96 research outputs found
Towards a population of HMXB/NS microquasars as counterparts of low-latitude unidentified EGRET sources
The discovery of the microquasar LS 5039 well within the 95% conficence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step
towards the possible association between microquasars (MQs) and UESs. The
recent discovery of precessing relativistic radio jets in LS I +61 303, a
source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently
proposed association between the microquasar candidate AX J1639.0-4642 and the
UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary
(HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude
unidentified EGRET sources.Comment: 12 pages, 7 figures. Proceedings of the Conference "The
Multiwavelength Approach to Unidentified Gamma-ray Sources", to appear in the
journal Astrophysics and Space Scienc
Gamma-ray binaries
Recent observations have shown that some compact stellar binaries radiate the
highest energy light in the universe. The challenge has been to determine the
nature of the compact object and whether the very high energy gamma-rays are
ultimately powered by pulsar winds or relativistic jets. Multiwavelength
observations have shown that one of the three gamma-ray binaries known so far,
PSR B1259-63, is a neutron star binary and that the very energetic gamma-rays
from this source and from another gamma-ray binary, LS I +61 303, may be
produced by the interaction of pulsar winds with the wind from the companion
star. At this time it is an open question whether the third gamma-ray binary,
LS 5039, is also powered by a pulsar wind or a microquasar jet, where
relativistic particles in collimated jets would boost the energy of the wind
from the stellar companion to TeV energies.Comment: 4 pages, 3 figures. Invited talk to appear in Proceedings of the
conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources",
Barcelona, 4-7 July 200
On the origin of the X-ray emission from a narrow-line radio quasar at z ; 1
We present new XMM?Newton X-ray observations of the z = 1.246 narrow-line radio quasar RX J1011.2+5545 serendipitously discovered by ROSAT. The flat X-ray spectrum previously measured by ROSAT and ASCA is shown to be the result of a steep ? 1.8 power-law spectrum seen through a moderate intrinsic absorbing column (N H ? 4 × 1021 cm?2). The position of the X-ray source is entirely coincident with the nucleus of the radio source that we have resolved in new sensitive VLA observations at 3.6 and 6 cm, implying that scattering in the radio lobes is not responsible for the bulk of X-ray emission. In the EPIC pn image, a faint patch of X-ray emission is apparent 14 arcsec to the north-east of the main X-ray source. The former is positionally coincident with an apparently extended optical object with R ? 21.9, but there is no associated radio emission, thus ruling out the possibility that this represents a hotspot in a jet emanating from the primary X-ray source. No reflection features are detected in the X-ray spectrum of the narrow-line radio quasar, although an Fe line with an equivalent width of up to 600 eV cannot be ruled out.The work reported herein is based partly on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA). The NOT telescope is operated by the Nordic Optical Telescope Scientific Association on the spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canarias. We are grateful to the service support for conducting the optical observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We acknowledge financial support by the Ministerio de Ciencia y Tecnolog´ıa (Spain), under grants AYA2000-1690 (XB, FJC, MTC), AYA2002-03326 (RC, JIGS) and AYA2001-3092 (MR, JMP). MR and JMP acknowledge also partial support by the European Regional Development Fund (ERDF/FEDER). During this work, MR has been supported by a fellowship from CIRIT (Generalitat de Catalunya, ref. 1999 F I 00199
INTEGRAL serendipitous detection of the gamma-ray microquasar LS 5039
LS 5039 is the only X-ray binary persistently detected at TeV energies by the
Cherenkov HESS telescope. It is moreover a gamma-ray emitter in the GeV and
possibly MeV energy ranges. To understand important aspects of jet physics,
like the magnetic field content or particle acceleration, and emission
processes, such as synchrotron and inverse Compton (IC), a complete modeling of
the multiwavelength data is necessary. LS 5039 has been detected along almost
all the electromagnetic spectrum thanks to several radio, infrared, optical and
soft X-ray detections. However, hard X-ray detections above 20 keV have been so
far elusive and/or doubtful, partly due to source confusion for the poor
spatial resolution of hard X-ray instruments. We report here on deep (300 ksec)
serendipitous INTEGRAL hard X-ray observations of LS 5039, coupled with
simultaneous VLA radio observations. We obtain a 20-40 keV flux of 1.1 +/- 0.3
mCrab (5.9 (+/-1.6) X 10^{-12} erg cm^{-2} s^{-1}), a 40-100 keV upper limit of
1.5 mCrab (9.5 x 10^{-12} erg cm^{-2}s^{-1}), and typical radio flux densities
of about 25 mJy at 5GHz. These hard X-ray fluxes are significantly lower than
previous estimates obtained with BATSE in the same energy range but, in the
lower interval, agree with extrapolation of previous RXTE measurements. The
INTEGRAL observations also hint to a break in the spectral behavior at hard
X-rays. A more sensitive characterization of the hard X-ray spectrum of LS 5039
from 20 to 100 keV could therefore constrain key aspects of the jet physics,
like the relativistic particle spectrum and the magnetic field strength. Future
multiwavelength observations would allow to establish whether such hard X-ray
synchrotron emission is produced by the same population of relativistic
electrons as those presumably producing TeV emission through IC.Comment: 4 pages LaTeX, 1 postscript figure, to appear in Proceedings of the
conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources"
Barcelona/Spain (2006
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
H.E.S.S. Observations of LS 5039
Recent observations of the binary system LS5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very High Energy (VHE) gamma-ray emission is modulated at the 3.9 days orbital period of the system. The bulk of the emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. The flux modulation provides the first indication of gamma-ray absorption by pair production on the intense stellar photon field. This implies that the production region size must be not significantly greater than the gamma-gamma photosphere size (~1 AU), thus excluding the large scale collimated outflows or jets (extending out to ~1000 AU). A hardening of the spectrum is also observed at the same epoch between 0.2 and a few TeV which is unexpected under a pure absorption scenario and could rather arise from variation with phase in the maximum electron energy and/or the dominant VHE gamma-ray production mechanism. This first-time observation of modulated gamma-ray emission allows precise tests of the acceleration and emission models in binary systems
Unfolding of differential energy spectra in the MAGIC experiment
The paper describes the different methods, used in the MAGIC experiment, to
unfold experimental energy distributions of cosmic ray particles (gamma-rays).
Questions and problems related to the unfolding are discussed. Various
procedures are proposed which can help to make the unfolding robust and
reliable. The different methods and procedures are implemented in the MAGIC
software and are used in most of the analyses.Comment: Submitted to NIM
Implementation of the Random Forest Method for the Imaging Atmospheric Cherenkov Telescope MAGIC
The paper describes an application of the tree classification method Random
Forest (RF), as used in the analysis of data from the ground-based gamma
telescope MAGIC. In such telescopes, cosmic gamma-rays are observed and have to
be discriminated against a dominating background of hadronic cosmic-ray
particles. We describe the application of RF for this gamma/hadron separation.
The RF method often shows superior performance in comparison with traditional
semi-empirical techniques. Critical issues of the method and its implementation
are discussed. An application of the RF method for estimation of a continuous
parameter from related variables, rather than discrete classes, is also
discussed.Comment: 16 pages, 8 figure
Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope
We analyze the timing of photons observed by the MAGIC telescope during a
flare of the active galactic nucleus Mkn 501 for a possible correlation with
energy, as suggested by some models of quantum gravity (QG), which predict a
vacuum refractive index \simeq 1 + (E/M_{QGn})^n, n = 1,2. Parametrizing the
delay between gamma-rays of different energies as \Delta t =\pm\tau_l E or
\Delta t =\pm\tau_q E^2, we find \tau_l=(0.030\pm0.012) s/GeV at the 2.5-sigma
level, and \tau_q=(3.71\pm2.57)x10^{-6} s/GeV^2, respectively. We use these
results to establish lower limits M_{QG1} > 0.21x10^{18} GeV and M_{QG2} >
0.26x10^{11} GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC
sensitivity to propagation effects at these levels. Thermal plasma effects in
the source are negligible, but we cannot exclude the importance of some other
source effect.Comment: 12 pages, 3 figures, Phys. Lett. B, reflects published versio
Observation of inverse Compton emission from a long γ-ray burst.
Long-duration γ-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10-6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs
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