INTEGRAL/IBIS observations of a hard X-ray outburst in high mass X-ray binary 4U 2206+54

Abstract

U 2206+54 is a wind-fed high mass X-ray binary with a main-sequence donor star. The nature of its compact object was recently identified as a slow-pulsation magnetized neutron star. INTEGRAL/IBIS observations have a long-term hard X-ray monitoring of 4U 2206+54 and detected a hard X-ray outburst around 15 December 2005 combined with the RXTE/ASM data.The hard X-ray outburst had a double-flare feature with a duration of $\sim$ 2 days. The first flare showed a fast rise and long time decaying light curve about 15 hours with a peak luminosity of $\sim 4\times 10^{36}$ erg s${}^{-1}$ from 1.5 -- 12 keV and a hard spectrum (only significantly seen above 5 keV). The second one had the mean hard X-ray luminosity of $1.3\times 10^{36}$ erg s${}^{-1}$ from 20 -- 150 keV with a modulation period at $\sim 5550$ s which is the pulse period of the neutron star in 4U 2206+54; its hard X-ray spectrum from 20 -- 300 keV can be fitted with a broken power-law model with the photon indexes ${\Gamma }_1\sim 2.3,{\Gamma }_2\sim 3.3$, and the break energy is $E_b\sim 31$ keV or a bremsstrahlung model of $kT\sim 23$ keV. We suggest that the hard X-ray flare could be induced by suddenly enhanced accretion dense materials from stellar winds hitting the polar cap region of the neutron star. This hard X-ray outburst may be a link to supergiant fast X-ray transients though 4U 2206+54 has a different type of companion.

4 pages, 5 figures, accepted for the publication in Astron. Astrophys

References in corpus (12)

• Unveiling supergiant fast X-ray transient sources with INTEGRAL
• Probing clumpy stellar winds with a neutron star
• IGR J18483-0311: an accreting X-ray pulsar observed by INTEGRAL
• Swift/BAT and RXTE Observations of the Peculiar X-ray Binary 4U 2206+54 - Disappearance of the 9.6 Day Modulation
• Discovery of a short orbital period in the Supergiant Fast X-ray Transient IGR J16479-4514
• Discovery of slow X-ray pulsations in the high-mass X-ray binary 4U 2206+54
• Spin-Down of the Long-Period Accreting Pulsar 4U 2206+54
• Discovery of a 30 day period in the supergiant fast X-ray transient SAX J1818.6-1703
• Further evidence for the presence of a neutron star in 4U 2206+54. INTEGRAL and VLA observations
• INTEGRAL and Swift/XRT observations of the SFXT IGR J16479-4514: from quiescence to fast flaring activity
• Evidence for a magnetic neutron star in high mass X-ray binary 4U 2206+54 with INTEGRAL/IBIS observations
• Discovery of X-ray Pulsations from the HMXB Source AXJ1749.1-2733

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• On the possibility of disk-fed formation in supergiant high-mass X-ray binaries
• Spatial and temporal tuning in void models for acceleration
• Spin and Spectral Variations of Peculiar High-Mass X-ray Binary 4U 2206+54
• On the spin-down mechanism of the X-ray pulsar 4U 2206+54
• Monte-Carlo simulations on possible collimation effects of outflows to fan-beamed emission of ultraluminous accreting X-ray pulsars