20 research outputs found
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.Comment: 8 pages, 8 figures, Astronomy and Astrophysics (in press
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.Comment: 5 pages, 3 figures, uses emulateapj styl
Isolated X-ray -- infrared sources in the region of interaction of the supernova remnant IC 443 with a molecular cloud
The nature of the extended hard X-ray source XMMU J061804.3+222732 and its
surroundings is investigated using XMM-Newton, Chandra, and Spitzer
observations. This source is located in an interaction region of the IC 443
supernova remnant with a neighboring molecular cloud. The X-ray emission
consists of a number of bright clumps embedded in an extended structured
non-thermal X-ray nebula larger than 30" in size. Some clumps show evidence for
line emission at ~1.9 keV and ~3.7 keV at the 99% confidence level. Large-scale
diffuse radio emission of IC 443 passes over the source region, with an
enhancement near the source. An IR source of about 14" x 7" size is prominent
in the 24 um, 70 um, and 2.2 um bands, adjacent to a putative Si K-shell X-ray
line emission region. The observed IR/X-ray morphology and spectra are
consistent with those expected for J/C-type shocks of different velocities
driven by fragmented supernova ejecta colliding with the dense medium of a
molecular cloud. The IR emission of the source detected by Spitzer can be
attributed to both continuum emission from an HII region created by the ejecta
fragment and line emission excited by shocks. This source region in IC 443 may
be an example of a rather numerous population of hard X-ray/IR sources created
by supernova explosions in the dense environment of star-forming regions.
Alternative Galactic and extragalactic interpretations of the observed source
are also discussed.Comment: The Astrophysical Journal, v. 677 (April 2008), in pres
Hard X-ray Emission Clumps in the gamma-Cygni Supernova Remnant: an INTEGRAL-ISGRI View
Spatially resolved images of the galactic supernova remnant G78.2+2.1
(gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained
with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics
Laboratory INTEGRAL. The images are dominated by localized clumps of about ten
arcmin in size. The flux of the most prominent North-Western (NW) clump is (1.7
+/- 0.4) 10^{-11} erg/cm^2/s in the 25-40 keV band. The observed X-ray fluxes
are in agreement with extrapolations of soft X-ray imaging observations of
gamma-Cygni by ASCA GIS and spatially unresolved RXTE PCA data. The positions
of the hard X-ray clumps correlate with bright patches of optical line
emission, possibly indicating the presence of radiative shock waves in a
shocked cloud. The observed spatial structure and spectra are consistent with
model predictions of hard X-ray emission from nonthermal electrons accelerated
by a radiative shock in a supernova interacting with an interstellar cloud, but
the powerful stellar wind of the O9V star HD 193322 is a plausible candidate
for the NW source as well.Comment: 5 pages, 5 figures, Astronomy and Astrophysics Letter
A population of isolated hard X-ray sources near the supernova remnant Kes 69
Recent X-ray observations of the supernova remnant IC443 interacting with
molecular clouds have shown the presence of a new population of hard X-ray
sources related to the remnant itself, which has been interpreted in terms of
fast ejecta fragment propagating inside the dense environment. Prompted by
these studies, we have obtained a deep {\sl XMM-Newton} observation of the
supernova remnant (SNR) Kes 69, which also shows signs of shock-cloud
interaction. We report on the detection of 18 hard X-ray sources in the field
of Kes 69, a significant excess of the expected galactic source population in
the field, spatially correlated with CO emission from the cloud in the remnant
environment. The spectra of 3 of the 18 sources can be described as hard power
laws with photon index <2 plus line emission associated to K-shell transitions.
We discuss the two most promising scenarios for the interpretation of the
sources, namely fast ejecta fragments (as in IC443) and cataclysmic variables.
While most of the observational evidences are consistent with the former
interpretation, we cannot rule out the latter.Comment: 9 pages, 5 figures, A&A in pres
Phase-resolved hard X-ray emission of the high-mass binary LS 5039: a spectral hardening above 50 keV detected with INTEGRAL
Aims. LS 5039 is an enigmatic high-mass gamma-ray binary which hosts a powerful O6.5V companion, but the nature of the compact object is still to be established using multi-wavelength observations.
Methods. We analyzed phase-resolved multi-instrument spectra of nonthermal emission from LS 5039 in order to produce reliable spectral models, which can be further employed to select between various scenarios and theoretical models of the binary.
Results. The combined phase-resolved hard X-ray and MeV-range gamma-ray spectra obtained with XMM-Newton, Suzaku, NuSTAR, INTEGRAL, and COMPTEL indicate a meaningful spectral hardening above 50 keV. The spectral break observed in both major phases of the binary may indicate the presence of an upturn in the spectrum of accelerated leptons which could originate from the interaction of wind from the O6.5V companion star with the relativistic outflow from a yet unidentified compact object