In this Letter we present the primary continuum parameters, the photon index Gamma, and the high-energy cut-off E sub(c) of 41 type-1 Seyfert galaxies extracted from the International Gamma-Ray ...Astrophysics Laboratory (INTEGRAL) complete sample of active galactic nuclei (AGNs). We performed broadband (0.3-100 keV) spectral analysis by simultaneously fitting the soft and hard X-ray spectra obtained by XMM and INTEGRAL/IBIS-Swift/BAT, respectively, in order to investigate the general properties of these parameters, in particular their distribution and mean values. We find a mean photon index of 1.73 with a standard deviation of 0.17 and a mean high-energy cut-off of 128 keV with a standard deviation of 46 keV for the whole sample. This is the first time that the cut-off energy is constrained in such a large number of AGNs. We have 26 measurements of the cut-off, which corresponds to 63% of the entire sample, distributed between 50 and 200 keV. There are a further 11 lower limits mostly below 300 keV. Using the main parameters of the primary continuum, we have been able to obtain the actual physical parameters of the Comptonizing region, i.e., the plasma temperature kT sub(e) from 20 to 100 keV and the optical depth tau < 4. Finally, with the high signal-to-noise ratio spectra starting to come from NuSTAR it will soon be possible to better constrain the cut-off values in many AGNs, allowing the determination of more physical models and thus better understand the continuum emission and geometry of the region surrounding black holes.
In order to investigate the role of absorption in active galactic nuclei (AGN) with jets, we have studied the column density distribution of a hard X-ray selected sample of radio galaxies, derived ...from the INTEGRAL/Imager on Board the Integral Satellite (IBIS) and Swift/The Burst Alert Telescope (BAT) AGN catalogues (∼7–10 per cent of the total AGN population). The 64 radio galaxies have a typical FR II radio morphology and are characterized by high 20–100 keV luminosities (from 1042 to 1046 erg s−1) and high Eddington ratios (log L
Bol/L
Edd typically larger than ∼0.01). The observed fraction of absorbed AGN (N
H > 1022 cm−2) is around 40 per cent among the total sample, and ∼75 per cent among type 2 AGN. The majority of obscured AGN are narrow-line objects, while unobscured AGN are broad-line objects, obeying to the zeroth-order predictions of unified models. A significant anti-correlation between the radio core dominance parameter and the X-ray column density is found. The observed fraction of Compton thick AGN is ∼2–3 per cent, in comparison with the 5–7 per cent found in radio-quiet hard X-ray selected AGN. We have estimated the absorption and Compton thick fractions in a hard X-ray sample containing both radio galaxies and non-radio galaxies and therefore affected by the same selection biases. No statistical significant difference was found in the absorption properties of radio galaxies and non-radio galaxies sample. In particular, the Compton thick objects are likely missing in both samples and the fraction of obscured radio galaxies appears to decrease with luminosity as observed in hard X-ray non-radio galaxies.
Using the recent INTEGRAL/IBIS and Swift/BAT surveys we have extracted a sample of 64 confirmed plus three candidate radio galaxies selected in the soft gamma-ray band. The sample covers all optical ...classes and is dominated by objects showing a Fanaroff–Riley type II radio morphology; a large fraction (70 per cent) of the sample is made of ‘radiative mode’ or high-excitation radio galaxies. We measured the source size on images from the NRAO VLA Sky Survey, the Faint Images of the Radio Sky at twenty-cm and the Sydney University Molonglo Sky Survey images and have compared our findings with data in the literature obtaining a good match. We surprisingly found that the soft gamma-ray selection favours the detection of large size radio galaxies: 60 per cent of objects in the sample have size greater than 0.4 Mpc while around 22 per cent reach dimension above 0.7 Mpc at which point they are classified as giant radio galaxies (GRGs), the largest and most energetic single entities in the Universe. Their fraction among soft gamma-ray selected radio galaxies is significantly larger than typically found in radio surveys, where only a few per cent of objects (1–6 per cent) are GRGs. This may partly be due to observational biases affecting radio surveys more than soft gamma-ray surveys, thus disfavouring the detection of GRGs at lower frequencies. The main reasons and/or conditions leading to the formation of these large radio structures are still unclear with many parameters such as high jet power, long activity time and surrounding environment all playing a role; the first two may be linked to the type of active galactic nucleus discussed in this work and partly explain the high fraction of GRGs found in the present sample. Our result suggests that high energy surveys may be a more efficient way than radio surveys to find these peculiar objects.
Polarized Gamma-Ray Emission from the Crab Dean, A. J.; Clark, D. J.; Stephen, J. B. ...
Science (American Association for the Advancement of Science),
08/2008, Letnik:
321, Številka:
5893
Journal Article
Recenzirano
Pulsar systems accelerate particles to immense energies. The detailed functioning of these engines is still poorly understood, but polarization measurements of high-energy radiation may allow us to ...locate where the particles are accelerated. We have detected polarized gamma rays from the vicinity of the Crab pulsar using data from the spectrometer on the International Gamma-Ray Astrophysics Laboratory satellite. Our results show polarization with an electric vector aligned with the spin axis of the neutron star, demonstrating that a substantial fraction of the high-energy electrons responsible for the polarized photons are produced in a highly ordered structure close to the pulsar.
Narrow-line Seyfert 1 galaxies at hard X-rays Panessa, F.; De Rosa, A.; Bassani, L. ...
Monthly Notices of the Royal Astronomical Society,
11/2011, Letnik:
417, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Narrow-line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 active galactic nuclei (broad-line Seyfert 1 galaxies, hereinafter BLSy1). The X-ray properties of individual objects belonging ...to this class are often extreme and associated with accretion at high Eddington ratios. Here, we present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (>20 keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show hard-X-ray photon indices flatly distributed (Γ20−100 keV ranging from ∼1.3 to ∼3.6) with an average value of 〈Γ20−100 keV〉= 2.3 ± 0.7, compatible with a sample of hard-X-ray BLSy1 average slopes. Instead, NLSy1 galaxies show steeper spectral indices with respect to BLSy1 galaxies when broad-band spectra are considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on the high energy cut-off and on the reflection component is achieved only in one source, SWIFT J2127.4+5654 (E
cut-off∼ 50 keV, R= 1.0+0.5
− 0.4). Hard-X-ray-selected NLSy1 galaxies do not display particularly strong soft excess emission, while absorption fully or partially covering the continuum is often measured as well as Fe line emission features. Variability is a common trait in this sample, both at X-rays and at hard X-rays. The fraction of NLSy1 galaxies in the hard-X-ray sky is likely to be ∼15 per cent, in agreement with estimates derived in optically selected NLSy1 samples. We confirm the association of NLSy1 galaxies with small black hole masses with a peak at 107 M⊙ in the distribution; however, hard-X-ray NLSy1 galaxies seem to occupy the lower tail of the Eddington ratio distribution of classical NLSy1 galaxies.
The INTEGRAL/IBIS AGN catalogue: an update Malizia, A; Landi, R; Molina, M ...
Monthly notices of the Royal Astronomical Society,
07/2016, Letnik:
460, Številka:
1
Journal Article
Recenzirano
In the most recent IBIS survey based on observations performed during the first 1000 orbits of INTEGRAL, are listed 363 high-energy emitters firmly associated with AGN, 107 of which are reported here ...for the first time. We have used X-ray data to image the IBIS 90 per cent error circle of all the AGN in the sample of 107, in order to obtain the correct X-ray counterparts, locate them with arcsec accuracy and therefore pinpoint the correct optical counterparts. This procedure has led to the optical and spectral characterization of the entire sample. This new set consists of 34 broad line or type 1 AGN, 47 narrow line or type 2 AGN, 18 blazars and 8 sources of unknown class. These eight sources have been associated with AGN from their positional coincidence with 2MASX/Radio/X-ray sources. Seven high-energy emitters have been included since they are considered to be good AGN candidates. Spectral analysis has been already performed on 55 objects and the results from the most recent and/or best statistical measurements have been collected. For the remaining 52 sources, we report the spectral analysis for the first time in this work. We have been able to obtain the full X-ray coverage of the sample making use of data from Swift/XRT, XMM–Newton
and NuSTAR. In addition to the spectral characterization of the entire sample, this analysis has enabled us to identify peculiar sources and by comparing different data sets, highlight flux variability in the 2–10 keV and 20–40 keV bands.
ABSTRACT
Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterized thanks to extensive, multiband follow-up campaigns, but there are still objects ...whose nature remains to be asserted. In this paper, we investigate the true nature of three high energy sources, IGR J12134−6015, IGR J16058−7253, and Swift J2037.2+4151, employing multiwavelength data from the near-infrared to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134−6015, arguing that the source is a Galactic object and in particular a cataclysmic variable. We were able to confirm, thanks toNuclear Spectroscopic Telescope Array(NuSTAR) observations, that the hard X-ray emission detected by INTEGRAL/IBIS and Swift/BAT from IGR J16058−7253 is coming from two Seyfert 2 galaxies which are both counterparts for this source. Through optical and X-ray spectral analysis of SwiftJ2037.2+4151 we find that this source is likely part of the rare and peculiar class of symbiotic X-ray binaries and displays flux and spectral variability as well as interesting spectral features, such as a blending of several emission lines around the iron line complex.
We present the results of the correlation between the nuclear 2–10 keV X-ray and radio (at 2 cm, 6 cm, and 20 cm) luminosities for a well-defined sample of local Seyfert galaxies. We use a sample of ...low luminosity radio galaxies (LLRGs) for comparison. In both Seyfert and LLRG samples, X-ray and radio luminosities are significantly correlated over 8 orders of magnitude, indicating that the X-ray and radio emission sources are strongly coupled. Moreover, both samples show a similar regression slope, LX $\propto$ $L_{\rm R}^{0.97}$, but Seyfert galaxies are three orders of magnitude less luminous in the radio band than LLRGs. This suggests that either similar physical mechanisms are responsible for the observed emission or a combination of different mechanisms ends up producing a similar correlation slope. Indeed, the common belief for LLRG is that both the X-ray and radio emission are likely dominated by a relativistic jet component, while in Seyfert galaxies the X-ray emission probably arises from a disk-corona system and the radio emission is attributed to a jet/outflow component. We investigate the radio loudness issue in the two samples and find that the Seyfert galaxies and the LLRGs show a different distribution of the radio loudness parameters. No correlation is found between the luminosity and the radio loudness; however, the latter is related to the black hole mass and anti-correlated with the Eddington ratio. The dichotomy in the radio loudness between Seyfert and LLRG observed down to low Eddington ratios, $L_{2-10~{\rm keV}}$/LEdd ~ 10-8, does not support the idea that the origin of the radio loudness is due to a switch in the accretion mode.
In this paper we report on the broad-band X-ray properties of a complete sample of absorbed Seyfert galaxies hard X-ray selected with INTEGRAL. Our sample is composed of 33 sources, of which 15 are ...newly discovered active galactic nuclei (AGN) above 20 keV (IGR sources), while 18 are already known type 2 AGN ('known'). For 17 sources (15 IGR + 2 'known' sources) we have performed a broad-band analysis using both XMM-Newton, and INTEGRAL-IBIS data. To have a full view of the complete sample we have then complemented the analysis of the 16 remaining sources with already existing broad-band studies in the same range. The high-quality broad-band spectra are well reproduced with an absorbed primary emission with a high-energy cut-off and its scattered fraction below 2-3 keV, plus the Compton reflection features (Compton hump and Fe line emission). This study permitted a very good characterization of the primary continuum and, in turn, of all the spectral features.
A high-energy cut-off is found in 30 per cent of the sample, with an average value below 150 keV, suggesting that this feature has to be present in the X-ray spectra of obscured AGN. The hard X-ray selection favours the detection of more obscured sources, with the log N
H average value of 23.15 (standard deviation of 0.89). The diagnostic plot N
H versus F
oss(2-10 keV)/F(20-100 keV) allowed the isolation of the Compton-thick objects, and may represent a useful tool for future hard X-ray observations of newly discovered AGN. We are unable to associate the reflection components (both continuum and Fe line) with the absorbing gas as a torus (as envisaged in the Unified Model), a more complex scenario being necessary. In the Compton-thin sources, a fraction (but not all) of the Fe K line needs to be produced in a gas located closer to the black hole than the Compton-thick torus, and this is possibly associated with the optical broad-line region, responsible also for the absorption. We still need a Compton-thick medium (not intercepting the line of sight) likely associated to a torus, which contributes to the Fe line intensity and produces the observed reflection continuum above 10 keV. The so-called Iwasawa-Taniguchi effect cannot be confirmed with our data. Finally, the comparison with a sample of unobscured AGN shows that type 1 and type 2 (once corrected for absorption) Seyfert are characterized by the same nuclear/accretion properties (luminosity, bolometric luminosity, Eddington ratio), supporting the 'unified' view.
The European Society of Breast Cancer Specialists (EUSOMA) has fostered a voluntary certification process for breast centres to establish minimum standards and ensure specialist multidisciplinary ...care. Prospectively collected anonymous information on primary breast cancer cases diagnosed and treated in the units is transferred annually to a central EUSOMA data warehouse for continuous monitoring of quality indicators (QIs) to improve quality of care. Units have to comply with the EUSOMA Breast Centre guidelines and are audited by peers. The database was started in 2006 and includes over 110,000 cancers from breast centres located in Germany, Switzerland, Belgium, Austria, The Netherlands, Spain, Portugal and Italy. The aim of the present study is assessing time trends of QIs in EUSOMA-certified breast centres over the decade 2006–2015.
Previously defined QIs were calculated for 22 EUSOMA-certified breast centres (46122 patients) during 2006–2015.
On the average of all units, the minimum standard of care was achieved in 8 of 13 main EUSOMA QIs in 2006 and in all in 2015. All QIs, except removal of at least 10 lymph nodes at axillary clearance and oestrogen receptor–negative tumours (T > 1 cm or N+) receiving adjuvant chemotherapy, improved significantly in this period. The desirable target was reached for two QIs in 2006 and for 7 of 13 QIs in 2015.
The EUSOMA model of audit and monitoring QIs functions well in different European health systems and results in better performance of QIs over the last decade. QIs should be evaluated and adapted on a regular basis, as guidelines change over time.
•The time trends of quality indicators in EUSOMA-certified breast centres over the decade 2006–2015 are evaluated.•The EUSOMA model of audit and monitoring QIs functions well in different European health systems.•Audit and measuring quality indicators result in better performance.
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