HST Pre-Discovery Detections of AT 2017jmk, a Probable Supernova in NGC 7541

ATel #11119; Subo Dong, Subhash Bose (KIAA-PKU)
on 1 Jan 2018; 09:06 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Subo Dong (dongsubo@pku.edu.cn)

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Supernova candidate AT 2017jmk in NGC 7541 (z = 0.008969 via NED) was discovered by the POSS team (R. Gagliano, R. Post, E. Weinberg, J. Newton, T. Puckett) at 18.5 mag on 2017-12-31 01:57:14. We detect AT 2017jmk using HST WFC3 archival images (HST Proposal 15145, PI: Riess) taken around UT 2017-12-30.5 with F160W, F350LP and F814W filters. The top-left two panels of this figure show the HST F160W and F350LP images on UT 2017-12-30. The red circle has a radius of 1" and is consistent with the position of the transient reported by the POSS team (RA: 23:14:45.10 Dec: +04:31:51.10). The centroid of AT 2017jmk is at position (551.59, 276.52) on the 2017-12-31 WFC3 F160W image (idgg9b020_drz.fits). Using Pyraf and WFC3 zero points, we derive preliminary magnitudes in the ST magnitude system:

 
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 JD           | Filter | ST Mag |              
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2458117.99776 | F814W  | 18.5   | 
2458117.98169 | F350LP | 18.4   |    
2458118.05069 | F160W  | 19.1   |     
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The field has been repeatedly monitored by WFC3 as part by an ongoing HST program (Proposal 15145, PI: Riess) with observations in F160W, F350LP, F555W and F814W filters from 2017-09-21 to 2017-12-30. Older HST archival images from ACS, WFPC2 and NICMOS also exist for NGC 7541. We show in the figure several HST archival images in this field: WFC3 F160W taken on 2017-12-30, WFC3 F350LP on 2017-12-30, WFC3 F350LP on 2017-12-23, WFC3 F350LP on 2017-12-16, WFC3 F350LP on 2017-09-21 (HST Proposal 15145, PI: Riess) and ACS F814W on 2006-08-09 (HST Proposal 10769, PI: Kaaret). There is no obvious source detected on the HST images taken on 2017-12-23 and before, while more careful analysis can be carried out on these images using the precise (relative) astrometry derived from the 2017-12-30 HST detections. These HST data can potentially provide excellent near-explosion and pre-explosion constraints on the probable supernova AT 2017jmk and its progenitor.

Applying a distance module of 32.9 derived using SN Ia 1998dh exploded in NGC 7541 (Jha et al. 2007) and A_V = 0.2 (via NED), the absolute magnitude AT 2017jmk at discovery was at about -14.6 mag (apparent magnitude 18.5 mag), suggesting that it is possibly young. Follow-up observations are strongly encouraged.