We report the INTernational Gamma-ray Astrophysics Laboratory (INTEGRAL) detection of the short gamma-ray burst GRB 170817A (discovered by Fermi-GBM) with a signal-to-noise ratio of 4.6, and, for the ...first time, its association with the gravitational waves (GWs) from binary neutron star (BNS) merging event GW170817 detected by the LIGO and Virgo observatories. The significance of association between the gamma-ray burst observed by INTEGRAL and GW170817 is 3.2 , while the association between the Fermi-GBM and INTEGRAL detections is 4.2 . GRB 170817A was detected by the SPI-ACS instrument about 2 s after the end of the GW event. We measure a fluence of (1.4 0.4 0.6) × 10−7 erg cm−2 (75-2000 keV), where, respectively, the statistical error is given at the 1 confidence level, and the systematic error corresponds to the uncertainty in the spectral model and instrument response. We also report on the pointed follow-up observations carried out by INTEGRAL, starting 19.5 hr after the event, and lasting for 5.4 days. We provide a stringent upper limit on any electromagnetic signal in a very broad energy range, from 3 keV to 8 MeV, constraining the soft gamma-ray afterglow flux to <7.1 × 10−11 erg cm−2 s−1 (80-300 keV). Exploiting the unique capabilities of INTEGRAL, we constrained the gamma-ray line emission from radioactive decays that are expected to be the principal source of the energy behind a kilonova event following a BNS coalescence. Finally, we put a stringent upper limit on any delayed bursting activity, for example, from a newly formed magnetar.
We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately ~$95\%$ ...of the celestial sphere. Within the exposed sky area, 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level, from the galactic disk. The bulge emission is highly symmetric and is centred on the galactic centre with an extension of ~$ 8\ensuremath{^\circ}$ (FWHM). The emission is equally well described by models that represent the stellar bulge or halo populations. The detection significance of the bulge emission is ~$ 50\sigma$, that of the galactic disk is ~$ 4\sigma$. The disk morphology is only weakly constrained by the present data, being compatible with both the distribution of young and old stellar populations. The 511 keV line flux from the bulge and disk components is $(1.05 \pm 0.06) \times 10^{-3}$ ph cm-2 s-1 and $(0.7 \pm 0.4) \times 10^{-3}$ ph cm-2 s-1 respectively, corresponding to a bulge-to-disk flux ratio in the range $1{-}3$. Assuming a positronium fraction of $f_{\rm p}=0.93$ this translates into annihilation rates of $(1.5 \pm 0.1) \times 10^{43}$ s-1and $(0.3 \pm 0.2) \times 10^{43}$ s-1, respectively. The ratio of the bulge luminosity to that of the disk is in the range $3{-}9$. We find no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of ~10-4 ph cm-2 s-1. We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our $3\sigma$ upper flux limit for this feature is $1.5 \times 10^{-4}$ ph cm-2 s-1. The disk emission can be attributed to the $\beta^+$-decay of the radioactive species 26 Al and 44Ti. The bulge emission arises from a different source which has only a weak or no disk component. We suggest that Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons. Light dark matter annihilation could also explain the observed 511 keV bulge emission characteristics.
We analyzed 16 yr of observations dedicated to the Crab (pulsar + nebula) with the SPectrometer on International Gamma-Ray Astrophysics Laboratory instrument to investigate its polarization ...properties. We find that the source presents a substantially polarized emission (PF = 24%) in the hard X-ray domain, with the electric vector aligned with the pulsar spin axis, which is in agreement with other results at various wavelengths. The stability of the polarization characteristics with energy and over the 16 yr covered by the data is remarkable, completing the standard candle status of the source in the spectral domain. The polarization measurements imply that the synchrotron emission is the dominant mechanism of photon production from radio to hard X-rays. The high level of polarized emission points out the steadiness of the source, in particular, of the magnetic field configuration and geometry.
We have processed the data accumulated with the INTEGRAL SPI instrument over 4 years (image51 Ms) to study the morphology of the Galactic 'diffuse' emission in the 20 keV to 8 MeV energy range. To ...achieve this, we simultaneously derived an all-sky census of emitting sources and images of the Galactic ridge (GR) emission. In the central radian, the resolved point-source emission amounts to 88%, 91%, and 68% of the total in the 25-50, 50-100, and 100-300 keV domains, respectively. We compare the spatial distribution of the GR emission with the distributions obtained from CO and near-IR maps and quantify our results through latitude and longitude profiles. Below 50 keV, the SPI data are better traced by the latter, supporting a stellar origin for this emission. Furthermore, we find that the GR emission spectrum follows a power law with a photon index image1.55 above 50 keV, while an additional component is required below that energy. This component shows a cutoff around 30 keV, reinforcing a stellar origin, as proposed by Krivonos et al. The component of the diffuse emission due to e super(+/-) annihilations is extracted simultaneously, leading to the determination of the related parameters (positronium flux and fraction). Specific discussion is devoted to the annihilation-line distribution, since significant emission is detected over a region as large as image80 degree x image10 degree , potentially associated with the disk or halo surrounding the central regions of our Galaxy.
Abstract
On 2017 September 2 MAXI J1535–571 went into outburst and peaked at ∼5 Crab in the 2–20 keV energy range. Early in the flare, the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) ...performed target of opportunity pointings and monitored the source as it transitioned from the hard state to the soft state. Using quasi-simultaneous observations from MAXI/GSC and INTEGRAL/SPI, we studied the temporal and spectral evolution of MAXI J1535–571 in the 2–500 keV range. Early spectra show a Comptonized spectrum and a high-energy component dominant above ∼150 keV.
CompTT
fits to the SPectrometer on INTEGRAL (SPI) data found electron temperatures (
kT
e
) evolve from ∼31 keV to 18 keV with a tied optical depth (
τ
∼ 0.85) or
τ
evolving from ∼1.2–0.65 with a tied
kT
e
(∼24 keV). To investigate the nature of the high-energy component, we performed a spectral decomposition of the 100–400 keV energy band. The
CompTT
flux varies significantly during the hard state while the high-energy component flux is consistent with a constant flux. This result suggests that the two components originate from different locations, which favors a jet origin interpretation for the high-energy component over a hybrid corona interpretation. Lastly, two short rebrightenings during the hard-to-soft transition are compared to similar events reported in MAXI J1820+070.
The Crab Nebula is used by many instruments as a calibration source, in particular at high energy, where it is one of the brightest celestial objects. The spectrometer INTEGRAL SPI (20 keV-8 MeV), in ...operation since 2002 October, offers a large data set dedicated to this source, with regular campaigns planned twice per year. We have analyzed the available data to quantify the source behavior on a long-term scale and examine the stability level on timescales from hours to years. As a result, the source flux variability appears to be contained within less than 5% around an ∼20 yr mean value for broad bands covering the 20-400 keV energy domain, above which statistics limits any firm conclusion. In terms of spectral shape, the Band model provides a good description of the observed emission between 20 keV and 2.2 MeV. The averaged spectrum best-fit parameters correspond to a low-energy slope of 1.99 0.01, a high-energy slope of −2.32 0.02, and a characteristic energy Ec of 531 50 keV to describe the curvature joining both power laws. The spectral parameters have then been determined on the revolution timescale (∼1-2 days), and their steadiness confirms the source emission stability. As a complementary result, this study demonstrates that the SPI instrument efficiency remains within 5% of its initial value after 17 yr of operation.
Xylosandrus compactus and X. crassiusculus are two polyphagous ambrosia beetles originating from Asia and invasive in circumtropical regions worldwide. Both species were recently reported in Italy ...and further invaded several other European countries in the following years. We used the MaxEnt algorithm to estimate the suitable areas worldwide for both species under the current climate. We also made future projections for years 2050 and 2070 using 11 different General Circulation Models, for 4 Representative Concentration Pathways (2.6, 4.5, 6.0 and 8.5). Our analyses showed that X. compactus has not been reported in all potentially suitable areas yet. Its current distribution in Europe is localised, whereas our results predicted that most of the periphery of the Mediterranean Sea and most of the Atlantic coast of France could be suitable. Outside Europe, our results also predicted Central America, all islands in Southeast Asia and some Oceanian coasts as suitable. Even though our results when modelling its potential distribution under future climates were more variable, the models predicted an increase in suitability poleward and more uncertainty in the circumtropical regions. For X. crassiusculus, the same method only yielded poor results, and the models thus could not be used for predictions. We discuss here these results and propose advice about risk prevention and invasion management of both species.
Operational since 2002 on board the INTEGRAL observatory, the SPI spectrometer can be used to perform polarization measurements in the hard X-ray/softy-ray domain (~130 keV-8 MeV). However, this ...phenomenon is complex to measure at high energy and requires high fluxes. Cyg X-1 appears to be the best candidate amongst the X-ray binaries since it is one of the brightest persistent sources in this energy domain. Furthermore, a polarized component has recently been reported above 400 keV from IBIS data. We have therefore dedicated our efforts to developing the required tools to study the polarization in the INTEGRAL SPI data and have first applied them to 2.6 Ms of Cyg X-1 observations, covering 6.5 years of the INTEGRAL mission. We have found that the high energy emission of Cyg X-1 is indeed polarized, with a mean polarization fraction of 76% + or - 15% at a position angle estimated to be 42degrees + or - 3degrees, for energies above 230 keV. The polarization fraction clearly increases with energy. In the 130-230 keV band, the polarization fraction is lower than 20%, but exceeds 75% between 370 and 850 keV, with the (total) emission vanishing above this energy. This result strongly suggests that the emission originates from the jet structure known to emit in the radio domain. The same synchrotron process could be responsible for the emission from radio to MeV, implying the presence of high energy electrons. This illustrates why the polarization of the high energy emission in compact objects is an increasingly important observational objective.
Abstract
The question of the origin of the hard X-ray/soft gamma-ray emission in Centaurus A (Cen A) persists despite decades of observations. Results from X-ray instruments suggest a jet origin ...since the implied electron temperature (
kT
e
) would cause runaway pair production in the corona. In contrast, instruments sensitive to soft gamma rays report electron temperatures indicating that a coronal origin may be possible. In this context, we analyzed archival INTEGRAL/IBIS-ISGRI and SPI data and observations from a 2022 Cen A monitoring program. Our analysis did not find any spectral variability. Thus we combined all observations for long-term average spectra, which were fit with a NuSTAR observation to study the 3.5 keV–2.2 MeV spectrum. Spectral fits using a
CompTT
model found
kT
e
∼ 550 keV, near runaway pair production. The spectrum was also well described by a log-parabola to model synchrotron self-Compton emission from the jet. Additionally, a spectral fit with the 12 yr catalog Fermi/LAT spectrum using a log-parabola can explain the data up to ∼3 GeV. Above ∼3 GeV, a power-law excess is present, which has been previously reported in LAT/H.E.S.S. analysis. However, including a coronal spectral component can also describe the data well. In this scenario, the hard X-rays/soft gamma rays are due the corona and the MeV to GeV emission is due to the jet.
Xylosandrus crassiusculus
is an invasive ambrosia beetle comprising two differentiated genetic lineages, named cluster 1 and cluster 2. These lineages invaded different parts of the world at ...different periods of time. We tested whether they exhibited different climatic niches using Schoener’s D and Hellinger’s I indices and modeled their current potential geographical ranges using the Maxent algorithm. The resulting models were projected according to future and recent past climate datasets for Europe and the Mediterranean region. The future projections were performed for the periods 2041–2070 and 2071–2100 using 3 SSPs and 5 GCMs. The genetic lineages exhibited different climate niches. Parts of Europe, the Americas, Sub-Saharan Africa, Asia, and Oceania were evaluated as suitable for cluster 1. Parts of Europe, South America, Central and South Africa, Asia, and Oceania were considered as suitable for cluster 2. Models projection under future climate scenarios indicated a decrease in climate suitability in Southern Europe and an increase in North Eastern Europe in 2071–2100. Most of Southern and Western Europe was evaluated as already suitable for both clusters in the early twentieth century. Our results show that large climatically suitable regions still remain uncolonized and that climate change will affect the geographical distribution of climatically suitable areas. Climate conditions in Europe were favorable in the twentieth century, suggesting that the recent colonization of Europe is rather due to an increase in propagule pressure via international trade than to recent environmental changes.
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