arXiv subjects

Neng-Hui Liao

Publications and source records attributed to Neng-Hui Liao.

36 records · Page 2Linked to original sources

arXiv2018

Search for GeV flare coincident with the IceCube neutrino flare

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 source was detected in the region of interest. Though PKS 0502+049 is $1.2^\circ$ separated from TXS 0506+056, it locates within the directional reconstruction uncertainties of 7 neutrinos, out of the 13 neutrino events during the neutrino flare. Together with the observed high flux of the $γ$-ray flare, it may be unreasonable to fully discard the (partial) contribution of PKS 0502+049 to the neutrino flare. The single source assumption used in the neutrino data analysis might need to be revisited.

astro-ph.HE↗

arXiv2018

Active galactic nuclei with GeV activities and the PeV neutrino source candidate TXS 0506+056

On 2017 September 22 the IceCube neutrino observatory detected a track-like, very-high-energy event (IceCube-170922A) that is spatially associated with TXS 0506+056, a quasar at a redshift of $z=0.3365$. This source is characterized by the increased acitivies in a very wide energy range (from radio to TeV) during these days. To investigate the possible connection of the PeV neutrino emission with the GeV activity of blazars, in this work we select 116 bright sources and analyze their lightcurves and spectra. We focus on the sources displaying GeV activities. Among these blazars, TXS 0506+056 seems to be typical in many aspects but is distinguished by the very strong GeV activties. We suggest to search for neutrino outburst in the historical data of IceCube, as recently done for TXS 0506+056, from the directions of these more energetic and harder blazars with strong GeV activities.

astro-ph.HE↗

arXiv2018

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 $σ\sim 0.5$ and radiative efficiency of $η\sim 0.4$ 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 ($n_{\rm pairs}/n_{\rm p}$, $σ$, and $η$) and the black hole mass, disk luminosity as well as Eddington ratio. No significant correlation is found, except that $σ$ shows possible correlation with disk luminosity.

astro-ph.GA↗

arXiv2018

Search for gamma-ray emission from the nearby dwarf spheroidal galaxies with 9 years of Fermi-LAT data

In this work, we search for $γ$-ray emission from the directions of some nearby Milky Way dwarf spheroidal galaxies (dSphs) and candidates with the publicly-available Pass 8 data of Fermi-LAT. Our sample includes 12 sources with the distances $<50$ kpc. Very weak $γ$-ray excesses ($\sim 2σ$) are found in some dSphs/candidates, consistent with that reported in the previous literature. Intriguingly, the peak test statistic (TS) value of the weak emission from the direction of Reticulum II rises continually. If interpreted as dark matter (DM) annihilation, the peak TS value is 13.5 for the annihilation channel of $χχ\rightarrow τ^{+}τ^{-}$ and the DM mass of $m_χ\sim 16$ GeV. The combination of all these nearby sources yields a more significant (with local significance $> 4σ$) $γ$-ray signal.

astro-ph.HE↗

arXiv2018

New Bounds on Axion-Like Particles From the Fermi Large Area Telescope observation of PKS $2155-304$

The axion-like particle (ALP)-photon mixing in the magnetic field around $γ$-ray sources or along the line-of-sight could induce oscillation between photons and ALPs, which then causes irregularities in the $γ$-ray spectra. In this work we try to search for such spectral irregularities in the spectrum of PKS $2155-304$ using 8.6 years of the Fermi Large Area Telescope (Fermi-LAT) data. No significant evidence for the presence of ALP-photon oscillation is obtained, and the parameter space of ALPs is constrained. The exclusion region sensitively depends on the poorly known magnetic field of host galaxy cluster of PKS $2155-304$. If the magnetic field is as high as $\sim 10~{\rm μG}$, the "hole"-like parameter region allowed in Ref.~\cite{Fermi} can be ruled out.

hep-ph↗

arXiv2018

Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011

We present our photometric monitoring of a flat spectrum radio quasar (FSRQ) 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15 mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in December 2009 are also compared with $γ$-ray data derived from Fermi $γ$-ray space telescope. The flux variation of these two bands follow a linear relation with $F_γ \propto F_R^{1.14\pm0.07}$, which provides an observational evidence for external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for variability origin. We also explore the variation of the flux ratio $F_γ/F_R$ and the detailed structures in the lightcurves, and discuss some possible origins for the detailed variability behaviors.

astro-ph.HE↗

arXiv2018

Fermi Large Area Telescope detection of gamma-ray emission from the direction of supernova iPTF14hls

The remnant of supernova explosion is widely believed to be the acceleration site of high-energy cosmic ray particles. The acceleration timescale is, however, typically very long. Here we report the detection of a variable $γ$-ray source with the Fermi Large Area Telescope, which is positionally and temporally consistent with a peculiar supernova, iPTF14hls. A quasi-stellar object SDSS J092054.04+504251.5, which is probably a blazar according to the infrared data, is found in the error circle of the $γ$-ray source. More data about the $γ$-ray source and SDSS J092054.04+504251.5 are needed to confirm their association. On the other hand, if the association between the $γ$-ray source and the supernova is confirmed, this would be the first time to detect high-energy $γ$-ray emission from a supernova, suggesting very fast particle acceleration by supernova explosions.

astro-ph.HE↗

arXiv2017

Detection of GeV $γ$-ray emission in the direction of HESS J1731-347 with Fermi-LAT

We report the detection of GeV $γ$-ray emission from supernova remnant HESS J1731-347 using 9 years of {\it Fermi} Large Area Telescope data. We find a slightly extended GeV source in the direction of HESS J1731-347. The spectrum above 1 GeV can be fitted by a power-law with an index of $Γ= 1.77\pm0.14$, and the GeV spectrum connects smoothly with the TeV spectrum of HESS J1731-347. Either a hadronic-leptonic or a pure leptonic model can fit the multi-wavelength spectral energy distribution of the source. However, the hard GeV $γ$-ray spectrum is more naturally produced in a leptonic (inverse Compton scattering) scenario, under the framework of diffusive shock acceleration. We also searched for the GeV $γ$-ray emission from the nearby TeV source HESS J1729-345. No significant GeV $γ$-ray emission is found, and upper limits are derived.

astro-ph.HE↗

arXiv2017

Fast $γ$-ray variability in blazars beyond redsift 3

High-redshift blazars are one of the most powerful monsters in the universe and $γ$-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 $γ$-ray blazars beyond redshift 3. Significant long-term $γ$-ray variability is found from five sources in monthly $γ$-ray light curves, in which three of them are reported for the first time. Furthermore, intraday $γ$-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 $γ$-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 $γ$-ray radiation region and indications for the SDSS high redshift jetted active galactic nuclei deficit are discussed.

astro-ph.HE↗

arXiv2017

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 $\sim 3.7σ$. 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 $\sim 4.2σ$ ($\sim 3.5σ$). 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.

astro-ph.HE↗

arXiv2017

GW170817/GRB 170817A/AT2017gfo association: some implications for physics and astrophysics

On 17 August 2017, a gravitational wave event (GW170817) and an associated short gamma-ray burst (GRB 170817A) from a binary neutron star merger had been detected. The followup optical/infrared observations also identified the macronova/kilonova emission (AT2017gfo). In this work we discuss some implications of the remarkable GW170817/GRB 170817A/AT2017gfo association. We show that the $\sim 1.7$s time delay between the gravitational wave (GW) and GRB signals imposes very tight constraint on the superluminal movement of gravitational waves (i.e., the relative departure of GW velocity from the speed of light is $\leq 4.3\times 10^{-16}$) or the possible violation of weak equivalence principle (i.e., the difference of the gamma-ray and GW trajectories in the gravitational field of the galaxy and the local universe should be within a factor of $\sim 3.4\times 10^{-9}$). The so-called Dark Matter Emulators and a class of contender models for cosmic acceleration ("Covariant Galileon") are ruled out, too. The successful identification of Lanthanide elements in the macronova/kilonova spectrum also excludes the possibility that the progenitors of GRB 170817A are a binary strange star system. The high neutron star merger rate (inferred from both the local sGRB data and the gravitational wave data) together with the significant ejected mass strongly suggest that such mergers are the prime sites of heavy r-process nucleosynthesis.

astro-ph.HE↗

arXiv2017

Discovery of $γ$-ray emission from steep radio spectrum NLS1s

Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jets and the detection of their $γ$-ray emissions is rarely reported. Evidences for strong relativistic beaming effect have been found in all $γ$-ray NLS1s to date and hence their jets are believed to be closely aligned. In this work we perform a systematic analysis of 7-year {\it Fermi} Large Area Telescope (LAT) data of 18 steep radio spectrum NLS1s (S-NLS1s) and report the {\it first} two detections of $γ$-ray emissions in this class, increasing the total number of known $γ$-ray NLS1s to 9. A strong and stable $γ$-ray signal (over 8$σ$) is produced by SDSS J144318.56+472556.7, and a significant $γ$-ray emission (4.5$σ$) of SDSS J130522.74+511640.2 has been detected in a monthly flare in November 2013. A thorough investigation of their multiwavelength properties from radio to X rays has been performed, finding no significant variability. Along with their spectral energy distributions and the radio morphology, these facts strongly suggest that these two sources harbor mis-aligned and possibly underdeveloped relativistic jets, which provides valuable targets to reveal the formation and evolution of relativistic jets under extreme circumstances.

astro-ph.HE↗

arXiv2017

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 $γ$-ray emission of it using seven years Pass 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The morphology of the $γ$-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 $γ$-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 $γ$-ray emission from Puppis A. The multi-wavelength observations favor a hadronic origin for the $γ$-ray emission.

astro-ph.HE↗

arXiv2017

Evaluating the bulk Lorentz factors of outflow material: lessons learned from the extremely-energetic outburst GRB 160625B

GRB 160625B is an extremely-bright outburst with well-monitored afterglow emission. The geometry-corrected energy is high up to $\sim 5.2\times10^{52}$ erg or even $\sim 8\times 10^{52}$ erg, rendering it the most energetic GRB prompt emission recorded so far. We analyzed the time-resolved spectra of the prompt emission and found that in some intervals there were likely thermal-radiation components and the high energy emission were characterized by significant cutoff. The bulk Lorentz factors of the outflow material are estimated accordingly. We found out that the Lorentz factors derived in the thermal-radiation model are consistent with the luminosity-Lorentz factor correlation found in other bursts as well as in GRB 090902B for the time-resolved thermal-radiation components. While the spectral cutoff model yields much lower Lorentz factors that are in tension with the constraints set by the electron pair Compoton scattering process. We then suggest that these spectral cutoffs are more likely related to the particle acceleration process and that one should be careful in estimating the Lorentz factors if the spectrum cuts at a rather low energy (e.g., $\sim$ tens MeV). The nature of the central engine has also been discussed and a stellar-mass black hole is likely favored.

astro-ph.HE↗

arXiv2016

HESS J1427-608: an unusual hard unbroken $γ-$ray spectrum in a very wide energy range

We report the detection of a GeV $γ$-ray source which is spatially overlapping and thus very likely associated with the unidentified very-high-energy (VHE) $γ$-ray source HESS J1427-608 with the Pass 8 data recorded by the Fermi Large Area Telescope. The photon spectrum of this source is best described by a power-law with an index of $1.85\pm0.17$ in the energy range of $3-500$ GeV, and the measured flux connects smoothly with that of HESS J1427-608 at a few hundred GeV. This source shows no significant extension and time variation. The broadband GeV-TeV emission over four decades of energies can be well fitted by a single power-law function with an index of 2.0, without obvious indication of spectral cutoff toward high energies. Such a result implies that HESS J1427-608 may be a PeV particle accelerator. We discuss possible nature of HESS J1427-608 according to the multi-wavelength spectral fittings. Given the relatively large errors, either a leptonic or a hadronic model can explain the multi-wavelength data from radio to VHE $γ$-rays. The inferred magnetic field strength is a few $μ$G, which is smaller than typical values of supernova remnants (SNRs), and is consistent with some pulsar wind nebulae (PWNe). On the other hand, the flat $γ$-ray spectrum is slightly different from typical PWNe but similar to that of some known SNRs.

astro-ph.HE↗

arXiv2016

Discovery of $γ$-ray emission from the radio-intermediate quasar III Zw 2: violent jet activity with intraday $γ$-ray variability

III Zw 2 is the prototype of radio-intermediate quasars. Although there is the evidence of possessing strong jet, significant $γ$-ray emission has not been reported before. In this work, we carry out a detailed analysis of the latest {\it Fermi}-LAT {\it Pass} 8 data. No significant $γ$-ray signal has been detected in the time-averaged 7-year {\it Fermi}-LAT data of III Zw 2, we however have identified two distinct $γ$-ray flares with isotropic luminosities of $\sim 10^{45}$ erg $\rm s^{-1}$. Multiwavelength data analysis (including also the optical photometric observations from Yunnan Observatories) are presented and the main finding is the simultaneous optical and $γ$-ray flares of III Zw 2 appearing in Nov. 2009. Violent $γ$-ray variability with doubling timescale of 2.5 hours was detected in another $γ$-ray flare in May 2010, for which the 3-hour $γ$-ray peak flux is $\sim 250$ times of the average flux in 7 years. Rather similar behaviors are observed in blazars and the blazar model can reasonably reproduce the spectral energy distribution of III Zw 2 in a wide energy range, strongly suggesting that its central engine resembles that of blazars. In view of its core which shares radio similarities with young radio sources together with the weak extended radio lobe emission, we suggest that III Zw 2 harbors a recurrent activity core and serves as a valuable target for investigating the fuelling and triggering of the activity in radio loud AGNs.

astro-ph.HE↗

arXiv2016

Search for gamma-ray emission from eight dwarf spheroidal galaxy candidates discovered in Year Two of Dark Energy Survey with Fermi-LAT data

Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for $γ-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $γ-$ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of $χχ\rightarrow τ^{+}τ^{-}$ is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass $m_χ>250$ GeV. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is $\sim 25$ kpc away, there is a weak $γ-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $χχ\rightarrow τ^{+}τ^{-1}$ is $\approx 6.7$ at $m_χ\sim 15$ GeV. The significance of the possible signal likely increases with time. More data is highly needed to pin down the physical origin of such a GeV excess.

astro-ph.HE↗

arXiv2015

Discovery of gamma-ray emission from a strongly lobe-dominated quasar 3C 275.1

We systematically analyze the 6-year {\it Fermi}/LAT data of the lobe-dominated quasars (LDQs) in the complete LDQ sample from 3CRR survey and report the discovery of high-energy $γ$-ray emission from 3C 275.1. The $γ$-ray emission of 3C 207 is confirmed and significant variability of the lightcurve is identified. We do not find statistically significant $γ$-ray emission from other LDQs. 3C 275.1 is the known $γ$-ray quasar with the lowest core dominance parameter (i.e., $R=0.11$). We also show that both the northern radio hotspot and parsec jet models can reasonably reproduce the $γ$-ray data. The parsec jet model, however, is favored by the potential $γ$-ray variability at the timescale of months. We suggest that some dimmer $γ$-ray LDQs will be detected in the future and LDQs could contribute non-negligibly to the extragalactic $γ$-ray background.

astro-ph.HE↗