The MAGIC collaboration has recently reported the discovery of g-ray emission from the binary system LS I +61°303 in the TeV energy region. Here we present new observational results on this source in ...the energy range between 300 GeV and 3 TeV. In total, 112 hr of data were taken between 2006 September and December covering four orbital cycles of this object. This large amount of data allowed us to produce an integral flux light curve covering for the first time all orbital phases of LS I +61°303. In addition, we also obtained a differential energy spectrum for two orbital phase bins covering the phase range 0.5 < < 0.6 and 0.6 < < 0.7. The photon index in the two phase bins is consistent within the errors with an average index = 2.6 ± 0.2stat ± 0.2sys. LS I +61°303 was found to be variable at TeV energies on timescales of days. These new MAGIC measurements allowed us to search for intranight variability of the very high energy emission; however, no evidence for flux variability on timescales down to 30 min was found. To test for possible periodic structures in the light curve, we apply the formalism developed by Lomb and Scargle to the LS I +61°303 data taken in 2005 and 2006. We found the LS I +61°303 data set to be periodic with a period of (26.8 ± 0.2) days (with a post-trial chance probability of 10-7), close to the orbital period.
Based on MAGIC observations from 2007 June to July, we have obtained an integral upper limit to the VHE energy emission of the globular cluster M13 of F(E>200 GeV) < 5.1 X 10-12 cm-2 s-1, and ...differential upper limits for E > 140 GeV. Those limits allow us to constrain the population of millisecond pulsars within M13 and to test models for acceleration of leptons inside their magnetospheres and surrounding. We conclude that in M13 either millisecond pulsars are fewer than expected or they accelerate leptons less efficiently than predicted.
One fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high-end region of a pulsar's spectrum would shed light on this question. By ...developing a new electronic trigger, we lowered the threshold of the Major Atmospheric gamma-ray Imaging Cherenkov (MAGIC) telescope to 25 giga-electron volts. In this configuration, we detected pulsed gamma-rays from the Crab pulsar that were greater than 25 giga-electron volts, revealing a relatively high cutoff energy in the phase-averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar-cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot-gap scenario. PUBLICATION ABSTRACT
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The MAGIC collaboration has recently reported correlated X-ray and VHE gamma-ray emission from the gamma-ray binary LS I +61?303 during ~60% of one orbit, thus suggesting that the emission in these ...two bands has its origin in a single particle population. Using a one zone population of relativistic leptonic particles with dominant adiabatic losses located at the position of the compact object we are able to reproduce the observed X-ray and VHE lightcurves. From the best fit result, we obtain the magnetic field, energy budget and acceleration efficiency of the accelerator, and discuss these in the context of the young non-acretting pulsar and acretting compact object scenarios. The results also confirm that the GeV emission detected by Fermi does not come from the same parent particle population as the X-ray and VHE emission.
Full text
Available for:
FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
\eta\ Car is the only colliding-wind binary for which high-energy \gamma\ rays are detected. Although the physical conditions in the shock region change on timescales of hours to days, the ...variability seen at GeV energies is weak and on significantly longer timescales. The \gamma-ray spectrum exhibits two features that can be interpreted as emission from the shocks on either side of the contact discontinuity. Here we report on the first time-dependent modelling of the non-thermal emission in \eta\ Car. We find that emission from primary electrons is likely not responsible for the \gamma-ray emission, but accelerated protons interacting with the dense wind material can explain the observations. In our model, efficient acceleration is required at both shocks, with the primary side acting as a hadron calorimeter, whilst on the companion side acceleration is limited by the flow time out of the system, resulting in changing acceleration conditions. The system therefore represents a unique laboratory for the exploration of hadronic particle acceleration in non-relativistic shocks.
ApJ, 743, 7 (2011) Gamma-ray loud X-ray binaries are binary systems that show non-thermal
broadband emission from radio to gamma rays. If the system comprises a massive
star and a young non-accreting ...pulsar, their winds will collide producing
broadband non-thermal emission, most likely originated in the shocked pulsar
wind. Thermal X-ray emission is expected from the shocked stellar wind, but
until now it has neither been detected nor studied in the context of gamma-ray
binaries. We present a semi-analytic model of the thermal X-ray emission from
the shocked stellar wind in pulsar gamma-ray binaries, and find that the
thermal X-ray emission increases monotonically with the pulsar spin-down
luminosity, reaching luminosities of the order of 10^33 erg/s. The lack of
thermal features in the X-ray spectrum of gamma-ray binaries can then be used
to constrain the properties of the pulsar and stellar winds. By fitting the
observed X-ray spectra of gamma-ray binaries with a source model composed of an
absorbed non-thermal power law and the computed thermal X-ray emission, we are
able to derive upper limits on the spin-down luminosity of the putative pulsar.
We applied this method to LS 5039, the only gamma-ray binary with a radial,
powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of
~6x10^36 erg/s. Given the energetic constraints from its high-energy gamma-ray
emission, a non-thermal to spin-down luminosity ratio very close to unity may
be required.
LS 5039 is a gamma-ray binary system observed in a broad energy range, from radio to TeV energies. The binary system exhibits both flux and spectral modulation as a function of its orbital period. ...The X-ray and very-high-energy (VHE, E > 100 GeV) gamma-ray fluxes display a maximum/minimum at inferior/superior conjunction, with spectra becoming respectively harder/softer, a behaviour that is completely reversed in the high-energy domain (HE, 0.1 < E < 100 GeV). The HE spectrum cuts off at a few GeV, with a new hard component emerging at E > 10 GeV that is compatible with the low-energy tail of the TeV emission. The low 10 - 100 GeV flux, however, makes the HE and VHE components difficult to reconcile with a scenario including emission from only a single particle population. We report on new observations of LS 5039 conducted with the High Energy Stereoscopic System (H.E.S.S.) telescopes from 2006 to 2015. This new data set enables for an unprecedentedly-deep phase-folded coverage of the source at TeV energies, as well as an extension of the VHE spectral range down to ~120 GeV, which makes LS 5039 the first gamma-ray binary system in which a spectral overlap between satellite and ground-based gamma-ray observatories is obtained.
MWC 656 (= HD 215227) was recently discovered to be the first binary system composed of a Be star and a black hole (BH). We observed it with \textit{XMM-Newton}, and detected a faint X-ray source ...compatible with the position of the optical star, thus proving it to be the first Be/BH X-ray binary. The spectrum analysis requires a model fit with two components, a black body plus a power law, with \(k_{\rm B}T = 0.07^{+0.04}_{-0.03}\)~keV and a photon index \(\Gamma= 1.0\pm0.8\), respectively. The non-thermal component dominates above \(\simeq\)0.8 keV. The obtained total flux is \(F(0.3\)--\(5.5~{\rm keV}) = (4.6^{+1.3}_{-1.1})\times10^{-14}\) erg cm\(^{-2}\) s\(^{-1}\). At a distance of \(2.6\pm0.6\)~kpc the total flux translates into a luminosity \(L_{\rm X} = (3.7\pm1.7)\times10^{31}\) erg s\(^{-1}\). Considering the estimated range of BH masses to be 3.8--6.9 \(M_{\odot}\), this luminosity represents \((6.7\pm4.4)\times10^{-8}~L_{\rm Edd}\), which is typical of stellar-mass BHs in quiescence. We discuss the origin of the two spectral components: the thermal component is associated with the hot wind of the Be star, whereas the power law component is associated with emission from the vicinity of the BH. We also find that the position of MWC~656 in the radio versus X-ray luminosity diagram may be consistent with the radio/X-ray correlation observed in BH low-mass X-ray binaries. This suggests that this correlation might also be valid for BH high-mass X-ray binaries (HMXBs) with X-ray luminosities down to \(\sim10^{-8} L_{\rm Edd}\). MWC~656 will allow the accretion processes and the accretion/ejection coupling at very low luminosities for BH~HMXBs to be studied.
PDF
