GCN Circular 45295
Subject
SN 2026stf / GRB 260708A: ATLAS forced photometry
Event
Date
2026-08-06T00:07:04Z (2 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
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)
We 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).
Using 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.
The 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.
MJD. | mag | e_mag |flux |e_flux| filter| observation
----------------------------------------------------------------------------------------------
61203.257379 18.634 0.491 128.0 63 o 04a61203o0384o
61203.260575 -18.648 0.712 -126.0 90 o 04a61203o0391o
61203.285519 20.077 0.581 34.0 20 o 04a61203o0444o
61203.29178 20.792 1.566 18.0 27 o 04a61203o0457o
61206.11809 21.107 4.412 13.0 58 o 04a61206o0248o
61206.12176 -18.955 0.647 -95.0 62 o 04a61206o0256o
61206.127177 -19.91 1.685 -39.0 66 o 04a61206o0268o
61206.137231 -18.837 0.787 -106.0 83 o 04a61206o0290o
61208.003738 -21.432 0.984 -10.0 10 c 03a61208o0094c
61208.006902 21.842 1.825 7.0 12 c 03a61208o0101c
61208.03234 -22.219 2.429 -5.0 11 c 03a61208o0156c
61208.037748 -23.402 7.111 -2.0 11 c 03a61208o0168c
61215.101062 20.405 0.87 25.0 22 o 04a61215o0341o
61215.106041 -20.875 1.571 -16.0 26 o 04a61215o0352o
61215.109687 21.063 1.366 14.0 19 o 04a61215o0360o
61215.116029 20.644 1.086 20.0 22 o 04a61215o0374o
61215.125947 23.114 8.294 2.0 17 o 04a61215o0396o
61220.18041 20.739 2.089 18.0 38 o 04a61220o0405o
61220.212007 -19.219 0.46 -74.0 34 o 04a61220o0473o
61220.215569 -20.976 2.384 -15.0 35 o 04a61220o0480o
61220.244229 -20.8 2.407 -17.0 42 o 04a61220o0541o
61221.106872 -20.685 1.464 -19.0 28 o 04a61221o0347o
61221.110508 19.599 0.571 52.0 30 o 04a61221o0355o
61221.114247 19.799 0.677 44.0 30 o 04a61221o0363o
61221.119822 19.554 0.429 55.0 24 o 04a61221o0375o
61221.129752 20.192 1.137 30.0 35 o 04a61221o0394o
61224.134068 17.646 2.756 317.0 875 o 04a61224o0172o
61224.137394 17.479 1.786 370.0 661 o 04a61224o0179o
61224.143895 -18.04 2.122 -221.0 468 o 04a61224o0193o
61224.153723 14.528 0.353 5608.0 1982 o 04a61224o0214o
61224.850689 -22.279 2.743 -4.0 12 o 03a61225o0364o
61224.854295 20.341 0.58 26.0 15 o 03a61225o0372o
61224.860177 20.367 0.6 26.0 16 o 03a61225o0385o
61224.870545 -21.838 2.262 -7.0 15 o 03a61225o0408o
61225.953387 -23.99 15.857 -1.0 15 o 03a61226o0036o
61225.957069 21.685 1.891 8.0 14 o 03a61226o0044o
61225.962523 20.444 0.561 24.0 14 o 03a61226o0056o
61225.982975 20.19 0.653 30.0 20 o 03a61226o0100o
61227.828562 21.292 0.881 11.0 10 o 03a61228o0314o
61227.831716 22.195 2.425 5.0 12 o 03a61228o0321o
61227.837861 21.672 1.562 8.0 12 o 03a61228o0334o
61227.847773 0.0 21.251 -0.0 12 o 03a61228o0356o
61228.828314 20.573 0.548 21.0 12 o 03a61229o0313o
61228.831947 23.404 7.462 2.0 12 o 03a61229o0321o
61228.837418 -21.735 1.435 -7.0 10 o 03a61229o0333o
61228.847822 23.144 4.533 2.0 9 o 03a61229o0356o
61230.825786 18.567 0.106 136.0 14 o 03a61231o0303o
61230.829421 18.463 0.089 150.0 13 o 03a61231o0311o
61230.83483 18.536 0.1 140.0 14 o 03a61231o0323o
61230.847461 18.6 0.098 132.0 13 o 03a61231o0351o
61233.132315 19.314 0.21 68.0 14 o 04a61233o0234o
61233.152559 19.689 0.312 48.0 15 o 04a61233o0277o
61233.155718 19.645 0.277 50.0 14 o 04a61233o0284o
61233.168334 19.367 0.185 65.0 12 o 04a61233o0311o
61234.819699 19.127 0.166 81.0 14 o 03a61235o0253o
61234.822959 19.42 0.243 62.0 15 o 03a61235o0260o
61234.828055 19.497 0.231 58.0 13 o 03a61235o0271o
61234.840874 19.112 0.161 82.0 13 o 03a61235o0299o
61236.79229 18.959 0.239 95.0 23 o 03a61237o0226o
61236.795085 19.905 0.853 40.0 34 o 03a61237o0232o
61236.801591 19.14 0.382 80.0 31 o 03a61237o0245o
61236.811886 18.648 0.173 126.0 22 o 03a61237o0267o
61237.809594 19.061 0.123 86.0 11 o 03a61238o0262o
61237.812764 19.156 0.163 79.0 13 o 03a61238o0269o
61237.8201 19.148 0.147 80.0 12 o 03a61238o0285o
61237.830145 19.069 0.121 86.0 10 o 03a61238o0307o
61240.79296 19.048 0.147 87.0 13 o 03a61241o0092o
61240.796119 19.057 0.157 86.0 14 o 03a61241o0099o
61240.801526 18.923 0.138 98.0 14 o 03a61241o0111o
61240.835558 19.297 0.213 69.0 15 o 03a61241o0184o
61242.787705 18.836 0.173 106.0 18 o 03a61243o0213o
61242.793772 18.852 0.164 104.0 17 o 03a61243o0226o
61242.796932 18.821 0.185 108.0 20 o 03a61243o0233o
61242.807162 18.875 0.223 102.0 23 o 03a61243o0255o
61243.802909 18.507 0.214 144.0 31 o 03a61244o0135o
61243.851004 18.728 0.234 117.0 28 o 03a61244o0151o
61243.856046 18.883 0.273 102.0 28 o 03a61244o0162o
61243.868817 18.547 0.206 138.0 28 o 03a61244o0190o
61245.908433 19.092 0.268 84.0 22 o 03a61246o0447o
61245.929595 18.977 0.271 93.0 25 o 03a61246o0492o
61245.935043 19.026 0.263 89.0 23 o 03a61246o0504o
61245.959763 19.081 0.37 85.0 31 o 03a61246o0558o
61247.804195 19.022 0.28 89.0 25 o 03a61248o0239o
61247.807349 18.81 0.239 109.0 26 o 03a61248o0246o
61247.812913 18.911 0.292 99.0 29 o 03a61248o0258o
61247.823386 19.47 0.493 59.0 29 o 03a61248o0281o
61249.247796 19.688 0.712 48.0 34 o 01a61249o0018o
61249.251905 18.651 0.255 126.0 32 o 01a61249o0027o
61249.2583 18.647 0.246 126.0 31 o 01a61249o0041o
61249.274816 18.898 0.294 100.0 29 o 01a61249o0077o
61253.787954 18.938 0.185 96.0 18 o 03a61254o0205o
61253.791569 18.882 0.144 102.0 15 o 03a61254o0213o
61253.797995 18.984 0.164 92.0 15 o 03a61254o0227o
61253.807829 19.042 0.217 88.0 19 o 03a61254o0248o
61256.862169 -20.237 10.875 -29.0 317 o 03a61257o0091o
61256.871251 -16.142 1.031 -1268.0 1308 o 03a61257o0111o
This 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.
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).