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4 results on '"Barnard, Monica"'

1. Probing the magnetic field in the GW170817 outflow using HESS observations

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., and H.E.S.S. Collaboration

Abstract

The detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short γ-ray bursts and BNS mergers. It also confirmed the forging of heavy elements in the ejecta (a so-called kilonova) via the r-process nucleosynthesis. The appearance of nonthermal radio and X-ray emission, as well as the brightening, which lasted more than 100 days, were somewhat unexpected. Current theoretical models attempt to explain this temporal behavior as either originating from a relativistic off-axis jet or a kilonova-like outflow. In either scenario, there is some ambiguity regarding how much energy is transported in the nonthermal electrons versus the magnetic field of the emission region. Combining the Very Large Array (radio) and Chandra (X-ray) measurements with observations in the GeV–TeV domain can help break this ambiguity, almost independently of the assumed origin of the emission. Here we report for the first time on deep H.E.S.S. observations of GW170817/GRB 170817A between 124 and 272 days after the BNS merger with the full H.E.S.S. array of telescopes, as well as on an updated analysis of the prompt (<5 days) observations with the upgraded H.E.S.S. phase-I telescopes. We discuss implications of the H.E.S.S. measurement for the magnetic field in the context of different source scenarios

Published
2020

2. TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S.

Author

24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

We 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 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a groundbased pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system

Published
2017

3. Multi-TeV emission from the Vela pulsar

Author

Alice K. Harding, Christo Venter, Constantinos Kalapotharakos, Monica Barnard, 20574266 - Barnard, Monica, and 12006653 - Venter, Christo

Subjects
Photon, Astrophysics::High Energy Astrophysical Phenomena, Magnetosphere, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Vela, 01 natural sciences, Article, law.invention, Current sheet, Pulsar, law, individual (Vela pulsar) [Pulsars], 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, stars [Gamma rays], Astronomy and Astrophysics, Synchrotron, Particle acceleration, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract

Pulsed emission from the Vela pulsar at energies above 3 TeV has recently been detected by the H.E.S.S. II air-Cherenkov telescope. We present a model for the broad-band spectrum of Vela from infra-red (IR) to beyond 10 TeV. Recent simulations of the global pulsar magnetosphere have shown that most of the particle acceleration occurs in the equatorial current sheet outside the light cylinder and that the magnetic field structure is nearly force-free for younger pulsars. We adopt this picture to compute the radiation from both electron-positron pairs produced in polar cap cascades and from primary particles accelerated in the separatrix and current sheet. The synchrotron spectrum from pairs resonantly absorbing radio photons at relatively low altitude can account for the observed IR-optical emission. We set the parallel electric field in the current sheet to produce the Fermi GeV emission through curvature radiation, producing particles with energies of 30-60 TeV. These particles then produce Very-High-Energy emission up to around 30 TeV through inverse-Compton scattering of the IR-Optical emission. We present model spectra and light curves that can match the IR-Optical, GeV and make predictions for the multi-TeV emission., Comment: 11 pages, 3 figures, accepted for publication in Astrophysical Journal Letters

Published
2018

4. Multi-TeV Emission From the Vela Pulsar.

Author

Harding AK, Kalapotharakos C, Barnard M, and Venter C

Abstract

Pulsed emission from the Vela pulsar at energies above 3 TeV has recently been detected by the H.E.S.S. II air-Cherenkov telescope. We present a model for the broad-band spectrum of Vela from infra-red (IR) to beyond 10 TeV. Recent simulations of the global pulsar magnetosphere have shown that most of the particle acceleration occurs in the equatorial current sheet outside the light cylinder and that the magnetic field structure is nearly force-free for younger pulsars. We adopt this picture to compute the radiation from both electron-positron pairs produced in polar cap cascades and from primary particles accelerated in the separatrix and current sheet. The synchrotron spectrum from pairs resonantly absorbing radio photons at relatively low altitude can account for the observed IR-optical emission. We set the parallel electric field in the current sheet to produce the Fermi GeV emission through curvature radiation, producing particles with energies of 30-60 TeV. These particles then produce Very-High-Energy emission up to around 30 TeV through inverse-Compton scattering of the IR-Optical emission. We present model spectra and light curves that can match the IR-Optical, GeV and make predictions for the multi-TeV emission.

Published
2018
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