lnu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 93) Show all publications
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Andersson, T., . . . Yoshiike, S. (2018). A search for new supernova remnant shells in the Galactic plane with HESS. Astronomy and Astrophysics, 612, Article ID A8.
Open this publication in new window or tab >>A search for new supernova remnant shells in the Galactic plane with HESS
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A8Article in journal (Refereed) Published
Abstract [en]

A 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 new SNR candidates were identified in the H.E.S.S. data set with this method. Extensive multiwavelength searches for counterparts were conducted. A radio SNR candidate has been identified to be a counterpart to HESS J1534-571. The TeV source is therefore classified as a SNR. For the other two sources, HESS J1614-518 and HESS J1912 + 101, no identifying counterparts have been found, thus they remain SNR candidates for the time being. TeV-emitting SNRs are key objects in the context of identifying the accelerators of Galactic cosmic rays. The TeV emission of the relativistic particles in the new sources is examined in view of possible leptonic and hadronic emission scenarios, taking the current multiwavelength knowledge into account.

Keywords
astroparticle physics, ISM: supernova remnants, cosmic rays
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76475 (URN)10.1051/0004-6361/201730737 (DOI)000429404700008 ()
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2018-07-10Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Anguenee, E. O., . . . Zywucka, N. (2018). A search for very high-energy flares from the microquasars GRS 1915+105, Circinus X-1, and V4641 Sgr using contemporaneous HESS and RXTE observations. Astronomy and Astrophysics, 612, Article ID A10.
Open this publication in new window or tab >>A search for very high-energy flares from the microquasars GRS 1915+105, Circinus X-1, and V4641 Sgr using contemporaneous HESS and RXTE observations
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A10Article in journal (Refereed) Published
Abstract [en]

Context. Microquasars 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 to better understand how gamma-ray emission can be produced in these systems. Aims. Theoretical models have predicted very high-energy (VHE) gamma-ray emission from microquasars during periods of transient outburst. Observations reported herein were undertaken with the objective of observing a broadband flaring event in the gamma-ray and X-ray bands. Methods. Contemporaneous observations of three microquasars, GRS 1915+105, Circinus X-1, and V4641 Sgr, were obtained using the High Energy Spectroscopic System (H.E.S.S.) telescope array and the Rossi X-ray Timing Explorer (RXTE) satellite. X-ray analyses for each microquasar were performed and VHE gamma-ray upper limits from contemporaneous H.E.S.S. observations were derived. Results. No significant gamma-ray signal has been detected in any of the three systems. The integral gamma-ray photon flux at the observational epochs is constrained to be I(>560 GeV) < 7.3 x 10(-13) cm(-2) S-1, I(>560 GeV) < 1.2 x 10-(12) cm s(-1), and I(>240 GeV) < 4.5 x 10(-12) cm(-2) s(-1) for GRS 1915+105, Circinus X-1, and V4641 Sgr, respectively. Conclusions. The gamma-ray upper limits obtained using H.E.S.S. are examined in the context of previous Cherenkov telescope observations of microquasars. The effect of intrinsic absorption is modelled for each target and found to have negligible impact on the flux of escaping gamma-rays. When combined with the X-ray behaviour observed using RXTE, the derived results indicate that if detectable VHE gamma-ray emission from microquasars is commonplace, then it is likely to be highly transient.

Keywords
gamma rays: general, X-rays: binaries, X-rays: individuals: GRS 1915+105, X-rays: individuals: Circinus X-1, X-rays: individuals: V4641 Sgr
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76466 (URN)10.1051/0004-6361/201527773 (DOI)000429404700010 ()
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2018-07-10Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Andersson, T., . . . Zywucka, N. (2018). Characterising the VHE diffuse emission in the central 200 parsecs of our Galaxy with HESS. Astronomy and Astrophysics, 612, Article ID A9.
Open this publication in new window or tab >>Characterising the VHE diffuse emission in the central 200 parsecs of our Galaxy with HESS
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A9Article in journal (Refereed) Published
Abstract [en]

The 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 dense matter distribution in the central molecular zone (CMZ) up to a longitudinal distance of about 130 pc to the Galactic centre (GC), where the flux rapidly decreases. This was initially interpreted as the result of a burst-like injection of energetic particles 104 yr ago, but a recent more sensitive H.E.S.S. analysis revealed that the cosmic-ray (CR) density profile drops with the distance to the centre, making data compatible with a steady cosmic PeVatron at the GC. In this paper, we extend this analysis to obtain, for the first time, a detailed characterisation of the correlation with matter and to search for additional features and individual gamma-ray sources in the inner 200 pc. Taking advantage of 250 h of H.E.S.S. data and improved analysis techniques, we perform a detailed morphology study of the diffuse VHE emission observed from the GC ridge and reconstruct its total spectrum. To test the various contributions to the total gamma-ray emission, we used an iterative 2D maximum-likelihood approach that allows us to build a phenomenological model of the emission by summing a number of different spatial components. We show that the emission correlated with dense matter covers the full CMZ and that its flux is about half the total diffuse emission flux. We also detect some emission at higher latitude that is likely produced by hadronic collisions of CRs in less dense regions of the GC interstellar medium. We detect an additional emission component centred on the GC and extending over about 15 pc that is consistent with the existence of a strong CR density gradient and confirms the presence of a CR accelerator at the very centre of our Galaxy. We show that the spectrum of full ridge diffuse emission is compatible with that previously derived from the central regions, suggesting that a single population of particles fills the entire CMZ. Finally, we report the discovery of a VHE gamma-ray source near the GC radio arc and argue that it is produced by the pulsar wind nebula candidate G0.13-0.11.

Keywords
gamma rays: general, gamma rays: ISM, Galaxy: center, cosmic rays
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76467 (URN)10.1051/0004-6361/201730824 (DOI)000429404700009 ()
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2018-07-10Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Andersson, T., . . . Zywucka, N. (2018). Deeper HESS observations of Vela Junior (RX J0852.0-4622): Morphology studies and resolved spectroscopy. Astronomy and Astrophysics, 612, Article ID A7.
Open this publication in new window or tab >>Deeper HESS observations of Vela Junior (RX J0852.0-4622): Morphology studies and resolved spectroscopy
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A7Article in journal (Refereed) Published
Abstract [en]

Aims. We study gamma-ray emission from the shell-type supernova remnant (SNR) RXJ0852.0-4622 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.) data set at very high energies (E > 100 GeV) permits detailed studies, as well as spatially resolved spectroscopy, of the morphology and spectrum of the whole RXJ0852.0-4622 region. The H.E.S.S. data are combined with archival data from other wavebands and interpreted in the framework of leptonic and hadronic models. The joint Fermi-LAT-H.E.S.S. spectrum allows the direct determination of the spectral characteristics of the parent particle population in leptonic and hadronic scenarios using only GeV-TeV data. Results. An updated analysis of the H.E.S.S. data shows that the spectrum of the entire SNR connects smoothly to the high-energy spectrum measured by Fermi-LAT. The increased data set makes it possible to demonstrate that the H.E.S.S. spectrum deviates significantly from a power law and is well described by both a curved power law and a power law with an exponential cutoff at an energy of E-cut = (6.7 +/- 1.2(stat) +/- 1.2(syst)) TeV. The joint Fermi-LAT-H.E.S.S. spectrum allows the unambiguous identification of the spectral shape as a power law with an exponential cutoff. No significant evidence is found for a variation of the spectral parameters across the SNR, suggesting similar conditions of particle acceleration across the remnant. A simple modeling using one particle population to model the SNR emission demonstrates that both leptonic and hadronic emission scenarios remain plausible. It is also shown that at least a part of the shell emission is likely due to the presence of a pulsar wind nebula around PSR J0855-4644.

Keywords
astroparticle physics, gamma rays: general, acceleration of particles, cosmic rays, ISM: supernova remnants
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76465 (URN)10.1051/0004-6361/201630002 (DOI)000429404700007 ()
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2018-07-10Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Anguner, E. O., Arakawa, M., . . . Zywucka, N. (2018). Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3 [Letter to the editor]. Astronomy and Astrophysics, 610, Article ID L17.
Open this publication in new window or tab >>Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 610, article id L17Article in journal, Letter (Refereed) Published
Abstract [en]

Context. 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. This work aims at the detection of very-high-energy (VHE, >100 GeV) gamma-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Results. VHE gamma-ray emission is detected with a statistical significance of 6.4 sigma. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the 1-10 TeV energy range is (1.4 +/- 0.2) x 10(35) erg s(-1). A luminosity of (5 +/- 1) x 10(35) erg s(-1) is reached during 20% of the orbit. HE and VHE gamma-ray emissions are anti-correlated. LMC P3 is the most luminous gamma-ray binary known so far.

Keywords
gamma rays: stars, binaries: general, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-72023 (URN)10.1051/0004-6361/201732426 (DOI)000427146200001 ()
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-03-29Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Anguener, E. O., . . . Zywucka, N. (2018). Extended VHE gamma-ray emission towards SGR1806-20, LBV 1806-20, and stellar cluster Cl*1806-20. Astronomy and Astrophysics, 612, Article ID A11.
Open this publication in new window or tab >>Extended VHE gamma-ray emission towards SGR1806-20, LBV 1806-20, and stellar cluster Cl*1806-20
Show others...
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A11Article in journal (Refereed) Published
Abstract [en]

Using 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 LBV 1806-20, massive stellar cluster Cl* 1806-20, and magnetar SGR 1806-20. The new VHE source, HESS J1808-204, was detected at a statistical significance of >6 sigma (post-trial) with a photon flux normalisation (2.9 +/- 0.4(stat) +/- 0.5(sys)) x 10(-13) ph cm(-2) s(-1) TeV-1 at 1 TeV and a power-law photon index of 2.3 +/- 0.2(stat) +/- 0.3(sys). The luminosity of this source (0.2 to 10 TeV; scaled to distance d = 8 : 7 kpc) is L-VHE similar to 1.6 x 10(34)(d = 8.7 kpc)(2) erg s(-1). The VHE gamma-ray emission is extended and is well fit by a single Gaussian with statistical standard deviation of 0.095 degrees +/- 0.015 degrees. This extension is similar to that of the synchrotron radio nebula G10.0-0.3, which is thought to be powered by LBV 1806-20. The VHE gamma-ray luminosity could be provided by the stellar wind luminosity of LBV 1806-20 by itself and/or the massive star members of Cl* 1806-20. Alternatively, magnetic dissipation (e.g. via reconnection) from SGR 1806-20 can potentially account for the VHE luminosity. The origin and hadronic and/or leptonic nature of the accelerated particles responsible for HESS J1808-204 is not yet clear. If associated with SGR 1806 20, the potentially young age of the magnetar (650 yr) can be used to infer the transport limits of these particles to match the VHE source size. This discovery provides new interest in the potential for high-energy particle acceleration from magnetars, massive stars, and/or stellar clusters.

Keywords
gamma rays: general, stars: magnetars, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76470 (URN)10.1051/0004-6361/201629695 (DOI)000429404700011 ()
Available from: 2018-07-10 Created: 2018-07-10 Last updated: 2018-07-10Bibliographically approved
Abdalla, H., Abramowski, A., Aharonian, F., Benkhali, F. A., Akhperjanian, A. G., Andersson, T., . . . Zywucka, N. (2018). HESS discovery of very high energy gamma-ray emission from PKS 0625-354. Monthly notices of the Royal Astronomical Society, 476(3), 4187-4198
Open this publication in new window or tab >>HESS discovery of very high energy gamma-ray emission from PKS 0625-354