21 research outputs found
High-redshift Blazars through NuSTAR Eyes
MeV blazars are the most powerful sources among the blazar class. With bolometric luminosities exceeding 1048 erg s−1 and powerful relativistic jets, they are usually detected at high-redshifts (z \u3e 2) and they generally harbor extremely massive black holes (MBH ∼ 109 M⊙ ). Being able to derive their physical properties such as jet power, accretion disk luminosity, bulk Lorentz factor of the jet (Γ) and black hole mass, enables us to put constraints in the understanding of this not well sampled class of objects and use them for example to probe the formation of massive black holes in the early universe. In this thesis we have analyzed the broadband emission of three high redshift blazars, focusing on the high energy part of their spectral energy distribution. In fact, being able to obtain hard X-ray data from the recently launched NuSTAR and having γ-ray detections from the Fermi-LAT, we were able to constrain more accurately the high energy peak of their distribution and therefore more precisely infer their jet power, underlying electron distribution, Γ and viewing angle (θv ). Gathering optical and UV data allowed us to determine the black hole mass of such powerful objects as well as their accretion disk luminosity. This work has recently been published in ApJ (Marcotulli et al., 2017). In Section 1, the broad family of active galactic nuclei (ANGs) and their main physical characteristics are introduced, with a focus on the subclass of blazars and specifically MeV blazars. In Section 2, the main instruments used in our research to gather and analyze data are described, with a particular interest on imaging in the hard X-ray regime. Section 3 contains the data analysis description, the results obtained combining the observations with a one-zone leptonic emission model and the discussion on our findings. In Section 4 we report our conclusions and present an outlook on future MeV blazars studies possibilities. Appendix A, B and C contain an overlook of relativistic beaming, radiative processes and model used for these sources
A new measurement of the Hubble constant and matter content of the Universe using extragalactic background light -ray attenuation
The Hubble constant and matter density of the Universe
are measured using the latest -ray attenuation results from Fermi-LAT
and Cherenkov telescopes. This methodology is based upon the fact that the
extragalactic background light supplies opacity for very high energy photons
via photon-photon interaction. The amount of -ray attenuation along the
line of sight depends on the expansion rate and matter content of the Universe.
This novel strategy results in a value of
~km~s~Mpc and
. These estimates are independent and
complementary to those based on the distance ladder, cosmic microwave
background (CMB), clustering with weak lensing, and strong lensing data. We
also produce a joint likelihood analysis of our results from rays and
these from more mature methodologies, excluding the CMB, yielding a combined
value of ~km~s~Mpc and .Comment: 9 pages, 6 figures, 1 table. Accepted by Ap
Compton thick AGN in the NuSTAR era
We present the 2-100 keV spectral analysis of 30 candidate Compton thick
(CT-) active galactic nuclei (AGN) selected in the Swift-BAT 100-month survey.
The average redshift of these objects is 0.03 and they
all lie within 500 Mpc. We used the MyTorus (Murphy et al. 2009) model to
perform X-ray spectral fitting both without and with the contribution of the
NuSTAR data in the 3-50 keV energy range. When the NuSTAR data are added to the
fit, 14 out of 30 of these objects (47% of the whole sample) have intrinsic
absorption N3 confidence level,
i.e., they are re-classified from Compton thick to Compton thin. Consequently,
we infer an overall observed fraction of CT-AGN with respect to the whole AGN
population lower than the one reported in previous works, and as low as
4%. We find evidence that this over-estimation of N is likely
due to the low quality of a subsample of spectra, either in the 2-10 keV band
or in the Swift-BAT one.Comment: 19 pages, 10 figures, accepted for publication on the Astrophysical
Journa
A Cross-correlation Study between IceCube Neutrino Events and the Fermi Unresolved Gamma-ray Sky
With the coincident detections of electromagnetic radiation together with
gravitational waves (GW170817) or neutrinos (TXS 0506+056), the new era of
multimessenger astrophysics has begun. Of particular interest are the searches
for correlation between the high-energy astrophysical neutrinos detected by the
IceCube Observatory and gamma-ray photons detected by the Fermi Large Area
Telescope (LAT). So far, only sources detected by the LAT have been considered
in correlation with IceCube neutrinos, neglecting any emission from sources too
faint to be resolved individually. Here, we present the first cross-correlation
analysis considering the unresolved gamma-ray background (UGRB) and IceCube
events. We perform a thorough sensitivity study and, given the lack of
identified correlation, we place upper limits on the fraction of the observed
neutrinos that would be produced in proton-proton (p-p) or proton-gamma
(p-gamma) interactions from the population of sources contributing to the UGRB
emission and dominating its spatial anisotropy (aka blazars). Our analysis
suggests that, under the assumption that there is no intrinsic cutoff and/or
hardening of the spectrum above Fermi-LAT energies, and that all gamma-rays
from the unresolved blazars dominating the UGRB fluctuation field are produced
by neutral pions from p-p (p-gamma) interactions, up to 60% (30%) of such
population may contribute to the total neutrino events observed by IceCube.
This translates into a O(1%) maximum contribution to the astrophysical
high-energy neutrino flux observed by IceCube at 100 TeV.Comment: This version is submitted to Ap
Identifying the 3FHL Catalog. IV. Swift Observations of Unassociated Fermi-LAT 3FHL Sources
The Fermi Large Area Telescope (Fermi-LAT) 3FHL catalog is the latest catalog
of >10 GeV sources and will remain an important resource for the high-energy
community for the foreseeable future. Therefore, it is crucial that this
catalog is made complete by providing associations for most sources. In this
paper, we present the results of the X-ray analysis of 38 3FHL sources. We
found a single bright X-ray source in 20 fields, two sources each in two fields
and none for the remaining 16. The analysis of the properties of the 22 3FHL
fields with X-ray sources led us to believe that most (19/22) are of
extra-galactic origin. A machine-learning algorithm was used to determine the
source type and we find that 15 potential blazars are likely BL Lacertae
objects (BL Lacs). This is consistent with the fact that BL Lacs are by far the
most numerous population detected above >10 GeV in the 3FHL
Compton-thick AGN in the NuSTAR era III: A systematic study of the torus covering factor
We present the analysis of a sample of 35 candidate Compton thick (CT-)
active galactic nuclei (AGNs) selected in the nearby Universe (average redshift
~0.03) with the Swift-BAT 100-month survey. All sources have available
NuSTAR data, thus allowing us to constrain with unprecedented quality important
spectral parameters such as the obscuring torus line-of-sight column density
(N_{H, z}), the average torus column density (N_{H, tor}) and the torus
covering factor (f_c). We compare the best-fit results obtained with the widely
used MyTorus (Murphy et al. 2009) model with those of the recently published
borus02 model (Balokovic et al. 2018) used in the same geometrical
configuration of MyTorus (i.e., with f_c=0.5). We find a remarkable agreement
between the two, although with increasing dispersion in N_{H, z} moving towards
higher column densities. We then use borus02 to measure f_c. High-f_c sources
have, on average, smaller offset between N_{H, z} and N_{H, tor} than low-f_c
ones. Therefore, low f_c values can be linked to a "patchy torus" scenario,
where the AGN is seen through an over-dense region in the torus, while high-f_c
objects are more likely to be obscured by a more uniform gas distribution.
Finally, we find potential evidence of an inverse trend between f_c and the AGN
2-10 keV luminosity, i.e., sources with higher f_c values have on average lower
luminosities.Comment: 35 Pages, 23 Figures. Accepted for publication in Ap
Supermassive black holes at high redshifts
MeV blazars are the most luminous persistent sources in the Universe and emit
most of their energy in the MeV band. These objects display very large jet
powers and accretion luminosities and are known to host black holes with a mass
often exceeding . An MeV survey, performed by a new generation
MeV telescope which will bridge the entire energy and sensitivity gap between
the current generation of hard X-ray and gamma-ray instruments, will detect
1000 MeV blazars up to a redshift of . Here we show that this would
allow us: 1) to probe the formation and growth mechanisms of supermassive black
holes at high redshifts, 2) to pinpoint the location of the emission region in
powerful blazars, 3) to determine how accretion and black hole spin interplay
to power the jet.Comment: 7 pages, 4 figure. Submitted to the Astro2020 call for Science White
Paper
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is
designed to identify and characterize gamma rays from extreme explosions and
accelerators. The main science themes include: supermassive black holes and
their connections to neutrinos and cosmic rays; binary neutron star mergers and
the relativistic jets they produce; cosmic ray particle acceleration sources
including Galactic supernovae; and continuous monitoring of other astrophysical
events and sources over the full sky in this important energy range. AMEGO-X
will probe the medium energy gamma-ray band using a single instrument with
sensitivity up to an order of magnitude greater than previous telescopes in the
energy range 100 keV to 1 GeV that can be only realized in space. During its
three-year baseline mission, AMEGO-X will observe nearly the entire sky every
two orbits, building up a sensitive all-sky map of gamma-ray sources and
emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of
Opportunity.Comment: 23 pages, 16 figures, Published Journal of Astronomical Telescopes,
Instruments, and System