Context. Very luminous quasars are unique sources for studying the circumnuclear environment around supermassive black holes. Several components contribute to the overall X-ray spectral shape of active galactic nuclei (AGN). The hot (kT(e) = 50-100 keV) and warm (kT(e) = 0.1-1 keV) coronae are responsible for the hard and soft power-law continua, while the circumnuclear toroidal reflector accounts for the Fe K emission line and the associated Compton hump. However, all these spectral features are simultaneously observed only in a handful of sources above z similar or equal to 0.1.Aims. An ideal astrophysical laboratory for this investigation is the quasar RBS 1055, at z similar or equal to 0.45. With a luminosity L-2-10(keV) = 2 x 10(45)( )erg s(-1), it is the brightest radio-quiet quasar from the ROSAT Bright Survey. Despite the known anti-correlation between the equivalent width (EW) of the narrow neutral Fe K alpha line and L2-10keV, an intense Fe K alpha was previously detected for this source.Methods. We report findings based on a long (250 ks) NuSTAR observation performed in March 2021 and archival XMM-Newton pointings (185 ks) taken in July 2014. We also analyzed an optical spectrum of the source taken with the Double Spectrograph at the Palomar Observatory quasi-simultaneously to the NuSTAR observations.Results. We find that the two-corona model, in which a warm and hot corona coexist, well reproduces the broad band spectrum of RBS 1055, with temperatures kT(e) = 0.12(-0.03)(+0.)(08) keV, kT(e) = 30(-10)(+40) keV and Thomson optical depths tau = 30(-1.4)(+1.0) and T = 3.01:4 for the former and the latter component, respectively. We confirm the presence of an intense Fe K alpha emission line (EW = 55 +/- 6 eV) and find, when a toroidal model is considered for reproducing the Compton reflection, a Compton-thin solution with N-H = (3.2(-0.8)(+0.9)) x 10(23) cm(-2) for the circumnuclear reflector. A detailed analysis of the optical spectrum reveals a likely peculiar configuration of our line of sight with respect to the nucleus, and the presence of a broad [O III] component tracing outflows in the Narrow Line Region, with a velocity shift v = 1500 +/- 100 km s(-1), leading to a mass outflow rate (M) over dot(out) = 25.4 +/- 1.5 M-circle dot yr(-1) and outflow kinetic power normalized by the bolometric luminosity (E)over dot(kin)/L-Bol similar to 0.33%. We estimate the BH mass to be in the range 2.8 x 10(8) -1.2 x 10(9) M-circle dot, according to different broad line region emission lines, with an average value of < M-BH > = 6.5 x 10(8) M-circle dot.Conclusions. With an Fe K alpha that is 3 sigma above the value predicted from the EW-L-2-(10keV) relation and an extreme source brightness at 2 keV (a factor 10-15 higher than the one expected from the optical/UV), we can confirm that RBS 1055 is an outlier in the X-rays compared to other objects in the same luminosity and redshift range.

Marinucci, A., Vietri, G., Piconcelli, E., Bianchi, S., Guainazzi, M., Lanzuisi, G., et al. (2022). Breaking the rules at z ??? 0.45: The rebel case of RBS 1055. ASTRONOMY & ASTROPHYSICS, 666 [10.1051/0004-6361/202244272].

Breaking the rules at z ??? 0.45: The rebel case of RBS 1055

A. Marinucci;S. Bianchi;M. Guainazzi;C. Vignali
2022

Abstract

Context. Very luminous quasars are unique sources for studying the circumnuclear environment around supermassive black holes. Several components contribute to the overall X-ray spectral shape of active galactic nuclei (AGN). The hot (kT(e) = 50-100 keV) and warm (kT(e) = 0.1-1 keV) coronae are responsible for the hard and soft power-law continua, while the circumnuclear toroidal reflector accounts for the Fe K emission line and the associated Compton hump. However, all these spectral features are simultaneously observed only in a handful of sources above z similar or equal to 0.1.Aims. An ideal astrophysical laboratory for this investigation is the quasar RBS 1055, at z similar or equal to 0.45. With a luminosity L-2-10(keV) = 2 x 10(45)( )erg s(-1), it is the brightest radio-quiet quasar from the ROSAT Bright Survey. Despite the known anti-correlation between the equivalent width (EW) of the narrow neutral Fe K alpha line and L2-10keV, an intense Fe K alpha was previously detected for this source.Methods. We report findings based on a long (250 ks) NuSTAR observation performed in March 2021 and archival XMM-Newton pointings (185 ks) taken in July 2014. We also analyzed an optical spectrum of the source taken with the Double Spectrograph at the Palomar Observatory quasi-simultaneously to the NuSTAR observations.Results. We find that the two-corona model, in which a warm and hot corona coexist, well reproduces the broad band spectrum of RBS 1055, with temperatures kT(e) = 0.12(-0.03)(+0.)(08) keV, kT(e) = 30(-10)(+40) keV and Thomson optical depths tau = 30(-1.4)(+1.0) and T = 3.01:4 for the former and the latter component, respectively. We confirm the presence of an intense Fe K alpha emission line (EW = 55 +/- 6 eV) and find, when a toroidal model is considered for reproducing the Compton reflection, a Compton-thin solution with N-H = (3.2(-0.8)(+0.9)) x 10(23) cm(-2) for the circumnuclear reflector. A detailed analysis of the optical spectrum reveals a likely peculiar configuration of our line of sight with respect to the nucleus, and the presence of a broad [O III] component tracing outflows in the Narrow Line Region, with a velocity shift v = 1500 +/- 100 km s(-1), leading to a mass outflow rate (M) over dot(out) = 25.4 +/- 1.5 M-circle dot yr(-1) and outflow kinetic power normalized by the bolometric luminosity (E)over dot(kin)/L-Bol similar to 0.33%. We estimate the BH mass to be in the range 2.8 x 10(8) -1.2 x 10(9) M-circle dot, according to different broad line region emission lines, with an average value of < M-BH > = 6.5 x 10(8) M-circle dot.Conclusions. With an Fe K alpha that is 3 sigma above the value predicted from the EW-L-2-(10keV) relation and an extreme source brightness at 2 keV (a factor 10-15 higher than the one expected from the optical/UV), we can confirm that RBS 1055 is an outlier in the X-rays compared to other objects in the same luminosity and redshift range.
Marinucci, A., Vietri, G., Piconcelli, E., Bianchi, S., Guainazzi, M., Lanzuisi, G., et al. (2022). Breaking the rules at z ??? 0.45: The rebel case of RBS 1055. ASTRONOMY & ASTROPHYSICS, 666 [10.1051/0004-6361/202244272].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/423272
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