{
  "subject": "GRB 210619B: Maidanak and Assy optical observations, broken power law parametrization",
  "eventId": "GRB 210619B",
  "bibcode": "2021GCN.30791....1B",
  "createdOn": 1631222726000,
  "circularId": 30791,
  "submitter": "Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>",
  "email": "apozanen@iki.rssi.ru",
  "body": "S. Belkin (IKI),  A. Pozanenko (IKI), O. Burhonov (UBAI), V. Kim (FAI, \nHSE), M. Krugov (FAI), N. Pankov (HSE), Sh. Ehgamberdiev (UBAI),  report \non behalf of IKI-GRB-FuN:\n\nWe observed the field of GRB 210619B (D'Avanzo et al. GCN 30261) with \nAZT-22 telescope of Maidanak Observatory and AZT-20 telescope of \nAssy-Turgen observatory. The optical afterglow (D'Avanzo et al. GCN \n30261; Jelinek et al., GCN 30263; Kong, GCN 30265; Pellegrin et al., GCN \n30268; Perley, GCN 30271; Zheng and Filippenko, GCN 30273; Blazek et \nal., GCN 30274; Kann et al., GCN 30275; Xin et al., GCN 30277; Kiun et \nal., GCN 30278; Shrestha et al., GCN 30280; Jelkinek et al., GCN 30281; \nKumar et al., GCN 30286; D'Avanzo et al., GCN 30288; Moskvitin and \nMaslennikova, GCN 303291; Romanov, GCN 30292; Hu et al., GCN 30293; Zhu \net al., GCN 30294; Belkin et al., GCN 30299; Moskvitin and Maslennikova, \nGCN 30303; Romanov and Lane, GCN 30305; Moskvitin and Maslennikova, GCN \n30309; Vinko et al., GCN 30320; Kann et al., GCN 30338; Zaznobin et al., \nGCN 30343) is clearly detected on the most of stacked images. \nPreliminary photometry of the afterglow of some of observations is \nfollowing.\n\nDate UT start t-T0 Filter Exp. OT UL(3sigma) Telescope\n                         (mid, days) (s)\n\n2021-06-20 19:02:53 0.79963  R 8*300  19.47 0.06 23.0 AZT-22\n2021-06-21 19:53:41 1.85019  R 12*300 20.43 0.05 23.2 AZT-22\n2021-06-22 17:15:29 2.74206  r 75*60  21.82 0.26 22.6 AZT-20\n2021-06-22 18:35:45 2.79606  R 12*300 21.21 0.09 23.1 AZT-22\n2021-06-26 20:15:18 6.86520  R 20*180 22.55 0.24 23.2 AZT-22\n2021-07-02 20:16:53 12.86630 R 12*300 23.5  0.3  23.5 AZT-22\n2021-07-08 19:16:40 18.83003 r 76*60  n/d   n/d  23.2 AZT-20\n2021-07-18 19:50:46 28.84816 R 12*300 n/d   n/d  23.9 AZT-22\n\nPhotometry is based on the USNO-B1.0 and PanSTARRS-PS1 nearby stars.\nUSNO-B1.0_id R2 I\n1238-0493928 15.08 14.33\n1238-0494511 15.67 15.03\n1238-0493842 17.53 17.36\n1238-0493787 16.81 16.12\n\nPanSTARRS-PS1\nRA DEC r\n21:18:52.24182 +33:49:14.6348 15.2925\n21:18:45.71408 +33:50:40.3319 18.1642\n\nUsing our data and those published in the GCN circulars cited above we \nplot a light curve which an be found at\n\nhttp://grb.rssi.ru/GRB210619B/GRB210619B_LC_all.png\n\nUsing only Maidanak data after 0.7 days, it was found that the light \ncurve can be fitted by a single power law with the index alpha = -1.48 \n+/-0.04. Using early data published in GCNs we can describe the LC by a \nbroken power law with parameters of alpha = -0.72+/-0.01, beta = -1.52 \n+/-0.04, and break time of 0.57+/-0.12.\n\nThe fitted LC can be found at\n\nhttp://grb.rssi.ru/GRB210619B/GRB210619B_AZT22_LC.png\n\nIt confirms the steeping decay suggested by Jelinek et al., GCN 30281, \nKumar et al., GCN 30286. The power-law index before the break is \napproximately the same as that obtained by Kann et al., GCN 30338 and \nOganesyan et al., arXiv:2109.00010, while the power law index after the \nbreak is steeper and coincides with XRT afterglow power law index.\n\nWe also not detected any influence of host galaxy on afterglow light \ncurve, and after late time observations we can estimate brightness of \nthe host galaxy R > 23.9."
}