TITLE: GCN CIRCULAR NUMBER: 24024 SUBJECT: MAGIC follow-up of the X-ray flares of LS I +61º303 dete DATE: 19/03/28 17:50:39 GMT FROM: Razmik Mirzoyan at MPI/MAGIC R. Mirzoyan, D. Hadasch, A. López-Oramas report on behalf of the MAGIC collaboration: The MAGIC telescopes have observed the direction (RA=+02:40:37h, DEC=+61:14:45deg, J2000.0) coincident with the location of the gamma-ray binary LS I +61º 303 (RA:+02:40:31.00, DEC:+61:13:45, J2000.0) in the very-high-energy (VHE; >100 GeV) range on March 23, 2019. The MAGIC observations were triggered by the flaring activity in X-rays measured by Swift-BAT on March 23, 2019 at 20:30:47 UT (S. D. Barthelmy et al., GCN circ. 23989, 2019) and by Swift-XRT at 20:32:12.5 UT. The preliminary Swift-BAT analysis showed multiple short spikes with a total duration of about 20 sec and a peak rate of about 2400 counts/sec (15-350 keV) 3 seconds after the trigger. The analysis of the MAGIC data taken ~20 minutes later on March 23, 2019 between 20:52:13.7 UTC (MJD 58565.8696) and 21:12:00.9 UTC (MJD 58565.8833) did not show any significant detection of LS I +61º 303 at VHE (significance (Li&Ma) < 0.5 sigma). After 0.33 hours of observations the integral flux upper limit for energies above 300 GeV is 2e-11 cm^-2 s^-1. The MAGIC contact persons for these observations are Razmik Mirzoyan ( Razmik.Mirzoyan@mpp.mpg.de), Daniela Hadasch ( hadasch@icrr.u-tokyo.ac.jp) and Alicia López-Oramas ( aloramas@iac.es).