Fermi-LAT Observations Research Articles

Impact of parameters in the toroidal blazar jet magnetic field model on axion-like particle constraints

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the γ-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. Many studies focus on a simple jet magnetic field model with a toroidal component exerting a predominant influence on regions far from the central region. While many investigations have explored the effects of ALP-photon oscillations using typical parameter values in this model, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy γ-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the simple toroidal balazar jet magnetic field model, and investigate their impacts on the ALP constraints.

PMN J1310–5552: A Gamma-Ray-emitting Blazar Candidate Harboring a Cosmic Monster

Relativistic jets manifest some of the most intriguing activities in the nuclear regions of active galaxies. Identifying the most powerful relativistic jets permits us to probe the most luminous accretion systems and, in turn, the most massive black holes. This paper reports the identification of one such object, PMN J1310−5552 (z = 1.56), a blazar candidate of uncertain type detected with the Fermi Large Area Telescope (LAT) and Swift Burst Alert Telescope. The detection of broad emission lines in its optical spectra taken with the X-Shooter and Goodman spectrographs classifies it to be a flat-spectrum radio quasar. The analysis of the Goodman optical spectrum has revealed PMN J1310−5552 harbors a massive black hole (log scale M BH = 9.90 ± 0.07, in M ⊙) and luminous accretion disk (log scale L disk = 46.86 ± 0.03, in erg s−1). The fitting of the observed big blue bump with the standard accretion disk model resulted in the log scale M BH =9.81−0.20+0.19 (in M ⊙) and L disk =46.86−0.09+0.09 (in erg s−1), respectively. These parameters suggest PMN J1310−5552 hosts one of the most massive black holes and the most luminous accretion disks among the blazar population. The physical properties of this enigmatic blazar were studied by modeling the broadband spectral energy distribution considering the data from NuSTAR, Swift, Fermi-LAT, and archival observations. Overall, PMN J1310−5552 is a powerful “MeV” blazar with physical parameters similar to other members of this unique class of blazars. These results provide glimpses of monsters lurking among the unknown high-energy emitters and demonstrate the importance of ongoing wide-field sky surveys to discover them.

Detection of a Transient Quasiperiodic Oscillation in γ-Rays from Blazar PKS 2255-282

We conducted a comprehensive variability analysis of the blazar PKS 2255-282 using Fermi-LAT observations spanning over 4 yr, from MJD 57783.5 to 59358.5. Our analysis revealed a transient quasiperiodic oscillation (QPO) with a period of 93 ± 2.6 days. We employed a variety of Fourier-based methods, including the Lomb–Scargle periodogram (LSP) and weighted wavelet Z-transform (WWZ), as well as time domain analysis techniques such as seasonal and nonseasonal autoregressive Integrated moving average models and the Stochastic modeling with stochastically driven damped harmonic oscillator models. Consistently, the QPO with a period of 93 days was detected across all methods used. The observed peak in LSP and time-averaged WWZ plots has a significance level of 4.06σ and 3.96σ, respectively. To understand the source of flux modulations in the light curve, we explored various physical models. A plausible scenario involves the precession of the jet with a high Lorentz factor or the movement of a plasma blob along a helical trajectory within the relativistic jet.

Study of γ-Ray Emission from a Compact Radio Galaxy with the Fermi Large Area Telescope

The radio galaxy PKS 1007+142 is classified as a compact steep-spectrum source (CSS) and belongs to the class of young active galactic nuclei (AGNs). In this paper, we investigate the γ-ray emission from this CSS by conducting a comprehensive analysis of the 15 yr Fermi Large Area Telescope (Fermi-LAT) observation data. The Fermi-LAT latest Source Catalog, 4FGL-DR4, includes an unassociated γ-ray source, 4FGL J1010.0+1416, located at 0.°24 away from the radio position of PKS 1007+142. Using the 15 yr Fermi-LAT observation data, we reestimate the best-fit position of the γ-ray source and find that PKS 1007+142 is in close proximity to the γ-ray source and falls within its 68% error circle. Therefore, we conclude that PKS 1007+142 is the most plausible counterpart to the unassociated LAT source with detection test statistics ∼ 43.4 (∼6.6σ). PKS 1007+142 exhibits a steep power-law spectrum in the 0.1–300 GeV band, with a photon spectral index (Γ γ ) of 2.86 ± 0.17. The average flux in the considered time interval is (2.14 ± 0.34) × 10−12 erg cm−2 s−1. Comparing PKS 1007+142 with other γ-ray emitting AGNs in both the L γ –Γ γ and L γ –L 1.4 GHz planes, it shows a softer γ-ray spectrum and lower luminosity compared to other γ-ray emitting CSSs. Furthermore, the possible origins of γ-ray in PKS 1007+142 are also discussed.

Indirect detection of dark matter with (pseudo)-scalar interactions

Indirect detection is one of the most powerful methods to search for annihilating dark matter. In this work, we investigate the impact of non-perturbative effects in the indirect detection of dark matter. For this purpose we utilize a minimal model consisting of a fermionic dark matter candidate in the TeV mass range that interacts via scalar- and pseudo-scalar interactions with a massive scalar mediator mixing with the Higgs. The scalar interaction induces an attractive Yukawa potential between dark matter particles, such that annihilations are Sommerfeld enhanced, and bound states can form. These non-perturbative effects are systematically dealt with (potential) non-relativistic effective field theories and we derive the relevant cross sections for dark matter. We discuss their impact on the relic density and indirect detection. Annihilations in dwarf galaxies and the Galactic Center require special care and we derive generalized J-factors for these objects that account for the non-trivial velocity dependence of the cross sections in our model. We use limits on the gamma-ray flux based on Fermi-LAT observations and limits on the rate of exotic energy injection from Planck to derive bounds on the parameter space of the model. Finally, we estimate the impact that future limits from the Cherenkov Telescope Array are expected to have on the model.

Estimating the jet power from Broadband SED modelling of Mkn 501 for different particle distributions

ABSTRACT We consider the broad-band spectral energy distribution of the high-energy-peaked blazar Mkn 501 using Swift-XRT/UVOT, NuSTAR and Fermi-LAT observations taken between 2013 and 2022. The spectra were fitted with a one-zone leptonic model using synchrotron and synchrotron self-Compton emission from different particle energy distributions such as a broken power law, log-parabola, as well as distributions expected when the diffusion or the acceleration time-scale are energy-dependent. The jet power estimated for a broken power-law distribution was ∼1047(1044) erg s−1 for a minimum electron energy γmin ∼ 10(103). However, for electron energy distributions with intrinsic curvature (such as the log-parabola form), the jet power is significantly lower at a few times 1042 erg s−1 which is a few per cent of the Eddington luminosity of a 107 M⊙ black hole, suggesting that the jet may be powered by accretion processes. We discuss the implications of these results.

First Constraints on the Photon Coupling of Axionlike Particles from Multimessenger Studies of the Neutron Star Merger GW170817.

We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axionlike particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant, and decay back into two photons, giving rise to a photon signal approximately along the line of sight to the merger. We analyze the spectral and temporal information of the ALP-induced photon signal and use the Fermi Large Area Telescope (Fermi-LAT) observations of GW170817 to derive our new ALP constraints. We also show the improved prospects with future MeV γ-ray missions, taking the spectral and temporal coverage of Fermi-LAT as an example.

Broad-band study of gamma-ray blazars at redshifts z = 2.0–2.5

ABSTRACT High redshift blazars are among the most powerful non-explosive sources in the Universe and play a crucial role in understanding the evolution of relativistic jets. To understand these bright objects, we performed a detailed investigation of the multiwavelength properties of 79 γ-ray blazars with redshifts ranging from z = 2.0 to 2.5, using data from Fermi LAT, Swift XRT/UVOT, and NuSTAR observations. In the γ-ray band, the spectral analysis revealed a wide range of flux and photon indices, from 5.32 × 10−10 to 3.40 × 10−7 photon cm−2 s−1 and from 1.66 to 3.15, respectively, highlighting the diverse nature of these sources. The detailed temporal analysis showed that flaring activities were observed in 31 sources. Sources such as 4C+71.07, PKS 1329-049, and 4C + 01.02, demonstrated significant increase in the γ-ray luminosity and flux variations, reaching peak luminosity exceeding 1050 erg s−1. The temporal analysis extended to X-ray and optical/ultraviolet (UV) bands, showed clear flux changes in some sources in different observations. The time-averaged properties of high redshift blazars were derived through modeling the spectral energy distributions with a one-zone leptonic scenario, assuming the emission region is within the broad-line region (BLR) and the X-ray and γ-ray emissions are due to inverse Compton scattering of synchrotron and BLR-reflected photons. This modeling allowed us to constrain the emitting particle distribution, estimate the magnetic field inside the jet, and evaluate the jet luminosity, which is discussed in comparison with the disc luminosity derived from fitting the excess in the UV band.

Constraining MeV-scale axionlike particles with Fermi-LAT observations of SN 2023ixf

The Fermi-LAT observations of SN 2023ixf, a type II supernova in the nearby Pinwheel Galaxy, Messier 101 (M101), presents us with an excellent opportunity to constrain MeV-scale axionlike particles (ALPs). By examining the photon decay signature from heavy ALPs that could be produced in the explosion, the existing constraints on the ALP-photon coupling can be improved, under optimistic assumptions, by up to a factor of ∼2 for masses ma≲3 MeV. Under very conservative assumptions, we find a bound that is slightly weaker than the existing ones for ma≲0.5 MeV. The exact reach of these searches depends mostly on properties of the SN progenitor. This study demonstrates the relevance of core-collapse supernovae, also beyond the Magellanic Clouds, as probes of fundamental physics. Published by the American Physical Society 2024

Fermi-LAT Detection of the Supernova Remnant G312.4-0.4 in the Vicinity of 4FGL J1409.1-6121e

Gamma-ray emission provides constraints on the nonthermal radiation processes at play in astrophysical particle accelerators. This allows both the nature of accelerated particles and the maximum energy that they can reach to be determined. Notably, it remains an open question to what extent supernova remnants contribute to the sea of Galactic cosmic rays. In the Galactic plane, at around 312° of Galactic longitude, Fermi-LAT observations show an extended source (4FGL J1409.1−6121e) around five powerful pulsars. This source is described by one large disk of 0.°7 radius with a high significance of 45σ in the 4FGL-DR3 catalog. Using 14 yr of Fermi-LAT observations, we revisited this region with a detailed spectro-morphological analysis in order to disentangle its underlying structure. Three sources have been distinguished, including the supernova remnant G312.4−0.4 whose gamma-ray emission correlates well with the shell observed at radio energies. The hard spectrum detected by the LAT, extending up to 100 GeV without any sign of a cutoff, is well reproduced by a purely hadronic model.

Understanding the broad-band emission process of 3C 279 through long term spectral analysis

ABSTRACT The long term broad-band spectral study of Flat Spectrum Radio Quasars during different flux states has the potential to infer the emission mechanisms and the cause of spectral variations. To scrutinize this, we performed a detailed broad-band spectral analysis of 3C 279 using simultaneous Swift-XRT/UVOT and Fermi-LAT observations spanning from 2008 August to 2022 June. We also supplement this with the simultaneous NuSTAR observations of the source. The optical/UV, X-ray, and γ-ray spectra were individually fitted by a power law to study the long term variation in the flux and the spectral indices. A combined spectral fit of simultaneous optical/UV and X-ray spectra was also performed to obtain the transition energy at which the spectral energy distribution is minimum. The correlation analysis suggests that the long term spectral variations of the source are mainly associated with the variations in the low energy index and the break energy of the broken power-law electron distribution which is responsible for the broad-band emission. The flux distribution of the source represents a lognormal variability while the γ-ray flux distribution showed a clear double lognormal behaviour. The spectral index distributions were again normal except for γ-ray which showed a double-Gaussian behaviour. This indicates that the lognormal variability of the source may be associated with the normal variations in the spectral index. The broad-band spectral fit of the source using synchrotron and inverse Compton processes indicates different emission processes are active at optical/UV, X-ray, and γ-ray energies.

Search for the gamma-ray spectral lines with the DAMPE and the Fermi-LAT observations

Search for the gamma-ray spectral lines with the DAMPE and the Fermi-LAT observations

Constraints on the Intergalactic Magnetic Field Strength from γ-Ray Observations of GRB 221009A

Characteristics of the cascade gamma-ray signal resulting from very-high-energy gamma-ray sources, such as gamma-ray bursts, can be used to constrain the strength and structure of intergalactic magnetic fields (IGMFs). There has been a debate on whether GRB 190114C, the first gamma-ray burst with observed TeV photons, can constrain the IGMF. Recently, LHAASO detected the brightest-of-all-time GRB 221009A, which has much larger energy in the TeV band, and the spectrum extends to energy above 10 TeV, providing an unprecedented opportunity to study IGMF. We perform a Monte Carlo simulation of the cascade process with the public ELMAG code, considering the TeV data of GRB 221009A observed by LHAASO. By comparing the resulting cascade emission with the flux limit obtained from Fermi-LAT observations, we infer a limit of B ≥ 10−18.5 G for IGMF. Though this limit may not be as strong as the limit from blazars, it serves as an independent constraint on IGMF from a new class of TeV sources.

Gamma Ray Pulsars and Opportunities for the MACE Telescope

Rapidly rotating neutron stars with very strong surface magnetic fields are observed to emit pulsed emission in the whole range of electromagnetic spectrum from radio to high-energy gamma rays. These so-called pulsars are known for their exceptional rotational stability. The radio emission from pulsars is generally believed to be powered by the rotational energy of neutron stars. More than 3000 pulsars have been currently known from radio observations; however, only about 10% are observed in the high-energy gamma ray band. The Fermi-LAT observations in the energy range above 100 MeV have discovered more than 300 pulsars. However, the origin of high-energy non-thermal radiation from pulsars is not completely understood and remains an active area of research. In this contribution, we report a summary of observational features of the gamma ray pulsars and briefly discuss observability for the MACE gamma ray telescope, which has just started its regular science operation at Hanle in India. Six gamma ray pulsars, other than the well-known Crab and Geminga, are identified as probable candidates for MACE observations.

Investigating Possible Correlations between Gamma-Ray and Optical Lightcurves for TeV-Detected Northern Blazars over 8 Years of Observations

Blazars are a subclass of active galactic nuclei (AGN) having relativistic jets aligned within a few degrees of our line-of-sight and form the majority of the AGN detected in the TeV regime. The Fermi-Large Area Telescope (LAT) is a pair-conversion telescope, sensitive to photons having energies between 20 MeV and 2 TeV, and is capable of scanning the entire gamma-ray sky every three hours. Despite the remarkable success of the Fermi mission, many questions still remain unanswered, such as the site of gamma-ray production and the emission mechanisms involved. The Asteroid Terrestrial-impact Last Alert System (ATLAS) is a high cadence all sky survey system optimized to be efficient for finding potentially dangerous asteroids, as well as in tracking and searching for highly variable and transient sources, such as AGN. In this study, we investigate possible correlations between the Fermi-LAT observations in the 100 MeV–300 GeV energy band and the ATLAS optical data in the R-band, centered at 679 nm, for a sample of 18 TeV-detected northern blazars over 8 years of observations between 2015 and 2022. Under the assumption that the optical and gamma-ray flares are produced by the same outburst propagating down the jet, the strong correlations found for some sources suggest a single-zone leptonic model of emission.

Classification of the Fermi-LAT blazar candidates of uncertain type using extreme gradient boosting

ABSTRACT Machine learning based approaches are emerging as very powerful tools for many applications including source classification in astrophysics research due to the availability of huge high quality data from different surveys in observational astronomy. The Large Area Telescope on board Fermi satellite (Fermi-LAT) has discovered more than 6500 high energy gamma-ray sources in the sky from its survey over a decade. A significant fraction of sources observed by the Fermi-LAT either remains unassociated or has been identified as Blazar Candidates of Uncertain type (BCUs). We explore the potential of eXtreme Gradient Boosting – a supervised machine learning algorithm to identify the blazar subclasses among a sample of 112 BCUs of the 4FGL catalogue whose X-ray counterparts are available within 95 per cent uncertainty regions of the Fermi-LAT observations. We have used information from the multiwavelength observations in IR, optical, UV, X-ray, and γ-ray wavebands along with the redshift measurements reported in the literature for classification. Among the 112 uncertain type blazars, 62 are classified as BL Lacertae objects and six have been classified as flat spectrum radio quasars. This indicates a significant improvement with respect to the multiperceptron neural network based classification reported in the literature. Our study suggests that the gamma-ray spectral index, and IR colour indices are the most important features for identifying the blazar subclasses using the XGBoost classifier. We also explore the importance of redshift in the classification BCU candidates.

Spatial Coincidence between Ultra-high Energy Cosmic Rays and TeV Gamma Rays in the Direction of GRB 980425/SN 1998bw

Gamma-ray bursts (GRBs) have long been suspected as possible ultra-high energy cosmic ray (UHECR) accelerators. In this brief note, I report that GRB 980425/SN 1998bw falls within the region of interest (ROI) with the highest significance in an all-sky blind search for magnetically induced effects in the arrival directions of UHECRs conducted by the Pierre Auger Collaboration with events detected up to to 2018 August 31. There is also report in the literature of delayed TeV emission in archival Fermi LAT observations from the direction of GRB 980425/SN 1998bw. The combined probability that two distinct cosmic ray acceleration signatures in two different multimessenger experiments may appear at the same spatial location by chance is estimated to be between 1.62 × 10−3 and 0.0157.

A new viable mass region of dark matter and dirac neutrino mass generation in a scotogenic extension of SM

In this paper, we propose a scotogenic extension of the Standard Model (SM) which can provide a scalar dark matter (DM) candidate in the new, theoretically previously unaddressed, intermediate region ([Formula: see text][Formula: see text]GeV) and also generate light Dirac neutrino masses. In this framework, the SM is extended by three gauge singlet fermions, two singlet scalar fields and one additional scalar doublet along with a continuous global symmetry [Formula: see text] and discrete symmetries [Formula: see text] and [Formula: see text]. These additional symmetries prevent the singlet fermions from obtaining Majorana mass terms along with providing the stability to the DM candidate. It is known that in the case of the scalar singlet DM model, the only region which is not yet excluded is a narrow region close to the Higgs resonance [Formula: see text] — others ruled out from different experimental and theoretical bounds. In the case of the inert doublet model, the mass region ([Formula: see text]–80[Formula: see text]GeV) and the high-mass region (heavier than 550[Formula: see text]GeV) are allowed. This motivates us to explore a parameter range in the intermediate-mass region [Formula: see text][Formula: see text]GeV, which we do in a scotogenic extension of SM with a scalar doublet and scalar singlets. The DM in our model is a mixture of singlet and doublet scalars, in the freeze-out scenario. We constrain the allowed parameter space of the model using the Planck bound on present DM relic abundance, neutrino mass and the latest bound on spin-independent DM-nucleon scattering cross-section from the XENON1T experiment. Further, we constrain the DM parameters from the indirect detection bounds arising from the global analysis of the Fermi-LAT observations of dwarf spheroidal satellite (dSphs) galaxies, Higgs invisible decay and Electroweak Precision Test (EWPT) as well. We find that our model findings may provide a viable DM candidate satisfying all the constraints on DM parameters in the new, previously unexplored mass range ([Formula: see text][Formula: see text]GeV). This new window for the DM candidate could be searched in future experiments along with an explanation of the Dirac mass of neutrinos since so far there is no strong evidence in support of the Majorana nature of neutrino mass.

The multiwavelength view of shocks in the fastest nova V1674 Her

ABSTRACT Classical novae are shock-powered multiwavelength transients triggered by a thermonuclear runaway on an accreting white dwarf. V1674 Her is the fastest nova ever recorded (time to declined by two magnitudes is t2 = 1.1 d) that challenges our understanding of shock formation in novae. We investigate the physical mechanisms behind nova emission from GeV γ-rays to cm-band radio using coordinated Fermi-LAT, NuSTAR, Swift, and VLA observations supported by optical photometry. Fermi-LAT detected short-lived (18 h) 0.1–100 GeV emission from V1674 Her that appeared 6 h after the eruption began; this was at a level of (1.6 ± 0.4) × 10−6 photons cm−2 s−1. Eleven days later, simultaneous NuSTAR and Swift X-ray observations revealed optically thin thermal plasma shock-heated to kTshock = 4 keV. The lack of a detectable 6.7 keV Fe Kα emission suggests super-solar CNO abundances. The radio emission from V1674 Her was consistent with thermal emission at early times and synchrotron at late times. The radio spectrum steeply rising with frequency may be a result of either free-free absorption of synchrotron and thermal emission by unshocked outer regions of the nova shell or the Razin–Tsytovich effect attenuating synchrotron emission in dense plasma. The development of the shock inside the ejecta is unaffected by the extraordinarily rapid evolution and the intermediate polar host of this nova.

The Fermi-LAT Lightcurve Repository* *For any questions about this work, contact in order: M. Negro, D. Kocevski, J. Valverde, A. Brill, S. Garrappa.

The Fermi Large Area Telescope (LAT) lightcurve repository (LCR) is a publicly available, continually updated library of gamma-ray lightcurves of variable Fermi-LAT sources generated over multiple timescales. The Fermi-LAT LCR aims to provide publication-quality lightcurves binned on timescales of 3, 7, and 30 days for 1525 sources deemed variable in the source catalog of the first 10 yr of Fermi-LAT observations. The repository consists of lightcurves generated through full likelihood analyses that model the sources and the surrounding region, providing fluxes and photon indices for each time bin. The LCR is intended as a resource for the time-domain and multimessenger communities by allowing users to search LAT data quickly to identify correlated variability and flaring emission episodes from gamma-ray sources. We describe the sample selection and analysis employed by the LCR and provide an overview of the associated data access portal.