Thierry J.-L. Courvoisier

INTEGRAL Observations of Gravitational-Wave Counterparts & Future Perspectives: Searching for GBM Un-Triggered SGRB with PICsIT

The X-ray/gamma-ray mission emph{INTEGRAL} detected the short GRB170817A and demonstrated its association to a gravitational wave trigger, GW170817. This marks the first time a binary neutron star merger was detected by the LIGO-Virgo collaboration and that an electromagnetic counterpart to a gravitational wave event has been observed. GRB170817A was detected by the SPI-ACS on-board emph{INTEGRAL} and the emph{Fermi}/GBM instruments ( sim 1.7) s after the GW event. Following the prompt emission, emph{INTEGRAL} performed pointed observations for 5.4 days. During this time the instruments provided stringent upper limits on any electromagnetic signal in the 3 keV to 8 MeV range. Interestingly, the GRB was found to be extremely subluminous.In light of these results from GRB170817A, we have begun analysis of soft gamma-ray data ((200 textrm{ keV } - 2.6 textrm{ MeV })) from emph{INTEGRAL}/PICsIT. With this wide field-of-view instrument, we have begun searching for untriggered SGRBs reported by emph{Fermi}/GBM as well as preparing for real-time analysis during future LIGO-Virgo observing runs.

Timing properties of gamma-ray bursts detected by SPI-ACS detector onboard of INTEGRAL

Aims. We study timing properties of a large sample of gamma-ray bursts (GRB) detected by the anti-coincidence shield (ACS) of the SPI spectrometer of INTEGRAL telescope. Methods. We identify GRB-like events in the SPI-ACS data. The data set under investigation is the history of count rate of the SPI-ACS detector recorded with a binning of 50 ms over the time span of ∼10 yr. In spite of the fact that SPI-ACS does not have imaging capability, it provides high statistics signal for each GRB event, because of its large effective area. Results. We classify all isolated excesses in the SPI-ACS count rate into three types: short spikes produced by cosmic rays, GRBs and Solar flare induced events. We find some ∼1500 GRB-like events in the 10 yr exposure. A significant fraction of the GRB-like events identified in SPI-ACS occur in coincidence with triggers of other gamma-ray telescopes and could be considered as confirmed GRBs. We study the distribution of durations of the GRBs detected by SPI-ACS and find that the peak of the distribution of long GRBs is at � 20 s, i.e. somewhat shorter than for the long GRBs detected by BATSE. Contrary to the BATSE observation, the population of short GRBs does not have any characteristic timescale. Instead, the distribution of durations extends as a powerlaw to the shortest timescale accessible for SPI-ACS, ≤50 ms. We also find that a large fraction of long GRBs has a characteristic variability timescale of the order of 1 s. We discuss the possible origin of this timescale.

INTEGRAL monitoring of NGC 4151: Evidence for a truncated accretion disk

Stéphane Paltani1, P. Lubiński2, A.A. Zdziarski3, R. Walter1, V. Beckmann4, S. Soldi5, C. Ferrigno1, T. J.-L. Courvoisier1 1 ISDC Data Centre for Astrophysics, Observatory of the University of Geneva, Switzerland 2 Centrum Astronomiczne im. M. Kopernika, Toruń, Poland 3 Centrum Astronomiczne im. M. Kopernika, Warszawa, Poland 4 APC, UMR 7164, Université Paris 7 Denis Diderot, France 5 Laboratoire AIM CNRS CEA/DSM Université Paris Diderot, France

INTEGRAL hard X-ray spectra of the cosmic X-ray background and the Galactic ridge

We derive the spectra of the cosmic X-ray background (CXB) an d of the Galactic ridge X-ray emission (GRXE) in the∼20–200 keV range from the data of the IBIS instrument aboard t he INTEGRAL satellite obtained during the four dedicated Earth-occult ation observations in early 2006. We analyze the modulation of the IBIS/ISGRI detector c ounts induced by the passage of the Earth through the field of view of the instrument. Unlike p r vious studies, we do not fix the spectral shape of the various contributions, but model inst ead heir spatial distribution and derive the expected modulation of the detector counts, which we the n fit to the data. The obtained CXB spectrum is consistent with the historic HEAO-1 results and falls slightly below the spectrum derived with Swift/BAT. A 10 % higher normalization of the CXB cannot be completely excluded, but it would imply an unrealistical ly high albedo of the Earth. The derived spectrum of the GRXE confirms the presence of a minimu m around 80 keV with improved statistics and yields an estimate of ∼0.6 M⊙ for the average mass of white dwarfs in the Galaxy. The analysis also provides updated normalizations for the s pectra of the Earth’s albedo and the cosmic-ray induced atmospheric emission. This study demonstrates the potential of INTEGRAL Earth-occultation observations to derive the hard X-ray spectra of three fundamental components: the CXB , the GRXE and the Earth emission. Further observations would be extremely valuable to c onfirm our results with improved statistics.

A possible feature of thermal matter in relativistic jets of radio-loud quasars

It has been suggested that relativistic jets in quasars may contain a considerable amount of thermal matter. In this paper, we explore the possibility that the Kα line from the thermal matter may appear at tens of keV due to a high Doppler blue-shift. In the jet comoving frame, the energy density of photons originally emitted by the accretion disk and reflected off the broad line region clouds dominates over that of photons of other origin. We discuss the photoionization states of the thermal matter and find that the irons elements are neutral. The high metallicity in quasars enhances the possibility to detect the thermal matter in the relativistic jet in some radio-loud quasars. A highly Doppler blue-shifted Kα line may be detected. We make a prediction for 3C 273, in which the Kα line luminosity might be of the order 3.0 × 10 44 erg s −1 with an equivalent width of 2.4 keV. Such a line could be detected in a future mission.