TITLE: GCN CIRCULAR NUMBER: 18390 SUBJECT: LIGO/Virgo G184098: MASTER OTs detection and Scenario Machine prediction DATE: 15/10/04 19:00:08 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M. Lipunov (Lomonosov Moscow State University, SAI MSU), E.S. Gorbovskoy (SAI Lomonosow MSU) and D. Buckley(SAAO) behalf MASTER-team MASTER-SAAO twin robotic telescope (MASTER-Net: http://observ.pereplet.ru, FOV= 2x4 square degrees) located in SAAO was starting survey on the aLIGO trigger G184098 error-box 220517 sec after trigger time at 2015-09-16 20:18:11 UT. The 5-sigma upper limit on our sets is about 18.4 mag - 19.9 mag (GCN ) . At this first night we observed 212 square degrees by 3 images for each field during ~2 hours. There are LMC near the center error box and Milky Way at the east edge of the error box. Because large number of stars the redaction is delay and continueted. The cover map is available at http://master.sai.msu.ru/static/G184098.png . We started from the left edge of the error box as its rise (see previous MASTER Circular). MASTER-SAAO continued survey in the coming days. By 22 September, we received about 900 images inside the error box. Each area was covered several times. The full time cover map is available at http://master.sai.msu.ru/static/G184098_full.png The total probability by covered fields is about 58%. We found two OT inside error box ( http://master.sai.msu.ru/static/G184098_tra.png). Unfortunatelly, both transient fall to common MASTER DATA Base OTs and automatically was published in usual way (ATel #8065 http://www.astronomerstelegram.org/?read=8065). I am sorry (VL). This is connected with new type error box (without edge) in our robotic system and some mixing between alerts and survey observations. 1) MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 04h 09m 38.68s -54d 13m 16.9s on 2015-09-16.87912 UT. The OT unfiltered magnitude is 17.3m (the limit is 17.8m). The OT is seen in 5 images. There is no minor planet at this place. We have reference image without OT on 2015-02-14.89772 UT with 20.0 unfiltered magnitude limit. This PSN is in 0.9"W and 3.6"N from the center of galaxy PGC421615 (Btot=18.4m). Spectral observations are required. The discovery and reference images are http://master.sai.msu.ru/static/OT/040938.68-541316.9.png There is no published spectrum and distance. 2)(ATel #8087 http://www.astronomerstelegram.org/?read=8087) MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 07h 07m 47.72s -67d 22m 05.6s on 2015-09-21.99535 UT. The OT unfiltered magnitude is 16.9m (limit 19.2m). The OT is seen in 8 images. There is no minor planet at this place. We have reference images without OT on 2014-12-25.02683 UT with unfiltered magnitude limit 20.0m, on 2015-02-24.863UT with m_lim=20.3. There is USNO-B1 star (0226-0200013) in 3.8" with blue B2=20.97 and R2=20.01, but AAVSO decided that our OT is this star - dwarf nova U Gem-type (accreting white dwarf in binary system). http://www.aavso.org/vsx/index.php?view=detail.top&oid=410052. Spectral observations are required. The discovery and reference images are available at http://master.sai.msu.ru/static/OT/MASTEROTJ070747.72-672205.6.png The possible BH nature of the LIGO/Virgo G184098 alert (GCN 18388) is in agreement with Scenario Machine Binary Population Synthesis prediction (Lipunov, V. M.; Postnov, K. A.; Prokhorov, M. E., First LIGO events: binary black holes mergings, New Astronomy, Volume 2, Issue 1, p. 43-52, 1997, http://www.sciencedirect.com/science/article/pii/S1384107697000079).See also Lipunov et al., 1997, Black holes and gravitational waves: Possibilities for simultaneous detection using first-generation laser interferometers, Astronomy Letters, vol.23, 1997, 492-497.