A two-year monitoring campaign of Supergiant Fast X-ray Transients with Swift

TL;DR

This paper reports on a two-year Swift monitoring campaign of Supergiant Fast X-ray Transients, revealing their long-term behavior, duty cycle, and new outbursts through frequent soft X-ray observations.

Contribution

It presents the first extensive, high-sensitivity, panchromatic monitoring of SFXTs over two years, capturing their evolution and outbursts in unprecedented detail.

Findings

Identification of new outbursts during the campaign

Measurement of duty cycle and long-term properties of SFXTs

Enhanced understanding of SFXT evolution and activity patterns

Abstract

Swift is the only observatory which, due to its unique fast-slewing capability and broad-band energy coverage, can detect outbursts from Supergiant Fast X-ray Transients (SFXTs) from the very beginning and study their evolution panchromatically. Thanks to its flexible observing scheduling, which makes monitoring cost-effective, Swift has also performed a campaign that covers all phases of the lives of SFXTs with a high sensitivity in the soft X-ray regime, where most SFXTs had not been observed before. Our continued effort at monitorning SFXTs with 2-3 observations per week (1-2 ks) with the Swift X-Ray Telescope (XRT) over their entire visibility period has just finished its second year. We report on our findings on the long-term properties of SFXTs, their duty cycle, and the new outbursts caught by Swift during the second year.