A detailed study of the BL Lacertae PKS 0903-57 has been done for the first time with 12 years of Fermi Large Area Telescope data. We have identified two bright gamma-ray flares in 2018 and 2020. Many sub-structures were observed during multiple time binning of these flares. We have performed detailed temporal and spectral study on all the sub-structures separately. A single-zone emission model is used for time-dependent leptonic modeling of the multi-wavelength spectral energy distributions. Our estimated values of variability time scale, magnetic field in the emission region, jet power obtained from leptonic modeling of PKS 0903-57 are presented in this work. Currently, we have a minimal number of observations in X-rays and other bands. Hence, more simultaneous multi-wavelength monitoring of this source is required to have a better understanding of the physical processes happening in the jet of the blazar PKS 0903-57.
PKS 1510--089 is a bright and active $γ$-ray source that showed strong and complex $γ$-ray flares in mid-2015 during which the Major Atmospheric Gamma Imaging Cherenkov telescopes detected variable very high energy (VHE; photon energies $>$100 GeV) emission. We present long-term multi-frequency radio, optical, and $γ$-ray light curves of PKS 1510--089 from 2013 to 2018, and results of an analysis of the jet kinematics and linear polarization using 43 GHz Very Long Baseline Array data observed between late 2015 and mid-2017. We find that a strong radio flare trails the $γ$-ray flares in 2015, s…
We report on temporal and spectral study of a flat spectrum radio quasar, PKS B1222+216, in flare state to get insight into acceleration and emission mechanisms inside the jet. This is one of the brightest and highly active blazar in the MeV-GeV regime. Long term multi-waveband light curves of this object showed a flaring activity in 2014 with two distinct flares. Work presented here includes the study of flux-index variation, flare fitting, hardness ratio and spectral modelling of both X-ray and $γ-$ray data. The flux-index correlation we have found in MeV-GeV regime indicates a 'softer when …
Context. The origin of blazar variability, seen from radio up to gamma rays, is still a heavily debated matter and broadband flares offer a unique testbed towards a better understanding of these extreme objects. Such an energetic outburst was detected by Fermi/LAT in 2008 from the blazar PKS 1502+106. The outburst was observed from gamma rays down to radio frequencies. Aims. Through the delay between flare maxima at different radio frequencies, we study the frequency-dependent position of the unit-opacity surface and infer its absolute position with respect to the jet base. This nuclear opacit…
We report Atacama-Large-millimeter-Array (ALMA) Band 6 full-polarization observations of the lensed blazar PKS1830-211 during its record-breaking radio and gamma-ray flare in the spring of 2019. The observations were taken close to the peak of the gamma activity and show a clear difference in polarization state between the two time-delayed images. The leading image has a fractional polarization about three times lower than the trailing image, implying that significant depolarization occurred during the flare. In addition, we observe clear intra-hour variability of the polarization properties b…
Following the detection of a $\sim$300 TeV neutrino potentially associated with the flaring blazar TXS 0506+056, an excess of neutrinos around its position in 2014-2015 was revealed by IceCube. However, its contemporaneous quiescence in $γ$-rays is challenging to interpret consistently. Meanwhile, the blazar PKS 0502+049, positioned within the neutrino localization uncertainties, was seen to be flaring in $γ$-rays. We show that dense, line-emitting gas clouds that interact with its jet and induce cosmic ray acceleration and hadronuclear interaction can plausibly explain the 2014-2015 neutrino …
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理学重点实验室（南京大学））；Centre for Space Research, North-West University（西北大学空间研究中心）
An analysis is presented of the optical polarimetric and multicolour photometric ($BVRJ$) behaviour of the blazar PKS 2155$-$304 during an outburst in 2010. This flare develops over roughly 117 days, with a flux doubling time $τ\sim 11$ days that increases from blue to red wavelengths. The polarization angle is initially aligned with the jet axis but rotates by roughly $90^\circ$ as the flare grows. Two distinct states are evident at low and high fluxes. Below 18 mJy, the polarization angle takes on a wide range of values, without any clear relation to the flux. In contrast, there is a positiv…
Recently the IceCube collaboration and 15 other collaborations reported the spatial and temporal coincidence between the neutrino event IceCube-170922A and the radio-TeV activity of the blazar TXS 0506+056. Their further analysis on 9.5 years of IceCube data discovered neutrino flare between September 2014 and March 2015, when TXS 0506+056 is however in "quiescent" state. We analyze the Fermi-LAT data in that direction, and find another bright GeV source PKS 0502+049, which is at an angle of $1.2^{\circ}$ from TXS 0506+056, with strong activties during the neutrino flare. No other bright GeV s…
We study the long-term behavior of the bright gamma-ray blazar PKS 0402-362. We collected approximately 13 years of Fermi-LAT data between Aug 2008 to Jan 2021 and identified three bright $γ$-ray activity epochs. The second was found to be the brightest epoch ever seen in this source. We observed most of the $γ$-ray flare peaks to be asymmetric in profile suggesting a slow cooling time of particles or the varying Doppler factor as the main cause of these flares. The $γ$-ray spectrum is fitted with PL and LP spectral models, and in both cases, the spectral index is very steep. The $γ$-ray spect…
We present the temporal and spectral study of blazar PKS 0208-512, using recent flaring activity from November 2019 to May 2020, as detected by the Fermi-LAT observatory. The contemporaneous X-ray, optical/UV observations from Swift-XRT/UVOT are also used. During the activity state, 2-days binned $γ$-ray lightcurve shows multiple peaks indicating sub-flares. To understand the possible physical mechanisms behind flux enhancement, we divided the activity state of the source into several flux-states and carried out detailed temporal and spectral studies. Timing analysis of lightcurves suggest tha…
On 2019 October 25, the Fermi-Large Area Telescope observed the first gamma-ray flare from the radio-loud narrow-line Seyfert 1 (NLSy 1) galaxy PKS 2004$-$447 ($z=0.24$). We report on follow-up observations in the radio, optical-UV, and X-ray bands that were performed by ATCA, the Neil Gehrels Swift observatory, XMM-Newton, and NuSTAR, respectively, and our multi-wavelength analysis. We study the variability across all energy bands and additionally produce $γ$-ray light curves with different time binnings to study the variability on short timescales during the flare. We examine the X-ray spect…
Rapid flares from blazars in very high energy (VHE) $γ$-rays challenge the common understanding of jets of active galactic nuclei (AGNs). The same population of ultra-relativistic electrons is often thought to be responsible for both X-ray and VHE emission. We thus systematically searched for X-ray flares at sub-hour timescales of TeV blazars in the entire Rossi X-ray Timing Explorer archival database. We found rapid flares from PKS 2005-489 and S5 0716+714, and a candidate rapid flare from 1ES 1101-232. In particular, the characteristic rise timescale of PKS 2005-489 is less than half a minut…
Since 2016 October, the active galaxy PKS 2247-131 has undergone a gamma-ray outburst, which we studied using data obtained with the Fermi Gamma-ray Space Telescope. The emission arises from a relativistic jet in PKS 2247-131, as an optical spectrum only shows a few weak absorption lines, typical of the BL Lacertae sub-class of the blazar class of active galactic nuclei. Here we report a ~34.5 day quasi-periodic oscillation (QPO) in the emission after the initial flux peak of the outburst. Compared to one-year time-scale QPOs, previously identified in blazars in Fermi energies, PKS 2247-131 ex…
PKS 0438$-$436 at a redshift of $z=2.856$ has been previously recognized as possessing perhaps the most luminous known synchrotron jet. Little is known about this source since the maximum elevation above the horizon is low for the Very Large Array (VLA). We present the first VLA radio image that detects the radio lobes. We use both the 151 MHz luminosity, as a surrogate for the isotropic radio lobe luminosity, and the lobe flux density from the radio image to estimate a long term, time averaged, jet power, $\overline{Q} =1.5\pm 0.7 \times 10^{47} \rm{ergs~s^{-1}}$. We analyze two deep optical …
In this paper, we characterize the first $γ$-ray flaring episode of the FSRQ PKS 0346-27 (z=0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays. The quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs). PKS 0346-27 entered an elevated $γ$-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to $\sim$1.5 h…
We carried a detailed spectral and temporal study of blazar, \mbox{PKS\,0903-57} using the \emph{Fermi}-LAT and \emph{Swift}-XRT/UVOT observations, during its brightest flaring period MJD\,58931--58970. During this period, the maximum daily averaged $γ$-ray flux ($\rm F_{0.1-500\,GeV}$) of $\rm9.42\times10^{-6}\,ph\,cm^{-2}\,s^{-1}$ is observed on MJD\,58951.5, the highest $γ$-ray flux detected from \mbox{PKS\,0903-57} till now. Several high-energy (HE) photons ($>\,10$\,GeV) consistent with the source location at high probability (>\,99\%) are detected, and the $γ$-ray lightcurve in the activ…
Long-term gamma-ray variability of a non-blazar Active Galactic Nucleus (AGN) PKS 0521-36 is investigated by using Fermi-LAT pass 8 data covering from 2008 August to 2021 March. The results show that the histogram of the gamma-ray fluxes follows a log-normal distribution. Interestingly, in the analysis of about 5.8-year (from MJD 56317 to 58447) LAT data between two outbursts (occurring during 2012 October and 2019 May respectively), a quasi-periodic oscillation (QPO) with a period of about 1.1 years (about 5 sigma of significance) is found in the Lomb-Scargle Periodogram (LSP), the Weighted W…
Detection of Quasiperiodic Oscillations in the Blazar PKS 0735+178 with TESS
Indian Institute of Astrophysics（印度天体物理研究所）；Aryabhatta Research Institute of Observational Sciences (ARIES)（阿亚巴塔观测科学研究所）；Department of Physics, The College of New Jersey（新泽西学院物理系）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学李政道研究所）
The physical nature of the mechanism responsible for the emission of neutrinos in active galactic nuclei (AGN) has been matter of debate in the literature, with relativistic jets of radio-loud AGNs as possible candidates to be the sources of high energy neutrinos. The most prominent candidate so far is the blazar TXS 0506+056, which is found to be associated with the neutrino event IceCube-170922A. Furthermore, the IceCube reported an excess of neutrinos towards TXS 0506+056 between September 2014 and March 2015, even though this association needs additional investigation, considering the pres…
Flat spectrum radio quasars (FSRQs) can suffer strong absorption above E = 25/(1+z) GeV, due to gamma-gamma interaction if the emitting region is at sub-parsec scale from the super-massive black hole (SMBH). Gamma-ray flares from these astrophysical sources can investigate the location of the high-energy emission region and the physics of the radiating processes. We present a remarkable gamma-ray flaring activity from FSRQ PKS 2023-07 during April 2016, as detected by both AGILE and Fermi satellites. An intensive multi-wavelength campaign, triggered by Swift, covered the entire duration of the…
The origin of the multi-band activities (outbursts/flares) of blazars is still a heavily debated topic. Shock and magnetic reconnection have long been considered as possible triggers for the multi-band activities. In this paper, we present an exploration of the origin of multi-band activities for a high-redshift (z =1.8385) FSRQ PKS 1502+106. Utilizing multi-band data from radio to $γ$-ray and optical polarization observations, we investigate two dramatic activities in detail: a $γ$-ray dominated outburst in 2015 and an optical dominated outburst in 2017. Our main results are as follows. (I) A…
PKS 1413+135, a compact symmetric object (CSO) with a two-side pc-scale structure in its miniature radio morphology, is spatially associated with 4FGL J1416.1+1320 and recently detected with MAGIC telescopes. We comprehensively analyze its X-ray and GeV gamma-ray observation data for revealing its high energy radiation physics. It is found that the source is in a low-flux stage before MJD 58500 and experiences violent outbursts after MJD 58500 in the GeV band. The flux at 10 GeV varies ~3 orders of magnitude, and the GeV-flux variation is accompanied by the clear spectral variation, which is c…
Blazars, a class of highly variable active galactic nuclei, sometimes exhibit Orphan $γ$-ray flares. These flares having high flux only in $γ$-ray energies do not show significant variations in flux at lower energies. We study the temporal and spectral profile of these Orphan $γ$-ray flares in detail from three $γ-ray$ bright blazars, 3C 273, PKS 1510-089 and 3C 279 and also their simultaneous broadband emissions. We find that the variability timescales of the Orphan $γ$-ray flares were $(0.96\pm0.28)$ days, $(3.12\pm2.40)$ hr and $(2.16\pm0.72)$ hr, for 3C 273, PKS 1510-089 and 3C 279, respec…
