The loud and the quiet: searching for radio counterparts of two radio-weak BL Lac candidates with VLBI

Cao, Hongmin; Frey, S.; Gabányi, K. É.; Yang, Jun; Cui, Lang; Hong, Xiaoyu; An, Tao

doi:10.1093/mnrasl/sly184

Cited by 5 publications

(5 citation statements)

References 43 publications

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“…This source was first detected in radio wavelengths by Schinzel et al (2017), and later by Cao et al (2019); both detections were published after the first claim of WISE J141046.00+740511.2 as a RWBL source (Massaro et al 2017). In all cases, at 1.4 GHz, the source was reported to be detected with a flux of ∼2 mJy, which is always compatible within the uncertainties related to the detection reported in this work.…”

Section: A Radio Criterionsupporting

confidence: 84%

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Disentangling the nature of the prototype radio weak BL Lac

Marchesini¹,

Reynaldi²,

Vieyro³

et al. 2023

A&A

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Context. The γ-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 γ-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.

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Section: A Radio Criterionsupporting

confidence: 84%

“…Recently, Bruni et al (2018) proposed new RWBL candidates, although the subject has been under debate (Cao et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Disentangling the nature of the prototype radio weak BL Lac

Marchesini¹,

Reynaldi²,

Vieyro³

et al. 2023

A&A

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“…These two sources were found to have mid-IR colours and SEDs consistent with those of BL Lacs, although they lacked counterparts in available radio surveys (Massaro et al 2017). Among them, one has only a weak radio core while the other is radio-quiet (Cao et al 2019). Concerning Fermi J1544-0639, its mid-IR colours built with the WISE magnitudes in the 3.4 µm (W1), 4.6 µm (W2), and 12 µm (W3) bands are W1-W2=0.55 and W2-W3=2.09, consistent with the WISE blazar strip (Massaro et al 2011(Massaro et al , 2017.…”

Section: Introductionmentioning

confidence: 96%

An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544–0639

Ursini¹,

Bassani²,

Panessa

et al. 2019

A&A

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Context. Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical transient on May 15, 2017. Subsequent multiwavelength observations suggest that this source may belong to the new class of radio-weak BL Lacs. Aims. We studied the X-ray spectral properties and short-term variability of Fermi J1544-0639 to constrain the X-ray continuum emission mechanism of this peculiar source. Methods. We present the analysis of an XMM-Newton observation, 56 ks in length, performed on February 21, 2018. Results. The source exhibits strong X-ray variability, both in flux and spectral shape, on timescales of ∼ 10 ks, with a harder-whenbrighter behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a variable broken power law, with a break energy of around 2.7 keV consistent with radiative cooling due to Comptonization of broad-line region photons. We find evidence for a 'soft excess', nicely described by a blackbody with a temperature of ∼ 0.2 keV, consistent with being produced by bulk Comptonization along the jet.

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“…Indeed, it was found recently that a significant fraction, 3% of the so-called confirmed Roma-BZCAT entries show an extended radio structure at ∼1 ′′ scale and are likely misclassified as blazars [66], not to mention VLBI imaging, which provides a higher resolution by orders of magnitude to potentially refute the blazar nature of certain candidates, e.g., [71]. Finally, to demonstrate the confusion about the blazar classification in the literature, we shall briefly mention the so-called "radio-weak" BL Lac objects, e.g., [72][73][74]. The term itself is contradictory since the presence of a small-inclination relativistic jet is an essential ingredient of a blazar, and should be a source of Doppler-beamed radio emission via the synchrotron process.…”

Section: Discussionmentioning

confidence: 99%

Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549

Kozák,

Frey,

Gabányi

2024

Galaxies

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Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and γ-ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, very long baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in six epochs between 1994 and 2018. Using the milliarcsecond-scale radio structure, we can resolve a core and a jet component whose angular separation increases by (0.055±0.006) mas yr−1. This corresponds to an apparent superluminal jet component motion of (3.5±0.4)c. From the core brightness temperature and the jet component proper motion, we determine the characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet viewing angle. We find no compelling evidence for a very closely aligned blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud quasar jets with a moderate Lorentz factor (Γ≈4) and ϑ≈24∘ inclination to the line of sight.

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The loud and the quiet: searching for radio counterparts of two radio-weak BL Lac candidates with VLBI

Cited by 5 publications

References 43 publications

Disentangling the nature of the prototype radio weak BL Lac

Disentangling the nature of the prototype radio weak BL Lac

An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544–0639

Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549

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