AstroNote 2020-168

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2020-08-31 15:07:04
Type: Object/s-Discovery/Classification
PS20gxa (AT2019aafl): PSST discovery of a super-long rising transient
Authors: T.-W. Chen (Stockholm), S. J. Smartt, K. W. Smith, D. R. Young, O. McBrien, J. Gillanders. S. Srivastav, D. O'Neill, P. Clark, S. Sim (Queen's University Belfast), K. C. Chambers, T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin, T. Lowe, E. Magnier, A. Schultz, R. J. Wainscoat, M. Willman (IfA, University of Hawaii), D. E. Wright (University of Minnesota)
Source Group: Pan-STARRS1
Keywords: Supernova
We report the discovery of transient object PS20gxa (AT2019aafl) as part of the Pan-STARRS Survey for Transients (PSST) at a current magnitude of w = 21.3. Through precovery detections and forced photometry, the transient has a remarkably long rise, lasting more than 576 days (in observed frame). It is offset from the core of its host galaxy, SDSS J013257.19+182049 which is faint and red. The host has a possible photoZ = 0.63 +/- 0.05, suggesting an absolute magnitude of M_w = -21.8. This is a possible very luminous supernova with a remarkably long rise time and follow-up spectroscopic and photometric observations are encouraged.

We report the discovery of the following transient object as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at (see Chambers et al. arXiv:1612.05560, Huber et al. ATel #7153). We release AstroNotes for transients of note (e.g. closer than 100Mpc, unusually faint or luminous, or rapidly evolving). 

The new transient source, is likely associated with the faint, red galaxy SDSS J013257.19+182049.5. We discovered PS20gxa (AT2019aafl) on MJD 59084.52  == 2020-08-23.52, at w = 21.3 +/- 0.10. However pre-discovery detections and forced photometry show that it was first detected on MJD = 58508 at w = 21.9 +/- 0.1 and has been rising smoothly (4 intermediate epoch detections) for at least 576 days in the observed frame. 

PS20gxa is slightly offset by 0.25 arcsec south, 0.28 arcsec east from the centre of the extended source and likely host SDSS J013257.19+182049.5. At r = 21.4 (r_P1 = 21.6 in Pan-STARRS DR2) the host galaxy has no spectroscopic redshift. The SDSS DR15 photoZ is z=0.626 +/- 0.053. This would imply a current absolute magnitude of M_w = -21.8 (assuming m-M = 42.92 and A_r = 0.15) and the lighcurve implies it may still be rising. If it were at this redshift, the restframe rise time would be at least 350 days. The longest observed rise time for a superluminous supernova is around 125 days (PS1-14bj; Lunnan et al. ApJ, 831, 144). 

We note another a nearby galaxy (8.4 arcsec away), SDSS J013256.64+182047.4, with a reported spectroscopic redshift at z=0.723 on the SDSS SAS (although the features of the BOSS spectrum on which this is based are not convincing).  

The  red nature of the host, its morphology, transient offset and long rise time all point to a very luminous, high redshift transient with an extraordinarily long  rise. Given the uncertainty in the photoZ, it could concievably be beyond z > 1. Followup spectroscopic classification and photometric follow-up are encouraged. 

The discoveries from this program are a byproduct of the Pan-STARRS NEO survey observations. Operation of the Pan-STARRS1 and Pan-STARRS2 telescopes is primarily supported by the National Aeronautics and Space Administration under Grant No. NNX12AR65G and Grant No. NNX14AM74G issued through the SSO Near Earth Object Observations Program. Data are processed at Queen's University Belfast enabled through the STFC grants ST/P000312/1 and ST/T000198/1. 


Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2019aafl [PS20gxa]01:32:57.198+18:20:49.5501:32:57.198+18:20:49.55AGN0.811