Swift observation of Nova Scuti 2019 (ASASSN-19aad)

ATel #13252; K. V. Sokolovsky, E. Aydi, L. Chomiuk, A. Kawash, J. Strader (MSU), K. Mukai (NASA/GSFC), K. Z. Stanek, C. S. Kochanek, Z. S. Way (OSU), B. J. Shappee (UoHawaii)
on 31 Oct 2019; 19:14 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Nova Scuti 2019 (ASASSN-19aad, V659 Sct) was discovered by the ASAS-SN survey (Shappee et al. 2014, ApJ, 788, 48) on 2019-10-29.05 UT at g=11.5. The transient was independently reported by K. Nishiyama, F. Kabashima (2019-10-29.397) and H. Nishimura (2019-10-29.421, CBET #4690). Visual, DSLR and CCD observations reported to the AAVSO together with follow-up ASAS-SN photometry show that the object was getting brighter reaching V=8.66 on 2019-10-30.074 and V=8.36 on 2019-10-30.750. The latest estimates suggest that it has passed peak brightness and has declined to visual magnitude 9 as of 2019-10-31.7. The object was classified as a He/N type Galactic nova based on observations with the 2-m Liverpool Telescope on 2019-10-29.81 (ATel #13241) and the 2-m Himalayan Chandra Telescope on 2019-10-29.54 (ATel #13245).

Swift observed Nova Scuti 2019 for 1.9ks on 2019-10-30.257 (1.2 days after the ASAS-SN detection). A marginally significant (2 sigma) source is identified on the Swift/XRT PC mode image at the nova position. However, its count rate of 0.004 +/-0.002 cts/s is consistent with the expected XRT optical loading from a magnitude 8 star of a late spectral type. Indeed, the simultaneous Swift/UVOT observations detect the nova at the ultraviolet magnitude of UVM2=14.27 +/-0.02 (Vega system). Comparing it to the AAVSO V band measurement taken 0.18 days earlier (and neglecting variability over that time), we estimate that the nova is affected by the Galactic reddening of E(B-V)=0.9 making its color similar to that of a late-type star. Here we assume the intrinsic (B-V)_0=0.0 for a nova around maximum light (Hachisu & Kato, 2016, ApJS, 223, 21) and use the relation between E(B-V) and the extinction in the UVOT bands from Roming et al. 2009, ApJ, 690, 163. We interpret the measured Swift/XRT count rate as an upper limit on the nova X-ray emission, corresponding to the unabsorbed 0.3-10 keV flux of 2x10^-13 ergs/cm^2/s for the fiducial HI column density of 3x10^20 cm^-2 and power law emission with the photon index of 1.7. We also use the Swift/UVOT image to measure the nova astrometric position relative to UCAC3 (Zacharias et al. 2010, AJ, 139, 2184) stars in the field of view: 18:39:59.70 -10:25:41.9 +/-0.2" J2000

We thank the Neil Gehrels Swift Observatory team and PI, Brad Cenko, for scheduling these ToO observations. We thank the AAVSO observers BLD, DMIB, FRF, HCW, HMB, KWO, MMAO, RFDA for their valuable contributions.

CBAT Transient Object Followup Reports page for Nova Scuti 2019