arXiv subjects

Erika Benítez

Publications and source records attributed to Erika Benítez.

15 recordsLinked to original sources

arXiv2026

Relativistic blob signatures in the M87 jet at sub-parsec scales

In this work, we present results from general-relativistic radiative-transfer calculations of black hole accretion and jet launching to reproduce the observed properties of the M\,87 jet at sub-parsec scales. For the first time, in the simulations we have included a blob component at the launching region of the jet that allowed us to reproduce the quasi-simultaneous low-energy spectral energy distribution ($10^{10} \text{ Hz} \leq ν\leq 10^{16} \text{ Hz}$). Moreover, we obtain a better fit of the synchrotron emission in the self-absorption region ($ν\leq 10^{11} \text{ Hz}$), showing that the inclusion of a blob component in our radiative transfer calculations results in a flatter spectrum ($α_{22-86\ \text{GHz}}=0.08$). Additionally, our simulations improved the accuracy of the observed morphology of M\,87's jet, matching the data up to a distance of 0.6 mas from the core at 86 GHz. Our results reproduce the edge-brightened structure up to $\sim1.3$ mas, i.e., in a more extended region compared with previous studies, with a brighter southern edge. The obtained synthetic image of the jet reproduces additional observed knots along the southern edge.

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arXiv2026

The Lockman-SpReSO Project: A Deep X-ray Spectral View of a FIR-selected AGN Population

We present a detailed X-ray spectral analysis of the active galactic nucleus (AGN) population in the Lockman-SpReSO project, a multiwavelength campaign of FIR sources in the Lockman Hole field. Using deep XMM-Newton observations cross-matched with FIR-selected galaxies, we characterize 94 AGNs based on their X-ray spectral properties. The sample is distributed over a large redshift range of $z = 0.07-5$, and reaches a flux limit of $5 \times 10^{-16}\, \mathrm{erg\, s^{-1}\, cm^{-2}}$ in the $0.3-10\, \mathrm{keV}$ band. We model the X-ray spectra using absorbed power-law, reflection, and soft excess components to estimate intrinsic column densities ($N_{\mathrm{H}}$), rest-frame $2-10\, \mathrm{keV}$ luminosities, and iron line equivalent widths $(EW)$. Additionally, we included an advanced model fitting for Compton-thick AGNs (CT-AGNs) using the XCLUMPY model. Our results show an increase in the fraction of obscured AGNs toward higher redshifts, including the identification of one strong and two borderline CT-AGN candidates with $N_{\mathrm{H}} \gtrsim 10^{24}\, \mathrm{cm^{-2}}$. Soft excess emission is detected in 10 AGNs, with an average blackbody temperature of $0.12 \pm 0.02\, \mathrm{keV}$. We also detect the X-ray Baldwin effect in both obscured and unobscured populations, and we found a strong correlation between the torus angular width $(σ_\mathrm{tor})$, dust covering factor $(f_{\mathrm{cov}})$, and X-ray luminosity, described by $f_{\mathrm{cov}} = (-0.1 \pm 0.01) \times \log(L_{2-10\, \mathrm{keV}}/(10^{44}\, \mathrm{erg\, s^{-1}})) + (0.65 \pm 0.01)$, supporting the receding torus scenario. While consistent with deep X-ray surveys, the FIR selection favours the identification of dusty star-forming host galaxies and heavily obscured AGNs.

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arXiv2024

Dense Molecular gas and Dusty Torus in NGC 4303

Spectrum analysis at 3 mm of the central region ($r\sim$800 pc) of NGC\,4303 showed molecular gas lines of both dense gas tracers (HCN, HNC, HCO$^+$, and C$_2$H) and diffuse gases ($^{13}$CO and C$^{18}$O). Molecular gas derived parameters: $H_2$ mass $M_{H_2}$=(1.75$\pm$0.32)$\times10^{8}$ M$_{\odot}$; radial velocity, V$_{dense}=$178$\pm$60 km\,s$^{-1}$, and V$_{CO}=$151$\pm$29 km\,s$^{-1}$; HCN luminosity $L_{HCN}$=(7.38$\pm$1.40)$\times10^{6}\,\,K\,\,km\,\,s^{-1}\,pc^{2}$; dense gas mass $M_{dense}$=(4.7$\pm$0.3) $\times 10^{7}$ M$_{\odot}$, and dense gas tracers abundances indicating that dense gas contributes significantly to the total molecular gas mass. To explore the AGN nature and central dusty torus of the galaxy, CIGALE was used to fit the integrated spectral energy distribution from submillimeter to UV frequencies. Large torus properties are estimated: luminosity $L_{TORUS}$\,=\,(7.1$\pm$2.8) $\times 10^{43}$ erg s$^{-1}$ and line of sight inclination of 67$\pm$16$^\circ$, which is consistent with a Type 2 AGN; total infrared luminosity $L_{IR}$=(3.51$\,\pm$\,0.30)$\times 10^{44}$ erg s$^{-1}$; star formation rate $SFR$=6.0$\pm$0.3 M$_{\odot}$\,yr$^{-1}$; and found that the AGN contribution is marginal at $\sim$20\%.

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arXiv2024

Exploring the nature of the jetted hybrid AGNs: PKS 2004-447, 3C 286 and PKS 0440-00 through the SED modeling

In this work, we explore the connection of three jetted $γ-$loud AGNs classes: Compact Steep-Spectrum Sources (CSS), Narrow-Line Seyfert 1 (NLS1), and Flat-Spectrum Radio Quasars, through the modeling of the spectral energy distribution (SED). We selected two sources identified as CSS/NLS1 hybrids, PKS 2004-440 and 3C 286. Additionally, we included the source PKS 0440-00, initially classified as an FSRQ in the first Fermi-LAT catalog, but recently reclassified as an NLS1. We present the results of their broadband SED modeling using a one-zone leptonic synchrotron-self Compton (SSC)+external Compton (EC) model. By exploring the parameter space and investigating the disk-jet connection in these sources, we analyze their classification in a model-dependent way. Our findings reveal that modeling PKS 2004-447 at relatively large angles, as expected for CSS, results in an SSC-dominated inverse Compton emission. In contrast, at low observing angles, the inverse Compton emission is dominated by external photon fields. Both scenarios result in a jet with a low radiative power. For 3C 286 we found that using a one-zone model limits the jet viewing angle to $\sim7^{\circ}$, mainly due to its impact on the $γ$-ray emission. Our model results show a magnetically dominated jet, consistent with $γ$-CSS sources. Our results suggest that PKS 0440-00, can be classified as a powerful $γ-$NLS1, characterized by high accretion power and a jet dominated by bulk motion, similar to FSRQs.

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arXiv2024

Testing particle acceleration in blazar jets with continuous high-cadence optical polarization observations

Variability can be the pathway to understanding the physical processes in astrophysical jets, however, the high-cadence observations required to test particle acceleration models are still missing. Here we report on the first attempt to produce continuous, >24 hour polarization light curves of blazars using telescopes distributed across the globe and the rotation of the Earth to avoid the rising Sun. Our campaign involved 16 telescopes in Asia, Europe, and North America. We observed BL Lacertae and CGRaBS J0211+1051 for a combined 685 telescope hours. We find large variations in the polarization degree and angle for both sources in sub-hour timescales as well as a ~180 degree rotation of the polarization angle in CGRaBS J0211+1051 in less than two days. We compared our high-cadence observations to Particle-In-Cell magnetic reconnection and turbulent plasma simulations. We find that although the state of the art simulation frameworks can produce a large fraction of the polarization properties, they do not account for the entirety of the observed polarization behavior in blazar jets.

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arXiv2024

The Lockman-SpReSO project. Galactic flows in a sample of far-infrared galaxies

Methods. We performed measurements of the \MgII, \MgI, \FeIIa, \FeIIb, and \FeIIc\ spectral lines present in the spectra of the selected sample to determine the EW and velocity of the flows observed in the star-forming galaxies. Subsequently, we conducted $10^7$ bootstrap simulations using Spearman's rank correlation coefficient ($ρ_s$) to explore correlations with galaxy properties. Furthermore, we calculated the covering factor, gas density, and optical depth for the measured \ion{Fe}{II} doublets. Results. Our analysis revealed strong correlations between the EW of \ion{Mg}{II} lines and both $M_{*}$ ($ρ_s=0.43$, 4.5$σ$) and SFR ($ρ_s=0.42$, 4.4$σ$). For the \ion{Fe}{II} lines, we observed strong correlations between the EW and SFR ($ρ_s\sim0.65$, $>3.9σ$), with a weaker correlation for $M_{*}$ ($ρ_s\sim0.35$, $>1.9σ$). No notable correlations were found between velocity measurements of \ion{Mg}{II} line and $M_{*}$, SFR, or sSFR of the objects ($ρ_s\sim0.1)$. However, a negative strong correlation was found between the velocity of the \ion{Fe}{II} lines and the SFR of the galaxies ($ρ_s\sim-0.45$, $\sim3σ$). Our results align with previous studies but studying FIR-selected objects. Finally, we detected a candidate \textit{loitering outflow}, a recently discovered subtype of FeLoBAL quasar, at redshift of $z=1.4399$, exhibiting emission in \ion{C}{III}] and low line velocities ($|v|\lesssim$ 200 km/s).

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arXiv2024

Multi-Epoch Optical Spectroscopy Variability of the Changing-Look AGN Mrk 883

In this work, we present multi-epoch optical spectra of the Seyfert 1.9 galaxy Mrk 883. Data were obtained with the Gran Telescopio Canarias and the \emph{MEGARA} Integral Field Unit mode, archival data from the SDSS-IV MaNGA Survey and the SDSS-I Legacy Survey, and~new spectroscopic observations obtained at San Pedro Mártir Observatory. We report the appearance of the broad component of Hb, emission line, showing a maximum FWHM $\sim$ 5927 $\pm$\, 481\,km\,s$^{-1}$ in the MaNGA spectra, finding evidence for a change from Seyfert 1.9 (23 June 2003) to Seyfert 1.8 (18 May 2018). The~observed changing-look variation from Sy1.9 to Sy1.8 has a timescale $Δ$t\,$\sim$15~y. In~addition, we observe profile and flux broad emission line variability from 2018 to 2023, and a wind component in [OIII]5007~Å, with~a maximum FWHM = 1758 $\pm$ 178 km\,s$^{-1}$, detected on 15 April 2023. In all epochs, variability of the broad lines was found to be disconnected from the optical continuum emission, which shows little or no variations. These results suggest that an ionized-driven wind in the polar direction could be a possible scenario to explain the observed changing-look variations.

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arXiv2023

3D spectroscopy with GTC-MEGARA of the triple AGN candidate in SDSS J102700.40+174900.8

Triple AGN systems are expected to be the result of the hierarchical model of galaxy formation. Since there are very few of them confirmed as such, we present the results of a new study of the triple-AGN candidate SDSS J102700.40+174900.8 (center nucleus) through observations with $\it{GTC}$-$\it{MEGARA}$ Integral Field Unit. 1D and 2D analysis of the line ratios of the three nuclei allow us to locate them in the EW(H$α$) vs. [Nii] /H$α$ diagram. The central nucleus is found to be a retired galaxy (or fake AGN). The neighbors are found to be a strong AGN (southeastern nucleus, J102700.55+174900.2) compatible with a Sy2 galaxy, and a weak AGN (northern nucleus, J102700.38+174902.6) compatible with a LINER2. We find evidence that the neighbors constitute a dual AGN system (Sy2-LINER2) with a projected separation of 3.98 kpc in the optical bands. The H$α$ velocity map shows that the northern nucleus has an H$α$ emission with a velocity offset of $\sim$-500 km s$^{-1}$, whereas the southeastern nucleus has a rotating disk and H$α$ extended emission at kpc scales. Chandra archival data confirm that the neighbors have X-ray (0.5-2) keV and (2-7) keV emission, whereas the center nucleus shows no X-ray emission. A collisional ring with knots is observed in the HST images of the southeastern nucleus. These knots coincide with star formation regions that along with the ring are predicted in a head-on collision. In this case, the morphology changes are probably due to a minor merger that was produced by the passing of the northern through the southeastern nucleus.

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arXiv2017

Long-term optical polarization variability and multiwavelength analysis of Blazar Mrk 421

The results of 8-year R-band photopolarimetric data of blazar Mrk 421 collected from February 2008 to May 2016 are presented, along with extensive multiwavelength observations covering from radio to TeV $γ$-rays around the flares observed in May 2008, March 2010, and April 2013. The most important results are found in 2013 when the source displayed in the R-band a very high brightness state of $11.29\pm 0.03$ mag ($93.60\pm 1.53$ mJy) on April 10th and a polarization degree of ($11.00\pm0.44$) on May 13th. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over 7 nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16 and 19. In addition, the flux shows a minimum variability timescale of $Δ\,t=$2.34$\pm$0.12 hours, and that the polarization degree presented variations of $\sim$ (1 - 2) in a timescale of $Δ\,t\sim$ minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of $l_B\simeq$ 0.3 pc which is the same order of magnitude to the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26 $\pm$ 1.78 years.

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arXiv2015

Flaring activity of Mrk 421 in 2012 and 2013: orphan flare and multiwavelength analysis

The first one started in 2012 July 16 (MJD 56124) and the second one in 2013 April 9 (MJD 56391). The multiwavelength data analysis shows that the $γ$-ray flare observed in 2012 was not detected in the hard-X ray bands. This result is usually interpreted as an "orphan" flare. In 2013, the analysis of the multiwavelength light curves shows that there are two very bright states detected in the optical R-band. The first one in 2013 April 9 (R =11.74 $\pm$ 0.04) and the second one in May 12 (R =11.62 $\pm$ 0.04). Also, high activity states were detected in the soft and hard X-rays. A discrete correlation function analysis of this last flare shows a strong correlation between the GeV $γ$-rays and the optical/hard-X ray emission. These results are discussed in terms of the more adequate standard scenarios that could explain the multiwavelength variations displayed by this blazar.

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arXiv2015

Discovery of a Highly Polarized Optical Microflare in the Blazar S5 0716+714 During 2014 WEBT Campaign

The occurrence of low-amplitude flux variations in blazars on hourly timescales, commonly known as microvariability, is still a widely debated subject in high-energy astrophysics. Several competing scenarios have been proposed to explain such occurrences, including various jet plasma instabilities leading to the formation of shocks, magnetic reconnection sites, and turbulence. In this letter we present the results of our detailed investigation of a prominent, five-hour-long optical microflare detected during recent WEBT campaign in 2014, March 2-6 targeting the blazar 0716+714. After separating the flaring component from the underlying base emission continuum of the blazar, we find that the microflare is highly polarized, with the polarization degree $\sim (40-60)\%$$\pm (2-10)\%$, and the electric vector position angle $\sim (10 - 20)$deg$\pm (1-8)$deg slightly misaligned with respect to the position angle of the radio jet. The microflare evolution in the $(Q,\,U)$ Stokes parameter space exhibits a looping behavior with a counter-clockwise rotation, meaning polarization degree decreasing with the flux (but higher in the flux decaying phase), and approximately stable polarization angle. The overall very high polarization degree of the flare, its symmetric flux rise and decay profiles, and also its structured evolution in the $Q-U$ plane, all imply that the observed flux variation corresponds to a single emission region characterized by a highly ordered magnetic field. As discussed in the paper, a small-scale but strong shock propagating within the outflow, and compressing a disordered magnetic field component, provides a natural, though not unique, interpretation of our findings.

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arXiv2014

Rotation of the optical polarization angle associated with the 2008 γ-ray flare of blazar w comae

An $R$--band photopolarimetric variability analysis of the TeV bright blazar W Comae, between 2008 February 28 and 2013 May 17, is presented. The source showed a gradual tendency to decrease its mean flux level with a total change of ~3~mJy. A maximum and minimum brightness states in the $R$-band of 14.25$\pm$0.04 and 16.52$\pm$0.1~mag respectively were observed, corresponding to a maximum variation of $Δ$F = 5.40 mJy. We estimated a minimum variability timescale of $Δ$t=3.3 days. A maximum polarization degree $P$=33.8\%$\pm$1.6\%, with a maximum variation of $Δ$P = 33.2\%, was found. One of our main results is the detection of a large rotation of the polarization angle from 78\degr to 315\degr ($Δθ\sim$237\degr) that coincides in time with the $γ$-ray flare observed in 2008 June. This result indicates that both optical and $γ$-ray emission regions could be co-spatial. During this flare, a correlation between the $R$-band flux and polarization degree was found with a correlation coefficient of $r_{F-p}=0.93\pm$0.11. From the Stokes parameters we infer the existence of two optically thin synchrotron components that contribute to the polarized flux. One of them is stable with a constant polarization degree of 11\%. Assuming a shock-in jet model during the 2008 flare, we estimated a maximum Doppler factor $δ_D\sim 27$ and a minimum of $δ_D\sim 16$; a minimum viewing angle of the jet $\sim$2\degr.0; and a magnetic field $B \sim$ 0.12~G.

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arXiv2013

Long-term optical polarization variability of the tev blazar 1es~1959+650

A detailed analysis of the optical polarimetric variability of the TeV blazar 1ES 1959+650 from 2007 October 18 to 2011 May 5 is presented. The source showed a maximum and minimum brightness states in the R-band of 14.08$\pm$0.03 mag and 15.20$\pm$0.03 mag, respectively, with a maximum variation of 1.12 mag, and also a maximum polarization degree of $P=$(12.2$\pm$0.7)%, with a maximum variation of 10.7%. From August to November 2009, a correlation between the optical $R$-band flux and the degree of linear polarization was found, with a correlation coefficient $r_{pol}$=0.984$\pm$0.025. The source presented a preferential position angle of optical polarization of $\sim153^{\circ}$, with variations of $10\degr$-$50\degr$, that is in agreement with the projected position angle of the parsec scale jet found at 43 GHz. From the Stokes parameters we infer the existence of two optically-thin synchrotron components that contribute to the polarized flux. One of them is stable, with a constant polarization degree of 4%. Assuming a stationary shock for the variable component, we estimated some parameters associated with the physics of the relativistic jet: the magnetic field, $B\sim$0.06 G, the Doppler factor, $δ_{0}\sim$23, the viewing angle, $Φ\sim2.4\degr$, and the size of the emission region $r_b\sim5.6\times10^{17}$ cm. Our study is consistent with the spine-sheath model to explain the polarimetric variability displayed by this source during our monitoring.

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arXiv2012

Characterization of a sample of intermediate-type AGN. II. Host Bulge Properties and Black Hole Mass Estimates

We present a study of the host bulge properties and their relations with the black hole mass on a sample of 10 intermediate-type active galactic nuclei (AGN). Our sample consists mainly of early type spirals, four of them hosting a bar. For 70$^{+10}_{-17}%$ of the galaxies we have been able to determine the type of the bulge, and find that these objects probably harbor a pseudobulge or a combination of classical bulge/ pseudobulge, suggesting that pseudobulges might be frequent in intermediate-type AGN. In our sample, 50\pm14% of the objects show double-peaked emission lines. Therefore, narrow double-peaked emission lines seem to be frequent in galaxies harboring a pseudobulge or a combination of classical bulge/ pseudobulge. Depending on the bulge type, we estimated the black hole mass using the corresponding $M_{BH} - {σ*}$ relation and found them with a range of: 5.69$\pm$0.21 $<$ $\log M_{BH}^{σ*}$ $<$ 8.09$\pm$0.24. Comparing these $M_{BH}^{σ*}$ values with masses derived from the FWHM of H$β$ and the continuum luminosity at 5100 Åfrom their SDSS-DR7 spectra ($M_{BH}$) we find that eight out of ten (80$^{+7}_{-17}$%) galaxies have black hole masses that are compatible within a factor of 3. This result would support that $M_{BH}$ and $M_{BH}^{σ*}$ are the same for intermediate-type AGN as has been found for type 1 AGN. However, when the type of the bulge is taken into account only 3 out of the 7 (43$^{+18}_{-15}%$) objects of the sample have their $M_{BH}^{σ*}$ and $M_{BH}$ compatible within 3-$σ$ errors. We also find that estimations based on the $M_{BH}-σ*$ relation for pseudobulges are not compatible in 50$\pm20%$ of the objects.

astro-ph.CO↗

arXiv2012

Characterization of a sample of intermediate-type AGN. I. Spectroscopic properties and serendipitous discovery of new Dual AGN

A sample of 10 nearby intermediate-type active galactic nuclei (AGN) drawn from the Sloan Digital Sky Survey (SDSS-DR7) is presented. The aim of this work is to provide estimations of the black hole mass for the sample galaxies from the dynamics of the broad line region. For this purpose, a detailed spectroscopic analysis of the objects was done. Using BPT diagnostic diagrams we have carefully classified the objects as true intermediate-type AGN and found that 80%$^{+7.2%}_{-17.3%}$ are composite AGN. The black hole mass estimated for the sample is within 6.54$\pm$0.16\,$<$\,log\,$M_{\rm BH}$\,$<$\,7.81$\pm$0.14. Profile analysis show that five objects (\object{J120655.63+501737.1}, \object{J121607.08+504930.0}, \object{J141238.14+391836.5}, \object{J143031.18+524225.8} and \object{J162952.88+242638.3}) have narrow double-peaked emission lines in both the red (H$α$, [\ion{N}{2}]$λλ$6548,6583 and [\ion{S}{2}]$λλ$6716,6731) and the blue (H$β$ and [\ion{O}{3}]$λλ$4959,5007) region of the spectra, with velocity differences ($ΔV$) between the double peaks within 114\,$<ΔV\,<$\,256 km s$^{-1}$. Two of them, \object{J121607.08+504930.0} and \object{J141238.14+391836.5} are candidates for dual AGN since their double-peaked emission lines are dominated by AGN activity. In searches of dual AGN; Type 1, Type 1I and intermediate-type AGN should be carefully separated, due to the high serendipitous number of narrow double-peaked sources (50%$\pm$14.4%) found in our sample.

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