ASASSN-16ne follow-up and archival outburst detection

ATel #9759; D. Denisenko (Sternberg Astronomical Institute, Lomonosov Moscow State University), S. Korotkiy (Ka-Dar observatory; Noosfera foundation)
on 14 Nov 2016; 13:01 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)

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Rapidly rising optical transient ASASSN-16ne was announced by ASAS-SN project (Shappee et al., 2014) on 2016 Nov. 11 via Transient Name Server as AT 2016iad. The following photometry was reported by ASAS-SN: 2016 Nov. 05.64 UT, <17m (last non-detection); 07.64, 16.5; 10.64, 15.7; 11.63, 15.1. The object is located in Crater constellation at R.A. = 11 43 39.42, Decl. = -10 16 11.2 (galactic latitude is +49). This area of sky is not covered by SDSS. There is nothing at this position on the DSS plates and on their sum to the limiting magnitude ~21. Color-combined DSS finder chart centered at ASASSN-16ne coordinates is posted at http://scan.sai.msu.ru/~denis/ASASSN-16ne-JRIR.jpg (10'x10' FOV).

We have obtained the follow up observations of ASASSN-16ne remotely using iTelescope.Net's T21 instrument (0.43-m f/6.8 reflector equipped with 6-Mpix FLI CCD and f/4.5 focal reducer) located in Mayhill (New Mexico, USA). Five unfiltered images with 60-sec exposures were taken from 12:14 to 12:25 UT on 2016 Nov. 14. USNO-B1.0 0797-0223782 (11 43 41.0 -10 15 50) located 32" NE of ASASSN-16ne was used as a reference star with Vmag=15.59 from APASS DR9 (Henden et al., 2016). The magnitude measured at 2016-11-14.513 UT (JD=2457707.013) is 15.26+/-0.04.

We have also checked the archival images of this field by NEAT project (S. Pravdo et al.) available at SkyMorph website. The object was detected on three 20-sec exposures taken on 2002 Mar. 23 at 07:54:51, 08:10:26 and 08:26:37 UT. Coordinates measured from the combined image (11 43 39.37 -10 16 11.4) are in excellent agreement with ASASSN-16ne. No minor planets were found at this position at 2002 03 23.34 UT, and the object did not move in 32 minutes. The magnitude measured from the sum of three NEAT images on 2002-03-23.34 UT (JD=2452356.840) is 18.9m. The object was not present on 3x60-sec exposures obtained 9 days before, on 2002-03-14.46 UT (JD=2452347.966, limiting magnitude ~20), as well as on 3x20-sec exposures taken 13 days later (JD=2452369.728, m_lim~20.5). Comparison of NEAT images from 2002 Mar. 14, Mar. 23 and Apr. 05 is uploaded to http://scan.sai.msu.ru/~denis/ASASSN-16ne-NEAT-2002-anim.gif

We consider 2002 March 23 detection to be a previous outburst of ASASSN-16ne. Taking into account the absence of host galaxy at the position of this transient and previous outburst lasting less than 20 days, ASASSN-16ne is likely not a supernova, but a cataclysmic variable (dwarf nova with outburst amplitude more than 6m). The rising rate of the current outburst (1.4m over 4 days) appears to be too slow for typical UGSU and USWZ dwarf novae, being more consistent with that of AM CVn type variable (IBWD).

Follow up observations of this optical transient are encouraged, despite the unfavorable object position in the sky. The current elongation from the Sun is only 53 degree, but it improves every morning while the Sun moves towards the southern declinations.

Authors thank Education Support Foundation "Noosfera" for providing the access to iTelescope network.