Search of MeV–GeV counterparts of TeV sources with AGILE in pointing mode

Rappoldi, A.; Lucarelli, F.; Pittori, C.; Longo, F.; Cattaneo, P. W.; Verrecchia, F.; Tavani, M.; Bulgarelli, A.; Chen, Andrew; Colafrancesco, S.; Donnarumma, I.; Giuliani, A.; Morselli, A.; Sabatini, S.; Vercellone, S.

doi:10.1051/0004-6361/201526709

Cited by 7 publications

(12 citation statements)

References 22 publications

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“…Further measurements with the CTA array of Cherenkov telescopes (Acharya et al (2013)) will likely clarify these issues. Together with existing instruments Fermi LAT (Atwood et al (2009)) and AGILE (Rappoldi et al (2016)), future experiments that have either high sensitivity or good angular resolution, such as GAMMA-400 (Galper et al (2013)) or the novel balloon-borne emulsion γ-ray telescope GRAINE (Takahashi et al (2015)), may also prove to be helpful in this task.…”

Section: Discussionmentioning

confidence: 99%

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

Dzhatdoev¹,

Khalikov²,

Kircheva³

et al. 2017

A&A

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Context. Most of the studies on extragalactic γ-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses ("absorption-only model"). However, there is growing evidence that this model is oversimplified and must be modified in some way. In particular, it was found that the intensity extrapolated from the optically-thin energy range of some blazar spectra is insufficient to explain the optically-thick part of these spectra. This effect was interpreted as an indication for γ-axion-like particle (ALP) oscillation. On the other hand, there are many hints that a secondary component from electromagnetic cascades initiated by primary γ-rays or nuclei may be observed in the spectra of some blazars. Aims. We study the impact of electromagnetic cascades from primary γ-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. Methods. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary γ-rays. For the case of primary proton, we develop a simple, fast and reasonably accurate hybrid method to calculate the observable spectrum. We perform the fitting of the observed spectral energy distributions (SEDs) with various physical models: the absorptiononly model, the "electromagnetic cascade model" (for the case of primary γ-rays), and several versions of the hadronic cascade model (for the case of primary proton). We distinguish the following species of hadronic cascade models: 1) "basic hadronic model", where it is assumed that the proton beam travels undisturbed by extragalactic magnetic field and that all observable γ-rays are produced by primary protons through photohadronic processes with subsequent development of electromagnetic cascades 2) "intermediate hadronic model", the same as the basic hadronic model, but the primary beam is terminated at some redshift z c 3) "modified hadronic model" that includes the contribution from primary (redshifted and partially absorbed) γ-rays. Results. Electromagnetic cascades show at least two very distinct regimes labeled by the energy of the primary γ-ray (E 0 ): the onegeneration regime for the case of E 0 <10 T eV and the universal regime for E 0 >100 T eV and redshift to the source z s >0.02. Spectral signatures of the observable spectrum for the case of the basic hadronic model, z s = 0.186 and low energy (E<200 GeV) are nearly the same as for purely electromagnetic cascade, but for E>200 GeV the spectrum is much harder for the case of the basic hadronic model. In the framework of the intermediate hadronic model, the observable spectrum depends only slightly on the primary proton energy, but it strongly depends on z c at E>500 GeV. As a rule, both electromagnetic and hadronic cascade models provide acceptable fits to the observed SEDs. We show that the best-fit model intensity in the multi-T eV region of the spectrum in the framework of the electromagnetic cascade model is typically greater than the one for the case of th...

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Section: Discussionmentioning

confidence: 99%

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

Dzhatdoev¹,

Khalikov²,

Kircheva³

et al. 2017

A&A

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“…Thirteen of the 52 sources of the AGILE TeVCat Rappoldi et al (2016) are not present in the 2AGL catalog. These sources are not confirmed due to a different analysis procedure, different Science Tools, different background cuts (albrad = 85, f ovradmax = 60) and improved IRFs, or to splitting the source in different 2AGL sources.…”

Section: Comparison With Agile Tevcatmentioning

confidence: 99%

“…Bulgarelli, e-mail: andrea.bulgarelli@inaf.it paper dedicated to the search of AGILE-GRID TeV source counterparts (Rappoldi et al 2016). Compared to previous investigations, we have implemented several refinements in the analysis of γ-ray sources : 1.…”

Section: Introductionmentioning

confidence: 99%

Second AGILE catalogue of gamma-ray sources

Bulgarelli

Fioretti

Parmiggiani

et al. 2019

A&A

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Aims. We present the second AGILE-GRID Catalog (2AGL) of γ-ray sources in the 100 MeV -10 GeV energy range. Methods. With respect to previous AGILE-GRID catalogs, the current 2AGL Catalog is based on the first 2.3 years of science data from the AGILE mission (the so called 'pointing mode') and incorporates more data and several analysis improvements, including better calibrations at the event reconstruction level, an updated model for the Galactic diffuse γ-ray emission, a refined procedure for point-like source detection, and the inclusion of a search for extended γ-ray sources.Results. The 2AGL Catalog includes 175 high-confidence sources (above 4σ significance) with their location regions and spectral properties, and a variability analysis with 4-day light curves for the most significant ones. Relying on the error region of each source position, including systematic uncertainties, 121 sources are considered as positionally associated with known couterparts at different wavelengths or detected by other γ-ray instruments. Among the identified or associated sources, 62 are Active Galactic Nuclei (AGNs) of the blazar class. Pulsars represent the largest Galactic source class, with 40 associated pulsars, 7 of them with detected pulsation; 8 Supernova Remnants and 4 high-mass X-ray binaries have also been identified. A substantial number of 2AGL sources are unidentified: for 54 sources no known counterpart is found at different wavelengths. Among these sources, we discuss a sub-class of 29 AGILE-GRID-only γ-ray sources that are not present in 1FGL, 2FGL or 3FGL catalogs; the remaining sources are unidentified in both 2AGL and 3FGL Catalogs. We also present an extension of the analysis of 2AGL sources detected in the 50 -100 MeV energy range.

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“…A new interactive web page of the catalog of TeV sources, including this coordinate revision and giving public access to light curves and spectra, is now available at the ASI Science Data Center (ASDC) 1 . The error region on each TeV source position has been calculated by quadratically summing the statistical uncertainties on the position coordinates and the systematic uncertainties on the instrument pointing, when available.…”

Section: The Tev Sources Input Samplementioning

confidence: 99%

“…Previous studies on the positional and spectral connection of GeV to TeV γ-ray sources performed on EGRET and Fermi-LAT satellite data indicate in particular that a single spectral component seems often unable to describe the MeV to TeV spectra of many coincident GeV/TeV sources, This search is particularly relevant since the two adjacent energy ranges may probe different regions of the source spectra, so we performed a systematic analysis on a sample of the known TeV sources with the purpose of detecting γ-ray emission associated with the TeV sources using the AGILE MeV-GeV γ-ray satellite data [1].…”

Section: Introductionmentioning

confidence: 99%