Swift observations of SDSS J141118.31+481257.6 during its first detected outburst

ATel #11668; L. E Rivera Sandoval, T. Maccarone (Texas Tech University)
on 23 May 2018; 15:55 UT
Credential Certification: Liliana Rivera Sandoval (liliana.rivera@ttu.edu)

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We report Swift observations of the AM CVn-type system SDSS J141118.31+481257.6 (RA=14:11:18.31, Dec=+48:12:57.6) during its first ever recorded outburst. The system was detected by Tadashi Kojima on 2018-May-20 with a V magnitude of 12.6 +- 0.2 (http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/22176), an increase of ~7 mags compared to any previous measurement in the same filter.

Using the XRT and UVOT instruments, we performed short observations (~1ks each) from 2018-May-21 to 2018-May-23. The source was found to have an X-ray count rate in the 0.3-10 keV band of (3.8 +/- 0.7)E-02 cts/s, (3.0 +/- 0.6)E-02 cts/s and (1.6 +/- 0.5)E-02 cts/s, respectively. In quiescence, the system has a count rate of (3.3 +/- 1.1)E-03 cts/s in the same energy band (Evans et al. 2014).

On the Swift/UVOT Vega-based photometric system, the object had <11 mags (saturated) in the filter UVW1 on 2018-May-21, 11.53 +/- 0.02 mags in the UVM2 filter on 2018-May-22, and 12.38 +/- 0.02 mags also in UVM2 on 2018-May-23 (magnitudes are uncorrected for Galactic reddening). A comparison to archival observations taken during quiescence shows that the system was brighter by at least 7 mags in UVW1 on 2018-May-21, and it is currently brighter by ~5.3 mags in UVM2. During outburst, the increase in the optical and UV flux is much higher than in the X-ray flux. This suggests that the system is in a high state with an optically thick accretion flow. However, the current fluxes have decreased compared to the ones of 2018-May-21 and May-22, indicating that the object might be returning to quiescence.

We thank the Swift team for approving and promptly executing the ToO.