Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userProbing the Scale of ALP Interactions with Fermi Blazars
59
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Gamma-rays from cosmological sources contain information about gamma-ray interactions. Standard model and non-standard model photon interactions along the path between the source and the observer can lead to changes in the energy or state of the photons, which in turn alters the observed energy spectrum of the source. In general, these interactions are a function of photon energy as well as source distance. Here we show how existing high energy (50 GeV -- 10TeV) gamma-ray observations of blazars can be used to constrain the coupling of axion-like-particles (ALPs) to the photon. The same ALP-photon coupling that has been invoked to explain the observations of TeV blazars beyond their pair production horizon is shown to have an effect of the data set of textit{Fermi} blazars.
rate research
Read More
We find evidence for large-scale clustering amongst Fermi-selected BL Lac objects but not amongst Fermi-selected FSRQs. Using two-point correlation functions we have investigated the clustering properties of different classes of objects from the Fermi LAT 4FGL catalogue. We wanted to test the idea based on optical polarization observations that there might be large volumes of space in which AGN axes are aligned. To do this we needed a clean sample of blazars as these are objects with their jet axes pointing towards the observer and Fermi sources provide such a sample. We find that high latitude Fermi sources taken as a whole show a significant clustering signal on scales up to 30 degrees. To investigate if all blazars behave in the same way we used the machine learning classifications of Kovacevic, et al. (2020), which are based only on gamma-ray information, to separate BL Lac-like objects from FSRQ-like objects. A possible explanation for the clustering signal we find amongst the BL Lac-like objects is that there are indeed large volumes of space in which AGN axes are aligned. This signal might be washed out in FSRQs since they occupy a much larger volume of space. Thus our results support the idea that large scale polarization alignments could originate from coherent alignments of AGN axes. We speculate that these axis alignments may be related to the well-known intrinsic alignments of galaxy optical position angles.
(Abridged) In this paper, multi-wavelength data are compiled for a sample of 1425 Fermi blazars to calculate their spectral energy distributions (SEDs). A parabolic function, $log( u F_{ u}) = P_1(log u - P_2)^2 + P_3,$ is used for SED fitting. Synchrotron peak frequency ($log u_p$), spectral curvature ($P_1$), peak flux ($ u_{rm p}F_{rm u_p}$), and integrated flux ($ u F_{ u}$) are successfully obtained for 1392 blazars (461 flat spectrum radio quasars-FSRQs, 620 BL Lacs-BLs and 311 blazars of uncertain type-BCUs, 999 sources have known redshifts). Monochromatic luminosity at radio 1.4 GHz, optical R band, X-ray at 1 keV and $gamma$-ray at 1 GeV, peak luminosity, integrated luminosity and effective spectral indexes of radio to optical ($alpha_{rm RO}$), and optical to X-ray ($alpha_{rm OX}$) are calculated. The Bayesian classification is employed to log$ u_{rm p}$ in the rest frame for 999 blazars with available redshift and the results show that 3 components are enough to fit the $log u_{rm p}$ distribution, there is no ultra high peaked subclass. Based on the 3 components, the subclasses of blazars using the acronyms of Abdo et al. (2010a) are classified, and some mutual correlations are also studied. Conclusions are finally drawn as follows: (1) SEDs are successfully obtained for 1392 blazars. The fitted peak frequencies are compared with common sources from samples available (Sambruna et al. 1996, Nieppola et al. 2006, 2008, Abdo et al. 2010a). (2) Blazars are classified as low synchrotron peak sources (LSPs) if $log u_{rm p}$(Hz) $leq 14.0$, intermediate synchrotron peak sources (ISPs) if $14.0 < log u_{rm p}$(Hz) $leq 15.3$, and high synchrotron peak sources (HSPs) if $log u_{rm p}$(Hz) $> 15.3$. (3) $gamma$-ray emissions are strongly correlated with radio emissions. (...)
High-$z$ blazars (z $geq 2.5$) are the most powerful class of persistent $gamma$-ray sources in the Universe. These objects possess the highest jet powers and luminosities and have black hole masses often in excess of $10^9$ solar masses. In addition, high-$z$ blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission typically peaks below the GeV range, which makes them difficult to study with Fermi/LAT. Therefore, only the very brightest objects are detectable and, to date, only a small number of high-z blazars have been detected with Fermi/LAT. In this work, we studied the monthly binned long-term $gamma$-ray emission of a sample of 176 radio and optically detected blazars that have not been reported as known $gamma$-ray sources in the 3FGL catalog. In order to account for false-positive detections, we calculated monthly Fermi/LAT light curves for a large sample of blank sky positions and derived the number of random fluctuations that we expect at various test statistic (TS) levels. For a given blazar, a detection of TS > 9 in at least one month is expected $sim 15%$ of the time. Although this rate is too high to secure detection of an individual source, half of our sample shows such single-month $gamma$-ray activity, indicating a population of high-energy blazars at distances of up to z=5.2. Multiple TS > 9 monthly detections are unlikely to happen by chance, and we have detected several individual new sources in this way, including the most distant $gamma$-ray blazar, BZQ J1430+4204 (z = 4.72). Finally, two new $gamma$-ray blazars at redshifts of z = 3.63 and z = 3.11 are unambiguously detected via very significant (TS > 25) flares in individual monthly time bins.
Beaming effect is important for the observational properties of blazars. In this work, we collect 91 $Fermi$ blazars with available radio Doppler factors. $gamma$-ray Doppler factors are estimated and compared with radio Doppler factors for some sources. The intrinsic (de-beamed) $gamma$-ray flux density ($f^{rm in}_{gamma}$), intrinsic $gamma$-ray luminosity ($L^{rm in}_{gamma}$), and intrinsic synchrotron peak frequency ($ u_{rm p}^{rm in}$) are calculated. Then we study the correlations between $f^{rm in}_{gamma}$ and redshift and find that they follow the theoretical relation: $log f = -2.0 log z + {rm const}$. When the subclasses are considered, we find that stationary jets are perhaps dominant in low synchrotron peaked blazars. 63 $Fermi$ blazars with both available short variability time scales ($Delta T$) and Doppler factors are also collected. We find that the intrinsic relationship between $L ^{rm in}_{gamma}$ and $Delta T^{rm in}$ obeys the Elliot & Shapiro and the Abramowicz & Nobili relations. Strong positive correlation between $f_{gamma}^{rm in}$ and $ u_{rm p}^{rm in}$ is found, suggesting that synchrotron emissions are highly correlated with $gamma$-ray emissions.
We present multiwavelength spectral analyses of two Fermi-LAT blazars, OJ 287 and 3C 279, that are part of the Boston University multiwaveband polarization program. The data have been compiled from observations with Fermi, RXTE, the VLBA, and various ground-based optical and radio telescopes. We simulate the dynamic spectral energy distributions (SEDs) within the framework of a multi-slice, time-dependent leptonic jet model for blazars, with radiation feedback, in the internal shock scenario. We use the physical jet parameters obtained from the VLBA monitoring to guide our modeling efforts. We discuss the role of intrinsic parameters and the interplay between synchrotron and inverse Compton radiation processes responsible for producing the resultant SEDs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
