24 research outputs found
FERMI transient J1544-0649: a flaring radio-weak BL Lac
On May 15th, 2017, the \emph{FERMI}/LAT gamma-ray telescope observed a
transient source not present in any previous high-energy catalogue: J1544-0649.
It was visible for two consecutive weeks, with a flux peak on May 21st.
Subsequently observed by a \emph{Swift}/XRT follow-up starting on May 26, the
X-ray counterpart position was coincident with the optical transient
ASASSN-17gs = AT2017egv, detected on May 25, with a potential host galaxy at
=0.171. We conducted a 4-months follow-up in radio (Effelsberg-100m) and
optical (San Pedro M\'artir, 2.1m) bands, in order to build the overall
Spectral Energy Distribution (SED) of this object. The radio data from 5 to 15
GHz confirmed the flat spectrum of the source, favoring a line of sight close
to jet axis, not showing significant variability in the explored post-burst
time-window. The Rx ratio, common indicator of radio loudness, gives a value at
the border between the radio-loud and radio-quiet AGN populations. The
Ca H\&K break value (0.290.05) is compatible with the range
expected for the long-sought intermediate population between BL Lacs and FRI
radio galaxies. An overall SED fitting from Radio to -ray band shows
properties typical of a low-power BL Lac. As a whole, these results suggest
that this transient could well be a new example of the recently discovered
class of radio-weak BL Lac, showing for the first time a flare in the
gamma/X-ray bands.Comment: Accepted for publication in ApJ Letter
Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
Context. The gamma-ray emitting source WISE J141046.00+740511.2 has been
associated with a Fermi-LAT detection by crossmatching with Swift/XRT data. It
has shown all the canonical observational characteristics of a BL Lac source,
including a power-law, featureless optical spectrum. However, it was only
recently detected at radio frequencies and its radio flux is significantly low.
Aims. Given that a radio detection is fundamental to associate lower-energy
counterparts to Fermi-LAT sources, we aim to unambiguously classify this source
by performing a multiwavelength analysis based on contemporaneous data.
Methods. By using multifrequency observations at the Jansky Very Large Array,
Giant Metrewave Radio Telescope, Gran Telescopio Canarias, Gemini, William
Herschel Telescope and Liverpool observatories, together with Fermi-LAT and
Swift data, we carried out two kinds of analyses. On one hand, we studied
several known parameters that account for the radio loudness or weakness
characterization and their application to blazars (in general) and to our
source (in particular). And, on the other hand, we built and analyzed the
observed spectral energy distribution (SED) of this source to try to explain
its peculiar characteristics. Results. The multiwavelength analysis indicates
that WISE J141046.00+740511.2 is a blazar of the high-frequency peaked (HBL)
type that emits highly polarized light and that is likely located at a low
redshift. In addition, the one-zone model parameters that best fit its SED are
those of an extreme HBL (EHBL); this blazar type has been extensively predicted
in theory to be lacking in the radio emission that is otherwise typical of
canonical gamma-ray blazars. Conclusions. We confirm that WISE
J141046.00+740511.2 is indeed a highly polarized BL Lac of the HBL type.
Further studies will be conducted to explain the atypical low radio flux
detected for this source.Comment: accepted for publication in A&A, in pres
Optical spectroscopic observations of gamma-ray blazar candidates, X: results from the 2018–2019 SOAR and OAN-SPM observations of blazar candidates of uncertain type
The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ-ray sources with statistical significance above 4 σ. About 23% of the sources listed in this catalog are unidentified/unassociated γ-ray sources while ∼26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects.Fil: de Menezes, Raniere. Universidade de Sao Paulo; Brasil. Università di Torino; ItaliaFil: Amaya Almazán, R. A.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Marchesini, Ezequiel Joaquín. Università di Torino; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Peña Herazo, H. A.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Massaro, F.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Chavushyan, V.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Paggi, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Landoni, M.. Osservatorio Astronomico Di Brera; ItaliaFil: Masetti, N.. Inaf Istituto Di Astrofisica Spaziale E Fisica Cosmica, Bologna; Italia. Universidad Andrés Bello; ChileFil: Ricci, F.. Universidad Católica de Chile; ChileFil: D'Abrusco, R.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: La Franca, F.. Università Degli Studi Roma Tre; ItaliaFil: Smith, Howard A.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Milisavljevic, D.. College Of Science; ItaliaFil: Tosti, G.. Università di Perugia; ItaliaFil: Jiménez Bailón, E.. Universidad Nacional Autónoma de México; MéxicoFil: Cheung, C. C.. Spece Sciences División. Naval Research Laboratory; Estados Unido
The cavity of 3CR 196.1: H emission spatially associated with an X-ray cavity
We present a multifrequency analysis of the radio galaxy 3CR 196.1 (), associated with the brightest galaxy of the cool core cluster
CIZAJ0815.4-0303. This nearby radio galaxy shows a hybrid radio morphology and
an X-ray cavity, all signatures of a turbulent past activity, potentially due
to merger events and AGN outbursts. We present results of the comparison
between and VLT/MUSE data for the inner region of the galaxy cluster,
on a scale of tens of kpc. We discovered H + [N II]
emission spatially associated with the X-ray cavity (at 10 kpc from the
galaxy nucleus) instead of with its rim. This result differs from previous
discoveries of ionized gas surrounding X-ray cavities in other radio galaxies
harbored in galaxy clusters and could represent the first reported case of
ionized gas filling an X-ray cavity, either due to different AGN outbursts or
to the cooling of warm ( K) AGN outflows. We also found that
the H, [N II] and [S
II] emission lines show an additional redward
component, at 1000 kms from rest frame, with no detection in
H or [O III]. We believe the most likely
explanation for this redward component is the presence of a background gas
cloud since there appears to be a discrete difference in velocities between
this component and the rest frame.Comment: 15 pages, 8 figures, ApJ accepted, pre-proof versio
Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources
A significant fraction of all -ray sources detected by the Large Area
Telescope aboard the \fer\ satellite is still lacking a low-energy counterpart.
In addition, there is still a large population of -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/unidentified -ray sources (UGSs), mainly
devoted to observing blazars and blazar candidates because they are the largest
population of -ray sources associated to date. Here we describe the
overall impact of our optical spectroscopic campaign on sources associated in
\fer-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 \fer-LAT catalog
sources. Our summary includes an analysis of an additional 30 newly-collected
optical spectra of counterparts or potential counterparts of \fer-LAT sources
of previously unknown nature.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. All new sources with optical spectra analyzed here
are classified as blazars. Thanks to our campaign, we altogether 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 \fer-LAT source catalogs (2FGL and 3FGL,
respectively), and classified about 25\% of the sources with uncertain nature
and discovered a blazar-like potential counterpart for 10\% of UGSs
listed therein. In the 4FGL catalog, about 350 \fer-LAT sources are classified
to date thanks to our campaign. [incomplete abstract]Comment: 31 pages, 12 tables, 32 figures, 2 appendices, accepted for
publication on A&A (pre-proofs version
Powerful radio sources in the southern sky: I. optical identifications
Since the early sixties, our view of radio galaxies and quasars has been drastically shaped by discoveries made thanks to observations of radio sources listed in the Third Cambridge Catalog and its revised version (3CR).
However, the largest fraction of data collected to date on 3CR sources was performed with relatively old instruments, rarely repeated and/or updated. Importantly, the 3CR contains only objects located in the Northern Hemisphere, thus having limited access to new and innovative astronomical facilities. To mitigate these limitations, we present a new catalog of powerful radio sources visible from the Southern Hemisphere, extracted from the GLEAM 4 Jy (G4Jy) catalog and based on equivalent selection criteria as the 3CR. This new catalog, named G4Jy- 3CRE, where the E stands for “equivalent,” lists a total of 264 sources at decl. below −5° and with 9 Jy limiting sensitivity at ∼178 MHz. We explored archival radio maps obtained with different surveys and compared them with optical images available in the Pan-STARRS, DES, and DSS databases to search for optical counterparts of their radio cores. We compared mid-infrared counterparts, originally associated in the G4Jy, with the optical ones identified here, and we present results of a vast literature search carried out to collect redshift estimates for all G4Jy-3CRE sources resulting in a total of 145 reliable z measurements.Instituto Argentino de RadioastronomíaInstituto de Astrofísica de La Plat
Turin-SyCAT: A multifrequency catalog of Seyfert galaxies
Aims. We present the first release of Turin-SyCAT, a multifrequency catalog of Seyfert galaxies.
Methods. We selected Seyfert galaxies considering criteria based on radio, infrared, and optical properties and starting from sources belonging to hard X-ray catalogs and surveys. We visually inspected optical spectra available for all selected sources. We adopted homogeneous and stringent criteria in the source selection aiming at reducing the possible contamination from other source classes.
Results. Our final catalog includes 351 Seyfert galaxies distinguished in 233 type 1 and 118 type 2. Type 1 Seyfert galaxies appear to have mid-IR colors similar to blazars, but are distinguished from them by their radio-loudness. Additionally, Seyfert 2 galaxies have mid-IR colors more similar to quasars than BL Lac objects. As expected from their spectral properties, type 1 and 2 Seyfert galaxies show a clear distinction when using the u − r color. Finally, we found a tight correlation between the mid-IR fluxes at both 12 and 22 μm (i.e., F12 and F22, respectively) and hard X-ray fluxes between 15 and 150 keV. Both Seyfert types appear to follow the same trend and share similar values of the ratios of F12 and F22 to FHX in agreement with expectations of the AGN unification scenario.
Conclusions. As future perspectives, the Turin-SyCAT will then be used to search for heavily obscured Seyfert galaxies among unidentified hard X-ray sources, given the correlation between mid-IR and hard X-rays, and to investigate their large-scale environments