NuSTAR Perspective on High-redshift MeV Blazars

Abstract

With bolometric luminosities exceeding 10 48 erg s −1 , powerful jets and supermassive black holes at their center, MeV blazars are some of the most extreme sources in the Universe. Recently, the Fermi-Large Area Telescope detected five new γ-ray emitting MeV blazars beyond redshift z = 3.1. With the goal of precisely characterizing the jet properties of these extreme sources, we started a multiwavelength campaign to follow them up with joint NuSTAR, Swift and SARA observations. We observe six high-redshift quasars, four of them belonging to the new γ-ray emitting MeV blazars. Thorough X-ray analysis reveals spectral flattening at soft X-ray for three of these objects. The source NVSS J151002+570243 also shows a peculiar re-hardening of the X-ray spectrum at energies E > 6 keV. Adopting a one-zone leptonic emission model, this combination of hard X-rays and γ-rays enables us to determine the location of the Inverse Compton peak and to accurately constrain the jet characteristics. In the context of the jet-accretion disk connection, we find that all six sources have jet powers exceeding accretion disk luminosity, seemingly validating this positive correlation even beyond z > 3. Our six sources are found to have 10 9 M ⊙ black holes, further raising the space density of supermassive black holes in the redshift bin z = [3, 4].

The Highly Self-Absorbed Blazar, PKS\,1351$-$018

“…With finer sampling (3 days), this increases to ≈ 10 49 erg s −1 , but TS falls below 25, TS 20. The SED in the γ-ray region is very steeply decreasing power law (α ≈ 2) as expected for strong external inverse Compton cooling from the existence of the luminous quasar environment that was described in the last section (Sahakyan et al 2020;Marcotulli et al 2020). This combined with the high redshift indicates that most of the γ-ray luminosity is most likely at observed energies < 0.1 GeV.…”

“…There is no observational evidence to justify a model more complicated than a homogeneous, spherical, single zone of plasma. Single zone spherical models are a standard technique even in blazar jet calculations out of practical necessity including previous treatments of this source (Ghisellini et al 2010;Sahakyan et al 2020;Marcotulli et al 2020). A simple homogeneous spherical volume model or plasmoid has historically provided an understanding of the spectra and the time evolution of astrophysical radio sources (van der Laan 1966).…”

“…The value of minimum lepton energy, E min , is not constrained directly by observation. Values of E min = m e c 2 and E min = 2.6m e c 2 are used in Marcotulli et al (2020) and Sahakyan et al (2020), respectively, to fit the synchrotron peak and the inverse Compton spectrum from the nucleus. Here m e denotes the electron mass.…”

Probing the physical properties of the intergalactic medium using blazars

“…Several studies have tentatively explored absorption scenarios, either neutral or a warm absorption component, as a minor part of their work, typically placing the absorber at the blazar redshift (e.g. Bottacini et al 2010;Paliya et al 2016;Ricci et al 2017;Marcotulli et al 2020;Haim et al 2019). Bottacini et al (2010) found they could not constrain their photo-ionized model parameter better than an upper limit.…”

“…We reviewed literature that studied large numbers of blazars (e.g. Perlman et al 1998;Donato, Sambruna & Gliozzi 2005;Eitan & Behar 2013;Ighina et al 2019;Marcotulli et al 2020) and, within our criteria, selected objects randomly for our sample. Our sample has 14 with z > 2, a high fraction of the total available as noted above.…”