TeV Excess Research Articles

TeV and keV–MeV Excesses as Probes for Hadronic Process in BL Lacertaes

Abstract A hard TeV γ-ray component excess over the single-zone leptonic model prediction (TeV excess) is observed in the spectral energy distributions (SEDs) of some BL Lacs. Its origin is uncertain. We revisit this issue with four BL Lacs (1ES 0229+200, 1ES 0347–121, 1ES 1101–232, and H2356–309), in which the TeV excess is detected in their intrinsic SEDs. We represent their SEDs with a single-zone leptohadronic model, where radiations of the electrons and protons as well as the cascade electrons produced by the γγ and pγ interactions within their jets are considered. We show that the observed SEDs below the GeV gamma-ray band are attributed to the synchrotron radiations and self-Compton process of the primary electrons, and the TeV excess is explained with the γ-ray emission from the pγ process via the π 0 decay. The cascade emission of the electrons produced via the γγ and pγ interactions results in a keV–MeV excess in the SEDs, illustrated as a bump or plateau. This extra photon field enhances the production of TeV photons from the p γ process, resulting in a reduction of the proton power by about one order of magnitude. However, the derived powers are still 3–4 orders of magnitude larger than the Eddington limit, being challenged by the current black hole accretion physics. Applying our model to Mrk 421, we propose that synergic observations with current and upcoming TeV and keV–MeV telescopes for its tentative TeV and MeV excesses can give insights to the hadronic process in its jet.

On the gamma-ray signals from UCMH/mini-spike accompanying the DAMPE 1.4 TeV e+e− excess

ABSTRACT The tentative 1.4 TeV e+e− excess observed by DAMPE, if not a statistical fluctuation, may be explained by dark matter (DM) annihilation within a nearby subhalo with a distance of <0.3 kpc. The process of DM annihilating to e+e− is accompanied by the production of gamma-ray photons, which could lead to detectable signals of Fermi-LAT. In this work, we focus on the model that the tentative 1.4 TeV signal is from a nearby ultracompact mini halo (UCMH). Due to the small angular extension, the counterpart gamma-ray signal would be hidden among Fermi-LAT unassociated point sources. We examine the point sources in 4FGL systematically by analyzing the Fermi-LAT data, aiming to investigate whether there exist sources with gamma-ray properties consistent with the UCMH model of the 1.4 TeV excess. We find more than 10 sources could be the candidates. Furthermore, we test the possibility that the excess signal is from a DM mini-spike around the nearest BH, but our result does not favour such a scenario.

A simple and natural interpretations of the DAMPE cosmic-ray electron/positron spectrum within two sigma deviations

The DArk Matter Particle Explorer (DAMPE) experiment has recently announced the first results for the measurement of total electron plus positron fluxes between 25 GeV and 4.6 TeV. A spectral break at about 0.9 TeV and a tentative peak excess around 1.4 TeV have been found. However, it is very difficult to reproduce both the peak signal and the smooth background including spectral break simultaneously. We point out that the numbers of events in the two energy ranges (bins) close to the 1.4 TeV excess have 1sigma deficits. With the basic physics principles such as simplicity and naturalness, we consider the -2sigma , +2sigma , and -1sigma deviations due to statistical fluctuations for the 1229.3 GeV bin, 1411.4 GeV bin, and 1620.5 GeV bin. Interestingly, we show that all the DAMPE data can be explained consistently via both the continuous distributed pulsar and dark matter interpretations, which have chi ^{2} simeq 17.2 and chi ^{2} simeq 13.9 (for all the 38 points in DAMPE electron/positron spectrum with 3 of them revised), respectively. These results are different from the previous analysis by neglecting the 1.4 TeV excess. At the same time, we do a similar global fitting on the newly released CALET lepton data, which could also be interpreted by such configurations. Moreover, we present a U(1)_D dark matter model with the Breit–Wigner mechanism, which can provide the proper dark matter annihilation cross section and escape the CMB constraint. Furthermore, we suggest a few ways to test our proposal.

Search for resonances in the mass spectrum of muon pairs produced in association with b quark jets in proton-proton collisions at sqrt{s}=8 and 13 TeV

A search for resonances in the mass range 12–70 GeV produced in association with a b quark jet and a second jet, and decaying to a muon pair, is reported. The analysis is based on data from proton-proton collisions at center-of-mass energies of 8 and 13 TeV, collected with the CMS detector at the LHC and corresponding to integrated luminosities of 19.7 and 35.9 fb−1, respectively. The search is carried out in two mutually exclusive event categories. Events in the first category are required to have a b quark jet in the central region (|η| ≤ 2.4) and at least one jet in the forward region (|η| > 2.4). Events in the second category are required to have two jets in the central region, at least one of which is identified as a b quark jet, no jets in the forward region, and low missing transverse momentum. An excess of events above the background near a dimuon mass of 28 GeV is observed in the 8 TeV data, corresponding to local significances of 4.2 and 2.9 standard deviations for the first and second event categories, respectively. A similar analysis conducted with the 13 TeV data results in a mild excess over the background in the first event category corresponding to a local significance of 2.0 standard deviations, while the second category results in a 1.4 standard deviation deficit. The fiducial cross section measurements and 95% confidence level upper limits on those for a resonance consistent with the 8 TeV excess are provided at both collision energies.

Pevatron at the Galactic Center: multi-wavelength signatures from millisecond pulsars

Diffuse TeV emission has been observed by H.E.S.S. in the Galactic Center region, in addition to the GeV gamma rays observed by Fermi. We propose that a population of unresolved millisecond pulsars located around the Galactic Center, suggested as possible candidates for the diffuse Galactic Center excess observed by Fermi, accelerate cosmic rays up to very high energies, and are thus also responsible for the TeV excess. We model analytically the diffusion of these accelerated protons and their interaction with the molecular clouds, producing gamma rays. The spatial and spectral dependences of the gamma rays produced can reproduce the H.E.S.S. observations, for a population of ∼ 104–105 millisecond pulsars above the cosmic-ray luminosity 1034 erg s−1, with moderate acceleration efficiency. More precise measurements at the highest energies would allow us to constrain the properties of the pulsar population, such as the magnetic field or initial spin distributions.

Pulsar TeV Halos Explain the Diffuse TeV Excess Observed by Milagro.

Milagro observations have found bright, diffuse TeV emission concentrated along the galactic plane of the MilkyWay. The intensity and spectrum of this emission is difficult to explain with current models of hadronic γ-ray production, and has been named the "TeV excess." We show that TeV emission from pulsars naturally explains this excess. Recent observations have detected "TeV halos" surrounding pulsars that are either nearby or particularly luminous. Extrapolating this emission to the full population of MilkyWay pulsars indicates that the ensemble of "subthreshold" sources necessarily produces bright TeV emission diffusively along the MilkyWay plane. Models indicate that the TeV halo γ-ray flux exceeds that from hadronic γ rays above an energy of ∼500 GeV. Moreover, the spectrum and intensity of TeV halo emission naturally matches the TeV excess. Finally, we show that upcoming HAWC observations will resolve a significant fraction of the TeV excess into individual TeV halos, conclusively confirming, or ruling out, this model.

Trinification can explain the di-photon and di-boson LHC anomalies

LHC data show a diphoton excess at 750 GeV and a less significant diboson excess around 1.9 TeV. We propose trinification as a common source of both anomalies. The 1.9 TeV excess can be produced by the lightest extra vector: a $W_R^\pm$ with a gauge coupling $g_R\approx 0.44$ that does not decay into leptons. Furthermore, trinification predicts extra scalars. One of them can reproduce the $\gamma\gamma$ excess while satisfying constraints from all other channels, given the specific set of extra fermions predicted by trinification.

Intersecting branes, SUSY breaking and the 2 TeV excess at the LHC

Intersecting D-brane models in string theory can naturally support the gauge and matter content of left-right symmetric extensions of the Standard Model with gauge symmetry SU(3)_c x SU(2)_L x SU(2)_R x U(1)_{B-L}. Considering such models as candidates for explaining the 2TeV excesses seen in Run-1 by both ATLAS and CMS, the minimal possible scale of supersymmetry breaking is determined by the requirement of precise one-loop gauge coupling unification. For the vector-like, bifundamental and (anti-)symmetric Higgs content of such brane configurations, this comes out fairly universally at around 19TeV. For the SU(2)_R gauge coupling one finds values 0.48<g_R(M_R)<0.6. Threshold corrections can potentially lower the scale of supersymmetry breaking.

Discovery of the VHE gamma-ray source HESS J1832-093 in the vicinity of SNR G22.7-0.2

The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the H.E.S.S. Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832-093, at the position $\rm RA=18^h 32^m 50^s \pm 3^s_{stat} \pm 2^s_{syst}, \rm Dec=-9^\circ 22' 36'' \pm 32''_{stat} \pm 20''_{syst} (J2000)$, spatially coincident with a part of the radio shell of the neighboring remnant G22.7-0.2. The photon spectrum is well described by a power-law of index $\Gamma = 2.6 \pm 0.3_{\rm stat} \pm 0.1_{\rm syst}$ and a normalization at 1 TeV of $\Phi_0=(4.8 \pm 0.8_{\rm stat}\pm 1.0_{\rm syst})\,\times\,10^{-13}\,\rm{cm} ^{-2}\,s^{-1}\,TeV^{-1}$. The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic-rays illuminating a nearby molecular cloud. Then a dedicated XMM-Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832-093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multi-wavelength observations will help to shed new light on this intriguing VHE source.

THE DIFFUSE GeV-TeV γ-RAY EMISSION OF THE CYGNUS REGION

Recently the Milagro experiment observed diffuse multi-TeV gamma ray emission in the Cygnus region, which is significantly stronger than what is predicted by the Galactic cosmic ray model. However, the sub-GeV observation by EGRET shows no excess to the prediction based on the same model. This TeV excess implies possible high-energy cosmic rays populated in the region with harder spectrum than that observed on the Earth. In the work we studied this theoretical speculation in detail. We find that, a diffuse proton source with power index {alpha} {sub p} {approx}< 2.3, or a diffuse electron source with power index {alpha} {sub e} {approx}< 2.6 can reproduce the Milagro's observation without conflicting with the EGRET data. Further detections on neutrinos, a diagnostic of the hadronic model, and hard X-ray synchrontron radiation, a diagnostic of the lepton model, help to break this degeneracy. In combination with the gamma ray observations to several hundred GeV by Fermi, we will be able to understand the diffuse emission mechanisms in the Cygnus region better.

Diffuse gamma rays from the Galactic Plane: Probing the “GeV excess” and identifying the “TeV excess”

Pion decay gamma rays have long been recognized as a unique signature of hadronic cosmic rays and their interactions with the interstellar medium. We present a model-independent way of constraining this signal with observations of the Galactic Plane in diffuse gamma rays. We combine detections by the EGRET instrument at GeV energies and the Milagro Čerenkov detector at TeV energies with upper limits from KASCADE and CASA-MIA ground arrays at PeV energies. Such a long “lever arm”, spanning at least six orders of magnitude in energy, reveals a “TeV excess” in the diffuse Galactic Plane gamma-ray spectrum. While the origin of this excess is unknown, it likely implies also enhanced TeV neutrino fluxes, significantly improving the prospects for their detection. We show that unresolved point sources are a possible source of the TeV excess. In fact, the spectra of the unidentified EGRET sources in the Milagro region must break between ∼10 GeV and ∼1 TeV to avoid strongly overshooting the Milagro measurement; this may have important implications for cosmic-ray acceleration. Finally, we use our approach to examine the recent suggestion that dark-matter annihilation may account for the observed excess in diffuse Galactic gamma-rays detected by EGRET at energies above 1 GeV. Within our model-independent approach, current data cannot rule this possibility in or out; however we point out how a long “lever arm” can be used to constrain the pionic gamma-ray component and in turn limit the “GeV excess” and its possible sources. Experiments such as HESS and MAGIC, and the upcoming VERITAS and GLAST, should be able to finally disentangle the main sources of the Galactic gamma rays.