Results for "Zorawar Wadiasingh"

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Standard supersymmetry from a Planck-scale statistical theoryNov 24 2007We outline three new ideas in a program to obtain standard physics, including standard supersymmetry, from a Planck-scale statistical theory: (1) The initial spin 1/2 bosonic fields are transformed to spin 0 fields together with their auxiliary fields. ... More
Cooling Rates for Relativistic Electrons Undergoing Compton Scattering in Strong Magnetic FieldsMar 17 2011For inner magnetospheric models of hard X-ray and gamma-ray emission in high-field pulsars and magnetars, resonant Compton upscattering is anticipated to be the most efficient process for generating continuum radiation. This is due in part to the proximity ... More
The Aid of Optical Studies in Understanding Millisecond Pulsar BinariesFeb 22 2016A large number of new "black widow" and "redback" energetic millisecond pulsars with irradiated stellar companions have been discovered through radio and optical searches of unidentified \textit{Fermi} sources. Synchrotron emission, from particles accelerated ... More
Opacities for Photon Splitting and Pair Creation in Neutron Star MagnetospheresApr 05 2019Over the last four decades, persistent and flaring emission of magnetars observed by various telescopes has provided us with a suite of light curves and spectra in soft and hard X-rays, with no emission yet detected above around 1 MeV. Attenuation of ... More
A Fundamental Plane for Gamma-Ray PulsarsApr 03 2019We show that the $\gamma$-ray pulsar observables, i.e., their total $\gamma$-ray luminosity, $L_{\gamma}$, spectrum cut-off energy, $\epsilon_{\rm cut}$, stellar surface magnetic field, $B_{\star}$, and spin-down power $\dot{\mathcal{E}}$, obey a relation ... More
Repeating Fast Radio Bursts from Magnetars with Low Magnetospheric TwistApr 26 2019We analyze the statistics of pulse arrival times in FRB 121102 and demonstrate that they are remarkably similar to statistics of magnetar high-energy short bursts. Motivated by this correspondence, we propose that repeating FRBs are generated during short ... More
Resonant Inverse Compton Scattering Spectra from Highly-magnetized Neutron StarsDec 27 2017Feb 11 2018Hard, non-thermal, persistent pulsed X-ray emission extending between 10 keV and $\sim 150$ keV has been observed in nearly ten magnetars. For inner-magnetospheric models of such emission, resonant inverse Compton scattering of soft thermal photons by ... More
Looking Under a Better Lamppost: MeV-scale Dark Matter CandidatesMar 14 2019The era of precision cosmology has revealed that about 85% of the matter in the universe is dark matter. Two well-motivated candidates are weakly interacting massive particles (WIMPs) and weakly interacting sub-eV particles (WISPs) (e.g. axions). Both ... More
Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonanceAug 09 2014The quantum electrodynamical (QED) process of Compton scattering in strong magnetic fields is commonly invoked in atmospheric and inner magnetospheric models of x-ray and soft gamma-ray emission in high-field pulsars and magnetars. A major influence of ... More
High Energy Emission from Black Widows and RedbacksDec 23 2015A large number of new black widow and redback energetic millisecond pulsars with irradiated stellar companions have been discovered through radio searches of unidentified \emph{Fermi} sources. We construct a 3D emission model of these systems to predict ... More
Resonant Compton Upscattering in High Field Neutron StarsJun 26 2012The extremely efficient process of resonant Compton upscattering by relativistic electrons in high magnetic fields is believed to be a leading emission mechanism of high field pulsars and magnetars in the production of intense X-ray radiation. New analytic ... More
Pressure Balance and Intrabinary Shock Stability in Rotation-Powered State Redback and Transitional Millisecond Pulsar Binary SystemsOct 30 2018A number of low-mass millisecond pulsar (MSP) binaries in their rotation-powered state exhibit double-peaked X-ray orbital modulation centered at inferior pulsar conjunction. This state, which has been known to persist for years, has recently been interpreted ... More
Constraining Relativistic Bow Shock Properties in Rotation-Powered Millisecond Pulsar BinariesMar 28 2017Multiwavelength followup of unidentified Fermi sources has vastly expanded the number of known galactic-field "black widow" and "redback" millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology ... More
Magnetar Hard Spectral TailsOct 27 2017Pulsed non-thermal quiescent emission between 10 keV and around 150 keV has been observed in $\sim10$ magnetars. For inner magnetospheric models of such hard X-ray signals, resonant Compton upscattering of soft thermal photons from the neutron star surface ... More
Supermassive black holes at high redshiftsMar 14 2019MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 ... More
Cosmic Rays and Interstellar Medium with Gamma-Ray Observations at MeV EnergiesMar 13 2019Latest precise cosmic-ray (CR) measurements and present gamma-ray observations have started challenging our understanding of CR transport and interaction in the Galaxy. Moreover, because the density of CRs is similar to the density of the magnetic field, ... More
Prospects for Pulsar Studies at MeV EnergiesMar 29 2019Enabled by the Fermi Large Area Telescope, we now know young and recycled pulsars fill the gamma-ray sky, and we are beginning to understand their emission mechanism and their distribution throughout the Galaxy. However, key questions remain: Is there ... More
Magnetars as Astrophysical Laboratories of Extreme Quantum Electrodynamics: The Case for a Compton TelescopeMar 13 2019A next generation of Compton and pair telescopes that improve MeV-band detection sensitivity by more than a decade beyond current instrumental capabilities will open up new insights into a variety of astrophysical source classes. Among these are magnetars, ... More
Energetic Particles of Cosmic Accelerators I: Galactic AcceleratorsMar 11 2019The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Energetic particles in our own galaxy, galactic cosmic rays (GCRs), engage in a ... More
Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray BurstsMar 11 2019The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Though they play a key role in cultivating the cosmological environment and/or enabling ... More
Prospects for AGN Studies at Hard X-ray through MeV EnergiesMar 18 2019This White Paper explores advances in the study of Active Galaxies which will be enabled by new observing capabilities at MeV energies (hard X-rays to gamma-rays; 0.1-1000 MeV), with a focus on multi-wavelength synergies. This spectral window, covering ... More
Neutrinos, Cosmic Rays and the MeV BandMar 13 2019The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where are cosmic rays produced ... More
High-Energy Polarimetry - a new window to probe extreme physics in AGN jetsMar 11 2019The constantly improving sensitivity of ground-based and space-borne observatories has made possible the detection of high-energy emission (X-rays and gamma-rays) from several thousands of extragalactic sources. Enormous progress has been made in measuring ... More
Gamma Rays and Gravitational WavesMar 11 2019The first multimessenger observation of a neutron star merger was independently detected in gamma-rays by Fermi-GBM and INTEGRAL SPI-ACS and gravitational waves by Advanced LIGO and Advanced Virgo. Gravitational waves are emitted from systems with accelerating ... More
A search for new supernova remnant shells in the Galactic plane with H.E.S.S.Jan 18 2018A search for new supernova remnants (SNRs) has been conducted using TeV gamma-ray data from the H.E.S.S. Galactic plane survey. As an identification criterion, shell morphologies that are characteristic for known resolved TeV SNRs have been used. Three ... More
The starburst galaxy NGC 253 revisited by H.E.S.S. and Fermi-LATJun 11 2018(Abridged) Context. NGC 253 is one of only two starburst galaxies found to emit $\gamma$-rays from hundreds of MeV to multi-TeV energies. Accurate measurements of the very-high-energy (VHE) (E $>$ 100 GeV) and high-energy (HE) (E $>$ 60 MeV) spectra are ... More
Measurement of the EBL spectral energy distribution using the VHE gamma-ray spectra of H.E.S.S. blazarsJul 19 2017Jul 20 2017Very high-energy gamma-rays (VHE, E>100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the universe to VHE gamma-rays ... More
H.E.S.S. observations of RX J1713.7-3946 with improved angular and spectral resolution; evidence for gamma-ray emission extending beyond the X-ray emitting shellSep 27 2016Feb 09 2017Supernova remnants exhibit shock fronts (shells) that can accelerate charged particles up to very high energies. In the past decade, measurements of a handful of shell-type supernova remnants in very-high-energy gamma rays have provided unique insights ... More
Particle Transport within the Pulsar Wind Nebula HESS J1825-137Oct 30 2018Nov 23 2018Aims: We present a detailed view of the pulsar wind nebula (PWN) HESS J1825-137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics. Methods: The ... More
Characterising the VHE diffuse emission in the central 200 parsecs of our Galaxy with H.E.S.SJun 14 2017The diffuse very high-energy (VHE, > 100 GeV) gamma-ray emission observed in the central 200 pc of the Milky Way by H.E.S.S. was found to follow the dense matter distribution in the Central Molecular Zone (CMZ) up to a longitudinal distance of about 130 ... More
H.E.S.S. limits on line-like dark matter signatures in the 100 GeV to 2 TeV energy range close to the Galactic CentreSep 26 2016Sep 29 2016A search for dark matter line-like signals was performed in the vicinity of the Galactic Centre by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis was developed to improve the sensitivity to line-like signals. ... More
Search for dark matter annihilations towards the inner Galactic halo from 10 years of observations with H.E.S.SJul 27 2016The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using $\gamma$-ray observations ... More
H.E.S.S. limits on line-like dark matter signatures in the 100 GeV to 2 TeV energy range close to the Galactic CentreSep 26 2016A search for dark matter line-like signals was performed in the vicinity of the Galactic Centre by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis was developed to improve the sensitivity to line-like signals. ... More
H.E.S.S. observations of RX J1713.7-3946 with improved angular and spectral resolution; evidence for gamma-ray emission extending beyond the X-ray emitting shellSep 27 2016Supernova remnants exhibit shock fronts (shells) that can accelerate charged particles up to very high energies. In the past decade, measurements of a handful of shell-type supernova remnants in very-high-energy gamma rays have provided unique insights ... More
Searches for gamma-ray lines and `pure WIMP' spectra from Dark Matter annihilations in dwarf galaxies with H.E.S.SOct 01 2018Dwarf spheroidal galaxies are among the most promising targets for detecting signals of Dark Matter (DM) annihilations. The H.E.S.S. experiment has observed five of these systems for a total of about 130 hours. The data are re-analyzed here, and, in the ... More
Characterizing the gamma-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LATOct 11 2016Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability ... More
First limits on the very-high energy gamma-ray afterglow emission of a fast radio burst: H.E.S.S. observations of FRB 150418Nov 28 2016Aims: Following the detection of the fast radio burst FRB150418 by the SUPERB project at the Parkes radio telescope, we aim to search for very-high energy gamma-ray afterglow emission. Methods: Follow-up observations in the very-high energy gamma-ray ... More
Deeper H.E.S.S. observations of Vela Junior (RX J0852.0$-$4622): Morphology studies and resolved spectroscopyNov 07 2016Apr 26 2018Aims. We study gamma-ray emission from the shell-type supernova remnant (SNR) RX J0852.0$-$4622 to better characterize its spectral properties and its distribution over the SNR. Methods. The analysis of an extended High Energy Spectroscopic System (H.E.S.S.) ... More
Deeper H.E.S.S. Observations of Vela Junior (RX J0852.0-4622): Morphology Studies and Resolved SpectroscopyNov 07 2016Aims. The gamma-ray emission from the shell-type supernova remnant (SNR) RX J0852.0-4622 is studied in order to better characterize its spectral properties and its distribution over the SNR. Methods. The analysis of an extended H.E.S.S. data set at very-high ... More
First Ground-based Measurement of Sub-20 GeV to 100 GeV $γ$-rays from the Vela Pulsar with H.E.S.S. IIJul 03 2018Jul 24 2018We report on the measurement and investigation of pulsed high-energy $\gamma$-ray emission from the Vela pulsar, PSR B0833$-$45, based on 40.3 hours of observations with the largest telescope of H.E.S.S., CT5, in monoscopic mode, and on 8 years of data ... More
VHE $γ$-ray discovery and multi-wavelength study of the blazar 1ES 2322-409Oct 10 2018A hotspot at a position compatible with the BL Lac object 1ES 2322-409 was serendipitously detected with H.E.S.S. during observations performed in 2004 and 2006 on the blazar PKS 2316-423. Additional data on 1ES 2322-409 were taken in 2011 and 2012, leading ... More
Population study of Galactic supernova remnants at very high $γ$-ray energies with H.E.S.S.Feb 14 2018Feb 15 2018Shell-type supernova remnants (SNRs) are considered prime candidates for the acceleration of Galactic cosmic rays (CRs) up to the knee of the CR spectrum at $\mathrm{E} \approx \mathrm{3}\times \mathrm{10}^\mathrm{15}$ eV. Our Milky Way galaxy hosts more ... More
HESS J1741-302: a hidden accelerator in the Galactic planeNov 03 2017The H.E.S.S. collaboration has discovered a new very high energy (VHE, E $>$ 0.1 TeV) $\gamma$-ray source, HESS J1741-302, located in the Galactic plane. Despite several attempts to constrain its nature, no plausible counterpart has been found so far ... More
TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.SOct 16 2017Nov 29 2017We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3h after GW170817. The H.E.S.S. target selection ... More
The population of TeV pulsar wind nebulae in the H.E.S.S. Galactic Plane SurveyFeb 27 2017Mar 10 2017The nine-year H.E.S.S. Galactic Plane Survey (HGPS) yielded the most uniform observation scan of the inner Milky Way in the TeV gamma-ray band to date. The sky maps and source catalogue of the HGPS allow for a systematic study of the population of TeV ... More
A search for very high-energy flares from the microquasars GRS 1915+105, Circinus X-1, and V4641 Sgr using contemporaneous H.E.S.S. and RXTE observationsJul 15 2016Jul 18 2016Microquasars are potential $\gamma$-ray emitters. Indications of transient episodes of $\gamma$-ray emission were recently reported in at least two systems: Cyg X-1 and Cyg X-3. The identification of additional $\gamma$-ray-emitting microquasars is required ... More
Extended VHE gamma-ray emission towards SGR1806-20, LBV1806-20, and stellar cluster Cl*1806-20Jun 17 2016Jun 27 2016Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have discovered a steady and extended very high-energy (VHE) gamma-ray source towards the luminous blue variable candidate LBV1806-20, massive stellar cluster Cl*1806-20, and magnetar ... More
H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211Apr 10 2019PKS 1830-211 is a known macrolensed quasar located at a redshift of z=2.5. Its high-energy gamma-ray emission has been detected with the Fermi-LAT instrument and evidence for lensing was obtained by several authors from its high-energy data. Observations ... More
Upper Limits on Very-High-Energy Gamma-ray Emission from Core-Collapse Supernovae Observed with H.E.S.SApr 23 2019Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray emission. We searched for gamma-ray emission from ten supernovae ... More
The $γ$-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LATJul 19 2018Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV-100 TeV) $\gamma$-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE $\gamma$-ray emitter, though its VHE flux exceeds both the ... More
The 2014 TeV Gamma-ray Flare of Mrk 501 Seen with H.E.S.S.: Temporal and Spectral Constraints on Lorentz Invariance ViolationJan 16 2019The blazar Mrk 501 (z=0.034) was observed at very-high-energy (VHE, $E\gtrsim 100$~GeV) gamma-ray wavelengths during a bright flare on the night of 2014 June 23-24 (MJD 56832) with the H.E.S.S. phase-II array of Cherenkov telescopes. Data taken that night ... More
Search for $γ$-ray line signals from dark matter annihilations in the inner Galactic halo from ten years of observations with H.E.S.SMay 15 2018Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy $\gamma$-rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity ... More
H.E.S.S. discovery of very high energy gamma-ray emission from PKS 0625-354Feb 21 2018PKS 0625-354 (z=0.055) was observed with the four H.E.S.S. telescopes in 2012 during 5.5 hours. The source was detected above an energy threshold of 200 GeV at a significance level of 6.1$\sigma$. No significant variability is found in these observations. ... More
Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3Jan 19 2018Context. Recently, the high-energy (HE, 0.1-100 GeV) $\gamma$-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic $\gamma$-ray binary. Aims. ... More
A search for new supernova remnant shells in the Galactic plane with H.E.S.SJan 18 2018Apr 27 2018A search for new supernova remnants (SNRs) has been conducted using TeV gamma-ray data from the H.E.S.S. Galactic plane survey. As an identification criterion, shell morphologies that are characteristic for known resolved TeV SNRs have been used. Three ... More
Systematic search for very-high-energy gamma-ray emission from bow shocks of runaway starsMay 05 2017Runaway stars form bow shocks by ploughing through the interstellar medium at supersonic speeds and are promising sources of non-thermal emission of photons. One of these objects has been found to emit non-thermal radiation in the radio band. This triggered ... More
The supernova remnant W49B as seen with H.E.S.S. and Fermi-LATSep 02 2016The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). $\gamma$-ray observations ... More
Constraints on particle acceleration in SS433/W50 from MAGIC and H.E.S.S. observationsJul 12 2017The large jet kinetic power and non-thermal processes occurring in the microquasar SS 433 make this source a good candidate for a very high-energy (VHE) gamma-ray emitter. Gamma-ray fluxes have been predicted for both the central binary and the interaction ... More
Gamma-ray blazar spectra with H.E.S.S. II mono analysis: the case of PKS 2155-304 and PG 1553+113Dec 06 2016The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies ... More