Monitoring Supergiant Fast X-ray Transients with Swift. Rise to the outburst in IGR J16479-4514

Abstract

IGR J16479-4514 is a Supergiant Fast X-ray Transient (SFXT), a new class of High Mass X-ray Binaries, whose number is rapidly growing thanks to the observations of the Galactic plane performed with the INTEGRAL satellite. IGR J16479-4514 has been regularly monitored with Swift/XRT since November 2007, to study the quiescent emission, the outburst properties and their recurrence. A new bright outburst, reaching fluxes above 10${}^{-9}$ erg cm${}^{-2}$ s${}^{-1}$, was caught by the Swift/BAT. Swift immediately re-pointed at the target with the narrow-field instruments so that, for the first time, an outburst from a SFXT where a periodicity in the outburst recurrence is unknown could be observed simultaneously in the 0.2--150 keV energy band. The X-ray emission is highly variable and spans almost four orders of magnitude in count rate during the Swift/XRT observations covering a few days before and after the bright peak. The X-ray spectrum in outburst is hard and highly absorbed. The power-law fit resulted in a photon index of 0.98$\pm 0.07$, and in an absorbing column density of $\sim 5\times 10^{22}$ cm${}^{-2}$. These observations demonstrate that in this source (similarly to what was observed during the 2007 outburst from the periodic SFXT IGR J11215-5952), the accretion phase lasts much longer than a few hours.

Accepted for publication on Astrophysical Journal Letters. 5 pages, 4 figures

References in corpus (5)

• Unveiling supergiant fast X-ray transient sources with INTEGRAL
• Probing clumpy stellar winds with a neutron star
• An alternative hypothesis for the outburst mechanism in Supergiant Fast X-ray Transients: the case of IGR J11215-5952
• Swift/XRT observes the fifth outburst of the periodic Supergiant Fast X-ray Transient IGR J11215-5952
• IGR J11215-5952: a hard X-ray transient displaying recurrent outbursts

Cited by in corpus (5)

• Multiple flaring activity in the supergiant fast X-ray transient IGR J08408-4503 observed with Swift
• Monitoring Supergiant Fast X-ray Transients with Swift. Results from the first year
• Two years of monitoring Supergiant Fast X-ray Transients with Swift
• IGRJ16479-4514: the first eclipsing supergiant fast X-ray transient?
• The first broad-band X-ray study of the Supergiant Fast X-ray Transient SAXJ1818.6-1703 in outburst