Flaring Red Dwarf with 8-mag Amplitude in Ursa Major

ATel #12699; H. Sielewicz (Comet Observatory, Lavoriskes, Lithuania), D. Denisenko (SAI MSU, Russia)
on 27 Apr 2019; 19:55 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)

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We report the discovery of the large amplitude flaring red dwarf in Ursa Major. The object was detected on 2019 Apr. 22 during the observations of M101 galaxy with the 0.465-m f/3 Deltagraph + ASA corrector and 9-Mpix 12-micron FLI ML09000 CCD giving a 1.5x1.5 square degree field of view. Observations were made using Astronomik L-1 UV IR blocking filter. A total of 10 images with 60-sec exposures were obtained on Apr. 22.86-22.92 UT, the typical upper limit being 19.5m. The new bright object has appeared on the second image obtained at 20:52 UT. It was not present on the first exposure at 20:43 UT and has faded below the detection limit on the eighth image at 21:40 UT. The photometry with UCAC-3 R zero point is given in the table.

Obs-Date, JD Magnitude SNR
2458596.36351 <19.6 N/A
2458596.36949 15.785 76.95
2458596.37462 16.904 33.91
2458596.37719 17.461 22.78
2458596.38023 17.403 24.42
2458596.38265 18.027 14.09
2458596.39433 19.645 3.35
2458596.40314 <19.6 N/A

The coordinates of the new object averaged from four images are: R.A. = 14 04 11.63, Decl. = +53 35 05.4 (J2000.0). There is a faint red star at this position on PanSTARRS-1 images in i, z and y filters. It is present in SDSS, CFHT Legacy Survey and WISE catalog with the following IDs and magnitudes: SDSS J140411.62+533505.0 (g=24.21+/-0.57 r=23.71+/-0.45 i=20.98+/-0.07 z=19.34+/-0.06), CFHTLS 1334_127622 (g=25.81+/-0.22 r=23.66+/-0.06 i=20.92+/-0.01 z=19.61+/-0.01), AllWISE J140411.66+533505.2 (W1=16.13+/-0.05 W2=16.11+/-0.13). Thus, the amplitude of flare is about 7.9 mag, from 23.7 to 15.8, or ~1500 times. The variable was designated Sielewicz 1. The light curve of 2019 Apr. 22 flare is uploaded to http://scan.sai.msu.ru/~denis/Sielewicz1-LC.gif

Sielewicz 1 is an extreme variable of UV Ceti type with the flare amplitude among the ten largest observed so far. The first extreme amplitude red dwarf flare was discovered by I. Sergey on 2011 Feb. 15, see GCN #11739. Its amplitude in the white light was about 9 magnitudes. The light curve of OT 110215 in Cepheus was followed for 1.5 hours. Since then such flares with amplitudes ~8m or larger are observed approximately once a year, see the list at http://scan.sai.msu.ru/~denis/superflares.html (very likely incomplete). However, most flares found by surveys have 3-4 positive detections due to the observing cadence. OT 110215 still remains the giant red dwarf flare with the best observed light curve structure. Its amplitude was likely surpassed only once, by ASASSN-16ae (ATel #8553) that has increased its brightness by 10 magnitudes, or ~10000 times.

The variable star Sielewicz 1 is located in the relative vicinity of M101 galaxy, 46' south of its nucleus and 9' west-south-west of NGC 5474. M101 is among the popular objects frequently imaged by astrophotographers and supernova hunters. Search for the past flares of this red dwarf on archival images is strongly recommended. Discovery image is posted at http://scan.sai.msu.ru/~denis/Sielewicz1-20190422.jpg

Extreme Flares from Red Dwarfs