Detection Of TeV Gamma-rays Research Articles

Red dwarfs as sources of cosmic rays and detection of TeV gamma-rays from these stars

A modern paradigm on the sources of galactic cosmic rays includes supernovae and supernova remnants as the powerful ones to accelerate particles up to ∼1017 eV. Meanwhile, the recent experimental data obtained by PAMELA, AMS-02, Fermi-LAT, CALET, and DAMPE require the existence of other cosmic-ray sources located nearby the solar system, at the distances less than 1 kpc. Presence of such local sources could explain the unexpected rise of the positron fraction in cosmic rays, the observed electron fluxes with the energies more than one TeV, complex shapes of the proton and helium spectra, and anomalous low-energy cosmic rays. Here we consider active dwarf stars as possible sources of Galactic cosmic rays in the energy range up to 1014 eV. These stars are producing powerful stellar flares sometimes with energy release more than 1036 erg. Meanwhile, the generation of high-energy cosmic rays should be accompanied by the high-energy γ-ray emission, which may be observed. Here we present the results of the SHALON long-term observations of generation of γ-ray emission above 800 GeV from the active red dwarf stars.

Multiwavelength Investigation of Pulsar Wind Nebula DA 495 with HAWC, VERITAS, and NuSTAR

Abstract Pulsar wind nebula DA 495 (G65.7+1.2) was detected in TeV gamma-rays by the High Altitude Water Cerenkov Observatory in 2017 (2HWC J1953+294). Follow-up observations by the Very Energetic Radiation Imaging Telescope Array System confirmed the association between 2HWC J1953+294 and DA 495 and found the TeV emission to be spatially coincident with the radio emission first reported in 1968. The detection of TeV gamma-rays from DA 495, along with past X-ray detection up to 10 keV, prompted high-energy X-ray observations as part of the NuSTAR Galactic Legacy Survey. We present the results of these NuSTAR observations, combined with archival Chandra and XMM-Newton observations, and confirm the previous X-ray photon index of Γ 2 – 20 keV = 2.0 ± 0.1 . We find no spectral cutoff up to 20 keV. With the spectral information for DA 495 extended to TeV gamma-rays, we were able to perform analytical modeling to test leptonic and hadronic emission scenarios. The leptonic models can explain the broadband emission, but also imply a diffuse X-ray nebula of similar extent to the radio and TeV nebulae, which cannot be confirmed by our observations. The hadronic models can simultaneously explain the spectrum and the spatial extent in all wavelengths; however, we need a very high magnetic field strength pervading the radio and TeV nebulae and a surprisingly high particle kinetic energy. These requirements deepen the mystery of the physical nature of DA 495. Future observations in radio to infrared bands and spatially resolved γ-rays can further constrain the physical conditions and radiation mechanisms in DA 495.

Red Dwarfs as Sources of Cosmic Rays and First Detection of TeV Gamma-rays from these stars

Conventional sources of Galactic cosmic rays are believed to be supernovae and supernova remnants that are powerful enough to accelerate particles up to 1017 eV. Meanwhile, an interpretation of recent experimental data obtained by PAMELA, Fermi-LAT, and AMS-02 spectrometers hints at a possibility that some cosmic-ray sources may be located in a close proximity of the solar system, at the distances less than 1 kpc. Presence of such local sources could explain the unexpected raise of the positron fraction in cosmic rays, complex shapes of the proton and helium spectra, and even anomalous low-energy cosmic rays. We consider active dwarf stars as possible sources of Galactic cosmic rays in the energy range up to 1014 eV. These stars are producing powerful stellar flares. Meanwhile, generation of high-energy cosmic rays should be accompanied by the high-energy γ-ray emission, which may be observed. Here we present the results of the SHALON long-term observations aimed to search for γ-ray emission above 800 GeV from the active red dwarf stars.

Galactic Cosmic Rays: The first detection of TeV gamma-rays from Red Dwarfs

The present point of view on the sources of cosmic rays in Galaxy considers explosions of supernovae as sources of these particles up to energies of 1017 eV. However, the experimental data obtained with Pamela, Fermi, AMS-02 spectrometers requires the existence of nearby sources of cosmic rays at distances less then 1 kpc from the solar system. These sources could explain such experimental data as the growth of the ratio of galactic positrons to electrons with increasing energy, the complex dependence of the exponent of the proton and alpha spectra from the energy of these particles, the appearance of an anomaly component in cosmic rays. We consider active dwarf stars as possible sources of galactic cosmic rays in the energy range up to 1014 eV. These stars produce powerful stellar flares. The generation of high-energy cosmic rays has to be accompanied by high-energy gamma-ray emission. Here we present the SHALON long-term observation data aimed at searching for gamma-ray emission above 800 GeV from active red dwarf stars. The data obtained during more than 10 years observations of the dwarf stars V962 Tau, V780 Tau, V388 Cas and V1589 Cyg were analyzed. The high-energy gamma-ray emission in the TeV energy range, mostly of the flaring type from the sources mentioned above, was detected. This result confirms that active dwarf stars are also the sources of high-energy galactic cosmic rays.

ORIGIN OF THE X-RAYS AND POSSIBLE GeV-TeV EMISSION FROM THE WESTERN HOT SPOT OF PICTOR A

Pictor A is a nearby Fanaroff-Riley class II (FR II) radio galaxy with a bright hot spot, the western hot spot. Observation of high polarization in the optical emission of the hot spot indicates that the optical emission could be synchrotron radiation of relativistic electrons in the hot spot. These electrons may be able to produce high energy gamma-ray photons through inverse Compton (IC) scattering. We use single-zone and multi-zone synchrotron + synchrotron-self-Compton (SSC) models to fit the observed spectral energy distribution (SED) from the radio to the X-ray band of the hot spot. Our esults show that in the case of a much weaker magnetic field strength than the equipartition magnetic field, both the single-zone and multi-zone models can fit the SED, but the multi-zone model significantly improves the fit. The two models predict the hot spot as a GeV-TeV source, which might be marginally detectable with Fermi/LAT and HESS. The inverse Compton scattering of cosmic microwave background (IC/CMB) is also considered, but its contribution to GeV-TeV emission is negligible. Note that under the equipartition condition, the SED can also be fit with the multi-zone model, but the predicted flux at 10^22 Hz is too weak to be detectable. The detection of TeV gamma-rays from this FR II radio galaxy, if confirmed, would establish a new subclass of extragalactic source in this energy regime since most of the AGNs detected to date at TeV energies are high-energy-peaked BL Lac objects.

VHE GAMMA-RAYS FROM GALACTIC X-RAY BINARY SYSTEMS

The detection of TeV gamma-rays from LS 5039 and the binary pulsar PSR B1259–63 by HESS, and from LS I +61 303 and the stellar-mass black hole Cygnus X-1 by MAGIC, provides clear evidence of very efficient acceleration of particles to multi-TeV energies in X-ray binaries. These observations demonstrate the richness of nonthermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. I review here some of the main observational results on very high energy (VHE) γ-ray emission from X-ray binaries, as well as some of the proposed scenarios to explain the production of VHE γ-rays. I put special emphasis on the flare TeV emission, suggesting that the flaring activity might be a common phenomena in X-ray binaries.

Detectors for cosmic rays on ground and in Space

The origin of cosmic rays has been a great mystery since they were discovered by Victor Hess in 1912. AGASA's observation of ultra-high-energy cosmic-rays (UHECR) possibly beyond the GZK (Greisen, Zatsepin and Kuzmin) cutoff stimulated the field in great deal. In addition, Kamiokande's detection of neutrinos from SN1987A and the detection of TeV gamma-rays from supernova remnants at H.E.S.S. have demonstrated the viability of neutrino and TeV gamma-ray astronomy for cosmic-ray research. A new generation of currently operating or soon-to-be-operating detectors for charged particles, gamma rays and neutrinos from cosmos will get us even closer to understanding the nature and origin of cosmic rays. Detectors for UHECRs, gamma rays and neutrinos are of particular importance in order to study the origins of cosmic rays since these particles are free from deflection due to magnetic fields. Detectors for antiparticles and gamma rays would be useful to detect cosmic rays originating from the decay of dark matter in the Universe. I will review these cosmic-ray detectors with particular emphasis on the differences of ground-based, balloon-borne and satellite-borne detectors.

Detection of TeVγ-ray emission from the shell-type supernova remnant RX J0852.0-4622 with HESS

We report the detection of TeV gamma-rays from the shell-type supernova remnant RX J0852.0-4622 with data of 3.2 h of live time recorded with H.E.S.S. in February 2004. An excess of (700 +/- 60) events from the whole remnant with a significance of 12 sigma was found. The observed emission region is clearly extended with a radius of the order of 1 degree and the spatial distribution of the signal correlates with X-ray observations. The spectrum in the energy range between 500 GeV and 15 TeV is well described by a power law with a photon index of 2.1 +/- 0.1(stat) +/- 0.2(syst) and a differential flux at 1 TeV of (2.1 +/- 0.2(stat) +/- 0.6(syst)) 10^{-11} cm^{-2} s^{-1} TeV^{-1}. The integral flux above 1 TeV was measured to be (1.9 +/- 0.3(stat) +/- 0.6(syst)) 10^{-11} cm^{-2} s^{-1}, which is at the level of the flux of the Crab nebula at these energies. More data are needed to draw firm conclusions on the magnetic field in the remnant and the type of the particle population creating the TeV gamma-rays.

TeV Gamma-Ray Observations of the Galactic Center

We report a possible detection of TeV gamma rays from the Galactic center by the Whipple 10 m gamma-ray telescope. Twenty-six hours of data were taken over an extended period from 1995 through 2003 resulting in a total significance of 3.7 σ. The measured excess corresponds to an integral flux of 1.6 × 10-8 ± 0.5 × 10-8 (stat) ± 0.3 × 10-8 (sys) photons m-2 s-1 above an energy of 2.8 TeV, roughly 40% of the flux from the Crab Nebula at this energy. The 95% confidence region has an angular extent of about 15' and includes the position of Sgr A*. The detection is consistent with a point source and shows no evidence of variability.

Detection of TeV gamma-rays from the BL Lac 1ES 1959+650 in its low states and during a major outburst in 2002

TeV γ-rays from the BL Lac object 1ES 1959+650 have been measured during the years 2000 and 2001 with a significance of 5.2 σ at a value of 5.3% of the Crab flux and in May 2002 during strong outbursts with >23 σ at a flux level of up to 2.2 Crab, making 1ES 1959+650 the TeV Blazar with the third best event statistics. The deep observation of 197.4 h has been performed with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes (IACT system). 1ES 1959+650 is located at a redshift of z = 0.047, providing an intermediate distance between the nearby Blazars Mkn 421 and Mkn 501, and the much more distant object H1426+428. This makes 1ES 1959+650 an important member of the class of TeV Blazars in view of the absorption of TeV photons by the diffuse extragalactic background radiation (DEBRA). The differential energy spectrum of 1ES 1959+650 during the flares can be fitted by a power law with a spectral index of 2.83 ± 0.14stat ± 0.08sys or by a power law with an exponential cut-off at (4.2 +0.8 −0.6 stat ± 0.9sys) TeV and a spectral index of 1.83 ± 0.15stat ± 0.08sys. The low state differential energy spectrum obtained with lower statistics can be described by a pure power law with a spectral index of 3.18 ± 0.17stat ± 0.08sys.

Is the giant radio galaxy M 87 a TeV gamma-ray emitter?

For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M87 has been measured at a significance level above 4 sigma. The data have been taken during the years 1998 and 1999 with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes. The excess of 107.4 +- 26.8 events above 730 GeV corresponds to an integral flux of 3.3% of the Crab flux or N_gamma(E > 730 GeV) = (0.96 +- 0.23) * 10^(-12) phot.cm^(-2)s^(-1). M87 is located at the center of the Virgo cluster of galaxies at a relatively small redshift of z = 0.00436 and is a promising candidate among the class of giant radio galaxies for the emission of TeV gamma-radiation. The detection of TeV gamma-rays from M87 -- if confirmed -- would establish a new class of extragalactic source in this energy regime since all other AGN detected to date at TeV energies are BL Lac type objects.

X-ray Emission as an Indicator of Cosmic ray Acceleration in Supernova Remnants

X-ray observations over the past several years have led to the discovery of nonthermal X-ray emission arising in the shells of many young supernova remnants, including SN 1006, Cas A, and Tycho. This emission is thought to be synchrotron emission from electrons that have been shock accelerated to hundreds of TeV, and thus represents strong evidence that cosmic rays are accelerated in SNR shocks. The X-ray observations are corroborated by detection of TeV gamma rays from two of these remnants. A systematic investigation of young, shell-like remnants suggests that the nonthermal X-ray emission from shock-accelerated electrons is a common, if not ubiquitous, feature. We review the status of the X-ray observations and describe how they can be used to provide insight into the shock acceleration process.

Detection of TeV Gamma Rays from SN1006

In spite of the recent progress of high energy gamma-ray astronomy, there still remains quite unclear and important problem about the origin of cosmic rays. Supernova remnants (SNRs) are the favoured site for cosmic rays up to 1016 eV, as they satisfy the requirements such as an energy input rate. But direct supporting evidence is sparse. Recently intense non-thermal X-ray emission from the rims of the Type Ia SNR SN1006 (G327.6+14.6) has been observed by ASCA (Koyama et al. 1995)and ROSAT (Willingale et al. 1996), which is considered, by attributing the emission to synchrotron radiation, to be strong evidence of shock acceleration of high energy electrons up to ~100 TeV. If so, TeV gamma rays would also be expected from inverse Compton scattering (IC) of low energy photons (mostly attributable to the 2.7 K cosmic background photons) by these electrons. By assuming the magnetic field strength (B) in the emission region of the SNR, several theorists (Pohl 1996; Mastichiadis 1996; Mastichiadis & de Jager 1996; Yoshida & Yanagita 1997) calculated the expected spectra of TeV gamma rays using the observed radio/X-ray spectra. Observation of TeV gamma rays would thus provide not only the further direct evidence of the existence of very high energy electrons but also the another important information such as the strength of the magnetic field and diffusion coefficient of the shock acceleration. With this motivation, SN1006 was observed by the CANGAROO imaging air Cerenkov telescope in 1996 March and June, also 1997 March and April.

Possible detection of TeV gamma rays from AM Herculis

view Abstract Citations (34) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Possible Detection of TeV Gamma Rays from AM Herculis Bhat, C. L. ; Kaul, R. K. ; Rawat, H. S. ; Senecha, V. K. ; Rannot, R. C. ; Sapru, M. L. ; Tickoo, A. K. ; Razdan, H. Abstract This paper reports a possible detection of TeV gamma rays from the magnetic white dwarf binary system AM Herculis, with a phase-averaged flux of (5.6 + or - 2.1) x 10 to the -11th photons/sq cm per sec at energies above 2 x 10 to the 12th eV. The gamma-ray light curve exhibits two broad emission peaks at magnetic phases around (0.1 + or - 0.2) and (0.6 + or - 0.2) and closely matches in shape the phase modulation of circularly polarized light emitted by the source. Publication: The Astrophysical Journal Pub Date: March 1991 DOI: 10.1086/169776 Bibcode: 1991ApJ...369..475B Keywords: Binary Stars; Circular Polarization; Gamma Ray Astronomy; Magnetic Stars; White Dwarf Stars; Phase Modulation; Polarized Light; Space Radiation; GAMMA RAYS: GENERAL; STARS: BINARIES; STARS: INDIVIDUAL CONSTELLATION NAME: AM HERCULIS; STARS: MAGNETIC full text sources ADS | data products SIMBAD (1)