31 research outputs found
Gamma-Ray Bursts Observed with the Spectrometer SPI Onboard INTEGRAL
The spectrometer SPI is one of the main detectors of ESA's INTEGRAL mission.
The instrument offers two interesting and valuable capabilities for the
detection of the prompt emission of Gamma-ray bursts. Within a field of view of
16 degrees, SPI is able to localize Gamma-ray bursts with an accuracy of 10
arcmin. The large anticoincidence shield, ACS, consisting of 512 kg of BGO
crystals, detects Gamma-ray bursts quasi omnidirectionally above ~70 keV. Burst
alerts from SPI/ACS are distributed to the interested community via the
INTEGRAL Burst Alert System. The ACS data have been implemented into the 3rd
Interplanetary Network and have proven valuable for the localization of bursts
using the triangulation method. During the first 8 months of the mission
approximately one Gamma-ray burst per month was localized within the field of
fiew of SPI and 145 Gamma-ray burst candidates were detected by the ACS from
which 40 % have been confirmed by other instruments.Comment: 4 pages, 2 figures, to appear in the Proceedings of the Conference
"30 Years of GRB Discovery", Santa Fe, New Mexico, USA, September 8-12, 200
Investigating the central engine of Seyfert 2 galaxies with and without Polarized Broad Lines
We study the hard X-ray emission of two samples of Seyfert 2 galaxies with
and without Polarized Broad Lines (PBL). In the hard X-ray domain, absorption
effects do not significantly modify the intrinsic emission allowing us a direct
access to the central engine. The purpose of this study is to compare the
primary emission of the two Seyfert 2 subclasses in order to investigate the
nature of their central engine and to test unified models according to which
they both have a hidden Seyfert 1 nucleus. We compute the average hard X-ray
spectra of Seyfert 2 galaxies with and without PBL observed with
BeppoSAX/PDS (15-136 keV).
The two spectra have a common general behavior at first sight, but
investigating deeper we find differences in the intrinsic properties of the two
categories of Seyfert 2 galaxies. Sy 2 with polarized broad lines have physical
conditions close to those of Sy 1 galaxies whereas Sy 2 without PBL differ
substantially, suggesting that they may have a particular place in the scheme
of Seyfert galaxies.Comment: 10 pages, accepted for publication in A&
Observation of GRB 030131 with the INTEGRAL satellite
A long Gamma-Ray Burst (GRB) was detected with the instruments on board the
INTEGRAL satellite on January 31 2003. Although most of the GRB, which lasted
150 seconds, occurred during a satellite slew, the automatic software of
the INTEGRAL Burst Alert System was able to detect it in near-real time. Here
we report the results obtained with the IBIS instrument, which detected GRB
030131 in the 15 keV - 200 keV energy range, and ESO/VLT observations of its
optical transient. The burst displays a complex time profile with numerous
peaks. The peak spectrum can be described by a single power law with photon
index 1.7 and has a flux of 2 photons cm s in
the 20-200 keV energy band. The high sensitivity of IBIS has made it possible
for the first time to perform detailed time-resolved spectroscopy of a GRB with
a fluence of 7 erg cm (20-200 keV).Comment: Accepted for publication in A&A, 5 pages, 4 figures, late
Scientific Performance of the ISDC Quick Look Analysis
The INTEGRAL Science Data Centre (ISDC) routinely monitors the Near Real Time
data (NRT) from the INTEGRAL satellite. A first scientific analysis is made in
order to check for the detection of new, transient or highly variable sources
in the data. Of primary importance for this work is the Interactive Quick Look
Analysis (IQLA), which produces JEM-X and ISGRI images and monitors them for
interesting astrophysical eventsComment: 4 pages, 3 figures. Proceedings of 5th INTEGRAL Workshop: The
INTEGRAL Universe, Munich, 16-20 February 2004. Accepted for publication in
European Space Agency Special Publication 552. See paper for institute
affiliation
A 100ks XMM-Newton view of the Seyfert 1.8 ESO113-G010. I. Discovery of large X-ray variability and study of the FeKalpha line complex
(Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert
1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a
longer time-scale its main X-ray properties. The source was found in a
higher/softer time-averaged flux state, and timing analysis of this source
reveals strong, rapid variability. The Power Spectral Density (PSD) analysis
indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is
comparable to those measured in some other rapidly-variable Seyferts, such as
MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that
M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close
to the Eddington rate (or even higher). The existing data cannot distinguish
between spectral pivoting of the continuum and a two-component origin for the
spectral softening, primarily because the data do not span a broad enough flux
range. In the case of the two-component model, the fractional offsets measured
in the flux-flux plots increase significantly toward higher energies (similar
to what is observed in MCG-6-30-15) as expected if there exists a constant
reflection component. Contrary to May 2001, no significant highly redshifted
emission line is observed (which might be related to the source flux level),
while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N
is not high enough to establish if the lines are variable or constant. As
already suggested by the 2001 observation, no significant constant narrow
6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission
from distant cold matter such as a torus in this Seyfert type 1.8 galaxy.Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 table
Reflection in Seyfert Galaxies and the Unified Model of AGN
We present a deep study of the average hard X-ray spectra of Seyfert
galaxies. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the
165 Seyfert galaxies detected at z<0.2. Our final sample consists of 44 Seyfert
1's, 29 Seyfert 1.5's, 78 Seyfert 2's, and 14 Narrow Line Seyfert 1's. We
derived the average hard X-ray spectrum of each subsample in the 17-250keV
energy range. All classes of Seyfert galaxies show on average the same nuclear
continuum, as foreseen by the zeroth order unified model, with a cut-off energy
of Ec>200keV, and a photon index of Gamma ~1.8. Compton-thin Seyfert 2's show a
reflection component stronger than Seyfert 1's and Seyfert 1.5's. Most of this
reflection is due to mildly obscured (10^23 cm^-2 < NH < 10^24 cm^-2) Seyfert
2's, which have a significantly stronger reflection component
(R=2.2^{+4.5}_{-1.1}) than Seyfert 1's (R<=0.4), Seyfert 1.5's (R<= 0.4) and
lightly obscured (NH < 10^23 cm^-2) Seyfert 2's (R<=0.5). This cannot be
explained easily by the unified model. The absorber/reflector in mildly
obscured Seyfert 2's might cover a large fraction of the X-ray source, and have
clumps of Compton-thick material. The large reflection found in the spectrum of
mildly obscured Seyfert 2's reduces the amount of Compton-thick objects needed
to explain the peak of the cosmic X-ray background. Our results are consistent
with the fraction of Compton-thick sources being ~10%. The spectra of Seyfert
2's with and without polarized broad lines do not show significant differences,
the only difference between the two samples being the higher hard X-ray and
bolometric luminosity of Seyfert 2's with polarized broad lines. The average
hard X-ray spectrum of Narrow line Seyfert 1's is steeper than those of Seyfert
1's and Seyfert 1.5's, probably due to a lower energy of the cutoff.Comment: 19 pages, accepted for publication in Astronomy and Astrophysics,
final versio
Simultaneous observations of the quasar 3C 273 with INTEGRAL, XMM-Newton and RXTE
INTEGRAL has observed the bright quasar 3C 273 on 3 epochs in January 2003 as
one of the first observations of the open programme. The observation on January
5 was simultaneous with RXTE and XMM-Newton observations. We present here a
first analysis of the continuum emission as observed by these 3 satellites in
the band from 3 keV to 500 keV. The continuum spectral energy distribution of
3C 273 was observed to be weak and steep in the high energies during this
campaign. We present the actual status of the cross calibrations between the
instruments on the three platforms using the calibrations available in June
2003.Comment: 4 figures, accepted for publication in A+A letter
POLAR: a compact detector for GRB polarization measurements
Présenté par J.P. VialleInternational audienceThrough polarization measurements of X-rays can provide essential information for identifying processes responsible of their emission by astrophysical objects, almost no experimental data exist yet. We propose here a novel wide field compact detector for hard X-ray polarization measurements based on Compton scattering process and made of low-Z fast scintillators
INTEGRAL and XMM-Newton observations of the X-ray pulsar IGR J16320-4751/AX J1631.9-4752
We report on observations of the X-ray pulsar IGR J16320-4751 (also known as AX J1631.9-4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at âŒ1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320-4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of âŒ0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedde