{
  "subject": "EP260806a: SAO RAS multicolor optical observations",
  "eventId": "EP260806a",
  "createdOn": 1787065831294,
  "eventType": [
    "X-ray Transient",
    "Optical Transient"
  ],
  "submitter": "Nicolai Pankov at IKI <colinsergesen@gmail.com>",
  "circularId": 45396,
  "submittedHow": "web",
  "editedOn": 1787151966167,
  "format": "text/plain",
  "body": "N. Pankov (IKI), A. Moskvitin (SAO RAS), A. Pozanenko (IKI), O. Spiridonova \n(SAO RAS), S. Kaisin (SAO RAS) report on behalf of IKI-GRB-FuN:\n\nWe observed the field of the X-ray transient EP260806a detected by EP \n(Li et al., GCN Circ. 45299) with the Zeiss-1000 1-meter and the BTA 6-meter \ntelescopes of Special Astrophysical Observatory (SAO RAS) on six epochs between \n2026-08-07T00:56:47 and 2026-08-10T23:19:45 UT. We have applied image \nsubtraction using PS1 g,r images as reference and clearly detected the optical \ncounterpart (He et al., GCN 45300; de Ugarte Postigo et al., GCN 45302; \nEyles-Ferris et al.,  GCN 45303; Ma et al., GCN 45304; de Ugarte Postigo et al., \nGCN 45306; Anumarlapudi et al., GCN 45312; Abidkhanov et al., GCN 45354; \nHua et al., GCN 45385; Maksut et al., GCN 45389) at each epoch. The observational \nsummary and preliminary photometry are presented below:\n\nDate       UTstart    t-T0    Exp.   Filter  Mag   Err.  Telescope\n                    (mid, d) (n*s)                       \n2026-08-07  00:56:47 0.08539   7*120  Rc     19.519 0.030 Zeiss-1000\n2026-08-07  23:18:25 1.01898   4*300  Rc     18.842 0.055 Zeiss-1000\n2026-08-08  23:18:25 2.02679   5*300  Rc     18.783 0.043 Zeiss-1000\n2026-08-10  02:53:28 3.16181   12*20  r      18.877 0.008 BTA-6m\n2026-08-10  04:25:25 3.22439   2*20   g      17.650 0.140 BTA-6m\n2026-08-10  00:57:26 3.08632   3*300  Rc     18.618 0.007 Zeiss-1000\n2026-08-10  23:19:45 4.02827   6*300  Rc     18.935 0.084 Zeiss-1000\n2026-08-11  23:26:37 5.02719   6*300  Rc     18.618 0.007 Zeiss-1000\n\nThe photometry is based on set of nearby stars from USNO-B1.0 (for Rc) \nand PS1 (for g,r) filters, respectively. No correction for the Galactic \nextinction was applied. The plot of the light curve derived from own data \nand GCN photometry is available online at: \n\nhttps://heaiki.ru/lvc/r/GRBs/EP260806a/EP260806a_lc.png.\n\nWe observe a significant g-r color evolution from -0.24 +/- 0.13 at ~0.5 days \n(Anumarlapudi et al., GCN 45312) to -1.23 +/- 0.16 at ~3.2 days since trigger.\n\nThe observed light curve behavior is consistent with an AGN outburst, as was \nsuggested by de Ugarte Postigo et al. (GCN 45302).",
  "version": 2,
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Zhanat Maksut at Nazarbayev University <zhanat.maksut@nu.edu.kz>"
}