OGLE-IV EARLY WARNING SYSTEM - 2019 SEASON


The Early Warning System (EWS) was designed for detection of microlensing events in progress and successfully implemented during the first phase of the OGLE experiment (Udalski et al. 1994, Acta Astron., 44, 227). During 1994 and 1995 observing seasons, this system detected 8 events. On May 6, 1998, the EWS system was reimplemented for the second phase of the OGLE experiment: OGLE-II. In 1998-2000 observing seasons of OGLE-II, about 170 microlensing events were discovered by EWS:

In April/May 2002 the new EWS system was implemented for the third phase of the OGLE project - OGLE-III. During the OGLE-III observing seasons the EWS system discovered the following number of microlensing event candidates:


In May 2011 new version of the EWS system was implemented for the fourth phase of the OGLE project - OGLE-IV. During the OGLE-IV observing seasons the EWS system discovered the following number of microlensing event candidates:


The Early Warning System implementation for OGLE-IV is very similar to its OGLE-III version. OGLE photometric data pipeline is based on Difference Image Analysis (DIA) photometry (Alard and Lupton 1998, ApJ, 503, 325, Alard 2000, Aston. Astrophys. Suppl. Ser., 144, 363, Wozniak 2000, Acta Astron., 50, 421). DIA photometry ensures better quality photometry in dense stellar fields compared to the classical approach with the profile fitting photometry.

Currently 51 OGLE-IV Galactic bulge fields containing about 300 million stars are regularly observed for microlensing and analyzed by OGLE-IV EWS: color marked fields in this map. See also the OGLE-IV Galactic bulge map for details.

The EWS analyzes photometry of all stars in the field and flags a star when it is detected in the difference images four times in a row. For microlensing event detection only objects increasing brightness are marked. Initial filtering masks the objects which were detected in difference images during the previous observing seasons (3-10% of all stars in the frame) to avoid false signals by variable stars.

The light curves of flagged stars are inspected visually, their positions on the recent CCD frames are checked for bad pixels, bleeding columns, very bright neighboring stars etc. If a star passes all these checks, it is announced as a microlensing candidate.

The second detection channel of microlensing events is based on objects stored in the OGLE databases as new objects, that is not registered as stellar on the reference images. The source stars of these events are usually below the standard threshold of stellar detection. Microlensing candidates from this channel can be recognized by letter N at the end of star number and are also described in Remarks record.

One has to remember that we cannot guarantee that all alerted stars are indeed true microlensing events. However, our experience from the previous years ensures that the number of false alerts should be relatively small.


So far, the EWS system has detected 71 candidate microlensing events in the 2019 observing season. The table given below provides interactive WWW access to the finding charts, photometry data and other information about all events. Currently ongoing events are marked with . Particularly interesting events are marked with .


Microlensing events data can also be found on Anonymous FTP.


There is also a mailing list providing on-line notification on the detected events. Astronomers interested in follow-up observations and willing to receive e-mail notification, should fill out subscribe/unsubscribe form. If you have any questions or comments, send us a message.


The following table contains basic parameters of the candidate events as well as the links to the WWW pages with finding charts, light curve plots and photometric data. The microlensing light curve model is a simple point mass approximation with blending to give a preliminary information on the event in progress. Blending is included only when (a) fbl + three times the formal error is less than 1.00 and (b) fbl is larger than its formal error. Please note that some of the fit parameters may change considerably when the event develops. No parameters are given for a possible binary microlensing. Microlensing light curve model fit parameters have following meaning:

The OGLE-IV interference I-band filter very closely reproduces the standard system. The photometric data are, however, not calibrated. They were just shifted to approximate the I-band system magnitudes. We estimate that the difference should not be larger than +/-0.1 mag. The data will eventually be calibrated but this will not happen soon. Star numbers within the field are also likely to change, because we plan to re-run photometric data pipeline on all the collected data when we have more good frames to replace our current provisional reference images (time scale of a few years). However, our "lens" notation, e.g., OGLE-2011-BLG-0001, will be kept for good. Please note that due to expected number of microlensing detections exceeding one thousand the event numbering in OGLE-IV consists of four digits.

The most RECENT and PREVIOUS updates of the OGLE-IV microlens database containing lens IDs and recent photometry.


The OGLE EWS photometry is provided here for informative purposes only to facilitate the microlensing community monitoring the on-going events and follow up observations. Please contact us if you want to use the data for publication. We may require to be co-authors when our photometry is important for analysis or refuse its usage if we are currently working or plan to work on the event.

When referring to the OGLE EWS system, please cite the paper by Udalski et al. 2015, Acta Astron., 65, 1 and provide the WWW address of the EWS system or the OGLE WWW home page.


Event Field Star No RA (J2000) Dec (J2000) Tmax (HJD) Tmax (UT) tau Umin Amax Dmag fbl Ibl I0
2019-BLG-0001 BLG500.01 179275 17:53:50.46 -29:08:57.9 2458529.870 2019-02-15.37 47.589 0.212 4.801 1.703 0.200 17.266 19.011
2019-BLG-0002 BLG500.02 152053 17:53:18.46 -28:58:01.9 2458525.463 2019-02-10.96 2.056 0.524 2.098 0.805 1.000 15.998 15.998
2019-BLG-0003 BLG500.03 34368 17:52:54.94 -29:00:36.2 2458484.590 2019-01-01.09 40.462 0.483 2.248 0.879 1.000 18.292 18.292
2019-BLG-0004 BLG500.04 28075 17:52:11.02 -29:03:02.7 2458523.572 2019-02-09.07 9.560 0.000 79744 12.254 0.172 19.770 21.684
2019-BLG-0005 BLG500.09 68592 17:54:08.38 -28:49:09.7 2458524.541 2019-02-10.04 11.627 0.671 1.731 0.596 1.000 18.584 18.584
2019-BLG-0006 BLG500.09 103865 17:54:08.08 -28:38:03.8 2458521.900 2019-02-07.40 13.396 0.541 2.046 0.777 1.000 19.362 19.362
2019-BLG-0007 BLG500.11 135730 17:52:23.68 -28:53:34.7 2458530.344 2019-02-15.84 9.010 0.370 2.842 1.134 1.000 18.977 18.977
2019-BLG-0008 BLG500.27 16035 17:53:38.69 -28:08:32.3 2458556.511 2019-03-14.01 68.451 0.504 2.167 0.840 1.000 18.373 18.373
2019-BLG-0009 BLG501.03 38167 17:52:58.94 -30:11:46.2 2458522.692 2019-02-08.19 85.758 0.004 233.5 5.921 0.078 19.064 21.837
2019-BLG-0010 BLG501.09 157250 17:53:53.66 -29:52:44.9 2458535.364 2019-02-20.86 15.563 1.133 1.261 0.252 1.000 13.683 13.683
2019-BLG-0011 BLG501.12 66879 17:51:55.92 -29:59:23.1 2458552.396 2019-03-09.90 68.474 0.481 2.255 0.883 1.000 16.103 16.103
2019-BLG-0012 BLG501.19 68431 17:53:27.09 -29:45:19.4 2458523.194 2019-02-08.69 9.343 1.424 1.152 0.154 1.000 16.689 16.689
2019-BLG-0013 BLG501.23 108138 17:50:10.30 -29:42:38.8 2458568.289 2019-03-25.79 59.818 0.000 7488.4 9.686 1.000 18.362 18.362
2019-BLG-0014 BLG501.29 105125 17:51:54.51 -29:18:14.7 2458633.075 2019-05-29.57 248.453 0.014 69.011 4.597 0.789 19.573 19.830
2019-BLG-0015 BLG504.13 110620 17:56:48.09 -28:17:08.4 2458525.366 2019-02-10.87 103.913 0.954 1.376 0.347 1.000 17.471 17.471
2019-BLG-0016 BLG504.14 37828 17:56:23.81 -28:04:09.7 2458517.361 2019-02-02.86 71.376 0.000 22167 10.864 0.118 18.891 21.210
2019-BLG-0017 BLG504.27 72160 17:59:03.52 -27:32:49.2 2458587.489 2019-04-13.99 131.121 0.000 20948 10.803 1.000 17.982 17.982
2019-BLG-0018 BLG505.02 81216 17:59:04.81 -29:40:22.6 2458524.435 2019-02-09.94 6.365 0.909 1.415 0.377 1.000 18.337 18.337
2019-BLG-0019 BLG505.03 144059 17:58:09.41 -29:41:21.3 2458544.137 2019-03-01.64 21.611 0.305 3.391 1.326 1.000 16.457 16.457
2019-BLG-0020 BLG505.06 11971 17:56:21.13 -29:44:53.7 2458524.822 2019-02-10.32 11.376 1.556 1.121 0.124 1.000 15.634 15.634
2019-BLG-0021 BLG505.18 21807 17:59:59.60 -29:04:11.2 2458523.827 2019-02-09.33 35.423 0.129 7.798 2.230 0.498 18.452 19.210
2019-BLG-0022 BLG505.24 85160 17:55:35.21 -29:00:17.2 2458594.809 2019-04-21.31 48.170 0.000 4296.7 9.083 1.000 16.664 16.664
2019-BLG-0023 BLG506.18 132357 17:59:32.38 -30:09:35.5 2458521.941 2019-02-07.44 13.359 1.158 1.249 0.241 1.000 16.033 16.033
2019-BLG-0024 BLG506.22 144415 17:56:29.97 -30:14:07.0 2458531.047 2019-02-16.55 12.828 0.032 30.894 3.725 1.000 15.234 15.234
2019-BLG-0025 BLG511.20 25257 18:04:01.25 -27:13:37.8 2458526.810 2019-02-12.31 16.691 0.006 156.3 5.485 0.614 18.485 19.014
2019-BLG-0026 BLG511.30 20564 18:02:36.95 -26:50:57.2 2458498.498 2019-01-15.00 38.112 0.867 1.456 0.408 1.000 17.226 17.226
2019-BLG-0027 BLG511.31 45957 18:01:45.65 -26:52:17.5 2458533.608 2019-02-19.11 10.964 1.773 1.085 0.089 1.000 15.891 15.891
2019-BLG-0028 BLG512.11 120146 18:03:45.73 -28:53:00.5 2458523.508 2019-02-09.01 7.844 0.018 56.632 4.383 1.000 19.397 19.397
2019-BLG-0029 BLG512.15 28690 18:01:17.18 -28:43:12.6 2458510.315 2019-01-26.82 13.437 0.000 22303 10.871 1.000 16.981 16.981
2019-BLG-0030 BLG512.22 163916 18:02:19.36 -28:20:14.8 2458560.726 2019-03-18.23 55.255 0.832 1.494 0.436 1.000 17.653 17.653
2019-BLG-0031 BLG512.27 335 18:04:43.14 -28:15:39.7 2458508.958 2019-01-25.46 14.794 0.944 1.385 0.353 1.000 16.265 16.265
2019-BLG-0032 BLG512.31 118842 18:01:34.88 -28:12:03.5 2458526.601 2019-02-12.10 21.265 0.468 2.308 0.908 1.000 19.526 19.526
2019-BLG-0033 BLG521.29 99418 18:08:38.26 -30:03:38.7 2458668.108 2019-07-03.61 121.222 0.000 6260.3 9.491 1.000 15.652 15.652
2019-BLG-0034 BLG534.05 79990 17:50:52.00 -31:29:53.8 2458531.373 2019-02-16.87 33.739 1.244 1.211 0.208 1.000 17.696 17.696
2019-BLG-0035 BLG534.23 74434 17:50:20.12 -30:56:02.3 2458580.502 2019-04-07.00 53.725 0.754 1.594 0.506 1.000 14.539 14.539
2019-BLG-0036 BLG534.30 112371 17:50:53.88 -30:44:28.4 2458544.403 2019-03-01.90 51.942 0.294 3.507 1.362 1.000 18.976 18.976
2019-BLG-0037 BLG611.02 28484 17:37:07.60 -27:43:26.8 2458544.957 2019-03-02.46 16.181 0.001 1210.7 7.708 1.000 17.536 17.536
2019-BLG-0038 BLG611.12 109226 17:35:30.91 -27:24:37.6 2458510.225 2019-01-26.73 29.495 0.000 313274 13.740 1.000 19.641 19.641
2019-BLG-0039 BLG611.17 99248 17:38:17.14 -26:55:11.4 2458520.192 2019-02-05.69 49.168 0.203 5.008 1.749 0.344 17.708 18.867
2019-BLG-0040 BLG613.03 27144 17:30:56.00 -29:35:27.8 2458526.761 2019-02-12.26 56.598 0.025 40.035 4.006 1.000 18.645 18.645
2019-BLG-0041 BLG613.24 57625 17:27:53.71 -29:00:30.5 2458515.916 2019-02-01.42 24.094 0.395 2.678 1.069 1.000 18.943 18.943
2019-BLG-0042 BLG613.27 116046 17:31:09.52 -28:44:20.5 2458517.582 2019-02-03.08 73.815 0.811 1.518 0.453 1.000 17.742 17.742
2019-BLG-0043 BLG613.30 86495 17:29:08.99 -28:44:18.3 2458524.034 2019-02-09.53 12.453 0.925 1.401 0.366 1.000 17.804 17.804
2019-BLG-0044 BLG613.32 11793 17:28:06.14 -28:46:33.3 2458484.978 2019-01-01.48 37.672 0.499 2.186 0.849 1.000 17.003 17.003
2019-BLG-0045 BLG614.04 19783 17:24:30.25 -29:06:43.1 2458529.300 2019-02-14.80 72.045 1.584 1.116 0.119 1.000 16.320 16.320
2019-BLG-0046 BLG615.13 38668 17:23:48.92 -30:04:40.7 2458518.966 2019-02-04.47 17.707 0.264 3.892 1.475 1.000 18.025 18.025
2019-BLG-0047 BLG615.28 80628 17:25:04.75 -29:28:12.3 2458512.027 2019-01-28.53 21.720 0.186 5.448 1.841 1.000 19.578 19.578
2019-BLG-0048 BLG615.29 76316 17:24:31.93 -29:13:53.4 2458510.599 2019-01-27.10 36.245 0.622 1.831 0.657 1.000 19.095 19.095
2019-BLG-0049 BLG632.28 121236 17:46:14.66 -22:52:13.1 2458518.258 2019-02-03.76 9.530 0.900 1.424 0.384 1.000 18.049 18.049
2019-BLG-0050 BLG633.12 26905 17:46:00.91 -24:45:33.0 2458523.564 2019-02-09.06 22.626 0.234 4.355 1.597 1.000 17.789 17.789
2019-BLG-0051 BLG633.25 56130 17:43:17.79 -24:26:00.5 2458531.913 2019-02-17.41 123.280 0.025 39.382 3.988 0.216 19.233 20.895
2019-BLG-0052 BLG648.18 7406 17:48:50.32 -26:33:53.7 2458533.142 2019-02-18.64 13.436 0.548 2.024 0.765 1.000 18.806 18.806
2019-BLG-0053 BLG648.24 19052 17:44:40.45 -26:45:16.5 2458509.628 2019-01-26.13 55.055 0.264 3.885 1.474 1.000 18.122 18.122
2019-BLG-0054 BLG652.07 862 17:39:24.72 -26:44:04.7 2458465.033 2018-12-12.53 48.870 0.000 75747 12.198 1.000 17.916 17.916
2019-BLG-0055 BLG652.08 73459 17:43:48.76 -26:13:34.7 2458528.186 2019-02-13.69 23.547 0.505 2.165 0.839 1.000 17.672 17.672
2019-BLG-0056 BLG652.15 61611 17:38:50.16 -26:19:45.5 2458579.722 2019-04-06.22 79.396 0.000 11224 10.125 1.000 18.258 18.258
2019-BLG-0057 BLG652.29 32738 17:41:26.44 -25:38:06.7 2458529.610 2019-02-15.11 24.821 0.605 1.871 0.680 1.000 18.135 18.135
2019-BLG-0058 BLG653.12 45048 17:35:41.82 -28:45:18.3 2458523.458 2019-02-08.96 15.455 0.395 2.678 1.070 1.000 19.629 19.629
2019-BLG-0059 BLG653.16 5139 17:33:01.06 -28:49:44.1 2458534.831 2019-02-20.33 22.442 1.540 1.125 0.128 1.000 16.178 16.178
2019-BLG-0060 BLG653.17 84689 17:38:04.05 -28:32:53.0 2458525.868 2019-02-11.37 11.083 0.513 2.135 0.824 1.000 19.397 19.397
2019-BLG-0061 BLG653.27 72298 17:36:41.50 -28:06:19.2 2458696.223 2019-07-31.72 119.607 0.001 1934.1 8.216 1.000 17.234 17.234
2019-BLG-0062 BLG654.06 7053 17:34:20.90 -30:23:34.9 2458527.810 2019-02-13.31 23.727 0.282 3.648 1.405 0.053 15.267 18.448
2019-BLG-0063 BLG654.31 73368 17:34:06.84 -29:22:13.1 2458536.195 2019-02-21.70 18.773 1.052 1.307 0.290 1.000 17.217 17.217
2019-BLG-0064 BLG662.02 61635 17:31:20.24 -30:51:52.4 2458496.503 2019-01-13.00 65.560 0.533 2.070 0.790 1.000 19.582 19.582
2019-BLG-0065 BLG662.13 12797 17:29:30.56 -30:32:29.3 2458576.514 2019-04-03.01 158.456 0.000 8713.0 9.850 1.000 18.842 18.842
2019-BLG-0066 BLG662.18 21914 17:32:17.39 -30:21:09.2 2458540.442 2019-02-25.94 27.655 0.000 2351.2 8.428 1.000 19.518 19.518
2019-BLG-0067 BLG662.31 58386 17:28:31.18 -30:05:51.7 2458549.542 2019-03-07.04 40.897 0.372 2.828 1.129 1.000 16.655 16.655
2019-BLG-0068 BLG675.05 51948 17:40:18.05 -27:44:18.6 2458499.932 2019-01-16.43 57.978 0.278 3.703 1.421 1.000 18.936 18.936
2019-BLG-0069 BLG675.11 10172 17:41:59.34 -27:32:20.7 2458516.548 2019-02-02.05 8.759 1.361 1.170 0.170 1.000 16.667 16.667
2019-BLG-0070 BLG675.15 20099 17:39:09.20 -27:30:29.6 2458516.527 2019-02-02.03 22.625 0.037 26.988 3.578 1.000 20.363 20.363
2019-BLG-0071 BLG675.29 17126 17:40:59.41 -27:02:19.9 2458514.748 2019-01-31.25 58.795 0.502 2.175 0.844 1.000 19.554 19.554

Andrzej Udalski and Michal Szymanski

Warsaw University Observatory

Warsaw, Poland

Last updated on Mon Feb 18 23:19:41 CET 2019