3,491 research outputs found
A possible magnetar nature for IGR J16358-4726
We present detailed spectral and timing analysis of the hard X-ray transient IGR J16358-4726 using multisatellite archival observations. A study of the source flux time history over 6 yr suggests that lower luminosity transient outbursts can be occurring in intervals of at most 1 yr. Joint spectral fits of the higher luminosity outburst using simultaneous Chandra ACIS and INTEGRAL ISGRI data reveal a spectrum well described by an absorbed power-law model with a high-energy cutoff plus an Fe line. We detected the 1.6 hr pulsations initially reported using Chandra ACIS also in the INTEGRAL ISGRI light curve and in subsequent XMM-Newton observations. Using the INTEGRAL data, we identified a spin-up of 94 s ( = 1.6 × 10-4), which strongly points to a neutron star nature for IGR J16358-4726. Assuming that the spin-up is due to disk accretion, we estimate that the source magnetic field ranges between 1013 and 1015 G, depending on its distance, possibly supporting a magnetar nature for IGR J16358-4726
Activity from SAX J1747.0-2853 and KS 1741-293 detected by INTEGRAL Galactic Bulge Monitoring
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The long outburst of the black hole transient GRS 1716-249 observed in the X-ray and radio band
We present the spectral and timing analysis of X-ray observations performed on the Galactic black hole transient GRS 1716-249 during the 2016-2017 outburst. The source was almost continuously observed with the Neil Gehrels Swift Observatory from 2016 December until 2017 October. The X-ray hardness ratio and timing evolution indicate that the source approached the soft state three times during the outburst, even though it never reached the canonical soft spectral state. Thus, GRS 1716-249 increases the number of black hole transients showing outbursts with 'failed' state transition. During the softening events, XRT and BAT broad-band spectral modelling, performed with thermal Comptonization plus a multicolour disc black-body, showed a photon index (G < 2) and an inner disc temperature (kTin = 0.2- 0.5 keV) characteristic of the hard intermediate state. This is in agreement with the root mean square amplitude of the flux variability (rms > 10 per cent). We find that, coherently with a scenario in which the disc moves closer to the compact object, the accretion disc inner radius decreases with the increase of the inner disc temperature, until a certain point when the temperature starts to increase at constant radius. This, in addition with the spectral analysis results, suggests that either the accretion disc reached the innermost stable circular orbit during the hard intermediate state or the hot accretion flow might recondensate in an inner mini-disc.We report on the radio observations performed during the outburst finding that GRS 1716-249 is located on the radio-quiet 'outlier' branch of the radio/X-ray luminosity plane
The INTEGRAL view of the Soft Gamma-ray Repeater SGR 1806-20
We present the results obtained by INTEGRAL on the Soft-Gamma Ray Repeater
SGR 1806-20. In particular we report on the temporal and spectral properties of
the bursts detected during a moderately active period of the source in
September and October 2003 and on the search for quiescent emission.Comment: To appear in the proceedings (ESA-SP) of the 5th INTEGRAL Workshop,
"The INTEGRAL UNIVERSE", Munich, 16-20 February 200
Non-Spinning Black Holes in Alternative Theories of Gravity
We study two large classes of alternative theories, modifying the action
through algebraic, quadratic curvature invariants coupled to scalar fields. We
find one class that admits solutions that solve the vacuum Einstein equations
and another that does not. In the latter, we find a deformation to the
Schwarzschild metric that solves the modified field equations in the small
coupling approximation. We calculate the event horizon shift, the innermost
stable circular orbit shift, and corrections to gravitational waves, mapping
them to the parametrized post-Einsteinian framework.Comment: 7 pages, submitted to PR
Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets
An experimental overview of reactions induced by the stable, but weakly-bound
nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F
on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data
on elastic scattering, total reaction cross sections, fusion processes, breakup
and transfer channels are discussed in the framework of a CDCC approach taking
into account the breakup degree of freedom.Comment: 7 pages, 6 figures, Invited Talk given by C. Beck to the 10th
International Conference on Nucleus-Nucleus Collisions, August 16-21, 2009
Beijing, China; Paper submitted to the NN2009 Proceedings, Nuclear Physics A
(to be published
The infrared/X-ray correlation of GX 339-4: Probing hard X-ray emission in accreting black holes
GX 339-4 has been one of the key sources for unravelling the accretion
ejection coupling in accreting stellar mass black holes. After a long period of
quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts
that have been intensively observed by many ground based observatories [radio,
infrared(IR), optical] and satellites (X-rays). Here, we present results of
these broad-band observational campaigns, focusing on the optical-IR
(OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray
correlations over four decades with the presence of a break in the IR/X-ray
correlation in the hard state. This correlation is the same for all four
outbursts. This can be interpreted in a consistent way by considering a
synchrotron self-Compton origin of the X-rays in which the break frequency
varies between the optically thick and thin regime of the jet spectrum. We also
highlight the similarities and differences between optical/X-ray and IR/X-ray
correlations which suggest a jet origin of the near-IR emission in the hard
state while the optical is more likely dominated by the blackbody emission of
the accretion disc in both hard and soft state. However we find a non
negligible contribution of 40 per cent of the jet emission in the V-band during
the hard state.
We finally concentrate on a soft-to-hard state transition during the decay of
the 2004 outburst by comparing the radio, IR, optical and hard X-rays light
curves. It appears that unusual delays between the peak of emission in the
different energy domains may provide some important constraints on jet
formation scenario.Comment: Accepted for publication in MNRAS, 12 pages, 8 figure
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