117 research outputs found
The properties of the AGN torus as revealed from a set of unbiased NuSTAR observations
The obscuration observed in active galactic nuclei (AGN) is mainly caused by
dust and gas distributed in a torus-like structure surrounding the supermassive
black hole (SMBH). However, properties of the obscuring torus of the AGN in
X-ray have not been fully investigated yet due to the lack of high-quality data
and proper models. In this work, we perform a broadband X-ray spectral analysis
of a large, unbiased sample of obscured AGN (with line-of-sight column density
23log(NH)24) in the nearby universe which has high-quality archival
NuSTAR data. The source spectra are analyzed using the recently developed
borus02 model, which enables us to accurately characterize the physical and
geometrical properties of AGN obscuring tori. We also compare our results
obtained from the unbiased Compton thin AGN with those of Compton-thick AGN. We
find that Compton thin and Compton-thick AGN may possess similar tori, whose
average column density is Compton thick (N
1.410 cm), but they are observed through different
(under-dense or over-dense) regions of the tori. We also find that the
obscuring torus medium is significantly inhomogeneous, with the torus average
column densities significantly different from their line-of-sight column
densities (for most of the sources in the sample). The average torus covering
factor of sources in our unbiased sample is c=0.67, suggesting that the
fraction of unobscured AGN is 33%. We develop a new method to measure the
intrinsic line-of-sight column density distribution of AGN in the nearby
universe, which we find the result is in good agreement with the constraints
from recent population synthesis models.Comment: 16 pages, 14 figures, 7 tables; accepted by A&
Multiwavelength Analysis of Fermi-LAT Blazars with High-Significance Periodicity: Detection of a Long-Term Rising Emission in PG 1553+113
Blazars display variable emission across the entire electromagnetic spectrum,
with timescales that can range from a few minutes to several years. Our recent
work has shown that a sample of five blazars exhibit hints of periodicity with
a global significance at -ray energies, in the range
of 0.1~GeVE800~GeV. In this work, we study their multiwavelength (MWL)
emission, covering the X-ray, ultraviolet, optical, and radio bands. We show
that three of these blazars present similar periodic patterns in the optical
and radio bands. Additionally, fluxes in the different bands of the five
blazars are correlated, suggesting a co-spatial origin. Moreover, we detect a
long-term (10 year) rising trend in the light curves of PG~1553+113,
and we use it to infer possible constraints on the binary black hole
hypothesis.Comment: 20 pages, 10 figures, 7 table
A Compton-thick nucleus in the dual AGN of Mrk 266
We present results of our analysis of NuSTAR data of the luminous infrared
galaxy Mrk 266, which contains two nuclei, SW and NE, resolved in previous
Chandra imaging. Combining with the Chandra data, we intepret the hard X-ray
spectrum obtained from a NuSTAR observation as resulting from steeply rising
flux from a Compton-thick AGN in the SW nucleus which is very faint in the
Chandra band, confirming the previous claim of Mazzarella et al. (2012). This
hard X-ray component is dominated by reflection, and its intrinsic 2-10 keV
luminosity is likely to be ~1e43 erg/s. Although it is bright in soft X-ray,
only moderately absorbed NE nucleus has a 2-10 keV luminosity of 4e41 erg/s,
placing it in the low-luminosity AGN class. These results have implications for
understanding the detectability and duty cycles of emission from dual AGN in
heavily obscured mergers.Comment: Accepted for publication in Astronomy and Astrophysics. 7 pages, 5
figures. Language corrections and a minor correction in Fig. 5 include
A Compton-thick nucleus in the dual active galactic nuclei of Mrk 266
We present the results from our analysis of NuSTAR data of the luminous infrared galaxy Mrk 266, which contains two nuclei, south-western (SW) and north-eastern (NE), which were resolved in previous Chandra imaging. Combining this with the Chandra data, we intepret the hard X-ray spectrum obtained from a NuSTAR observation to result from a steeply rising flux from a Compton-thick active galactic nuclei (AGN) in the SW nucleus which is very faint in the Chandra band, confirming the previous claim. This hard X-ray component is dominated by reflection, and its intrinsic 2–10 keV luminosity is likely to be ∼1 × 10⁴³ erg s⁻¹. Although it is bright in soft X-ray, only a moderately absorbed NE nucleus has a 2–10 keV luminosity of 4 × 10⁴¹ erg s⁻¹, placing it in the low-luminosity AGN class. These results have implications for understanding the detectability and duty cycles of emission from dual AGN in heavily obscured mergers
C-GOALS II. Chandra Observations of the Lower Luminosity Sample of Nearby Luminous Infrared Galaxies in GOALS
We analyze Chandra X-ray observatory data for a sample of 63 luminous
infrared galaxies (LIRGs), sampling the lower-infrared luminosity range of the
Great Observatories All-Sky LIRG survey (GOALS), which includes the most
luminous infrared selected galaxies in the local universe. X-rays are detected
for 84 individual galaxies within the 63 systems, for which arcsecond
resolution X-ray images, fluxes, infrared and X-ray luminosities, spectra and
radial profiles are presented. Using X-ray and MIR selection criteria, we find
AGN in (315)% of the galaxy sample, compared to the (386)% previously
found for GOALS galaxies with higher infrared luminosities (C-GOALS I). Using
mid-infrared data, we find that (599)% of the X-ray selected AGN in the
full C-GOALS sample do not contribute significantly to the bolometric
luminosity of the host galaxy. Dual AGN are detected in two systems, implying a
dual AGN fraction in systems that contain at least one AGN of (2914)%,
compared to the (1110)% found for the C-GOALS I sample. Through analysis
of radial profiles, we derive that most sources, and almost all AGN, in the
sample are compact, with half of the soft X-ray emission generated within the
inner kpc. For most galaxies, the soft X-ray sizes of the sources are
comparable to those of the MIR emission. We also find that the hard X-ray
faintness previously reported for the bright C-GOALS I sources is also observed
in the brightest LIRGs within the sample, with
L.Comment: 24 pages, 13 figures, 11 tables, accepted for publication in A&
MAGIC Observations of the Nearby Short Gamma-Ray Burst GRB 160821B
Acciari, A. V., et al.The coincident detection of GW170817 in gravitational waves and electromagnetic radiation spanning the radio to MeV gamma-ray bands provided the first direct evidence that short gamma-ray bursts (GRBs) can originate from binary neutron star (BNS) mergers. On the other hand, the properties of short GRBs in high-energy gamma-rays are still poorly constrained, with only ∼20 events detected in the GeV band, and none in the TeV band. GRB 160821B is one of the nearest short GRBs known at z = 0.162. Recent analyses of the multiwavelength observational data of its afterglow emission revealed an optical-infrared kilonova component, characteristic of heavy-element nucleosynthesis in a BNS merger. Aiming to better clarify the nature of short GRBs, this burst was automatically followed up with the MAGIC telescopes, starting from 24 s after the burst trigger. Evidence of a gamma-ray signal is found above ∼0.5 TeV at a significance of ∼ 3σ during observations that lasted until 4 hr after the burst. Assuming that the observed excess events correspond to gamma-ray emission from GRB 160821B, in conjunction with data at other wavelengths, we investigate its origin in the framework of GRB afterglow models. The simplest interpretation with one-zone models of synchrotron-self-Compton emission from the external forward shock has difficulty accounting for the putative TeV flux. Alternative scenarios are discussed where the TeV emission can be relatively enhanced. The role of future GeV-TeV observations of short GRBs in advancing our understanding of BNS mergers and related topics is briefly addressed.We would like to thank the Instituto de Astrofísica de Canarias
for the excellent working conditions at the Observatorio del
Roque de los Muchachos in La Palma. The financial support of
the German BMBF and MPG; the Italian INFN and INAF; the
Swiss National Fund SNF; the ERDF under the Spanish
MINECO (FPA2017-87859-P, FPA2017-85668-P, FPA2017-
82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-
R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2017-
87055-C2-2-P, FPA2017-90566-REDC); the Indian Department
of Atomic Energy; the Japanese ICRR, the University of Tokyo,
JSPS, and MEXT; the Bulgarian Ministry of Education and
Science, National RI Roadmap Project DO1-268/16.12.2019 and
the Academy of Finland grant No. 320045 is gratefully
acknowledged. This work was also supported by the Spanish
Centro de Excelencia “Severo Ochoa” SEV-2016-0588, SEV2015-0548 and SEV-2012-0234, the Unidad de Excelencia
“María de Maeztu” MDM-2014-0369 and the “la Caixa”
Foundation (fellowship LCF/BQ/PI18/11630012), by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the
University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the
Polish National Research Centre grant UMO-2016/22/M/ST9/
00382 and by the Brazilian MCTIC, CNPq and FAPERJ. K.N. is
thankful for the support by Marie Skłodowska-Curie actions (H2020-MSCA-COFUND-2014, Project P-Sphere GA 665919),
and JSPS KAKENHI grant No. JP20KK0067 from MEXT,
Japan. L.N. acknowledges funding from the European Union’s
Horizon 2020 research and innovation program under the Marie
Skłodowska-Curie grant agreement No. 664931. S.I. is supported
by JSPS KAKENHI grant No. JP17K05460 from MEXT, Japan,
and the RIKEN iTHEMS program
Multiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and γ-ray activity in 2015-2016
Acciari, V. A., et al. (MAGIC Collaboration)We report a characterization of the multiband flux variability and correlations of the nearby (z = 0.031) blazar Markarian 421 (Mrk 421) using data from Metsähovi, Swift, Fermi-LAT, MAGIC, FACT, and other collaborations and instruments from 2014 November till 2016 June. Mrk 421 did not show any prominent flaring activity, but exhibited periods of historically low activity above 1 TeV (F>1 TeV 0.1 TeV) γ-rays, which, despite the low activity, show a significant positive correlation with no time lag. The HRkeV and HRTeV show the harder-when-brighter trend observed in many blazars, but the trend flattens at the highest fluxes, which suggests a change in the processes dominating the blazar variability. Enlarging our data set with data from years 2007 to 2014, we measured a positive correlation between the optical and the GeV emission over a range of about 60 d centred at time lag zero, and a positive correlation between the optical/GeV and the radio emission over a range of about 60 d centred at a time lag of 43+9-6 d. This observation is consistent with the radio-bright zone being located about 0.2 parsec downstream from the optical/GeV emission regions of the jet. The flux distributions are better described with a lognormal function in most of the energy bands probed, indicating that the variability in Mrk 421 is likely produced by a multiplicative process.The financial support of the German BMBF and MPG; the Italian INFN and INAF; the Swiss National Fund SNF; the ERDF under the Spanish MINECO (FPA2017-87859-P, FPA2017-85668-P, FPA2017-82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2017-87055-C2-2-P, FPA2017-90566-REDC); the Indian Department of Atomic Energy; the Japanese ICRR, the University of Tokyo, JSPS, and MEXT; the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-268/16.12.2019 and the Academy of Finland grant nr. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia ‘Severo Ochoa’ SEV-2016-0588 and SEV-2015-0548, the Unidad de Excelencia ‘María de Maeztu’ MDM-2014-0369 and the ‘la Caixa’ Foundation (fellowship LCF/BQ/PI18/11630012), by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq, and FAPERJ
An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state
Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at vs ≥ 1017 Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state without showing any extreme behaviours. In 2016 August, 1ES 2344+514 was detected with the groundbased γ -ray telescope FACT during a high γ -ray state, triggering multiwavelength (MWL) observations. We studied the MWL light curves of 1ES 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (VHE) γ -rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, Swift-UVOT, Swift-XRT, Fermi-LAT, FACT, and MAGIC. With simultaneous observations of the flare, we built the broad-band SED and studied it in the framework of a leptonic and a hadronic model. The VHE γ -ray observations show a flux level of 55 per cent of the Crab Nebula flux above 300 GeV, similar to the historical maximum of 1995. The combination of MAGIC and Fermi-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The _ index of the intrinsic spectrum in the VHE γ -ray band is 2.04 ± 0.12stat ± 0.15sys.We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 Hz.The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2017-87859-P, FPA2017-85668-P, FPA2017-82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2017-87055-C2-2-P, and FPA2017-90566-REDC), the Indian Department of Atomic Energy, the Japanese JSPS and MEXT, the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-153/28.08.2018, and the Academy of Finland grant no. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia ‘Severo Ochoa’ SEV-2016-0588 and SEV-2015-0548, and Unidad de Excelencia ‘María de Maeztu’ MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq, and FAPERJ. The FACT collaboration acknowledges the important contributions from ETH Zurich grants ETH-10.08-2 and ETH-27.12-1 as well as the funding by the Swiss SNF and the German BMBF (Verbundforschung Astro- und Astroteilchenphysik) and HAP (Helmoltz Alliance for Astroparticle Physics) are gratefully acknowledged. Part of this work is supported by Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Center SFB 876 ‘Providing Information by Resource-Constrained Analysis’, project C3
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