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Roberto Angioni - VLBI and gamma-ray studies of TANAMI radio galaxies
abstractToggle Cloak Cloak Fermi-LAT radio galaxies, a class of -ray emitters, provide us with a way to study AGN jets at high-energy not heavily affected by relativistic effects. Unfortunately, this also means that these sources are faint high-energy emitters, and therefore more difficult to detect, making up only 1-2% of all LAT-detected AGN. The recent implementation of the Pass8 data analysis holds some potential to expand this sample, and also to detect new AGN classes at high energies, such as young radio sources. Many of the southern radio galaxies, in particular, are also poorly studied at radio wavelengths, at milliarcsecond resolution. During my PhD I will characterize the pc-scale properties of the radio galaxies in the TANAMI VLBI monitoring program, using multi-frequency radio imaging. I will also attempt to expand the -ray radio galaxy sample by analyzing LAT Pass8 data on a sample of candidate sources, with particular focus on the young sources in the TANAMI sample. Additionally, I will study the SED of the TANAMI AGN which are not detected in -rays, to search for common properties that might explain why they are still missed by the LAT. Raniere Menezes - Gamma-ray Variability of Low-luminosity AGN
abstractToggle Cloak Cloak Low-luminosity AGN (LLAGNs) are the most common population of active galaxies at z = 0 and are therefore very important for our understanding of AGN physics. In this talk, we will report the results from our variability survey of LLAGNs in the northern hemisphere based on 7 years of LAT observations and Pass 8. In particular, we will present the light curves and associated results – including search for flares and periodicity – for the ten brightest LLAGNs in our sample. - Laurel Kaye
- Peter Breiding
- Pfesesani van Zyl
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Nenghui Liao - Discovery of gamma-ray emission from the steep radio spectrum NLS1 B3 1441+476
abstractToggle Cloak Cloak Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jet and the gamma-ray NLS1s are expected to be rare. All the gamma-ray NLS1s reported to date have flat radio spectra and the jets are found to be closely aligned. We analyze the first seven-year Fermi/Large Area Telescope (LAT) data of a steep radio spectrum NLS1 B3 1441+476 and report the first detection of gamma-rays in such a kind of objects. No rapid variability is observed from radio to gamma rays and additionally low core dominance (< 0.7) and Compton dominance (< 1) are found. A radiation model successfully reproducing some steep-spectrum radio quasars provides an acceptable description of SED of B3 1441+476. B3 1441+476 has a compact radio morphology and a radio spectrum turnover at ~ 100MHz. All these facts strongly suggest that B3 1441+476 hosts a mis-aligned and plausibly underdeveloped relativistic jet, which provides a valuable target to reveal the formation and evolution of relativistic jets in NLS1s. Michael Kreter - Blazars as Potential High-Energy Neutrino Sources
abstractToggle Cloak Cloak Jets from Active Galactic Nuclei (AGN) are among the best candidates for the recently detected extraterrestrial neutrino flux. Specifically, gamma-ray blazars have been predicted to yield a cumulative neutrino signal exceeding the atmospheric background above energies of 100 TeV, assuming that both the neutrinos and the gamma-ray photons are produced by accelerated protons in relativistic jets. Since the background spectrum falls steeply with increasing energy, the individual events with the clearest signature of being of an extraterrestrial origin are those at the highest energies. Hadronic AGN jet emission models predict a tight correlation between the neutrino flux and the time-variable gamma-ray emission.
We develop a strategy to search for high-energy neutrinos from promising blazar jets from the TANAMI sample using the ANTARES telescope, Fermi gamma-ray light curves, and time-resolved multiwavelength SED data.
An unbinned maximum-likelihood method is applied to maximize the probability of a neutrino detection with ANTARES or alternatively constrain the possible neutrino spectra for candidate associations with IceCube neutrino events.- Jamie Graham
- Natalia Zywucka
Yuliang Xin
Sat., June 4
Vera Nievas - Very-high-energy gamma-rays from the Universe's middle age: detection of B0218+357 and PKS1441+25 with the MAGIC telescopes
abstractToggle Cloak Cloak Flat Spectrum Radio Quasars (FSRQs) remain uncommon members of the Very High Energy (VHE, E>100GeV) source family. The reason is twofold. First, they typically have strong emission in the optical-UV coming from the Broad Line Region, which can interact with the gamma-rays, determining a strong absorption. Second, their spectrum is typically soft and may exhibit intrinsic cut-offs. With redshifts of z=0.944 and z=0.940 respectively, blazars B0218+357 (detection in Jul. 2014) and PKS1441+25 (Feb. 2015) are the furthest FSRQs ever detected in VHE. The detection of this new z~1 blazar class by the MAGIC telescopes gives us a chance to study the processes that allow a typically VHE-obscured blazar to emit sub-TeV photons when strong flares occur and set limits on the EBL density at redshift ~1 for the first time with the Cherenkov technique. The VHE observations of both blazars were triggered after a high-state alert coming from Fermi-LAT in the High Energy band (HE, 100 MeV < E < 300GeV). For B0218+357, a known gravitationally lensed blazar with two image components separated by ~0.3 arcsec and with a delay of 10-12 days, MAGIC observations were scheduled for the trailing pulse after a strong flare in July 2014 and resulted in a detection during only 2 nights. For PKS1441+25, the long-lasting flare allowed the MAGIC collaboration to cover the highest activity state and its gradual decay to the quiescent state. Stephan O’Brien - TeV Observations of Hard Spectrum BL Lac objects with VERITAS
abstractToggle Cloak Cloak High-Frequency-Peaked BL Lac objects (HBLs) are the most-intense sources of VHE emission, dominating the extragalactic VHE (E > 100 GeV) night sky. HBLs have been observed to vary across all wavelengths and on timescales ranging from minutes to years. VHE observations of a number of HBLs made with the VERITAS telescope array will be reported. Combined data taken between 2007 and 2016 will be used to derive time-averaged spectra, compare spectral models and determine the highest energies probed by the observations. This will be done using advanced forward-folding spectral reconstruction methods. Flux variability will also be investigated on nightly and seasonal timescales. Methods for combining the VHE spectra with Fermi-LAT data, allowing constraints to be placed on the extragalactic background light (EBL), will also be discussed.
Paul Morris
- Zhaoqiang Shen
Bing Li
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Mon., June 6
Wed., June 8
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