AstroNote 2020-96

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DRAFT
2020-05-03 17:17:10
Type: Object/s-Discovery/Classification
Pan-STARRS Search for Kilonovae: PS20cph (AT2020inm) is a faint and fast transient in M104
Authors: S. Srivastav, S. J. Smartt, K. W. Smith (QUB), K. C. Chambers, M. Huber (IfA, Hawaii), O. McBrien, D. R. Young, J. Gillanders, D. O'Neill, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, C.-C. Lin, T. Lowe, E. Magnier, A. Schultz, R. J. Wainscoat, M. Willman (IfA), T.-W. Chen (Stockholm), D. E. Wright (University of Minnesota), C. Stubbs (Harvard), A. Rest (STScI)
Source Group: Pan-STARRS1
Abstract:
We report the Pan-STARRS2 discovery of PS20cph (AT2020inm), an intrinsically faint transient in the likely host M104. Combined PS1 and PS2 w-band photometry indicates a rapid rise and fade. At an absolute magnitude of -10.3, this is possibly a nova and would be on the extreme end of the MMRD (maximum magnitude vs rate of decline relationship e.g. see Della Valle & Izzo 2020, arXiv:2004.06540).

We are carrying out the "Pan-STARRS Search for Kilonovae" which is a focused search for intrinsically faint transients, or rapidly evolving transients in galaxies which are closer than 200 Mpc in the ongoing Pan-STARRS Near Earth Object surveys (see Smartt et al. AstroNote 2019-48 for details). 

In normal survey mode, Pan-STARRS takes 4 x 45s exposures in w, i or z each night reaching 5 sigma magnitudes of w<22, i<21 and z<20.5 in each frame (see Chambers et al. 2016, 1612.05560). 

We draw attention to PS20cph (AT2020inm) in the nearby host galaxy M104, discovered by Pan-STARRS2. It was discovered on MJD 58965.35 (2020-04-26.35) at a magnitude of w = 20.03 +/- 0.10. It was also detected in Pan-STARRS1 data either side of the PS2 discovery on MJD 58961.37 (at w = 22.24 +/- 0.34, from a forced photometry measurement at the position) and again on MJD 58966.32 (at w = 20.9 +/- 0.50).  We give a large error because this PS1 detection is close to a chip gap (masked region), and while the transient is clearly visible the photometry has a large systematic error. We provide a lightcurve and finder attached. 

This indicates a rapid rise (at least ~2 mags in a maximum of 5 days) and rapid decline (between ~0.4 to 0.9 mag in 1 day). The transient is not detected in a subsequent 20 min r-band exposure (limiting magnitude of r ~ 19.5 due to high background counts) on MJD 58971.88 obtained at the Liverpool Telescope (Steele et al. 2004). PS1 followup optical photometry could not be carried out due to proximity with the Moon. 

Adopting a distance modulus of 30.2 +/- 0.6 mag for M104 (from NED), the absolute magnitude for the PS2 detection is w = -10.3 +/- 0.6.  This is possibly a nova and would be on the extreme end of the MMRD (maximum magnitude vs rate of decline relationship e.g. see Della Valle & Izzo 2020, arXiv:2004.06540)

Followup photometric and spectroscopic observations are encouraged to determine if it is indeed a nova or some other unusual faint transient. 

 

Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2020inm [PS20cph]12:39:44.477-11:38:16.9812:39:44.482-11:38:16.93