TeV γ-ray fluxes from the long campaigns on Mrk 421 as constraints on the emission of TeV–PeV neutrinos and UHECRs

Long TeV γ-ray campaigns have been carried out to study the spectrum, variability and duty cycle of the BL Lac object Markarian 421. These campaigns have given some evidence of the presence of protons in the jet: (i) Its spectral energy distribution which shows two main peaks; one at low energies (∼1 keV) and the other at high energies (hundreds of GeV), has been described by using synchrotron proton blazar model. (ii) The study of the variability at GeV γ-rays and X-rays has indicated no significant correlation. (iii) TeV γ-ray detections without activity in X-rays, called “orphan flares” have been observed in this object.Recently, The Telescope Array Collaboration reported the arrival of 72 ultra-high-energy cosmic rays with some of them possibly related to the direction of Markarian 421. The IceCube Collaboration reported the detection of 37 extraterrestrial neutrinos in the TeV–PeV energy range collected during three consecutive years. In particular, no neutrino track events were associated with this source. In this paper, we consider the proton–photon interactions to correlate the TeV γ-ray fluxes reported by long campaigns with the neutrino and ultra-high-energy cosmic ray observations around this blazar. Considering the results reported by The IceCube and Telescope Array Collaborations, we found that only from ∼25% to 70% of TeV fluxes described with a power law function with exponential cutoff can come from the proton–photon interactions.     

Injected spectrum for TeV γ-ray emission from the galactic center

The detection of very high energy γ-ray emission from the Galactic center has been reported by four independent groups. One of these γ-ray sources, the 10 TeV -γ-ray radiation reported by HESS, has been suggested as having a hadronic origin when relativistic protons are injected into and interact with the dense ambient gas. Assuming that such relativistic protons required by the hadronic model come from the tidal disruption of a star by the massive black hole of Sgr A＊, we explore the spectrum of the relativis- tic protons. In the calculations, we investigate cases where different types of stars are tidally disrupted by the black hole of Sgr A＊, and we consider that different diffusion mechanisms are used for the propagation of protons. The initial energy distribution of the injected spectrum of protons is assumed to follow a power-law with an exponential cut-off, and we derive the different indices of the injected spectra for the tidal disruption of different types of stars. For the best fit to the spectrum of photons detected by HESS, the spectral index of the injected relativistic protons is about 2.05 when a red giant is tidally disrupted by the black hole of Sgr A＊ and the diffusion mechanism is the Effective Confinement of Protons.     

Study of X-ray and γ-ray flare from Mkn-421 during February 2010 using Swift and Fermi observations

In this work, we report on the intense flaring activity from Mkn-421 in X-ray and γ-ray regimes simultaneously observed by Swift-XRT/BAT and Fermi-LAT satellite telescopes in February 2010. With the aim of understanding the underlying physics of the flaring state in Mkn-421, we have performed a detailed spectral analysis of Swift/XRT and Fermi/LAT observations of Mkn-421 during February 12–25, 2010 (MJD 55239–55252). Over this period, we study the daily light curves and spectral variability of the source in 1–10 keV, 0.1–1 GeV and 1–100 GeV energy bands. We have performed the spectral analysis of Swift-XRT and Fermi/LAT observations to study the spectral evolution in the X-ray and gamma-ray energy domains respectively. We also compute the fractional variability amplitude in both the energy bands during the above period. We study trends between spectral parameters and physical insights provided by the parameter responsible for X-ray and γ-ray emission from the source. We search for energetic features phenomenologically linked to the single zone SSC model for blazar emission. We also produce the broad band SED with a leptonic single zone SSC model for the source.     

Searching for γ-ray emission from LOTAAS pulsars

The LOw-Frequency ARray(LOFAR)has recently conducted a survey(LOFAR Tied-Array Allsky Survey;LOTAAS)for pulsars in the Northern hemisphere that resulted in discoveries of 73 new pulsars.For the purpose of studying the properties of these pulsars,we search for theirγ-ray counterparts using the all-sky survey data obtained with the Large Area Telescope(LAT)onboard the Fermi Gamma-Ray Space Telescope(Fermi).We analyze the LAT data for 70 LOTAAS pulsars(excluding two millisecond pulsars and one with the longest known spin period of 23.5 s).We find one candidate counterpart to PSR J1017+30,which should be searched for theγ-ray pulsation signal once its timing solution is available.For other LOTAAS pulsars,we derive their 0.3-500 GeV flux upper limits.In order to compare the LOTAAS pulsars with the knownγ-ray pulsars,we also derive the 0.3-500 GeVγ-ray fluxes for 112 of the latter contained in the Fermi LAT fourth source catalog.Based on the properties of theγ-ray pulsars,we derive upper limits on the spin-down luminosities of the LOTAAS pulsars.The upper limits are not very constraining but help suggest that most of the LOTAAS pulsars probably have<10³³ erg s^-1 spin-down luminosities and are not expected to be detectable with Fermi LAT.     

Simultaneous Multi-Wavelength Observations of the TeV Blazar Mrk 421 during February - March, 2003： X-Ray and NIR Correlated Variability

We report the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February - March 2003. We observed Mrk 421 using the Pachmarhi Array of Cerenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the literature and public data archives. We have analyzed the high quality X-ray (2-20keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We obtained a possible correlated variability between X-ray and J band (1.25 μ) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here indicates a similar origin for the NIR and X-ray emissions. The emission is not affected much by the environment of the surrounding medium of the central engine of Mrk 421. The observations are consistent with the shock-in-jet model for the emissions.     

The γ-ray emission from the Seyfert galaxy NGC 4151

Light curves at X-ray, ultraviolet, optical and infrared wavelengths of NGC 4151 over the period 1977–1980 are presented together with a summary of the large amount of observational data relating to this Seyfert galaxy. Intensity variations in different wavebands are discussed and compared with recent low energy -ray observations of this object. The positive measurement of gamma-radiation in May 1977 is shown to have been characterised by a high optical state and a possible infrared maximum. The data presented are compared with the predictions of some emission mechanisms, which have been proposed to account for the gamma-radiation. In particular, a synchrotron self-Compton model, which relates the infrared/optical emission to the X-ray/low energy -ray emission is discussed.     

A time dependent approach to model X-ray and γ–ray light curves of Mrk 421 observed during the flare in February 2010

Strong X-ray and γ–ray flares have been detected in February 2010 from the high synchrotron peaked blazar Mrk 421 (z = 0.031). With the motivation of understanding the physics involved in this flaring activity, we study the variability of the source in X-ray and γ–ray energy bands during the period February 10–23, 2010 (MJD 55237–55250). We use near simultaneous X-ray data collected by MAXI, Swift-XRT and γ–ray data collected by Fermi-LAT and TACTIC along with the optical V-band observations by SPOL at Steward Observatory. We observe that the variation in the one day averaged flux from the source during the flare is characterized by fast rise and slow decay. Besides, the TeV γ–ray flux shows a strong correlation with the X-ray flux, suggesting the former to be an outcome of synchrotron self Compton emission process. To model the observed X-ray and γ–ray light curves, we numerically solve the kinetic equation describing the evolution of particle distribution in the emission region. The injection of particle distribution into the emission region, from the putative acceleration region, is assumed to be a time dependent power law. The synchrotron and synchrotron self Compton emission from the evolving particle distribution in the emission region are used to reproduce the X-ray and γ–ray flares successfully. Our study suggests that the flaring activity of Mrk 421 can be an outcome of an efficient acceleration process associated with the increase in underlying non-thermal particle distribution.     

R-band host galaxy contamination of TeV γ-ray blazar Mrk 501: effects of aperture size and seeing

We simulated the R-band contribution of the host galaxy of TeV γ-ray BL Lac object Mrk 501 in different aperture sizes and seeing conditions. An intensive set of observations was acquired with the 1.02 m optical telescope, managed by Yunnan Observatories, from 2010 May 15 to 18. Based on the host subtraction data usually used in the literature, the subtraction of host galaxy contamination results in significant seeing-brightness correlations. These correlations would lead to illusive large amplitude variations at short timescales, which will mask the intrinsic microvariability, thus giving rise to difficulty in detecting the intrinsic microvariability. Both aperture size and seeing condition influence the flux measurements, but the aperture size impacts the result more significantly. Based on the parameters of an elliptical galaxy provided in the literature, we simulated the host contributions of Mrk 501 in different aperture sizes and seeing conditions. Our simulation data of the host galaxy obviously weaken these significant seeing-brightness correlations for the host-subtracted brightness of Mrk 501, and can help us discover the intrinsic short timescale microvariability. The pure nuclear flux is ~8.0 m Jy in the R band,i.e., the AGN has a magnitude of R ~13.96 mag.     

On a new class of impulsive flares with no nuclear γ-ray line emission

The new class of -ray spectra from impulsive flares without nuclear -ray lines is compared with bremsstrahlung spectra of energetic electrons undergoing stochastic acceleration, Coulomb and synchrotron losses. The remarkable agreement of both the produced -spectra from the precipitated electrons and the electron spectra measured in the interplanetary space leads to the conclusion that seed population and acceleration process are identical for both classes of electrons. A new estimate of the electron bremsstrahlung contribution in -spectra of impulsive solar flares seems to be necessary.     

The γ-ray emission produced by protons that escape from supernova remnant G349.7+0.2

G349.7+0.2 is an interacting supernova remnant(SNR) expanding in a dense medium.Recently,a very strong γ-ray source coincident with this SNR has been revealed by Fermi-LAT and H.E.S.S.observations which shows a broken power-law-like spectrum.An escaping-diffusion model,including the power-law and δ-function injection,is applied to this source which can naturally explain the spectral feature in both the GeV and TeV regime.We use the Markov Chain Monte Carlo method to constrain the model parameters and find that the correction factor of slow diffusion around this SNR,χ~0.01 for power-law injection and χ~0.1 for δ-function injection,can fit the data best with reasonable molecular cloud mass.This slow diffusion is also consistent with previous results from both phenomenological models and theoretical predication.     

Possible modulated γ-ray emission from the transitional millisecond pulsar binary PSR J1023+0038

We report the results from our analysis of Fermi Large Area Telescope(LAT) data for the transitional millisecond pulsar binary PSR J1023+0038. The time period of the data is nearly 9 yr, and that after the source's transition, in June 2013 from the disk-free state to the active state of having an accretion disk, is approximately 4 yr. We identify a high-energy 5.5 GeV component in the source's spectrum in the active state, and find this component is only significantly detected in half of the orbital phase centered at the descending node(when the pulsar is moving towards the Earth). Considering the pulsar scenario proposed for multi-frequency emission from the source, in which the pulsar is still active and a cold-relativistic pulsar wind inverse-Compton scatters the photons from the accretion disk, we discuss the origin of the high-energy component. In order to explain the observed spectrum, a power-law distribution of particles, with an index of ～3, in the pulsar wind is required, while the orbital variations are possibly due to changes in power-law index as a function of orbital phase.     

High energy γ-ray emission from compact galactic sources in the context of observations with the next generation Cherenkov Telescope Arrays

The observational progress in the γ-ray astronomy in the last few years has led to the discovery of more than a thousand sources at GeV energies and more than a hundred sources at TeV energies. A few different classes of compact objects in the Galaxy have been established. They show many unexpected features at high energies the physics of which remains mainly unknown. At present it is clear that detailed investigation of these new phenomena can be performed only with the technical equipment which offer an order of magnitude better sensitivity, and a few times better energy, angular and time resolution in the broad energy range staring from a few tens of GeV up to a few hundreds TeV. Such facilities can be realized by the next generation of instruments such as the planned Cherenkov Telescope Array (CTA).The aim of this report is to summarize up to date observational results on the compact galactic sources in the GeV–TeV γ-ray energy range, discuss their theoretical implications, and indicate which hypothesis considered at present might be verified with the next generation of telescopes. We point out which of the observational features of the γ-ray sources are important to investigate with special care with the planned CTA in order to throw new light on physical processes involved. Their knowledge should finally allow us to answer the question on the origin of energetic particles in our Galaxy.     

Upper limit on the steady emission of the 2.223 MeV neutron capture γ-ray line from the Sun

Data accumulated by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) have been searched for evidence of the 2.223 MeV neutron capture line from the Sun, outside the times of -ray-emitting solar flares. Background-corrected spectra accumulated over 3-day intervals between 1980 and 1989 show no evidence of the line. Upper limits are reported separately for periods of high and low solar activity.A conservative 3 upper limit of 5.7 × 10^–5 (cm² s)^–1 is placed on the steady flux in the 2.223 MeV line during inactive periods, which is nearly two orders of magnitude lower than previously published results. After correction for limb darkening of the line emission from off-center positions, this upper limit becomes 7.1 × 10^–5 (cm²s)^–1. Our 3 upper limit on the steady flux in the line during periods of high solar activity is 6.9 × 10^–5 (cm² s)^–1, or 8.6 × 10^–5 (cm² s)^–1 after correction for limb darkening. Our results imply that the quiescent solar corona cannot be heated by ions accelerated above 1 MeV in microflares (or a continuous acceleration process), so long as the ion energy spectrum is similar to that measured in large flares. We also use our results to derive the rate of tritium production at the solar surface; our upper limit of 9 nuclei (cm² s)^–1 is about a factor of 9 below the upper limit from searches for ³H in the solar wind. We place upper limits of the order 10³³ on the number of energetic (> 30 MeV) protons which can be stored in active regions prior to being released in solar flares, which imply that the strongest observed flares cannot be produced by such a mechanism.     

The EUV continuum emission (1400–1960 Å) in a solar flare observed from Skylab

The total radiative output in the EUV continuum (1400–1960 Å) from the 5 September 1973 flare has been obtained from the EUV spectra of the flare observed with the NRL slit spectrograph (SO82B) on Skylab. The radiative energy in the EUV continuum is of the order of 10²⁹ ergs, which is more than a factor of 2 greater than those radiated in soft X-rays (8–20 Å) and in H for the flare. Thus, the EUV continuum emission is an important radiative energy loss, and should be included in the consideration of the energy balance of the flare.Ball Corporation.Now at the Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway.     

The GeV emission of PSR B1259–63 during its last three periastron passages observed by Fermi-LAT

PSR B1259–63 is a γ-ray emitting high mass X-ray binary system, in which the compact object is a millisecond pulsar.The system has an orbital period of 1236.7 d and shows peculiar γ-ray flares when the neutron star moves out of the stellar disk of the companion star.The γ-ray flare events were firstly discovered by using Fermi-LAT around the 2010 periastron passage, which was repeated for the 2014 and 2017 periastron passages.We analyze the Fermi-LAT data for all the three periastron passages and found that in each flare the energy spectrum can be represented well by a simple power law.The γ-ray light curves show that in 2010 and 2014 after each periastron there are two main flares,but in 2017 there are four flares including one precursor about 10 d after the periastron passage.The first main flares in 2010 and 2014 are located at around 35 d after the periastron passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to that in 2010.In the 2017 flare, the source shows a precursor about 10 d after the periastron passage, but the following two flares become weaker and lag behind those in 2010 by roughly 5 d.The strongest flares in 2017 occurred 58 d and 70 d after the periastron passage.These results challenge the previous models.     

An association of CMEs with solar flares detected by Fermi γ-ray burst monitor during solar cycle 24

By performing certain spatial and temporal criteria, we obtained 492 CME events simultaneously associated with GBM solar flare events (hereafter, GBM-flare–CME) from the total number 5123 Gamma-ray Burst Monitor (GBM) solar flares and 15228 Coronal Mass Ejections (CMEs) detected during the solar cycle 24 (2008–2019). Among these 492 events, which represent about 9.6% of the total number of the detected GBM flares, there are just 381 events (77.4%) representing the CMEs associated with the flares that are detected instantly by both GBM and RHESSI detectors. We found no significant distinction in the results after applying the spatial criteria compared with those arising from applying the temporal criteria only.Actually, all CMEs are ejected within the flare's preflare and the impulsive phases only. From our results, we conclude that the GBM flares whose long duration are most frequently associated with faster and wider CMEs and vice versa. In addition, the longer the flare's duration, the more interval time between the start time of GBM solar flare and CME's ejection time through a linear correlation [Mean Interval = 0.464 × Duration (min)] with a correlation coefficient equals 0.93. We conclude also that, the highly probable, γ-ray emitting flares (detected by GBM only) have a shorter duration and time interval than X-ray flares (detected also by RHESSI). As well as the GBM - CMEs events, without RHESSI associated CMEs are faster and wider than those associated with RHESSI events.     

Chaos and Periodicities in Solar Flare Index from Kandilli Observatory during 1976–2014

The Solar Flare Index is regarded as one of the most important solar indices in the field of solarterrestrial research. It has the maximum effect on Earth of all other solar activity indices and is being considered for describing the short-lived dynamo action inside the Sun. This paper attempts to study the short as well as long-term temporal fluctuations in the chromosphere region of the Sun using the Solar Flare Index. The daily Solar Flare Index for Northern, Southern Hemisphere and Total Disk are considered for a period from January 1976 to December 2014(total 14 245 days) for chaotic as well as periodic analysis.The 0–1 test has been employed to investigate the chaotic behavior associated with the Solar Flare Index.This test revealed that the time series data is non-linear and multi-periodic in nature with deterministic chaotic features. For periodic analysis, the Raleigh Power Spectrum algorithm has been used for identifying the predominant periods within the data along with their confidence score. The well-known fundamental period of 27 days and 11 years along with their harmonics are well affirmed in our investigation with a period of 28 days and 10.77 years. The presence of 14 days and 7 days periods in this investigation states the short-lived action inside the Sun. Our investigation also demonstrates the presence of other mid-range periods including the famous Rieger type period which are very much confirming the results obtained by other authors using various solar activity indicators.