FermiFermi-LAT detection of a transient γ\gamma-ray source in the direction of a distant blazar B3 1428+422 at z=4.72z =4.72

We report the detection of a transient $\gamma$-ray source in the direction of B3 1428+422 ($z=4.72$) by analyzing the 110-month {\it Fermi}-LAT Pass 8 data. The new transient $\gamma-$ray source is far away from the Galactic plane and has a rather soft spectrum, in agreement with being a high redshift blazar. We suggest that the newly discovered transient is the $\gamma$-ray counterpart of B3 1428+422, which could be the {\it most distant} GeV source detected so far. The detection of a group of such distant $\gamma-$ray blazars will be helpful to reconstruct the evolution of the luminosity function and to study the extragalactic background light at such high redshifts.Comment: 9 pages, 4 figures, ApJL in pres

Circinus Galaxy Revisted with 10 Years of Fermi-LAT Data

Circinus galaxy is a nearby composite starburst/AGN system. In this work we re-analyze the GeV emission from Circinus with 10 years of {\it Fermi}-LAT Pass 8 data. In the energy range of 1-500 GeV, the spectrum can be well fitted by a power-law model with a photon index of $\Gamma$ = $2.20\pm0.14$, and its photon flux is $(5.90\pm1.04) \times 10^{-10}$ photons cm$^{-2}$ s$^{-1}$. Our 0.1-500 GeV flux is several times lower than that reported in the previous literature, which is roughly in compliance with the empirical relation for star-forming and local group galaxies and might be reproduced by the interaction between cosmic rays and the interstellar medium. The ratio between the $\gamma$-ray luminosity and the total infrared luminosity is near the proton calorimetric limit, indicating that Circinus may be a proton calorimeter. However, marginal evidence for variability of the $\gamma$-ray emission is found in the timing analysis, which may indicate the activity of AGN jet. More {\it Fermi}-LAT data and future observation of CTA are required to fully reveal the origin of its $\gamma$-ray emission.Comment: 11 pages, 7 figures, 4 tables, accepted for publication by Ap

Constraints on the composition, magnetization, and radiative efficiency in jet of blazar

The composition and energy dissipation in jets are two of the fundamental questions of jet physics that are not fully understood. In this paper, we attempt to constrain the composition, magnetization as well as radiative efficiency for blazar with the recently released low-frequency radio catalog of the TIFR GMRT Sky Survey at 150 MHz. The jet power estimated from the low-frequency radio emission is much lower than that derived from spectral energy distribution fitting assuming one proton per electron. Assuming the jet power estimated from low-frequency radio emission is physical, the fraction of electron/positron pairs can be constrained with $n_{\rm pairs}/n_{\rm p} \sim 10$. By comparing the power carried by magnetic field and radiation with the jet power estimated from the low-frequency radio emission, we find both relatively high magnetization parameter of $\sigma \sim 0.5$ and radiative efficiency of $\eta \sim 0.4$ in the dissipation region of blazars. These results suggest that the magnetic reconnection processes may play an important role in the energy dissipation of blazars. We also explore the connection between these three parameters ($n_{\rm pairs}/n_{\rm p}$, $\sigma$, and $\eta$) and the black hole mass, disk luminosity as well as Eddington ratio. No significant correlation is found, except that $\sigma$ shows possible correlation with disk luminosity.Comment: accepted for publication in The Astrophysical Journal. 10 pages, 3 figures, 2 tabl

The Connection between Radio and Gamma Ray Emission in Fermi/LAT Blazars

We collect the 2LAC and MOJAVE quasi-simultaneous data to investigate the radio-gamma connection of blazars. The cross sample contains 166 sources. The statistic analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the gamma-ray energy increases. The statistic results between various parameters show negative correlations of gamma-ray photon spectral index with gamma-ray loudness for both FSRQs and BL Lacertae objects, positive correlations of gamma-ray variability index with the gamma-ray loudness for FSRQs, a negative correlation of the gamma-ray variability index with the gamma-ray photon spectral index for FSRQs, and negative correlations of gamma-ray photon spectral index with gamma-ray luminosity for FSRQs. These results suggest that the gamma-ray variability may be due to changes inside the gamma-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the gamma-rays are closer to the high energy peak of spectral energy distribution. No correlation of variability index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.Comment: 10 pages, 10 figures, Accepted by RA

Fast γ\gamma-ray variability in blazars beyond redsift 3

High-redshift blazars are one of the most powerful monsters in the universe and $\gamma$-ray variability carries crucial information of their relativistic jets. In this work we present results of the first systematical temporal analysis of {\it Fermi}-LAT data of all known seven $\gamma$-ray blazars beyond redshift 3. Significant long-term $\gamma$-ray variability is found from five sources in monthly $\gamma$-ray light curves, in which three of them are reported for the first time. Furthermore, intraday $\gamma$-ray variations are detected from NVSS J053954$-$283956 and NVSS J080518$+$614423. Doubling variability timescale of the former source is limited as short as $\lesssim$ 1 hour (at the source frame). Together with variability amplitude over one order of magnitude, NVSS J053954$-$283956 is the most distant $\gamma$-ray flaring blazar so far. Meanwhile, intraday optical variability of NVSS J163547$+$362930 is found based on archival PTF/iPTF light curve. Benefited from multiwavelength activity of these sources, constraints of their Doppler factors as well as locations of $\gamma$-ray radiation region and indications for the SDSS high redshift jetted active galactic nuclei deficit are discussed.Comment: 25 pages, 8 figures, 2 tables, ApJ in pres

The SNR Puppis A Revisited with Seven Years of Fermi Large Area Telescope Observations

Puppis A is a very famous and extensively studied supernova remnant (SNR) that shows strong evidence of shock-cloud interaction. We re-analyze the GeV $\gamma$-ray emission of it using seven years Pass 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The morphology of the $\gamma$-ray emission is more compatible with that of the thermal X-ray and IR emissions than the radio image, which suggests a possible correlation between the gamma-ray emitting region and dense clouds. The $\gamma$-ray spectrum in the energy range of 1-500 GeV shows a break at $7.92\pm1.91$ GeV with the photon indices of $1.81\pm0.08$ below the break and $2.53\pm0.12$ above the break, which can naturally explain the lack of TeV $\gamma$-ray emission from Puppis A. The multi-wavelength observations favor a hadronic origin for the $\gamma$-ray emission.Comment: 9 pages, 4 figures, 4 tables, Accepted for publication in Ap

Multi-wavelength variability of CGRaBS J0733+0456: identifying a distant γ\gamma-ray blazar at z = 3.01

We report on OVRO, WISE, Swift and Fermi-LAT observations of the high redshift blazar CGRaBS J0733+0456, from which significant flux variations in radio, infrared (IR) as well as $\gamma$-ray domains are detected. Particularly, the amplitude of long-term IR variation is over one order of magnitude and the IR variability timescale can be constrained as short as a few hours in the source frame. The IR and $\gamma$-ray light curves are found to be rather similar, and the strong quasi-simultaneous infrared and $\gamma$-ray flares are proved to be unique among the nearby $\gamma$-ray sources. This is the first time to identify a $\gamma-$ray blazar at redshift $z\geq 3$ with multi-wavelength flux variations (flares). Broadband spectral energy distributions in different flux states are constructed and theoretically described. The $\gamma-$ray flares from some blazars as distant as redshift $\sim$ 5 are expected to be detectable for Fermi-LAT.Comment: 13 pages, 4 figures and 1 table, ApJL in pres

Two transient X-ray Quasi-Periodic Oscillations separated by an intermediate state in 1H 0707-495

In the narrow-line Seyfert 1 galaxy 1H 0707-495, recently a transient quasi-periodic oscillation (QPO) signal with a frequency of $\sim 2.6\times 10^{-4}$ Hz has been detected at a high statistical significance. Here, we reanalyze the same set of XMM-Newton data observed on 2008 February 4 with the Weighted-Wavelet Z-transform (WWZ) method. In addition to confirming the previous findings, we also find another QPO signal with a frequency of $\sim 1.2\times 10^{-4}$ Hz in a separated X-ray emission phase at the significance level of $\sim 3.7\sigma$. The signal is also found fitting an auto-regressive model though at a lower significance. The frequency ratio between these two signals is $\sim 2:1$. The analysis of other XMM-Newton measurements of 1H 0707-495 also reveals the presence of the $\sim 2.6\times 10^{-4}$ Hz ($\sim 1.2\times 10^{-4}$ Hz) QPO signal on 2007 May 14 (2010 September 17) at the significance level of $\sim 4.2\sigma$ ($\sim 3.5\sigma$). The QPO frequency found in this work follows the $f_{QPO}-M_{BH}$ relation reported in previous works spanning from stellar-mass to supermassive black holes. This is the first time to observe two separated transient X-ray QPO signals in active galactic nuclei (AGNs), which sheds new light on the physics of accreting supermassive black holes.Comment: 9 pages, 9 figures, 1 table; Accepted for publication in Ap

Detections of simultaneous brightening of gamma-ray and optical emissions of a distant blazar GB 1508+5714 at redshift 4.3

GB 1508+5714 is a high-redshift blazar ($z$ = 4.3) and a spectrally soft $\gamma$-ray source has been detected in its direction. By analyzing 11.4-yr {\it Fermi}-LAT data, significant long-term variability of the $\gamma$-ray source is confirmed. More importantly, a $\gamma$-ray emission flare appeared in an epoch of several tens of days in year 2018, when the flux is about four times of the value from the global fit. Meanwhile, optical flares displayed in both $r$- and $i$-bands from the {\it Zwicky} Transient Facility light curves. Detections of the simultaneous $\gamma$-ray and optical brightening provide a decisive evidence to pin down the association between the $\gamma$-ray source and GB 1508+5714, which makes it the {\it first} identified $\gamma$-ray blazar beyond redshift 4. A broadband spectral energy distribution in the high flux state is constructed and the origin of the multiwavelength brightening is also briefly discussed. Upcoming wide-deep-fast optical telescopes together with the $\gamma$-ray sky surveyors will shed lights on the role that the AGN jets play in the early cosmic time.Comment: 15 pages, 5 figures, ApJL in pres

Awakening of two γ\gamma-ray high redshift flat-spectrum radio quasars in the southern hemisphere

High-redshift blazars are valuable tools to study the early Universe. So far only a handful of $\gamma$-ray blazars have been found at redshifts above 3. $\gamma$-ray signals are detected in the direction of PMN J2219-2719 ($z=3.63$) and PMN J2321-0827 ($z=3.16$) by analyzing the 10-year $Fermi$-LAT Pass 8 data. PMN J2219-2719 is not distinguished from the background in the global analysis. During the 5-month epoch, the TS value is 47.8 and the flux is more than 10 times of the 10-year averaged flux. In addition, the angular distance between the $\gamma$-ray position and the radio position of PMN J2219-2719 is only ${0.04}^{\circ}$. Moreover, the $\gamma$-ray and infrared light curves of long time scale are very similar, which support the association between the $\gamma$-ray source and PMN J2219-2719. The global analysis of PMN J2321-0827 suggest a new $\gamma$-ray source, during the flare phase, the TS value is 61.4 and the $\gamma$-ray flux increased significantly. The association probability suggests that PMN J2321-0827 may be the counterpart of the new $\gamma$-ray source. In the future, the number of high-redshift $\gamma$-ray sources will increase by combining $Fermi$-LAT and the upcoming Large Synoptic Survey Telescope.Comment: 12 pages, 6 figures. Accepted for publication in Ap