ABSTRACT
A detailed multiwavelength study of the properties of the triple-peaked active galactic nucleus (AGN) Mrk 622 showing different aspects of the nuclear emission region is presented. Radio, ...near- and mid-infrared, optical, and X-ray data have been considered for the analysis. In the optical, the WHAN diagnostic diagrams show that the three nuclear peaks are strong active galactic nuclei since the equivalent width of H α is > 6 Å and log N ii λ6584/H α ratio is > −0.4. Optical variability of both the continuum flux and intensity of the narrow emission lines is detected in a time span of 13 yr. The size of the narrow-line region is found to be 2.7 pc, with a light-crossing time of 8.7 yr. Analysis done to an archival Hubble Space Telescope image at 1055.2 nm shows that the host galaxy has a 3.6 kpc inner bar with PA = 74°, faint spiral arms, and a pseudobulge, evolving through secular processes. High-resolution mid-infrared images obtained with the Gran Telescopio Canarias (GTC) and the instrument CanariCam show that the nuclear emission at 11.6 $\rm{\mu m}$ is not spatially resolved. Very Large Array archival observations at 10 GHz reveal a core source with a total flux density of 1.47 ± 0.03 mJy. The spectral index of the core between 8 and 12 GHz is −0.5 ± 0.2, characteristic of AGN. The core deconvolves into a source with dimensions of 82 ± 13 mas $\, \times \,$ 41 ± 20 mas, and a PA = 70 ± 18 deg, which suggests that the core is elongated or that it is constituted by multiple components distributed along a ∼65° axis.
We recently developed a procedure to recognize
γ
-ray blazar candidates within the positional uncertainty regions of the unidentified/unassociated
γ
-ray sources (UGSs). Such procedure was based on ...the discovery that
Fermi
blazars show peculiar infrared colors. However, to confirm the real nature of the selected candidates, optical spectroscopic data are necessary. Thus, we performed an extensive archival search for spectra available in the literature in parallel with an optical spectroscopic campaign aimed to reveal and confirm the nature of the selected
γ
-ray blazar candidates. Here, we first search for optical spectra of a selected sample of
γ
-ray blazar candidates that can be potential counterparts of UGSs using the Sloan Digital Sky Survey (SDSS DR12). This search enables us to update the archival search carried out to date. We also describe the state-of-art and the future perspectives of our campaign to discover previously unknown
γ
-ray blazars.
Context.
A significant fraction of all
γ
-ray sources detected by the Large Area Telescope aboard the
Fermi
satellite is still lacking a low-energy counterpart. In addition, there is still a large ...population of
γ
-ray sources with associated low-energy counterparts that lack firm classifications. In the last 10 years we have undertaken an optical spectroscopic campaign to address the problem of unassociated or unidentified
γ
-ray sources (UGSs), mainly devoted to observing blazars and blazar candidates because they are the largest population of
γ
-ray sources associated to date.
Aims.
Here we describe the overall impact of our optical spectroscopic campaign on sources associated in
Fermi
-LAT catalogs, coupled with objects found in the literature. In the literature search we kept track of efforts by different teams that presented optical spectra of counterparts or potential counterparts of
Fermi
-LAT catalog sources. Our summary includes an analysis of additional 30 newly collected optical spectra of counterparts or potential counterparts of
Fermi
-LAT sources of a previously unknown nature.
Methods.
New spectra were acquired at the
Blanco
4 m and OAN-SPM 2.1 m telescopes, and those available in the Sloan Digital Sky Survey (data release 15) archive.
Results.
All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, altogether we discovered and classified 394 targets with an additional 123 objects collected from a literature search. We began our optical spectroscopic campaign between the release of the second and third
Fermi
-LAT source catalogs (2FGL and 3FGL, respectively), classified about 25% of the sources that had uncertain nature and discovered a blazar-like potential counterpart for ∼10% of UGSs listed therein. In the 4FGL catalog, about 350
Fermi
-LAT sources have been classified to date thanks to our campaign.
Conclusions.
The most elusive class of blazars are found to be BL Lacs since the largest fraction of
Fermi
-LAT sources targeted in our observations showed a featureless optical spectrum. The same conclusion applied to the literature spectra. Finally, we confirm the high reliability of mid-IR color-based methods to select blazar-like candidate counterparts of unassociated or unidentified
γ
-ray sources.
In the last decade, an increase in honey bee (Apis mellifera L.) colony losses has been reported in several countries. The causes of this decline are still not clear. This study was set out to ...evaluate the pesticide residues in stored pollen from honey bee colonies and their possible impact on honey bee losses in Spain. In total, 1,021 professional apiaries were randomly selected. All pollen samples were subjected to multiresidue analysis by gas chromatography-mass spectrometry ( MS ) and liquid chromatography-MS; moreover, specific methods were applied for neonicotinoids and fipronil. A palynological analysis also was carried out to confirm the type of foraging crop. Pesticide residues were detected in 42% of samples collected in spring, and only in 31% of samples collected in autumn. Fluvalinate and chlorfenvinphos were the most frequently detected pesticides in the analyzed samples. Fipronil was detected in 3.7% of all the spring samples but never in autumn samples, and neonicotinoid residues were not detected. More than 47.8% of stored pollen samples belonged to wild vegetation, and sunflower (Heliantus spp.) pollen was only detected in 10.4% of the samples. A direct relation between pesticide residues found in stored pollen samples and colony losses was not evident accordingly to the obtained results. Further studies are necessary to determine the possible role of the most frequent and abundant pesticides (such as acaricides) and the synergism among them and with other pathogens more prevalent in Spain.
ABSTRACT Blazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of γ-ray sources, and their number is continuously growing in the Fermi catalogs. ...However, in the latest release of the Fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (BCUs) for which optical spectroscopic observations are necessary to confirm their nature and their associations. In addition, about one-third of the γ-ray point sources listed in the Third Fermi-LAT Source Catalog (3FGL) are still unassociated and lacking an assigned lower-energy counterpart. Since 2012 we have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. In this paper, the sixth of the series, we present optical spectroscopic observations for 30 γ-ray blazar candidates from different observing programs we carried out with the Telescopio Nazionale Galileo, William Herschel Telescope, Observatorio Astronómico Nacional, Southern Astrophysical Research Telescope, and Magellan Telescopes. We found that 21 out of 30 sources investigated are BL Lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. We conclude that our selection of γ-ray blazar candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the Fermi unidentified gamma-ray sources and to confirm the nature of BCUs.
Nearly one third of the sources in the
Fermi
-LAT catalogs lacks a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify ...them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic
γ
-ray sources. In Fermi-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofísico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts.
The third
Fermi
source catalog lists 3033
γ
-ray sources above
4
σ
significance. More than 30% are classified as either unidentified/unassociated Gamma-ray sources (UGSs), with about 20% classified ...as Blazar candidates of uncertain types (BCUs). To confirm the blazar-like nature of candidate counterparts of UGSs and BCUs, we started in 2012 an optical spectroscopic follow up campaign. We report here the spectra of 36 targets with observations from the Observatorio Astronómico Nacional San Pedro Mártir, the Southern Astrophysical Research Observatory, the Kitt Peak National Observatory and the Northern Optical Telescope, between 2016 and 2017. We confirm the BL Lac nature of 23 sources, and the flat spectrum radio quasar nature of other 7 ones. We also provide redshift estimates for 19 out of these 30 confirmations, with only one being a lower limit due to spectral features ascribable to intervening systems along the line of sight. As in previous analyses, the largest fraction of now-classified BCUs belong to the class of BL Lac objects, that appear to be the most elusive class of active galactic nuclei. One of the BL Lacs identified in this work, associated with 3FGL J2213.6-4755, lies at a redshift of
z
>
1.529
, making it one of the few distant gamma-ray BL Lac objects.
Searching for low energy counterparts of
γ
-rays sources is one of the major challenges in modern
γ
-ray astronomy. In the third Fermi source catalog about 30% of detected sources are ...unidentified/unassociated Gamma-ray Sources (UGSs). We recently started an optical spectroscopic follow up campaign to confirm the blazar-like nature of candidates counterparts of UGSs. Here we report the spectra of
61
targets collected with the Southern Astrophysical Research Telescope (SOAR) between 2014 and the 2017. Our sample includes
33
potential counterparts of UGSs, selected on the basis of WISE colors, and
27
blazar candidates of uncertain type associated with gamma-ray sources of the last release of the Fermi catalog. We confirm the BZB nature of
20
sources lying within the positional uncertainty region of the UGSs. All the observed BCUs show blazar-like spectra, classified as 2 BZQs and
25
BZBs, for which we obtained 6 redshift estimates. Within the BCUs observations we report the redshift estimate for the BZB associated with, 3FGL J1106.4-3643 that is the second most distant BL Lac known to date, at
z
≥
1.084
.
We present the nature of 50 hard X-ray emitting objects unveiled through an optical spectroscopy campaign performed at seven telescopes in the northern and southern hemispheres. These objects were ...detected with the Burst Alert Telescope (BAT) instrument onboard the Swift satellite and listed as of unidentified nature in the 54-month Palermo BAT catalogue. In detail, 45 sources in our sample are identified as active galactic nuclei of which, 27 are classified as type 1 (with broad and narrow emission lines) and 18 are classified as type 2 (with only narrow emission lines). Among the broad-line emission objects, one is a type 1 high-redshift quasi-stellar object, and among the narrow-line emission objects, one is a starburst galaxy, one is a X-ray bright optically normal galaxy, and one is a low ionization nuclear emission line region. We report 30 new redshift measurements, 13 confirmations and 2 more accurate redshift values. The remaining five objects are galactic sources: three are Cataclismic Variables, one is a X-ray Binary probably with a low mass secondary star, and one is an active star.
ABSTRACT
Star formation accretion on to the super massive black holes (SMBHs) and feedback processes link the evolution of galaxies with their SMBHs. X-ray observations in the imaging and spectral ...regime have revealed to be an important tool to study the connection between nuclear activity and circumnuclear star formation in nearby active galactic nuclei (AGN). X-ray spectral diagnostics can lead to disentangle, which is the ionization mechanism in the central kiloparsecs of nearby AGN. In this paper, we investigate, by means of XMM-Newton observations, the nuclear X-ray emission of the changing-look AGN NGC 1566 during its quiescent state. European Photon Imaging Camera (EPIC) soft X-ray images show an extended arm-like morphology. A detailed analysis of the high-resolution Reflection Grating Spectrometer (RGS) and medium resolution EPIC spectra shows that the material concentrated in the central kiloparsecs region is not in the photoionization-dominated regime while the presence of collisionally ionized plasma is needed to explain the observed spectral features. In the inner region (∼1.5 kpc), the brightness of the collisionally ionized gas is comparable to the brightness of the photoionized gas: the inner region hosts a luminous starburst whose ionized gas shows up bright in the X-rays when the AGN is in quiescence.
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