{ "subject": " SN 2026stf / GRB 260708A: ATLAS forced photometry ", "circularId": 45295, "createdOn": 1785974824069, "submittedHow": "web", "format": "text/plain", "eventType": [ "GRB", "SN", "Optical Transient" ], "submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias ", "eventId": "GRB 260708A", "bibcode": "2026GCN.45295....1P", "body": "I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), A. López-Oramas (IAC and ULL), D. Aguado (IAC and ULL), N. Abreu García (ULL), D. Cano-Morales (ULL), I. Correa-Plasencia (ULL), A.E. Hernández-Díaz (ULL), E. Lekaroz-Urriza (ULL), M. Magdalena-Rodríguez (ULL), M. Quintana-Ansaldo (ULL), D. Rodríguez-Fernández (ULL), and J. Uríbarri-Dermit (ULL)\n\nWe report results of ATLAS forced photometry of the type Ic-BL SN 2026stf at z = 0.055 (Corcoran et al., GCN 45283) which appears associated with the LONG GRB 260708A detected by Fermi-GBM, Fermi-LAT, GECAM, and Glowbug (Fermi-GBM Team, GCN 45115; Holzmann Airasca et al., GCN 45117; Malacaria, GCN 45124; Ren et al., GCN 45126; Cheung et al., GCN 45130) and EP/FXT (Li et al., GCN 45150). The optical counterpart (AT 2026stf, MASTER OT J150237.02-435307.7) was discovered by MASTER (Shilova et al., GCN 45123; and Zhirkov et al., TNS Astronomical Transient Report No. 313535), with other reported optical detections (Freeberg et al., GCN 45127, Shi et al., GCN 45140, Sheng et al. GCN 45147, Shi et al., GCN 45280, Corcoran et al., GCN 45283, and O'Neill et al., TNS photometry report).\n\nUsing the ATLAS forced-photometry server (Shingles et al. 2021, Transient Name Server AstroNote 2021-7), we find four detections of the fading afterglow in the ATLAS orange filter starting on MJD = 61230.82579, at about 1.40 days after the Fermi trigger, at an ATLAS orange magnitud of o = 18.567 +/- 0.106, and more detections close to the minimum of the light curve and in 10 more epochs that include the rebrightening in the SN Ic-BL phase. The last ATLAS non detection was on MJD = 61228.84782, about 0.58 days before the Fermi trigger.\n\nThe following table gives the ATLAS forced photometry since MJD = 61200. We note that according to the methods of the ATLAS forced photometry, if the flux is negative, then a magnitude is still quoted and denoted with a negative sign (see https://fallingstar-data.com/forcedphot/resultdesc/). Magnitudes are in the AB system and are not corrected for interstellar medium absorption. Fluxes are in uJy.\n\n\n MJD. | mag | e_mag |flux |e_flux| filter| observation\n----------------------------------------------------------------------------------------------\n\n 61203.257379 18.634 0.491 128.0 63 o 04a61203o0384o\n 61203.260575 -18.648 0.712 -126.0 90 o 04a61203o0391o\n 61203.285519 20.077 0.581 34.0 20 o 04a61203o0444o\n 61203.29178 20.792 1.566 18.0 27 o 04a61203o0457o\n 61206.11809 21.107 4.412 13.0 58 o 04a61206o0248o\n 61206.12176 -18.955 0.647 -95.0 62 o 04a61206o0256o\n 61206.127177 -19.91 1.685 -39.0 66 o 04a61206o0268o\n 61206.137231 -18.837 0.787 -106.0 83 o 04a61206o0290o\n 61208.003738 -21.432 0.984 -10.0 10 c 03a61208o0094c\n 61208.006902 21.842 1.825 7.0 12 c 03a61208o0101c\n 61208.03234 -22.219 2.429 -5.0 11 c 03a61208o0156c\n 61208.037748 -23.402 7.111 -2.0 11 c 03a61208o0168c\n 61215.101062 20.405 0.87 25.0 22 o 04a61215o0341o\n 61215.106041 -20.875 1.571 -16.0 26 o 04a61215o0352o\n 61215.109687 21.063 1.366 14.0 19 o 04a61215o0360o\n 61215.116029 20.644 1.086 20.0 22 o 04a61215o0374o\n 61215.125947 23.114 8.294 2.0 17 o 04a61215o0396o\n 61220.18041 20.739 2.089 18.0 38 o 04a61220o0405o\n 61220.212007 -19.219 0.46 -74.0 34 o 04a61220o0473o\n 61220.215569 -20.976 2.384 -15.0 35 o 04a61220o0480o\n 61220.244229 -20.8 2.407 -17.0 42 o 04a61220o0541o\n 61221.106872 -20.685 1.464 -19.0 28 o 04a61221o0347o\n 61221.110508 19.599 0.571 52.0 30 o 04a61221o0355o\n 61221.114247 19.799 0.677 44.0 30 o 04a61221o0363o\n 61221.119822 19.554 0.429 55.0 24 o 04a61221o0375o\n 61221.129752 20.192 1.137 30.0 35 o 04a61221o0394o\n 61224.134068 17.646 2.756 317.0 875 o 04a61224o0172o\n 61224.137394 17.479 1.786 370.0 661 o 04a61224o0179o\n 61224.143895 -18.04 2.122 -221.0 468 o 04a61224o0193o\n 61224.153723 14.528 0.353 5608.0 1982 o 04a61224o0214o\n 61224.850689 -22.279 2.743 -4.0 12 o 03a61225o0364o\n 61224.854295 20.341 0.58 26.0 15 o 03a61225o0372o\n 61224.860177 20.367 0.6 26.0 16 o 03a61225o0385o\n 61224.870545 -21.838 2.262 -7.0 15 o 03a61225o0408o\n 61225.953387 -23.99 15.857 -1.0 15 o 03a61226o0036o\n 61225.957069 21.685 1.891 8.0 14 o 03a61226o0044o\n 61225.962523 20.444 0.561 24.0 14 o 03a61226o0056o\n 61225.982975 20.19 0.653 30.0 20 o 03a61226o0100o\n 61227.828562 21.292 0.881 11.0 10 o 03a61228o0314o\n 61227.831716 22.195 2.425 5.0 12 o 03a61228o0321o\n 61227.837861 21.672 1.562 8.0 12 o 03a61228o0334o\n 61227.847773 0.0 21.251 -0.0 12 o 03a61228o0356o\n 61228.828314 20.573 0.548 21.0 12 o 03a61229o0313o\n 61228.831947 23.404 7.462 2.0 12 o 03a61229o0321o\n 61228.837418 -21.735 1.435 -7.0 10 o 03a61229o0333o\n 61228.847822 23.144 4.533 2.0 9 o 03a61229o0356o\n 61230.825786 18.567 0.106 136.0 14 o 03a61231o0303o\n 61230.829421 18.463 0.089 150.0 13 o 03a61231o0311o\n 61230.83483 18.536 0.1 140.0 14 o 03a61231o0323o\n 61230.847461 18.6 0.098 132.0 13 o 03a61231o0351o\n 61233.132315 19.314 0.21 68.0 14 o 04a61233o0234o\n 61233.152559 19.689 0.312 48.0 15 o 04a61233o0277o\n 61233.155718 19.645 0.277 50.0 14 o 04a61233o0284o\n 61233.168334 19.367 0.185 65.0 12 o 04a61233o0311o\n 61234.819699 19.127 0.166 81.0 14 o 03a61235o0253o\n 61234.822959 19.42 0.243 62.0 15 o 03a61235o0260o\n 61234.828055 19.497 0.231 58.0 13 o 03a61235o0271o\n 61234.840874 19.112 0.161 82.0 13 o 03a61235o0299o\n 61236.79229 18.959 0.239 95.0 23 o 03a61237o0226o\n 61236.795085 19.905 0.853 40.0 34 o 03a61237o0232o\n 61236.801591 19.14 0.382 80.0 31 o 03a61237o0245o\n 61236.811886 18.648 0.173 126.0 22 o 03a61237o0267o\n 61237.809594 19.061 0.123 86.0 11 o 03a61238o0262o\n 61237.812764 19.156 0.163 79.0 13 o 03a61238o0269o\n 61237.8201 19.148 0.147 80.0 12 o 03a61238o0285o\n 61237.830145 19.069 0.121 86.0 10 o 03a61238o0307o\n 61240.79296 19.048 0.147 87.0 13 o 03a61241o0092o\n 61240.796119 19.057 0.157 86.0 14 o 03a61241o0099o\n 61240.801526 18.923 0.138 98.0 14 o 03a61241o0111o\n 61240.835558 19.297 0.213 69.0 15 o 03a61241o0184o\n 61242.787705 18.836 0.173 106.0 18 o 03a61243o0213o\n 61242.793772 18.852 0.164 104.0 17 o 03a61243o0226o\n 61242.796932 18.821 0.185 108.0 20 o 03a61243o0233o\n 61242.807162 18.875 0.223 102.0 23 o 03a61243o0255o\n 61243.802909 18.507 0.214 144.0 31 o 03a61244o0135o\n 61243.851004 18.728 0.234 117.0 28 o 03a61244o0151o\n 61243.856046 18.883 0.273 102.0 28 o 03a61244o0162o\n 61243.868817 18.547 0.206 138.0 28 o 03a61244o0190o\n 61245.908433 19.092 0.268 84.0 22 o 03a61246o0447o\n 61245.929595 18.977 0.271 93.0 25 o 03a61246o0492o\n 61245.935043 19.026 0.263 89.0 23 o 03a61246o0504o\n 61245.959763 19.081 0.37 85.0 31 o 03a61246o0558o\n 61247.804195 19.022 0.28 89.0 25 o 03a61248o0239o\n 61247.807349 18.81 0.239 109.0 26 o 03a61248o0246o\n 61247.812913 18.911 0.292 99.0 29 o 03a61248o0258o\n 61247.823386 19.47 0.493 59.0 29 o 03a61248o0281o\n 61249.247796 19.688 0.712 48.0 34 o 01a61249o0018o\n 61249.251905 18.651 0.255 126.0 32 o 01a61249o0027o\n 61249.2583 18.647 0.246 126.0 31 o 01a61249o0041o\n 61249.274816 18.898 0.294 100.0 29 o 01a61249o0077o\n 61253.787954 18.938 0.185 96.0 18 o 03a61254o0205o\n 61253.791569 18.882 0.144 102.0 15 o 03a61254o0213o\n 61253.797995 18.984 0.164 92.0 15 o 03a61254o0227o\n 61253.807829 19.042 0.217 88.0 19 o 03a61254o0248o\n 61256.862169 -20.237 10.875 -29.0 317 o 03a61257o0091o\n 61256.871251 -16.142 1.031 -1268.0 1308 o 03a61257o0111o\n\n\n\nThis work is part of grant CEX2025-001609-S, awarded to the Instituto de Astrofísica de Canarias under the Severo Ochoa Centre of Excellence program and funded by MICIU/AEI/10.13039/501100011033.\n\nThis work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).\n\n" }