arXiv subjects

M. Renaud

Publications and source records attributed to M. Renaud.

At least 55 records · Page 3Linked to original sources

arXiv2009

New unidentified Galactic H.E.S.S. sources

H.E.S.S. is one of the most sensitive instruments in the very high energy (VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004, H.E.S.S. has continued and extended that survey in 2005-2008, discovering a number of new sources, many of which are unidentified. Some of the unidentified H.E.S.S. sources have several positional counterparts and hence several different possible scenarios for the origin of the VHE gamma-ray emission; their identification remains unclear. Others have so far no counterparts at any other wavelength. Particularly, the lack of an X-ray counterpart puts serious constraints on emission models. Several newly discovered and still unidentified VHE sources are reported here.

astro-ph.HE↗

arXiv2009

The 4th IBIS/ISGRI soft gamma-ray survey catalog

In this paper we report on the fourth soft gamma-ray source catalog obtained with the IBIS gamma-ray imager on board the INTEGRAL satellite. The scientific dataset is based on more than 70Ms of high quality observations performed during the first five and a half years of Core Program and public observations. Compared to previous IBIS surveys, this catalog includes a substantially increased coverage of extragalactic fields, and comprises more than 700 high-energy sources detected in the energy range 17--100 keV, including both transients and faint persistent objects which can only be revealed with longer exposure times. A comparison is provided with the latest Swift/BAT survey results.

astro-ph.HE↗

arXiv2009

Unidentified Gamma-Ray Sources as Ancient Pulsar Wind Nebulae

In this paper we explore the evolution of a PWN while the pulsar is spinning down. An MHD approach is used to simulate the evolution of a composite remnant. Particular attention is given to the adiabatic loss rate and evolution of the nebular field strength with time. By normalising a two component particle injection spectrum (which can reproduce the radio and X-ray components) at the pulsar wind termination shock to the time dependent spindown power, and keeping track with losses since pulsar/PWN/SNR birth, we show that the average field strength decreases with time as $t^{-1.3}$, so that the synchrotron flux decreases, whereas the IC gamma-ray flux increases, until most of the spindown power has been dumped into the PWN. Eventually adiabatic and IC losses will also terminate the TeV visibility and then eventually the GeV visibility.

astro-ph.HE↗

arXiv2008

Morphology and hardness ratio exploitation under limited statistics

Gamma-ray astronomy has produced for several years now sky maps for low photon statistics, non-negligible background and comparatively poor angular resolution. Quantifying the significance of spatial features remains difficult. Besides, spectrum extraction requires regions with large statistics while maps in energy bands allow only qualitative interpretation. The two main competing mechanisms in the VHE domain are the Inverse-Compton emission from accelerated electrons radiating through synchrotron in the X-ray domain and the interactions between accelerated hadrons and the surrounding medium, leading to the production and subsequent decay of Pi0 mesons. The spectrum of the VHE emission from leptons is predicted to steepen with increasing distance from the acceleration zone, owing to synchrotron losses (i.e. cooled population). It would remain approximately constant for hadrons. Ideally, spectro-imaging analysis would have the same spatial scale in the TeV and X-ray domains, to distinguish the local emission mechanisms. More realistically, we investigate here the possibility of improving upon the currently published HESS results by using more sophisticated tools.

astro-ph↗

arXiv2008

On the nature of HESS J1503-582 revealed by the H.E.S.S. experiment: Coincidence with a FVW?

The H.E.S.S. survey of the inner Galaxy in the very-high-energy gamma-ray domain has led to the discovery of many extended sources, some of which do not appear to be associated with any obvious counterpart at traditional wavelengths (radio, infrared and X-ray). In this contribution, preliminary H.E.S.S. results on one of these so-called "dark" sources, namely HESS J1503-582, are presented. After introducing the properties of this source candidate, results of the search for counterparts in several astronomical windows are shown. Finally, its possible association with a "Forbidden-Velocity-Wing", a characteristic 21 cm HI line structure that appears as a deviation from the canonical Galactic rotation curve, is discussed.

astro-ph↗

arXiv2008

Pulsar Wind Nebula candidates recently discovered by H.E.S.S

H.E.S.S. is currently the most sensitive instrument in the very-high-energy gamma-ray domain and has revealed many new sources along the Galactic Plane, a significant fraction of which seems to be associated with energetic pulsars. HESS J1825-137 and Vela X are considered to be the prototypes of such sources in which the large VHE nebula results from the whole history of the pulsar wind and the supernova remnant host, both evolving in a complex interstellar medium. These nebulae are seen to be offset from the pulsar position and, for HESS J1825-137, a spectral steepening at increasing distance from the pulsar has been measured. In this context, updated H.E.S.S. results on two previously published sources, namely HESS J1809-193 and HESS J1912+101, and preliminary results on the newly discovered HESS J1356-645, are presented. These extended VHE sources are thought to be associated with the energetic pulsars PSR J1809-1917, PSR J1913+1011 and PSR J1357-6429, respectively. Properties of each source in the VHE regime, together with those measured in the radio and X-ray domains, are discussed.

astro-ph↗

arXiv2007

H.E.S.S. Galactic Plane Survey unveils a Milagro Hotspot

We report here on a new VHE source, HESS J1908+063, disovered during the extended H.E.S.S. survey of the Galactic plane and which coincides with the recently reported MILAGRO unidentied source MGRO J1908+06. The position, extension and spectrum measurements of the HESS source are presented and compared to those of MGRO J1908+06. Possible counterparts at other wavelenghts are discussed. For the first time one of the low-lattitude MILAGRO sources is confirmed.

astro-ph↗

arXiv2007

44Ti nucleosynthesis gamma-ray lines with SIMBOL-X

In this contribution we discuss the 44Ti nucleosynthesis gamma-ray lines and their visibility with SIMBOL-X from simulations based on its expected sensitivity and spectro-imaging capabilities. The 44Ti radioactive nucleus can provide invaluable information on the details of supernova explosions. Its lifetime of about 85 yrs makes it the best indicator of the youth of these stellar explosions through its three gamma-ray lines at 67.9, 78.4 keV and 1.157 MeV. We focus on the youngest Galactic supernova remnants, namely: Cassiopeia A, for which the location and Doppler-velocity estimates of the 44Ti-emitting regions in the remnant would offer for the first time a unique view of nucleosynthesis processes which occurred in the innermost layers of the supernova; SN 1987A, in the Large Magellanic Cloud, whose progenitor is known, and for which the expected measurement of these lines would greatly constrain the stellar evolution models; Tycho and Kepler SNRs for which 44Ti lines have never been detected so far. The issue of the "young, missing and hidden" supernova remnants in the Galaxy will also be addressed using SIMBOL-X observations at the position of the 44Ti excesses that wide-field instruments like those onboard INTEGRAL and SWIFT/BAT should be able to reveal.

astro-ph↗

arXiv2007

The 3rd IBIS/ISGRI soft gamma-ray survey catalog

In this paper we report on the third soft gamma-ray source catalog obtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRAL satellite. The scientific dataset is based on more than 40 Ms of high quality observations performed during the first three and a half years of Core Program and public IBIS/ISGRI observations. Compared to previous IBIS/ISGRI surveys, this catalog includes a substantially increased coverage of extragalactic fields, and comprises more than 400 high-energy sources detected in the energy range 17-100 keV, including both transients and faint persistent objects which can only be revealed with longer exposure times.

astro-ph↗

arXiv2006

On the nature of the hard X-ray source IGR J2018+4043

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018+4043 in the multi-wavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4 +/- 0.4) x 10(-11) erg cm(-2) s(-1). A 5 ks Swift observation of the IGR J2018+4043 field revealed a hard point-like source with the observed 0.5-10 keV flux of 3.4(+0.7)(-0.8) x 10(-12) erg cm(-2) s(-1) (90% confidence level) at alpha = 20h18m38.55s, delta = +40d41m00.4s (with a 4.2" uncertainty). The combined Swift-INTEGRAL spectrum can be described by an absorbed power-law model with photon index gamma = 1.3 +/- 0.2 and N_H = 6.1(+3.2)(-2.2) x 10(22) cm(-2). In archival optical and infrared data we found a slightly extended and highly absorbed object at the Swift source position. There is also an extended VLA 1.4 GHz source peaked at a beam-width distance from the optical and X-ray positions. The observed morphology and multiwavelength spectra of IGR J2018+4043 are consistent with those expected for an obscured accreting object, i.e. an AGN or a Galactic X-ray binary. The identification suggests possible connection of IGR J2018+4043 to the bright gamma-ray source GEV J2020+4023 (3EG J2020+4017) detected by COS B and CGRO EGRET in the gamma-Cygni SNR field.

astro-ph↗

arXiv2006

High-energy particles in the wind nebula of pulsar B1509-58 as seen by INTEGRAL

We present observations with the INTEGRAL/IBIS telescope of the wind nebula powered by the young pulsar B1509-58 and we discuss the spatial and spectral properties of the unpulsed emission in the 20-200 keV energy band. The source extension and orientation along the northwest-southeast axis corresponds to the jet emission seen at keV and TeV energies. The hard X-ray spectrum is consistent with the earlier Beppo-SAX measurements. It follows a power law with a photon index alpha = -2.12 pm 0.05 up to 160 keV. A possible break at this energy is found at the 2.9 sigma confidence level. The 0.1-100 keV data are consistent with synchrotron aging of pairs in the jet and yield a magnetic field strength of 22-33 muG for a bulk velocity of 0.3-0.5c. The synchrotron cut-off energy thus corresponds to a maximum electron energy of 400-730 TeV.

astro-ph↗

arXiv2006

The signature of 44Ti in Cassiopeia A revealed by IBIS/ISGRI on INTEGRAL

We report the detection of both the 67.9 and 78.4 keV 44Sc gamma-ray lines in Cassiopeia A with the INTEGRAL IBIS/ISGRI instrument. Besides the robustness provided by spectro-imaging observations, the main improvements compared to previous measurements are a clear separation of the two 44Sc lines together with an improved significance of the detection of the hard X-ray continuum up to 100 keV. These allow us to refine the determination of the 44Ti yield and to constrain the nature of the nonthermal continuum emission. By combining COMPTEL, BeppoSAX/PDS and ISGRI measurements, we find a line flux of (2.5 +/- 0.3)*10(-5) cm(-2) s(-1) leading to a synthesized 44Ti mass of 1.6 (+0.6-0.3)*10(-4) solar mass. This high value suggests that Cas A is peculiar in comparison to other young supernova remnants, from which so far no line emission from 44Ti decay has been unambiguously detected.

astro-ph↗

arXiv2006

Towards grid-enabled telemedicine in Africa

Telemedicine services are very relevant tools to train local physicians and to improve diagnosis by exchanging medical data. Telemedicine networks allow these exchanges but the set-up of multipoint dynamic telemedicine requires moving towards GRID technologies. A healthgrid is an environment where data of medical interest can be stored and is easily available between the different actors of healthcare. Two telemedicine applications were developed to link physicians from Burkina Faso and France with the perspective of setting up a grid infrastructure between the participating medical sites. A web site to exchange diagnosis on diabetic retinopathy was developed in PHP and another application using web services was developed to exchange patient information between two databases.

physics.ins-det↗

arXiv2006

X-Ray Observations of SN 1006 with Integral

The remnant of the supernova of 1006 AD, the remnant first showing evidence for the presence of X-ray synchrotron emission from shock-accelerated electrons, was observed for ~1000 ksec with INTEGRAL for the study of electron acceleration to very high energies. The aim of the observation was to characterize the synchrotron emission, and attempt to detect non-thermal bremsstrahlung, using the combination of IBIS and JEM-X spatial and spectral coverage. The source was detected with JEM-X between 2.4 and 8.4 keV bands, and not detected with either ISGRI or SPI above 20 keV. The ISGRI upper limit is about a factor of four above current model predictions, but confirms the presence of steepening in the power-law extrapolated from lower energies (< 4 keV).

astro-ph↗

arXiv2006

An INTEGRAL/IBIS view of Young Galactic SNRs through the 44Ti gamma-ray lines

We present preliminary results of INTEGRAL/IBIS observations on Cas A, Tycho and Vela Junior Supernova remnants in the line emission of 44Ti. This radioactive nucleus is thought to be exclusively produced in supernovae during the first stages of the explosion. It has a lifetime of about 87 y and is then the best indicator of young SNRs, as exemplified by the detection of 44Ti in the youngest known Galactic SNR Cas A with GRO/COMPTEL and latter with BeppoSAX. In this paper, we will focus on this SNR for which we confirm the detection of 44Ti and point out the importance to know the nature of the hard X-ray continuum, the Tycho SNR, for which no indication of 44Ti was ever reported, and Vela Junior, for which the claimed detection of 44Ti with COMPTEL is still controversial. The INTEGRAL/IBIS observations bring new constraints on the nature of these SNRs and on the nucleosynthesis which took place during the explosions.

astro-ph↗

arXiv2005

INTEGRAL detection of hard X-rays from NGC 6334: Nonthermal emission from colliding winds or an AGN?

We report the detection of hard X-ray emission from the field of the star-forming region NGC 6334 with the the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The JEM-X monitor and ISGRI imager aboard INTEGRAL and Chandra ACIS imager were used to construct 3-80 keV images and spectra of NGC 6334. The 3-10 keV and 10-35 keV images made with JEM-X show a complex structure of extended emission from NGC 6334. The ISGRI source detected in the energy ranges 20-40 keV and 40-80 keV coincides with the NGC 6334 ridge. The 20-60 keV flux from the source is (1.8+-0.37)*10(-11) erg cm(-2) s(-1). Spectral analysis of the source revealed a hard power-law component with a photon index about 1. The observed X-ray fluxes are in agreement with extrapolations of X-ray imaging observations of NGC 6334 by Chandra ACIS and ASCA GIS. The X-ray data are consistent with two very different physical models. A probable scenario is emission from a heavily absorbed, compact and hard Chandra source that is associated with the AGN candidate radio source NGC 6334B. Another possible model is the extended Chandra source of nonthermal emission from NGC 6334 that can also account for the hard X-ray emission observed by INTEGRAL. The origin of the emission in this scenario is due to electron acceleration in energetic outflows from massive early type stars. The possibility of emission from a young supernova remnant, as suggested by earlier infrared observations of NGC 6334, is constrained by the non-detection of 44Ti lines.

astro-ph↗

arXiv2005

G0.57-0.018: A young supernova remnant? INTEGRAL and VLA observations

We report INTEGRAL/IBIS gamma-ray and VLA radio observations of G0.570-0.018, a diffuse X-ray source recently discovered by ASCA and Chandra in the Galactic center region. Based on its spectrum and morphology, G0.570-0.018 has been proposed to be a very young supernova remnant. In this scenario, the presence of gamma-ray lines coming from the short-lived radioactive nucleus 44Ti as well as synchrotron radio continuum emission are expected. The first could provide informations on nucleosynthesis environments in the interior of exploding stars, the latter could probe the interaction between the supernova blast wave and the circumstellar/interstellar matter. We have not detected 44Ti lines nor any conspicuous radio feature associated with this source down to the achieved sensitivities. From the derived upper limits we set constraints on the nature of G0.570-0.018.

astro-ph↗

arXiv2005

The INTEGRAL/IBIS source AXJ1838.0-0655: a soft X-ray to TeV gamma-ray broad band emitter

We report on INTEGRAL observations of AX J1838.0-0655, one of the unidentified objects listed in the first IBIS/ISGRI survey catalogue and located in the Scutum arm region. This object, detected in the 20-300 keV band at a confidence level of 15.3 sigma (9 x 10^-11 erg cm-2 s-1) is the likely counterpart of the still unidentified TeV source HESS J1837-069. It has been detected in the past by various X-ray telescopes, including ASCA, implying that it is a persistent rather than a transient source; the ASCA image is compatible with the source not being resolved. The broad 1-300 keV spectrum is characterized by an absorbed (NH = 6.7+/-1.3 x 10^22 cm-2) and hard (Gamma =1.5 +/- 0.2) power law continuum. Possible counterparts (radio and infrared) present within the X-ray error box are discussed, even if no clear association can be identified. The broad band spectrum together with the TeV detection suggests that AX J1838.0-0655 maybe a supernova remnant or a pulsar wind nebula, which has so far eluded detection in the radio band. This is the second unidentified HESS source that shows a substantial soft gamma-ray emission.

astro-ph↗