AstroNote 2020-228

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2020-11-15 12:57:40
Type: Object/s-Discovery/Classification
Pan-STARRS Search for Kilonovae: discovery of a faint transient offset from 2MASXJ00085765-0836093 (75 Mpc)
Authors: S. J. Smartt, M. Fulton, K. W. Smith (QUB), K. C. Chambers, M. Huber (IfA, Hawaii), O. R. McBrien, S. Srivastav, D. R. Young, J. Gillanders, 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
We are carrying out the "Pan-STARRS Search for Kilonovae" 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).  Here we report the discovery of a (possible) intrinsically faint transient PS20kxg (AT2020zck) at a large offset from a potential host 2MASXJ00085765-083609 (redshift of z = 0.018, or d = 75 Mpc, from NED).  Its discovery magnitude (MJD = 59161.28) is w = 20.5 +/- 0.1, and hence an absolute magnitude of M_w = -14.0 +/- 0.1 (if associated with that galaxy). ZTF detected AT2020zck on 59164.3 at r = 20.2 +/- 0.3 and g = 19.9 +/- 0.3, and on the subsequent night at g = 20.65 +/- 0.3. Although the uncertainties are large, a rapid colour change is possible. The object is 22kpc offset from the possible host (if they are at a common redshift). Follow-up is needed to determine if this is an unusual transient at this distance.

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, arXiv:1612.05560). 

We report the discovery of a (possible) intrinsically faint transient PS20kxg (AT2020zck) with PS2.  It is offset from a possible host (14.6" N, 54.2" E) 2MASXJ00085765-0836093 which has a redshift of z = 0.108, or d = 75 Mpc (from NED).  The transient was discovered at MJD 59161.275 (2020-11-08 06:36 UTC) at mag w = 20.5 +/- 0.1. At this distance the absolute magnitude is M_w = -14.0 +/- 0.1 (assuming m-M = 34.4 and foreground exinction of  A_w = 0.1). 

ZTF detected AT2020zck (see lightcurve on Lasair, object ZTF20acppuiq ) on 59164.3 at r = 20.2 +/- 0.3 and g = 19.9 +/- 0.3, and the recent lightcurve points are given below. The uncertainties on the ZTF magnitudes are large, but could imply a large colour change. Non-detections by PS1, ATLAS and ZTF imply this is not a normal, old supernova in 2MASXJ00085765-0836093 . Given it is offset from the host (22 kpc projected), intrinsically faint and (possibly) an unusual colour change, follow-up is encouraged.

It could also be a background SN or foreground galactic outburst. There is no obvious distant host galaxy in the  PS1 3Pi grizy stacks, but a faint source marginally detected, is visible in our w-band reference stack. This could imply a background galaxy or satellite of 2MASXJ00085765-0836093. 

59111.478 w   PS2    >21

59158.227 r   ZTF    >19.8

59158.195 g   ZTF    >19.8

59160.400 o   ATLAS  >19.7 

59161.275 w   PS2    20.50 +/- 0.1

59164.253 g   ZTF    19.86 +/- 0.31

59164.277 r   ZTF    20.19 +/- 0.28

59165.171 g   ZTF    20.65 +/- 0.25

59165.212 r   ZTF    20.30 +/- 0.17

59167.372 w   PS1    20.35 +/- 0.07

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
TNS2020zck [PS20kxg]00:09:01.318-08:35:54.680.01800:09:01.327-08:35:54.70