¹³ Inter-University Centre for Astronomy and Astrophysics (IUCAA), Ganeshkhind, Pune 411007, India

¹⁴ James Madison University, 800 South Main Street, Harrisonburg, VA 22807, USA

¹⁵ Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Departamento de Astronomia, São Paulo, SP 05508-090, Brazil

¹⁶ Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA

¹⁷ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

¹⁸ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People's Republic of China

Received 2025 March 2; revised 2025 June 5; accepted 2025 June 24; published 2025 August 29

## Abstract

Low-luminosity active galactic nuclei (LLAGN) provide a unique view of Comptonization and nonthermal emission from accreting black holes in the low accretion rate regime. However, to decipher the exact nature of the Comptonizing corona in LLAGN, its geometry and emission mechanism must be understood beyond the limits of spectro-timing techniques. Spectropolarimetry offers the potential to break the degeneracies between different coronal emission models. Compton-thin LLAGN provide an opportunity for such spectropolarimetric exploration in the 2–8 keV energy range using the Imaging X-Ray Polarimetry Explorer (IXPE). In this work, we carry out a spectropolarimetric analysis of the first IXPE observation, in synergy with a contemporaneous Nuclear Spectroscopic Telescope Array observation, of an LLAGN: NGC 2110. Using 554.4 ks of IXPE data from 2024 October, we constrain the 99% upper limit on the polarization degree (PD) to be less than 8.3% assuming the corresponding polarization angle (PA) to be aligned with the radio jet, and less than 3.6% if in the perpendicular direction. In the absence of a significant PD detection, the PA remains formally unconstrained, yet the polarization significance contours appear to be aligned with the radio jet, tentatively supporting models in which the corona is radially extended in the plane of the disk. We also carry out detailed Monte Carlo simulations using MONK and STOKES codes to test different coronal models against our results and compare the polarization properties between NGC 2110 and brighter Seyferts.

*Unified Astronomy Thesaurus concepts: Polarimetry (1278); Low-luminosity active galactic nuclei (2033); Active galactic nuclei (16); Astronomical simulations (1857); X-ray astronomy (1810); X-ray active galactic nuclei (2035); Astrophysical black holes (98); Supermassive black holes (1663)*

## 1. Introduction

Accretion flows surrounding accreting black holes are thought to consist of hot, geometrically thick coronae Comptonizing lower-energy seed photons originating from cooler, geometrically thin accretion disk. In the X-ray spectrum, this gives rise to the dominant power-law component, along with a high-energy cutoff determined by the temperature of the corona (L. W. Brenneman et al. 2014). X-ray spectra of accreting black holes often contain additional features, such as an iron line complex around 6.4 keV

and an occasional “Compton hump” around 30 keV, both originating from reflection of the Comptonized photons off the disk. The disk-corona systems of both stellar-mass black holes in Galactic black hole X-ray binaries (BHBs) and supermassive black holes (SMBHs) in active galactic nuclei (AGN) undergo evolution in terms of the overall accretion rate, as well as the properties and relative contribution of the accretion disk and the corona. In BHBs, this manifests as the “q”-diagram (R. P. Fender et al. 2004; R. A. Remillard & J. E. McClintock 2006). The AGN population also occupies a similar parameter space (E. G. Körding et al. 2006; Y. Diaz et al. 2023). Accreting black holes, across several orders of magnitude in the black hole masses and accretion rates, also display a remarkable similarity in their Comptonization properties, manifesting as a geometry-

<figure><img src="image_2.png" /></figure>

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
independent strong anticorrelation between the electron temperature ($kT_e$) and the optical depth ($\tau$) of the coronae (S. Chakraborty et al. 2023).

The geometry of the corona can have a significant impact on Comptonization processes and on the ionization structure of the inner accretion flow (J. Poutanen et al. 2018). However, X-ray spectroscopy is often insufficient in differentiating between the coronal geometries on its own, due to the myriad of degeneracies in Comptonization and reflection features. The launch of the Imaging X-Ray Polarimetry Explorer (IXPE; M. C. Weisskopf et al. 2022) has demonstrated how invaluable polarization is to break these degeneracies and to distinguish the coronal geometries of BHBs (H. Krawczynski et al. 2022) and luminous radio-quiet AGN (e.g., NGC 4151, V. E. Gianolli et al. 2023; MCG-05-23-16, A. Marinucci et al. 2022; D. Tagliacozzo et al. 2023; IC 4329A, A. Ingram et al. 2023) alike.

Low-luminosity AGN (LLAGN) are low intrinsic luminosity (bolometric luminosities $L_{bol} \sim 10^{38}-10^{43}$ erg s⁻¹) and low-accretion (significantly sub-Eddington, with Eddington ratio $\lambda_{Edd} \sim 10^{-2}$ to $10^{-5}$; L. C. Ho 2009) AGN, possibly constituting a notable evolutionary stage for SMBHs (M.-S. Shin et al. 2010). Despite exhibiting power-law-dominated X-ray spectra akin to their higher accretion rate counterparts, LLAGN diverge from brighter AGN in several key aspects. Notably, their broadband spectral energy distributions lack the characteristic UV “big blue bump,” suggesting a potential absence of a standard, optically thick, geometrically thin accretion disk (R. S. Nemmen et al. 2006). Instead, accretion in LLAGN is believed to be governed by radiatively inefficient accretion flows, which are a subset of advection-dominated accretion flows (ADAFs; R. Narayan & I. Yi 1995). Furthermore, LLAGN typically display weak or undetectable narrow Fe Kα emission lines (Y. Terashima et al. 2002). The power-law X-ray emission in LLAGN may originate from various mechanisms, including Comptonization of synchrotron or thermal bremsstrahlung photons, or even soft blackbody radiation from a truncated accretion disk beyond $\gtrsim 100GM/c^2$ (R. S. Nemmen et al. 2014). Analogous to the low/hard states of BHBs in the BHB “q”-diagram, LLAGN typically occupy a comparable region in the $\lambda_{Edd}$ versus disk fraction parameter space, in contrast to the soft state analog commonly seen in higher-luminosity Seyfert galaxies (E. G. Körding et al. 2006; J. A. Fernández-Ontiveros et al. 2023).

The coronal geometry in LLAGN remains unknown and ill explored. Additionally, although LLAGN follow the same electron temperature versus optical depth anticorrelation as its brighter AGN counterparts, the derived lack of correlation between the $\tau$ and mass accretion rate in LLAGN stands at odds with the predictions from the ADAF model. Therefore, a polarimetric exploration of LLAGN is long overdue. Compared to their brighter counterparts, LLAGN provide certain distinct advantages for polarimetry:

(a) Their 2–8 keV X-ray spectra are composed of a simple power law, thereby reducing degeneracy between polarization from different emission processes/regions. That apart, unpolarized thermal disk emission is absent from LLAGN spectra. Therefore, 2–8 keV spectropolarimetry of LLAGN should give us an uncontaminated view of the Comptonization region.

(b) As for reflection, the Fe Kα emission is rather weakly polarized, whereas the Compton hump could in principle be highly polarized (G. Matt 1993), albeit having rather a minimal effect in the IXPE bandpass (F. Marin et al. 2018). Compton-thin LLAGN are relatively unobscured and typically

contain negligible reflection features, so the observed polarization should not be altered too much by those features.

NGC 2110 (R.A. = 88.0°474; decl. = -7.0°45622) is a nearby (redshift $z = 0.007$) S0 galaxy (G. de Vaucouleurs 1991) with a low accretion rate ($\log_{10}\lambda_{Edd} = -3.67$) Seyfert 2 AGN harboring a massive black hole ($\log(M/M_{\odot}) = 9.38$; Y. Diaz et al. 2023). NGC 2110 is thought to possess an intermediate/ high inclination of 42°–65° (L. Peralta de Arriba et al. 2023). The broadband X-ray spectrum of NGC 2110 is well described by an absorbed power law with a neutral hydrogen column density of $N_H \sim 4 \times 10^{22}$ cm⁻², a spectral index of $\Gamma \sim 1.65$ (F. Ursini et al. 2019), and a high-energy cutoff. Fitting with a Comptonization model yields an optical depth of $\sim 2$ and $kT_e \sim 75$ keV (F. Ursini et al. 2019). The X-ray spectrum also contains a narrow (equivalent width $\sim 20$ eV) Fe Kα line. However, it does not exhibit strong Compton reflection features, such as a “Compton hump,” suggesting that the reflecting matter is Compton thin (A. Marinucci et al. 2015). NGC 2110 exhibits significant infrared emission, suggesting the presence of an extended dusty wind or a Compton-thin torus, which may account for the Compton-thin reflection (P. Gandhi et al. 2009; S. F. Hönig et al. 2013; A. Marinucci et al. 2015). Further, the optical polarized light spectrum of NGC 2110 has a double- peaked broad Hα emission line indicating a hidden broad-line region shaped like a disk (E. C. Moran et al. 2007). The polarization angle (PA) in optical is almost perpendicular to arcsecond-scale radio structures, indicating scattering along the direction parallel to the axis of the surrounding dust torus (R. M. González Delgado et al. 2002).

In this paper, we report the polarimetric results from the first IXPE observation of an LLAGN, NGC 2110. In Section 2, we describe the IXPE and other simultaneous observations and the data reduction procedures that followed. We present our analysis and results in Section 3 and discuss the implications of our results in Section 4.

## 2. Spectropolarimetric Observation of NGC 2110

The first X-ray polarization observations of NGC 2110 using IXPE were complemented with simultaneous broad X-ray band observations using the Nuclear Spectroscopic Telescope Array (NuSTAR; F. A. Harrison et al. 2013). The details of both IXPE and NuSTAR data are given in the subsequent subsections.

### 2.1. IXPE

IXPE contains three X-ray telescopes, each consisting of a mirror module assembly (MMA; B. D. Ramsey et al. 2022) and a detector unit (DU). Each of these DUs, in turn, contains a gas pixel detector (GPD) that is polarization sensitive. The tracks of photoelectrons produced by incident X-rays in the GPD are imaged to measure the linear polarization between 2 and 8 keV (E. Costa et al. 2001; P. Soffitta et al. 2021).

NGC 2110 was observed by IXPE as a part of the Guest Observer (GO) cycle 1 (ObsID 03008799, PI: Chakraborty) in two snapshots: first on 2024 October 16–22 and then on 2024 October 26–30, for a total exposure time of 554.4 ks. To reduce the instrumental background, we first process the IXPE level 2 photon event list through the rejection algorithm of A. Di Marco et al. (2023).<fnref n="19" /> Just before the onset of the second IXPE snapshot, there was a prominent and long-duration solar

<footnote n="19">¹⁹ https://github.com/aledimarco/IXPE-background</footnote>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Contemporaneous NuSTAR (FPMA in red and FPMB in black) and IXPE (DU1 in blue, DU2 in cyan, and DU3 in green), fitted with a combination of an absorbed power law and a Gaussian. The fit is carried out in the 2–8 keV energy range for IXPE and the 3–8 keV energy range for NuSTAR. The Gaussian component is statistically unimportant in the standalone 2–8 keV IXPE spectra.</figcaption></figure>

flare that affected the IXPE data. We carried out a detailed investigation of the effects of the solar flare in the spectra and polarization signatures and systematically filtered the flares out (refer to Appendix A for details on the effects of the solar flare on the data and the filtering strategy adopted). Upon the solar flare filtering, the total live times for DU1, DU2, and DU3 are 538.1, 537.2, and 537.3 ks, respectively.

After filtering, we extract the source and background counts from a circular region with 60" radius and a concentric annulus with radii between 150" and 300", respectively. This combination of source and background region selection has been demonstrated to optimize the signal-to-background ratio for weak sources (A. Di Marco et al. 2023). We use the *ftools* command *ixpepolarization*, in conjunction with this source region, to assess the minimum detectable polarization at 99% confidence (MDP<sub>99</sub>), and find it to be 6.78%. We then extract the source and background spectra using XSELECT. Finally, we create the vignetting and aperture-corrected Ancillary Response File (for Stokes *I*) and Modulation Response Files (for Stokes *Q* and *U*) files using the *ftools* task *ixpecalcarf*. Throughout this paper, we use unweighted analysis (weights = NONE). We also use the appropriate response matrices for GPD (ver. 20240125) and

MMA (ver. 20231201). We find the source spectrum to be consistently above the background spectrum (scaled for the region sizes) throughout the 2–8 keV band. Although we report the results in this paper using tools from HEASoft version 6.33.2, we find consistent results with *ixpeobssim* (L. Baldini et al. 2022) as well.

## 2.2. NuSTAR

NuSTAR carried out a contemporaneous observation of NGC 2110 during 2024 October 19–21 for a net exposure time of 53.4 ks in FPMA and 52.9 ks in FPMB, as a part of GO cycle 10. We use the most recent NuSTAR calibration database (2024 November 26) and process the data using the standard *nupipeline* routine. We find that the standard routine sufficiently removes the aforementioned solar flare from the background light curve while creating the good time intervals (GTIs). Afterward, we select circular source regions of 120" radii to extract source and background counts, respectively. Then, we compute the spectra of both source and background regions using the *nuproducts* routine, and we bin the spectral files consistently with a minimum of 25 counts per bin using *ftgrouppha*.
## 3. Results

### 3.1. Spectropolarimetric Analysis

We first jointly fit the two NuSTAR Focal Plane Module (FPM) spectra in XSPEC (K. A. Arnaud 1996) using an absorbed cutoff power law in conjunction with a Gaussian to account for the iron line. We also used a constant to account for the cross-normalization between FPMA and FPMB, set at 1 for FPMA and left to vary for FPMB. We also restrict the fit within 3–50 keV since at larger energies the background exceeds the source count rates. We also use a neutral hydrogen column density of $4 \times 10^{22} \text{ cm}^{-2}$ following A. Marinucci et al. (2015). This $\text{const}^*\text{TBabs}^*(\text{cutoffpl}+\text{Gaussian})$ model results in a reasonable fit with a $\chi^2$ of 974 for 1020 degrees of freedom (dof), with a best-fit power-law photon index ($\Gamma$) of $1.60 \pm 0.03$, a cutoff energy $E_{\text{cut}}$ of $185_{-69}^{+257}$ keV, a Gaussian central energy of $6.26 \pm 0.02$ keV, and a width of $0.27 \pm 0.03$ keV (at $1\sigma$ confidence level). The cross-normalization is found to be 1.006 for FPMB, and the 2–8 keV flux is found to be $2.2 \times 10^{-11} \text{ erg cm}^{-2} \text{ s}^{-1}$. These results are consistent with archival values and demonstrate that even though NGC 2110 has demonstrated flux variability over the years, the broadband spectrum has remained consistent. Modeling the Fe K line with a neutral distance reflection component xillver results in a reflection fraction of $-0.78$, with the xillver component contributing $\sim 10\%$ of the 2–8 keV flux.

To arrive at the best spectral model for IXPE, we then conduct a joint spectral fit between NuSTAR and IXPE (all DUs, I spectra). To minimize the effect of the Gaussian line, we restrict both fitting ranges to 5.5 keV. As IXPE extends to lower energies than NuSTAR, it could provide a better handle over the neutral hydrogen column density ($N_H$), while NuSTAR provides us a better estimate of the power-law photon index. With this in mind, we set up the joint fit between 2–5.5 keV IXPE and 3–5.5 keV NuSTAR with a $\text{const}^*\text{TBabs}^*\text{powerlaw}$ model in XSPEC, where we fix the cross-normalization constant to 1 for NuSTAR FPMA and set to vary for all others, tie the NuSTAR $N_H$ to IXPE, and tie the IXPE $\Gamma$ to the NuSTAR value. The resulting fit yields a $\chi^2$ of 410 for 377 dof, with a best-fit $N_H$ of $(4.8 \pm 0.2) \times 10^{22} \text{ cm}^{-2}$ and a $\Gamma$ of $1.47 \pm 0.06$ (at $1\sigma$ confidence level). The cross-normalization constants between NuSTAR FPMA and IXPE are found to be 0.76, 0.76, and 0.74 for DU1, DU2, and DU3, respectively. Finally, we use these $N_H$ and $\Gamma$ values to fit the full 2–8 keV spectra for all IXPE DUs with a $\text{const}^*\text{TBabs}^*\text{powerlaw}$ model (cross-normalization constant fixed at 1 for DU1 and free to vary for the other DUs), which yields a best-fit $\chi^2$ of 304 for 257 dof. The 2–8 keV flux is found to be $1.7 \times 10^{-11} \text{ erg cm}^{-2} \text{ s}^{-1}$, which is $\sim 23\%$ lower than the NuSTAR flux and within the cross-calibration uncertainties. The 2–8 keV IXPE I spectra, along with the 3–8 keV NuSTAR spectra, are shown in Figure 1. Addition of a Gaussian component to this model provides no improvement in the fit statistic, with the resultant f-test probability of 0.6. Therefore, we use this simple absorbed power-law model with $N_H$ of $4.8 \times 10^{22} \text{ cm}^{-2}$ and $\Gamma$ of 1.47 for further spectropolarimetric analysis.

Thus, we fit the I, Q, and U spectra from all IXPE DUs simultaneously with $\text{const}^*\text{TBabs}^*\text{polconst}^*\text{powerlaw}$, with the previously discussed spectral parameter values and assuming an energy-independent polarization signal. The

best-fit polarization degree (PD) is found to be $\Pi < 10.1\%$ at 99% confidence level<fnref n="20" /> (see Figure 2). Although our results are consistent with an upper limit, and thus the PA is formally unconstrained as well, we can still compare the overall PD–PA contours to the position angle of the radio structure in NGC 2110 in order to infer the possible alignment with the radio jet and infer the geometry of the X-ray corona. J. S. Ulvestad & A. S. Wilson (1984) used the Karl G. Jansky Very Large Array to map the radio structure of NGC 2110 at 2, 6, and 20 cm and reported a radio extension along the position angles $0^\circ-20^\circ$, depending on the projected distance to the core; see Figure 3. This radio position angle is consistent with being aligned with the X-ray PD–PA contour from IXPE. The alignment of the radio position angle and the X-ray PD–PA contours favors models in which the corona is radially extended in the plane of the disk (V. E. Gianolli et al. 2023).

Since we find the PD–PA contour aligned with the radio jet, we can try to project the PD along two orthogonal axes, parallel and perpendicular to the PA, and find their respective bounds. As we are decomposing the 2D contour into two 1D contours in $\Delta\chi^2$ space, the individual limits would be lower than the overall 10.1% upper limit. We use the best-fit PA and rotate the Stokes Q and U parameters in the level 2 event file by that amount to align them with $0^\circ$. The corresponding transformations between the initial $(q, u)$ and aligned $(q', u')$ are $q' = \frac{qq_0+uu_0}{2}$, $u' = \frac{uq_0-qu_0}{2}$, with $q_0 = 2 \cos(2\psi)$, $u_0 = 2 \sin(2\psi)$. This Stokes parameter alignment can transform the original 2D problem into a 1D problem, with PD being the only polarization parameter now. With the Stokes-aligned level 2 event file, we carry out the same data reduction procedure in Section 2 and fit with the same $\text{const}^*\text{TBabs}^*\text{polconst}^*\text{powerlaw}$, this time freezing the PA to $0^\circ$. We find the best-fit PD to be $\Pi < 8.3\%$ at a 99% confidence level and $\Pi < 6.1\%$ at a 90% confidence level. Similarly, aligning the Stokes parameters to $90^\circ$, we find the corresponding 99% and 90% upper limit on PD to be $\Pi < 3.6\%$ and $\Pi < 1.8\%$, respectively. The stricter constraint on the PD along $\Psi = 90^\circ$, once again, indicates that the IXPE data favor a PA parallel to the jet.

### 3.2. Simulations

#### 3.2.1. MONK Simulations

We performed detailed Monte Carlo simulations to analyze the expected polarization properties from the corona of NGC 2110. For this, we utilized the radiative transfer code MONK (W. Zhang et al. 2019), which models the spectrum and polarization of Comptonized radiation emitted by a corona illuminated by a standard accretion disk. The seed optical and UV photons are derived based on the Novikov–Thorne disk emissivity, exhibiting polarization that varies from zero (when viewed face-on) to 11.7% (when viewed edge-on), consistent with a semi-infinite, plane-parallel, scattering-dominated atmosphere (S. Chandrasekhar 1960). Once emitted from the disk, the photons travel along geodesic trajectories in Kerr spacetime around the black hole, potentially reaching a distant observer, being redirected back to the disk, or disappearing through the event horizon. Photons entering the corona may undergo Compton upscattering, which not only results in a Comptonized spectrum but also modifies their polarization

<footnote n="20">²⁰ https://heasarc.gsfc.nasa.gov/docs/ixpe/analysis/IXPE_Stats-Advice.pdf</footnote>
<figure><img src="image_4.png" /><figcaption>**Figure 2.** The 2–8 keV IXPE PA–PD contour plot from the best-fit spectropolarimetric model on the joint *I*, *Q*, and *U* spectra from all DUs in XSPEC. The radial axis is the PD (Π), and the polar axis is the PA (Ψ). 0° is along the north, and 90° is along the east. The three contours are at 68.3% (blue), 90% (orange), and 99% (green) levels. The best-fit solution from XSPEC is denoted by a red star, with the connector to the origin displayed to guide to the corresponding PA. The shaded region denotes the MDP<sub>99</sub>. See Section 3 for a detailed description of the best-fit model.</figcaption></figure>

characteristics. These scatterings significantly influence the radiation emitted by the disk in two primary ways: first, by altering the original spectrum through inverse Compton scattering, which elevates the photon energy (primarily shifting from optical/UV to X-ray wavelengths), thereby producing a harder spectrum; and second, by changing both the intensity and alignment of the overall polarization signature at higher energies. The Stokes parameters of the scattered photons are computed in the electron rest frame before being converted to the observer’s frame (Boyer–Lindquist). By counting the photons that successfully reach the observer, we generate a flux and polarization spectrum. Since scattering results in linearly polarized photons, the code specifically calculates the Stokes parameters *Q* and *U*, while the parameter *V* is set to zero.

We tested four coronal models: the “spherical lamppost,” consisting in a spherical source (of radius $R_c$) placed at a certain height ($H$) on the spin axis of the black hole (F. Ursini et al. 2022); the “conical outflow,” characterized by a distance ($d$) from the black hole, a thickness ($t$), an opening ($\theta$), and an outflowing velocity ($v$), and which is commonly associated with an aborted jet (G. Henri & P. O. Petrucci 1997; G. Ghisellini et al. 2004); the “slab corona” (E. P. T. Liang 1979; F. Haardt & L. Maraschi 1991), which is featured by an inner and an outer radius ($R_{in}$ and $R_{out}$) and a height above the disk plane ($h$) and can occur when magnetic loops extend well above the disk plane and release energy through reconnection (e.g., A. M. Beloborodov 2017); and the “wedge corona,” consisting of a homogeneous cloud of

electrons characterized by an opening ($\alpha$), an inner radius ($R_{in}$) that extends down to the innermost stable circular orbit around the central black hole, and an outer radius ($R_{out}$) (A. A. Esin et al. 1997, 1998; J. D. Schnittman & J. H. Krolik 2010; J. Poutanen et al. 2018). In Figure B1 we show sketches of the aforementioned coronal models.

For each of these models we built a few different configurations of geometrical parameters and black hole spins, as summarized in Table B1. For each different model we built two main configurations, named “standard” and “ADAF”: the former represents a coronal configuration mostly used for luminous radio-quiet unobscured AGN (A. Marinucci et al. 2022; V. E. Gianolli et al. 2023, 2024; A. Ingram et al. 2023; D. Tagliacozzo et al. 2023), while the latter aims to represent LLAGN configurations by truncating the accretion disk at higher radii. For each of these geometries and configurations, we test out two extreme cases of black hole spins, $a = 0$ and maximal ($a = 0.998$), and for the “standard” configuration in slab, conical, and spherical coronae we set the corresponding inner edge of the accretion disk ($R_{disk}^{in}$) at $6R_G$ and $1.5R_G$, respectively. For the wedge corona, we test out different $R_{disk}^{in}$ as detailed in Table B1. For the ADAF configurations in all coronal geometries, we set the $R_{disk}^{in}$ at $100R_G$. We also set the outer edge of the accretion disk $R_{disk}^{out}$ at $1000R_G$ for ADAF configurations and $100R_G$ for “standard” configurations. The coronal parameters listed in Table B1 are further illustrated in Figure B1. Aside from the parameters listed in Table B1, we assumed the following: an opening $\theta = 30^\circ$ and a velocity $v = 0.3c$ (where $c$ represents the speed of light) for the conical
<figure><img src="image_5.png" /><figcaption>**Figure 3.** PA–PD contours overplotted on the 2 cm radio image taken by J. S. Ulvestad & A. S. Wilson (1984) to highlight the possible parallel orientation between the X-ray PA and jet.</figcaption></figure>

outflow, a height above the disk plane $h = 1R_G$ for the slab, and an opening angle $\alpha = 30^\circ$ for the wedge. Moreover, we built a seed photon source reproducing the physical parameters of NGC 2110 (mass, Eddington ratio, and coronal temperature), and for each different model configuration we fine-tuned the Thomson optical depth ($\tau$), reproducing a primary continuum spectral index compatible with what has been found for this source via spectroscopical analysis (see the last column in Table B1).

The models of the spherical lamppost and the conical outflow produce PAs ($\Psi$) that are perpendicular to the axis of the accretion disk, whereas the slab and wedge configurations yield angles that are parallel to it, as previously established in earlier studies (e.g., F. Ursini et al. 2022). In Figures 4 and 5, we present the PD ($\Pi$) for the various models and configurations, analyzed as a function of the disk’s inclination, based on

the MONK simulations. As expected, the slab corona exhibits the highest polarization fraction among the models tested, reaching $\Pi$ values of up to 12%. Conversely, the spherical lamppost displays the lowest polarization fraction, ranging from 0% to 1%, due to its high symmetry. The conical outflow and wedge corona yield intermediate results, with $\Pi$ values of up to 3% and 7%, respectively. Our findings indicate that $\Pi$ is greater when the disk is closer to the black hole. Consequently, configurations identified as ADAF, which truncate the disk at greater distances from the system’s center, correspond to lower $\Pi$ values. This is primarily because the blackbody temperature of the accretion disk decreases with increasing truncation radii, necessitating more scatterings to energize the seed photons into the X-ray band. This process leads to a greater degree of randomization in the radiation and subsequently lower polarization values. Additionally, we observe that a higher
<figure><img src="image_6.png" /><figcaption>**Figure 4.** Π, summed between 2 and 8 keV, as a function of the inclination of the source ($\cos(\theta_{\text{disk}}) = 1$ corresponds to the face-on view) in the slab corona (left panel) and wedge ($a = 0$ in the middle panel and $a = 0.998$ in the right panel) cases, as found via MONK simulations. The green area represents the constraints put using IXPE data (when $\Psi$ is fixed to be parallel to the accretion disk axis $\Pi < 8.3\%$ at 99% c.l. and $\Pi < 6.1\%$ at 90% c.l.) and HST images ($42^{\circ} < \theta_{\text{disk}} < 65^{\circ}$).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 5.** Same as Figure 4, but for the spherical lamppost (left panel) and the conical outflow (right panel). The green area represents the constraints put using HST images and IXPE data, but here with $\Psi$ fixed to be perpendicular to the accretion disk axis ($\Pi < 3.6\%$ at 99% c.l. and $\Pi < 1.8\%$ at 90% c.l.).</figcaption></figure>

spin of the black hole correlates with an increased polarization fraction. This effect primarily arises from the combination of two effects: (i) the correlation between the disk temperature and the black hole spin (N. I. Shakura & R. A. Sunyaev 1973; J. Poutanen et al. 2018), for which if the spin is higher, the blackbody disk radiation peaks at higher energies, leading to, as noted earlier, a smaller number of scatterings needed to energize the photons toward the X-ray band, and thus to a smaller randomization of the radiation (or radiation de-randomization); and (ii) the increased Keplerian velocities of the corona and disk, which disrupt system symmetry more significantly at higher spin rates (W. Zhang et al. 2019).

We also compared our simulation findings with the constraints put on the source polarization by IXPE ($\Pi < 8.3\%$ when $\Psi$ is parallel to the accretion disk axis and $\Pi < 3.6\%$ when $\Psi$ is perpendicular to it, at 99% c.l.) and on the source inclination by the Hubble Space Telescope (HST; $42^{\circ} < \theta_{\text{disk}} < 65^{\circ}$; R. M. González Delgado et al. 2002). These constraints are represented by the green regions in Figures 4 and 5. In addition, in Figure 6 we show the expected polarization properties of the different models superimposed on the contour plot obtained from the analyses. Unfortunately, as we can see from all of that, we were not able to rule out any of the tested geometric configurations, due to the relatively high upper limit on the polarization fraction found within this work.

### 3.2.2. Simulations of Distant Reflection

The MONK simulations presented in the previous section do not take into account reprocessing in the distant, parsec-scale components of AGN. To quantitatively estimate the corresponding simulation uncertainty, i.e., the alteration of the polarization state of the X-rays from the entire nucleus by including such components, we performed additional calculations. First, we used the XSSTOKES_DISC model (J. Podgorný et al. 2024a) to estimate X-ray polarization due to reflection from a distant nearly neutral accretion disk and the broad-line region, both assumed to reside in the equatorial plane with negligible height relative to radial extension from the center. If, on the contrary, the corona has nonnegligible height above the equatorial plane (such as for the hot inner accretion flows, ADAF-like coronal geometries, wedges, or coronae extended along the polar axis), it will subtend some solid angle from the point of view of the equatorial reflector. For simplicity, we integrated the reflected emission uniformly in azimuthal direction and assumed some maximum subtending angle $\delta_i$ measured from the normal toward the equatorial plane, which effectively represents the geometrical extension of the corona for the reflector. We refer to J. Podgorný et al. (2024a) for all details on the adopted geometry of scattering and on the reprocessing spectropolarimetric tables used. For a primary power-law emission with $\Gamma = 1.5$, in the most extreme scenario for $\cos \delta_i = 0.2$, for 7% polarized primary emission
<figure><img src="image_8.png" /><figcaption>**Figure 6.** Comparison between MONK simulations and the contour plot of the IXPE data analysis. Different coronal geometries are shown: slab (in blue) and spherical lamppost (in orange) in the left panel, wedge (in green) and cone (in red) in the right panel. Colored regions of the plot represent the expected ΙΙ for all the tested configurations in the 42° < θ<sub>disk</sub> < 65° range. The black dotted line at 18° represents the supposed elongation of the radio emission, while the black dotted line at −78° represents the direction orthogonal to the radio extension.</figcaption></figure>

<figure><img src="image_9.png" /></figure>

with PA parallel to the principal axis, and for an observer inclined at 65°, we obtained the 2–8 keV reflected emission to be 30% polarized with PA parallel to the principal axis. Any corona subtending a larger solid angle, and/or any less polarized primary emission, and/or any lower inclination would result in a lower PD induced by such reflection. The best-fit xillver flux estimate from the NuSTAR fit does not distinguish between different reflection components. Thus, we can conservatively assign at most 5% of the total 2–8 keV flux to reflection from the equatorial components, such as distant accretion disk and the broad-line region, but not to reflection from the elevated dusty torus or polar reflectors. Hence, if such reflection would produce at most 5% of the total flux in 2–8 keV, it will add at most ~1% of polarization on top of the MONK simulation PD results presented for the wedge or slab coronae in Figure 4. For the wedge or slab configurations leading to unpolarized distant reflection, on the contrary, we estimate additional dilution to the expected PD of the inner emission by at most ~0.4%. For the spherical lamppost or conical coronae, where MONK predicts perpendicularly polarized inner emission (see Figure 5), distant equatorial reprocessing will generally depolarize such primary emission, or in the most extreme case cause the total 2–8 keV total emission to be at most ~0.3% polarized parallelly with the axis.

Lastly, we estimated the impact of reprocessing of the
Comptonized emission inside a purely neutral dusty torus and
scattering off fully ionized polar winds or narrow-line regions
by performing additional simulations with the Monte Carlo
code STOKES (R. W. Goosmann & C. M. Gaskell 2007;
F. Marin et al. 2012, 2015, 2018). We followed the exact same
procedures as in J. Podgorný et al. (2024b), but we assumed a
Compton-thin AGN with equatorial column density
N_H = 5 × 10²² cm⁻² for the torus. We chose τ_wind = 0.03
for the winds, as the necessity of adding such a highly elevated
(or polar) component for interpretation of the IXPE data of the
Compton-thick type 2 AGN the Circinus galaxy has been
shown in J. Podgorný et al. (2024b) and A. Tanimoto et al.
(2023). We tested a simplified primary source of emission,
located in the center of the axially symmetric system,
producing unpolarized power-law emission toward the poles
and polarized power-law emission toward the equator:
PD = 2% with perpendicular PA with the axis; PD = 0%;
and PD = 4%, 6%, and 10% with parallel PA to the axis.
Assuming inclinations 65°, 54°, and 61° and half-opening
angles of the torus 45°, 60°, and 75°, both measured from the

polar axis, we obtained at most 0.5% difference in the total
polarization fraction in 2–8 keV with respect to the primary
source emission. We conclude that any additional contribution
from distant reprocessing will not significantly deviate the
MONK simulation predictions away from the PD upper limits
for NGC 2110 obtained by IXPE and presented in this study.

4. Discussions and Conclusions

To summarize, we have carried out a detailed polarimetric
investigation of the first LLAGN observed by IXPE,
NGC 2110. We found the 2024 October IXPE observation to
be affected by a solar flare, having its imprint in both the
spectrum and polarization signatures. Therefore, we carefully
investigated and removed the corresponding times while
creating the GTI. We utilized the superior spectral capability
of the simultaneous NuSTAR observation to find the spectral
model that best describes the IXPE I spectra of all DUs. We
used this best-fit model in XSPEC to determine the corresp-
onding PD and PA. Furthermore, we used a rotation of Stokes
Q and U parameters for the events to turn the problem into a
1D problem, thereby resulting in a tighter constraint on the PD.
Even though we get an upper limit instead of detection, we
have a positive indication that the 2–8 keV PA is parallel to the
radio jet for NGC 2110. For PA parallel to the radio jet axis,
we determine the 99% upper limit on the PD to be 8.3%, and
for PA perpendicular to the jet, we find the 99% upper limit on
the PD to be 3.6%.

To explore the physical implications of the measured upper
limits on the PD, we carried out Monte Carlo simulations with
the MONK code for four different coronal models (spherical
lamppost, conical outflow, slab, and wedge) and two different
configurations each: a “standard” one used by previous studies
of luminous radio-quiet AGN, and an “ADAF” proxy where
the accretion disk is considerably truncated. The spherical
lamppost and conical outflow models produce PA perpend-
icular to the accretion disk axis, with the spherical lamppost
yielding the lowest PD ~0%–1% and the conical outflow
leading to PD ≲ 3%. On the other hand, the slab and wedge
geometries produce PA parallel to the accretion disk axis, with
wedge corona producing intermediate PD ≲ 7% and slab
corona producing the highest PD of values up to 12%. In all
the cases, the ADAF scenario results in a lower PD than the
“standard” one, possibly due to the randomization from
multiple scatterings required for Comptonization of relatively
low energy seed photons (from the highly truncated disk) into
the 2–8 keV energy band in the ADAF scenario. The PD is
<figure><img src="image_10.png" /><figcaption>**Figure 7.** Long-term X-ray light curves for NGC 2110; 2–10 keV MAXI/GSC with 100-day bins in blue, and 0.3–10 keV Swift/XRT in red, plotted per ObsID. We used the daily light curves (http://maxi.riken.jp/top/lc.html) for MAXI/GSC and automated Swift/XRT light curves from UKSSDC (https://www.swift.ac.uk/user_objects/).</figcaption></figure>

also found to be generally higher for higher black hole spin values. Although the current upper limits both along the radio jet (or accretion disk) axis and orthogonal to it are not sufficient to meaningfully rule out any of the models, certain “standard” configurations (slab, wedge, conical outflow) predict PD close to the 90% upper limits, especially for high spin values (Figures 4 and 5). For a Compton-thin, LLAGN source viewed under a moderate inclination, the distant reflection has a rather small to negligible impact on observable 2–8 keV polarization properties. Therefore, the polarization predictions from the MONK simulations carried out for the Comptonization component can be considered as representative of the observed total emission from NGC 2110.

The PA of the Compton-upscattered X-ray photons from the corona aligning with the extended radio jet has also been observed in other bright Seyfert 1 AGNs, in sources such as NGC 4151 (V. E. Gianolli et al. 2023, 2024), IC 4329A (A. Ingram et al. 2023), and MCG-05-23-16 (A. Marinucci et al. 2022; D. Tagliacozzo et al. 2023). A similar trend is seen in certain BHBs, including Cyg X-1 (H. Krawczynski et al. 2022), Swift J1727.8–1613 (A. Veledina et al. 2023; A. Ingram et al. 2024; J. Podgorný et al. 2024c), and GX 339-4 (G. Mastroserio et al. 2025), especially in the hard state and intermediate states when the emission from the corona dominates in the IXPE band. This suggests that the geometry of the Comptonizing region in both highly accreting AGNs and LLAGNs may have similarities, with the corona being horizontally extended along the plane of the accretion disk. An intriguing comparison can be made with the black hole binary

Swift J1727.8–1613, where the coronal geometry remains similar in the hard state across two different luminosities, differing by approximately two orders of magnitude, corresponding to the upper right and lower right regions of the hysteresis loop in the hardness-intensity diagram (J. Podgorný et al. 2024c). Hence, Comptonizing geometry being similar across different luminosities could be a universal feature in black hole systems. Furthermore, the similarities of Comptonizing region in black hole binaries and AGNs indicate a universal coronal geometry across different mass scales. S. Chakraborty et al. (2023) found an anticorrelation between the optical depth and the electron temperature that holds for LLAGN, brighter AGNs, and BHBs, indicating a similarity in physics of Comptonization across mass scales and luminosities. The upper limit on the PD of NGC 2110 by IXPE in this work is consistent with the idea that both the physics and geometry of Comptonization in black hole systems could be similar across varying black hole masses and accretion rates.

It has to be mentioned, however, that NGC 2110 diminished by at least a factor of 2 in 2–8 keV flux between the IXPE GO1 deadline and the eventual observation (as can be seen from the long-term light curve in Figure 7), thereby significantly increasing the MDP<sub>99</sub> for IXPE. Despite this rapid change in flux, the spectrum has stayed relatively unchanged. Therefore, further IXPE observations should result in a lower MDP<sub>99</sub> overall and can potentially lead to a proper detection of the X-ray polarization from NGC 2110. This calls for a subsequent follow-up of NGC 2110 by IXPE. From Figures 4 and 5, we can see that a confirmed detection of PA along the jet axis will
rule out conical outflow and lamppost coronae, and a PD
detection even within a few percent of the 90% upper limit
could potentially rule out certain configurations of slab and
wedge coronae. Future X-ray polarization observations of
AGNs with IXPE and next-generation X-ray polarimeters like
eXTP (A. Santangelo et al. 2024) across various luminosity
ranges, especially the low-luminosity regime, would definitely
improve our understanding of accretion–ejection processes in
black holes.

Acknowledgments

The Imaging X-ray Polarimetry Explorer (IXPE) is a joint
US and Italian mission. The US contribution is supported by
the National Aeronautics and Space Administration (NASA)
and led and managed by its Marshall Space Flight Center
(MSFC), with industry partner Ball Aerospace (contract
NNM15AA18C). The Italian contribution is supported by the
Italian Space Agency (Agenzia Spaziale Italiana, ASI) through
contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-
12-H0 and ASI-INFN-2017.13-H0, its Space Science Data
Center (SSDC), and the Istituto Nazionale di Astrofisica
(INAF) and the Istituto Nazionale di Fisica Nucleare (INFN)
in Italy. This research used data products provided by the
IXPE Team (MSFC, SSDC, INAF, and INFN) and distributed
with additional software tools by the High-Energy Astro-
physics Science Archive Research Center (HEASARC) at
NASA Goddard Space Flight Center (GSFC). This research
has also made use of data from the NuSTAR mission, a project
led by the California Institute of Technology, managed by the
Jet Propulsion Laboratory, and funded by the National
Aeronautics and Space Administration. Data analysis was
performed using the NuSTAR Data Analysis Software
(NuSTARDAS), jointly developed by the ASI Science Data
Center (SSDC, Italy) and the California Institute of Technol-
ogy (USA). The USRA coauthors gratefully acknowledge
NASA funding through contract 80NSSC24M0035. I.L. was
funded by the European Union ERC-2022-STG—BOOTES—
101076343. J.P. and J.S. acknowledge the GACR project 21-
06825X and the institutional support from RVO:67985815.
Views and opinions expressed are, however, those of the
author(s) only and do not necessarily reflect those of the
European Union or the European Research Council Executive
Agency. Neither the European Union nor the granting
authority can be held responsible for them. We thank the
anonymous referee for the insightful comments that helped
improve this paper.

Facilities: IXPE, NuSTAR

Software: astropy (Astropy Collaboration et al. 2013, 2018), ixpeobssim (L. Baldini et al. 2022), XSPEC (K. A. Arnaud 1996), MONK (W. Zhang et al. 2019), STOKES (R. W. Goosmann & C. M. Gaskell 2007; F. Marin et al. 2012, 2015, 2018).

**Appendix A**
**Effects and Filtering of the Solar Flare**

As mentioned in Section 2.1, a long-duration solar flare
occurred immediately before the second IXPE snapshot, the
effect of which can be seen in the IXPE light curve in
Figure A1. The effect of the solar flare was also prominent in
the channel spectrum of the DUs, especially DU2 and DU3.

<figure><img src="image_11.png" /><figcaption>**Figure A1.** Binned and unweighted 2–8 keV IXPE I counting light curve, for all DUs. The effect of the solar flare can be noticed at the onset of the second observation segment.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Figure A2.** Effect of the solar flare in the unweighted IXPE I channel spectrum during the day (red) and night (black) for DU2. Left panel: the channel spectra for the entire field of view without any region election. The prominent effect of the Si and Al activation lines can be observed in the daytime spectrum. Right panel: the channel spectrum after source region selection and background rejection and subtraction. The effect of the solar flare is greatly minimized after the region selection and taking into account the background. The nighttime spectrum has been shifted by one channel for better visibility.</figcaption></figure>

The resulting Si and Al activation lines can be observed in the spacecraft daytime spectra (in red) as opposed to the nighttime spectra (Figure A2, left panel). Upon selecting the source/ background regions and doing background subtraction, the day/night differences vanish (Figure A2, right panel). To remove the solar flares from the data, we filtered the count rates in the 2–8 keV band in all the DUs. We excised the intervals in which the count rate in any DU within a 240 s time bin exceeded the mean count rate in that DU by ≥3 times the error on the count rate. To test the effectiveness of this solar flare mitigation strategy, we investigate the polarization signal in background regions in the IXPE image during the solar flare time intervals (Figure A3, left panel) and the time intervals with the flares removed (Figure A3, right panel). From Figure A3, we can note strong polarization signal in the background region during the flare, which vanishes upon the removal of the flare.
<figure><img src="image_13.png" /></figure>

**Figure A3.** Polarization signal from unweighted events in IXPE DU1 (blue), DU2 (red), and DU3 (green), as well as over all the DUs (black), arising from the solar flare in the background region described in Section 2.1. The contours are at 99%. The radial axis is the PD, and the polar axis is the PA. 0° is along the north, and 90° is along the east. Top panel: the strong 2–8 keV polarization signal in the background region during the time of the solar flare. Bottom panel: the significantly unpolarized background during the times excluding the solar flare.

# Appendix B

## MONK Simulation Setup of the Tested Geometries

In Figure B1, we provide a pictorial description of the simulation setup of the different coronal geometries we tested

in our MONK simulations. For details of the simulations, please refer to Section 3.2.1.

<figure><img src="image_14.png" /></figure>

**Figure B1.** Coronal models tested with MONK. Upper left: spherical lamppost; upper right: conical outflow; lower left: slab corona; lower right: wedge corona. Sketches are from F. Ursini et al. (2022) and D. Tagliacozzo et al. (2023).
<table><caption>Table B1
List of Physical and Geometrical Parameters for the Various Tested Coronal Models within the MONK Simulations</caption><thead><tr><th>Geometry</th><th>Model</th><th>BH Spin</th><th>R<sup>in</sup><sub>disk</sub> [R<sub>G</sub>]</th><th>R<sup>out</sup><sub>disk</sub> [R<sub>G</sub>]</th><th>H [R<sub>G</sub>]</th><th>R<sub>C</sub> [R<sub>G</sub>]</th><th>τ</th></tr></thead><tbody><tr><td rowspan="4">Spherical Lamppost</td><td>STANDARD</td><td>0</td><td>6</td><td>100</td><td>10</td><td>7</td><td>1.78</td></tr><tr><td>...</td><td>0.998</td><td>1.5</td><td>100</td><td>5</td><td>2</td><td>1.66</td></tr><tr><td>ADAF</td><td>0</td><td>100</td><td>1000</td><td>10</td><td>7</td><td>1.79</td></tr><tr><td>...</td><td>0.998</td><td>100</td><td>1000</td><td>5</td><td>2</td><td>1.67</td></tr><tr><td rowspan="4">Conical Outflow</td><td>STANDARD</td><td>0</td><td>6</td><td>100</td><td>5</td><td>15</td><td>1.16</td></tr><tr><td>...</td><td>0.998</td><td>1.5</td><td>100</td><td>3</td><td>10</td><td>1.06</td></tr><tr><td>ADAF</td><td>0</td><td>100</td><td>1000</td><td>5</td><td>15</td><td>1.21</td></tr><tr><td>...</td><td>0.998</td><td>100</td><td>1000</td><td>3</td><td>10</td><td>1.09</td></tr><tr><td rowspan="4">Geometry</td><td>Model</td><td>BH Spin</td><td>R<sup>in</sup><sub>disk</sub> [R<sub>G</sub>]</td><td>R<sup>out</sup><sub>disk</sub> [R<sub>G</sub>]</td><td>R<sup>in</sup><sub>corona</sub> [R<sub>G</sub>]</td><td>R<sup>out</sup><sub>corona</sub> [R<sub>G</sub>]</td><td>τ</td></tr><tr><td rowspan="4">Slab Corona</td><td>STANDARD</td><td>0</td><td>6</td><td>100</td><td>6</td><td>100</td><td>0.66</td></tr><tr><td>...</td><td>0.998</td><td>1.5</td><td>100</td><td>1.5</td><td>100</td><td>0.60</td></tr><tr><td>ADAF</td><td>0</td><td>100</td><td>1000</td><td>6</td><td>100</td><td>0.76</td></tr><tr><td>...</td><td>0.998</td><td>100</td><td>1000</td><td>1.5</td><td>100</td><td>0.75</td></tr><tr><td rowspan="4">Geometry</td><td>Model</td><td>BH Spin</td><td>R<sup>in</sup><sub>disk</sub> [R<sub>G</sub>]</td><td>R<sup>out</sup><sub>disk</sub> [R<sub>G</sub>]</td><td>R<sup>in</sup><sub>corona</sub> [R<sub>G</sub>]</td><td>R<sup>out</sup><sub>corona</sub> [R<sub>G</sub>]</td><td>τ</td></tr><tr><td rowspan="10">Wedge Corona</td><td>STANDARD</td><td>0</td><td>25</td><td>100</td><td>6</td><td>25</td><td>2.24</td></tr><tr><td>...</td><td>...</td><td>12</td><td>100</td><td>6</td><td>25</td><td>3.10</td></tr><tr><td>...</td><td>...</td><td>6</td><td>100</td><td>6</td><td>25</td><td>3.50</td></tr><tr><td>...</td><td>0.998</td><td>25</td><td>100</td><td>1.5</td><td>25</td><td>2.63</td></tr><tr><td>...</td><td>...</td><td>12</td><td>100</td><td>1.5</td><td>25</td><td>3.49</td></tr><tr><td>...</td><td>...</td><td>1.5</td><td>100</td><td>1.5</td><td>25</td><td>4.37</td></tr><tr><td>ADAF</td><td>0</td><td>100</td><td>1000</td><td>6</td><td>25</td><td>2.19</td></tr><tr><td>...</td><td>...</td><td>100</td><td>1000</td><td>6</td><td>100</td><td>2.84</td></tr><tr><td>...</td><td>0.998</td><td>100</td><td>1000</td><td>1.5</td><td>25</td><td>2.53</td></tr><tr><td>...</td><td>...</td><td>100</td><td>1000</td><td>1.5</td><td>100</td><td>2.95</td></tr></tbody></table>

ORCID iDs

Sudip Chakraborty https://orcid.org/0000-0003-4872-8159

Ajay Ratheesh https://orcid.org/0000-0003-0411-4243

Daniele Tagliacozzo https://orcid.org/0000-0003-3745-0112

Philip Kaaret https://orcid.org/0000-0002-3638-0637

Jakub Podgorný https://orcid.org/0000-0001-5418-291X

Frédéric Marin https://orcid.org/0000-0003-4952-0835

Francesco Tombesi https://orcid.org/0000-0002-6562-8654

Steven R. Ehlert https://orcid.org/0000-0003-4420-2838

Chien-Ting J. Chen https://orcid.org/0000-0002-4945-5079

Dawoon E. Kim https://orcid.org/0000-0001-5717-3736

Ioannis Liodakis https://orcid.org/0000-0001-9200-4006

Francesco Ursini https://orcid.org/0000-0001-9442-7897

Riccardo Middei https://orcid.org/0000-0001-9815-9092

Alessandro Di Marco https://orcid.org/0000-0003-0331-3259

Fabio La Monaca https://orcid.org/0000-0001-8916-4156

Srimanta Banerjee https://orcid.org/0000-0002-6051-6928

Keigo Fukumura https://orcid.org/0000-0001-5709-7606

W. Peter Maksym https://orcid.org/0000-0002-2203-7889

Romana Mikušincová https://orcid.org/0000-0001-7374-843X

Rodrigo Nemmen https://orcid.org/0000-0003-3956-0331

Pierre-Olivier Petrucci https://orcid.org/0000-0001-6061-3480

Paolo Soffitta https://orcid.org/0000-0002-7781-4104

Jiří Svoboda https://orcid.org/0000-0003-2931-0742

Wenda Zhang https://orcid.org/0000-0003-1702-4917

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