Gammablitz aus der kosmischen Nachbarschaft

Seit ihrer Urgeschichte haben Menschen den Nachthimmel mit ehrfürchtigem Staunen bewundert. Auch wenn ein Großteil des Nachthimmels unveränderlich erscheint, weiß man schon seit langer Zeit, dass einige der hellsten Objekte nur temporär am Himmel aufleuchten. Das gilt insbesondere für Supernovae, die nun auch neues Licht auf eines der ungelösten Rätsel der Astrophysik werfen. Denn der Ursprung der höchstenergetischen kosmischen Strahlungsteilchen ist unbekannt. Können sterbende massive Sterne eine der lang gesuchten Quellen sein

Probing the multiwavelength emission scenario of GRB 190114C

Multiwavelength observation of the gamma-ray burst, GRB 190114C, opens a new window for studying the emission mechanism of GRB afterglows. Its very high energy (VHE; ≳ 100 GeV) detection has motivated an inverse Compton interpretation for the emission, but this has not been tested. Here, we revisit the early afterglow emission from 68 to 180 s and perform the modelling likelihood analysis with the keV to TeV data sets. We compute for the first time the statistical preference in the combined synchrotron (syn) and synchrotron self-Compton (SSC) model over the syn-only model. In agreement with earlier analyses, between 68 and 110 s an unstable preference for the SSC model can be found, which can also be explained by systematic cross-calibration effect between the included instruments. We conclude that there is no stable statistical preference for one of the two models

Making cosmic particle accelerators visible and audible

In a collaboration between astroparticle physicists, animation artists from the award-winning Science Communication Lab, and musician Carsten Nicolai (a.k.a. Alva Noto), two cosmic particle accelerators have been brought to life: the massive binary star Eta Carinae, and the exploding star, which resulted in the gamma-ray burst GRB190829A. For Eta Carinae, the computer-generated images are close to reality because the measured orbital, stellar, and wind parameters were used for this purpose. Particle acceleration in the jet of GRB190829A has also been animated at a level of detail not seen before. The internationally acclaimed multimedia artist Carsten Nicolai, who uses the pseudonym Alva Noto for his musical works, exclusively composed the sound for the animations. The multimedia projects aim at making the discoveries more accessible to the general public, and to mediate scientific results and their reference to reality from an artistic point of view

Making cosmic particle accelerators visible and audible

In a collaboration between astroparticle physicists, animation artists from the award-winning Science Communication Lab, and musician Carsten Nicolai (a.k.a. Alva Noto), two cosmic particle accelerators have been brought to life: the massive binary star Eta Carinae, and the exploding star, which resulted in the gamma-ray burst GRB190829A. For Eta Carinae, the computer-generated images are close to reality because the measured orbital, stellar, and wind parameters were used for this purpose. Particle acceleration in the jet of GRB190829A has also been animated at a level of detail not seen before. The internationally acclaimed multimedia artist Carsten Nicolai, who uses the pseudonym Alva Noto for his musical works, exclusively composed the sound for the animations. The multimedia projects aim at making the discoveries more accessible to the general public, and to mediate scientific results and their reference to reality from an artistic point of view

Einstein@Home All-sky Search for Continuous Gravitational Waves in LIGO O2 Public Data

We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly monochromatic signals with frequency 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down Hz s−1. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the h 0 amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is h 0 = 1.3 × 10−25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10−7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models

Evidence for γ\gamma-ray emission from the remnant of Kepler’s supernova based on deep H.E.S.S. observations

Observations with imaging atmospheric Cherenkov telescopes (IACTs) have enhanced our knowledge of nearby supernova (SN) remnants with ages younger than 500 yr by establishing Cassiopeia A and the remnant of Tycho’s SN as very-high-energy (VHE) γ-ray sources. The remnant of Kepler’s SN, which is the product of the most recent naked-eye SN in our Galaxy, is comparable in age to the other two, but is significantly more distant. If the γ-ray luminosities of the remnants of Tycho’s and Kepler’s SNe are similar, then the latter is expected to be one of the faintest γ-ray sources within reach of the current generation IACT arrays. Here we report evidence at a statistical level of 4.6σ for a VHE signal from the remnant of Kepler’s SN based on deep observations by the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 h. The measured integral flux above an energy of 226 GeV is ∼0.3% of the flux of the Crab Nebula. The spectral energy distribution (SED) reveals a γ-ray emitting component connecting the VHE emission observed with H.E.S.S. to the emission observed at GeV energies with Fermi-LAT. The overall SED is similar to that of the remnant of Tycho’s SN, possibly indicating the same nonthermal emission processes acting in both these young remnants of thermonuclear SNe

H.E.S.S. Follow-up Observations of Binary Black Hole Coalescence Events during the Second and Third Gravitational-wave Observing Runs of Advanced LIGO and Advanced Virgo

We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe 20 deg$^{2}$ of the sky at a time and follows up gravitational-wave (GW) events by “tiling” localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35% and 75%, for four BBH mergers (GW170814, GW190512_180714, GW190728_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and we set upper limits on the very high energy (>100 GeV) γ-ray emission. The 1–10 TeV isotropic luminosity of these GW events is below 10$^{45}$ erg s$^{−1}$ at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency

Observation of burst activity from SGR1935+2154 associated to first galactic FRB with H.E.S.S.

Fast radio bursts (FRB) are enigmatic powerful single radio pulses with durations of several milliseconds and high brightness temperatures suggesting coherent emission mechanism. For the time being a number of extragalactic FRBs have been detected in the high-frequency radio band including repeating ones. The most plausible explanation for these phenomena is magnetar hyperflares. The first observational evidence of this scenario was obtained in April 2020 when an FRB was detected from the direction of the Galactic magnetar and soft gamma repeater SGR1935+2154. The FRB was preceded with a number of soft gamma-ray bursts observed by Swift-BAT satellite, which triggered the follow-up program of the H.E.S.S. imaging atmospheric Cherenkov telescopes (IACTs). H.E.S.S. has observed SGR1935+2154 over a 2 hour window few hours prior to the FRB detection by STARE2 and CHIME. The observations overlapped with other X-ray bursts from the magnetar detected by INTEGRAL and Swift-BAT, thus providing first observations of a magnetar in a flaring state in the very-high energy domain. We present the analysis of these observations, discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma repeaters and anomalous X-ray pulsars

Search for dark matter annihilation in the Wolf-Lundmark-Melotte dwarf irregular galaxy with H.E.S.S.

We search for an indirect signal of dark matter through very high-energy γ rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as γ rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well-measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the five-telescopes of the high energy stereoscopic system observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation ⟨σv⟩ as a function of the dark matter particle mass for various continuum channels, as well as the prompt γγ emission. For the τ+τ- channel, the limits reach a ⟨σv⟩ value of about 4×10-22  cm3 s-1 for a dark matter particle mass of 1 TeV. For the prompt γγ channel, the upper limit reaches a ⟨σv⟩ value of about 5×10-24  cm3 s-1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200, with respect to previous results for the dwarf irregular galaxies for TeV dark matter search

Evidence of 100 TeV gamma-ray emission from HESS J1702-420: A new PeVatron candidate

Aims. The identification of PeVatrons, hadronic particle accelerators reaching the knee of the cosmic ray spectrum (few × 1015 eV), is crucial to understand the origin of cosmic rays in the Galaxy. We provide an update on the unidentified source HESS J1702-420, a promising PeVatron candidate. Methods. We present new observations of HESS J1702-420 made with the High Energy Stereoscopic System (H.E.S.S.), and processed using improved analysis techniques. The analysis configuration was optimized to enhance the collection area at the highest energies. We applied a three-dimensional likelihood analysis to model the source region and adjust non thermal radiative spectral models to the γ-ray data. We also analyzed archival Fermi Large Area Telescope data to constrain the source spectrum at γ-ray energies > 10 GeV. Results. We report the detection of γ-rays up to 100 TeV from a specific region of HESS J1702-420, which is well described by a new source component called HESS J1702-420A that was separated from the bulk of TeV emission at a 5.4σ confidence level. The power law γ-ray spectrum of HESS J1702-420A extends with an index of Γ = 1.53 ± 0.19stat ± 0.20sys and without curvature up to the energy band 64-113 TeV, in which it was detected by H.E.S.S. at a 4.0σ confidence level. This makes HESS J1702-420A a compelling candidate site for the presence of extremely high energy cosmic rays. With a flux above 2 TeV of (2.08 ± 0.49stat ± 0.62sys) × 10-13 cm-2 s-1 and a radius of (0.06 ± 0.02stat ± 0.03sys)°, HESS J1702-420A is outshone - below a few tens of TeV - by the companion HESS J1702-420B. The latter has a steep spectral index of Γ = 2.62 ± 0.10stat ± 0.20sys and an elongated shape, and it accounts for most of the low-energy HESS J1702-420 flux. Simple hadronic and leptonic emission models can be well adjusted to the spectra of both components. Remarkably, in a hadronic scenario, the cut-off energy of the particle distribution powering HESS J1702-420A is found to be higher than 0.5 PeV at a 95% confidence level. Conclusions. For the first time, H.E.S.S. resolved two components with significantly different morphologies and spectral indices, both detected at > 5σ confidence level, whose combined emissions result in the source HESS J1702-420. We detected HESS J1702-420A at a 4.0σ confidence level in the energy band 64-113 TeV, which brings evidence for the source emission up to 100 TeV. In a hadronic emission scenario, the hard γ-ray spectrum of HESS J1702-420A implies that the source likely harbors PeV protons, thus becoming one of the most solid PeVatron candidates detected so far in H.E.S.S. data. However, a leptonic origin of the observed TeV emission cannot be ruled out either