<i>Swift</i>/XRT counterparts to unassociated<i>Fermi</i>high-energy LAT sources

Landi, R.; Bassani, L.; Stephen, J. B.; Masetti, N.; Malizia, A.; Ubertini, P.

doi:10.1051/0004-6361/201526221

Cited by 28 publications

(46 citation statements)

References 33 publications

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“…Our proposed counterparts for the sources 1FHL J0644.2+6036, 1FHL J1223.3+7953 and 1FHL J0601.0+3838 are compatible with the X-ray associations proposed by Landi et al (2015) and Paggi et al (2013), as indicated in the notes in Table 5.…”

Section: Proposed Counterparts For Unassociated Sourcessupporting

confidence: 84%

“…For all of the detected sources we reveal a VLBI compact component and we confirm their blazar nature. This finding provides an independent validation of other association methods based on the analysis of their multi-wavelength properties, such as the investigation of infrared colors, the low frequency spectral index and the X-ray association (e.g., D 'Abrusco et al 2013;Massaro et al 2013a;Nori et al 2014;Landi et al 2015).…”

Section: Vlbi Properties and Unassociated Sourcessupporting

confidence: 53%

“…(6) Association also proposed by Paggi et al (2013). (7) Association also proposed by Landi et al (2015).…”

Section: General Characterization Of the Observed Samplementioning

confidence: 99%

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VLBA observations of radio faintFermi-LAT sources above 10 GeV

Lico

Giroletti

Orienti

et al. 2016

A&A

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Context. The first Fermi-LAT High-energy source catalog (1FHL), containing γ-ray sources detected above 10 GeV, is an ideal sample to characterize the physical properties of the most extreme γ-ray sources. Aims. We investigate the pc scale properties of a sub-sample of radio faint 1FHL sources with the aim to confirm the proposed blazar associations, by revealing a compact high brightness temperature radio core, and we propose new low-frequency counterparts for the unassociated γ-ray sources (UGS). Moreover, we increase the number of 1FHL sources with high resolution observations to explore the possible connection between radio and γ rays at E >10 GeV. Methods. We observed 84 1FHL sources, mostly blazars of High Synchrotron Peaked (HSP) type, in the northern sky with the Very Long Baseline Array (VLBA) at 5 GHz. These sources lack high resolution radio observations and have at least one NRAO VLA sky survey counterpart within the 95% confidence radius. For those sources without a well identified radio counterpart we exploit the VLBA multiple phase-center correlation capability to discern among the possible low-frequency candidates.Results. For ∼93% of the sources of our sample we reveal a compact high brightness temperature radio core, supporting their proposed blazar association. The vast majority of the detected sources are radio weak, with a median VLBI flux density value of 16.3 mJy. For the detected sources we obtain an average brightness temperature of the order of 2 ×10 10 K.We find a compact component for 16 UGS, for which we propose a new low-frequency association. Conclusions. We find brightness temperature values which do not require high Doppler factors, and are in agreement with the expected values for the equipartition of energy between particles and magnetic field. We find strong indications about the blazar nature of all of the detected UGS, for which we propose new low-frequency associations. The characterization of the physical properties of this emerging population is relevant in view of the construction of the new generation Cherenkov Telescope Array.

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Section: Proposed Counterparts For Unassociated Sourcessupporting

confidence: 84%

Section: Vlbi Properties and Unassociated Sourcessupporting

confidence: 53%

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VLBA observations of radio faintFermi-LAT sources above 10 GeV

Lico

Giroletti

Orienti

et al. 2016

A&A

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“…3FGL J1730.6-0357). This source was also found while carrying out spectroscopic observations of UGS listed in the First Fermi-LAT Catalog of Sources above 10 GeV (1FHL; Ackermann et al 2013) selected on the basis of the SWIFT X-ray observations (Landi et al 2015). It has been indicated as potential counterpart of 1FHL J1410.4+7408 (a.k.a.…”

Section: Radio Weak Bl Lacsmentioning

confidence: 87%

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

Massaro

Marchesini

D’Abrusco

et al. 2017

ApJ

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The existence of "radio weak BL Lac objects" (RWBLs) has been an open question, still unsolved, since the discovery that quasars could be radio-quiet or radio-loud. Recently several groups identified RWBL candidates, mostly found while searching for low energy counterparts of the unidentified/unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs or weak emission line quasars when there are not sufficient data to precisely draw their broad band spectral energy distribution and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs and BL Lacs using the [3.4]-[4.6]-[12]µm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with those of the BL Lac population.

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“…Although the Fermi-LAT observatory is greatly improving it by the continuous signal addition over the years, the task remains challenging, if we consider that one third of the 3FGL lastly-released source catalog are still unassociated to counterparts in other frequency band. Preliminary searches of these unassociated/unidentified gamma-ray sources (henceforth UGS) by various authors (Mirabal et al 2012;Massaro et al 2012;D'Abrusco et al 2013;Acero et al 2013a;Doert & Errando 2014;Landi et al 2015;Paiano et al 2017a) found clear indications that the large majority of them are AGNs of the blazar class.…”

Section: Introductionmentioning

confidence: 99%

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

Paiano

Falomo

Franceschini

et al. 2017

ApJ

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We present optical spectroscopy secured at the 10m Gran Telescopio Canarias of the counterparts of 20 extragalactic γ-ray sources detected by the Fermi satellite. The observations allow us to investigate the nature of these sources and to determine their redshift. We find that all optical counterparts have a spectrum that is consistent with a BL Lac object nature. We are able to determine the redshift for 11 objects and set spectroscopic redshift limits for five targets. Only for four sources the optical spectrum is found featureless. In the latter cases we can set lower limits on the redshift based on the assumption that they are hosted by a typical massive elliptical galaxy whose spectrum is diluted by the non thermal continuum. The observations allow us to unveil the nature of these gamma-ray sources and provide a sanity check of a tool to discover the counterparts of γ-ray emitters/blazars based on their multiwavelength emission.

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Swift/XRT counterparts to unassociatedFermihigh-energy LAT sources

Cited by 28 publications

References 33 publications

VLBA observations of radio faintFermi-LAT sources above 10 GeV

VLBA observations of radio faintFermi-LAT sources above 10 GeV

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

Optical Spectroscopic Survey of a Sample of Unidentified Fermi Objects

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