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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

16161 results found.

  1. EP260324a: GROWTH-India Telescope optical observation
  2. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  3. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  4. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  5. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  6. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  7. EP260321a: JinShan near-infrared observations
  8. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  9. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  10. EP260321a: Gemini-South confirmation of a supernova
  11. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  12. GRB 260310A: LBT optical observations
  13. EP260321A: Mondy optical observations
  14. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  15. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  16. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  17. EP260321a: COLIBRÍ further optical observations and brightening
  18. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  19. EP260214b: ATCA 6 GHz detection
  20. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  21. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  22. EP260321a: GOTO detection of blue variable source
  23. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  24. EP260321a: further Kinder optical observations
  25. GRB 260321A: SVOM/VT optical upper limits
  26. EP260321a: Las Cumbres upper limit
  27. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  28. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  29. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  30. EP260321a: SVOM/VT optical upper limit
  31. GRB 260310A: continued optical observation at Mondy
  32. GRB 260321A: SVOM detection of a burst
  33. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  34. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  35. GRB 260310A / AT 2026fgk: KAIT optical observations
  36. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  37. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  38. GRB 260318A: SVOM/GRM observation
  39. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  40. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  41. GRB 260310A / AT 2026fgk: radio detection with the VLA
  42. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  43. GRB 260310A / AT2026fgk: LCO optical observations
  44. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  45. GRB 260316B: SVOM/GRM observation
  46. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  47. EP260316a: COLIBRÍ faint optical counterpart candidate
  48. EP260316a: Xinglong optical upper limit
  49. EP260316a: optical upper limit with Kinder observations
  50. IceCube-260315A: COLIBRÍ optical observations
  51. EP260314a: Xinglong optical upper limit
  52. EP260314a: optical upper limit with Kinder observations
  53. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  54. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  55. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  56. GRB 260310A / AT 2026fgk: iTelescope optical observations
  57. EP260314a: COLIBRÍ optical upper limit
  58. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  59. EP260314a: BOOTES-6/DPR optical upper limits at early times
  60. EP260314a: SVOM/VT optical candidate
  61. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  62. GRB 260310A / AT2026fgk: SAO RAS optical observations
  63. GRB 260310A / AT2026fgk: TNG NIR detection
  64. GRB 260310A / AT2026fgk: OASDG optical observations
  65. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  66. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  67. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  68. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  69. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  70. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  71. GRB 260310A: NOT optical polarimetry
  72. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  73. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  74. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  75. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  76. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  77. GRB260310A / AT2026fgk: P200 Spectroscopy
  78. GRB 260310A: Fermi GBM Observation
  79. GRB 260310A: potential optical counterpart
  80. GRB 260131A/B: radio detection with the VLA
  81. GRB 260308A: SVOM/GRM observation of a short GRB
  82. EP260306a: Mondy optical upper limit
  83. GRB 260208A: radio detection with the VLA
  84. GRB 260307B: Mephisto optical upper limits
  85. GRB 260307B: possible NOT optical counterpart
  86. GRB260307B: GROWTH-India Telescope optical upper limit
  87. GRB 260307B: SVOM/VT optical candidate
  88. GRB 260307B: SVOM detection of a burst
  89. GRB 260211A: late-time NOT i-band observations consistent with archival flux
  90. EP260306a: refined analysis of the EP-WXT and EP-FXT observations
  91. EP260302a: SVOM/VT optical observation
  92. EP260306a: Gemini-North redshift z = 4.773
  93. EP260306a: SVOM/VT optical observation
  94. EP260302a: Gemini-South redshift z = 1.535
  95. EP260306a: COLIBRÍ optical observations of the fading and red counterpart
  96. EP260306a: Einstein Probe detection of an X-ray transient
  97. The EP-WXT trigger 01709258759: Las Cumbres discovery of the optical counterpart
  98. EP260302a: Optical afterglow rebrightening
  99. GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
  100. GRB 260303A: 1.3m DFOT optical upper limit (duplicate submission)

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