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Swift Observation during the 2019 outburst of Swift J1357.2-0933

ATel #12816; Aru Beri (IISER Mohali), Rudy Wijnands, T. Russell , Nathalie Degenaar, J. van den Eijnden (U. Amsterdam), Poshak Gandhi , J. A. Paice, Diego Altamirano (U. Southampton), M. Armas Padilla (Instituto de Astrofisica de Canarias)
on 29 May 2019; 12:58 UT
Credential Certification: Aru Beri (aru.beri8@gmail.com)

Subjects: X-ray, Black Hole, Transient

Referred to by ATel #: 12821, 14573, 14729

The Galactic black-hole candidate Swift J1357.2-0933 has been reported to be in a new outburst by the Zwicky Transient Factory (ZTF; Bellm et al 2019, PASP 131, 018002). Where optical monitoring (ATel #12796) suggests the source was in outburst at least as early as 2019 March 21.

On 2019 May 23 the NICER X-ray telescope detected Swift J1357.2-0933 with a 0.3-10 keV flux of 1.1e-11 erg/s/cm^2 (Atel #12801). In addition, flaring activity was reported from the source.

The Swift X-ray telescope observed Swift J1357.2-0933 on 2019 May 27. Swift/XRT observed for ~1.5 ks in Windowed Timing mode. The target was detected, with an average source count rate of ~0.07 c/s (0.5-10 keV) in the WT data.

These data were fit using an absorbed*power-law model and using W-statistics (background subtracted Cash statistics; Wachter et al. 1979). Fixing the N_H to 1.2x10^{20}/cm^2 (Armas Padilla et al. 2013), we measure a power-law index of 1.61+/-0.4 and an unabsorbed 0.5-10keV flux of (7.13+/-0.02)x 10^-12 erg/s/cm^2. This flux translates to an X-ray luminosity of L_X (0.5-10 keV)= 2.1x10^{34} (D/5)^2 erg/s.

The source was also detected with Swift/UVOT at the following magnitudes in the AB system: UVW2 = 15.64 +/- 0.04 UVM2 = 15.56 +/- 0.04, (not corrected for extinction).

Further Swift observations are planned.

Acknowledgement: We thank the Swift team members for scheduling the ToO observation.