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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"

15506 results found.

  1. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  2. EP260321a: Upper limits from ATCA radio observations
  3. GRB 260421B: Kilonova-Catcher optical afterglow detection
  4. The EP-WXT trigger 01709258652: Mondy optical observations
  5. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  6. EP260416a: Mondy optical observations
  7. GRB 260421B: 3.6m DOT optical observation
  8. EP260416a: ZTSh R band observations
  9. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  10. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  11. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  12. GRB 260421B: SVOM/GRM observation
  13. GRB 260421B: EP-FXT follow-up observation
  14. GRB 260421B: J-band upper limit with WINTER
  15. GRB 260421B: LCO optical counterpart detection
  16. GRB 260421B: SVOM/VT optical observations
  17. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  18. GRB 260310A: Late-time Chandra X-ray Detection
  19. EP260416a: 1.3m DFOT optical observation
  20. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  21. GRB 260421B: BOOTES-7 early optical afterglow detection
  22. GRB 260421B: LCO optical afterglow confirmation
  23. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  24. GRB 260421B: TRT optical counterpart detection
  25. GRB 260412A: LCOGT Optical Upper Limits
  26. EP260416a: Optical follow-up observations with Kinder
  27. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  28. EP-WXT trigger 01709260303: KAIT optical observations
  29. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  30. GRB 260417A: SVOM/GRM observation
  31. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  32. EP260417a: GROWTH-India Telescope optical upper limit
  33. EP260417b: GROWTH-India Telescope optical upper limit
  34. EP260416a: Ondrejov D50 optical detection
  35. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  36. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  37. EP260416a: GMG Optical Observation
  38. EP260416a: LCO observations confirm end of flaring phase
  39. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  40. EP260417a: TRT optical counterpart detection
  41. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  42. EP-WXT trigger 01709259586: KAIT optical observations
  43. EP260416a: KAIT optical upper limit
  44. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  45. EP260416a: WFST optical observations and rebrightening
  46. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  47. EP260416a: SVOM/VT optical observation
  48. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  49. EP260416a: COLIBRÍ optical counterpart candidate
  50. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  51. GOTO26djh/AT2026jpw : MASTER OT observation
  52. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  53. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  54. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  55. EP260321a: CMO SAI J,K observations
  56. EP260321a: SVOM/VT optical observations and color changes around peak
  57. GRB 260411B: Fermi-LAT detection
  58. GRB 260412A: SVOM detection of a long burst
  59. GRB 260411B: COLIBRÍ optical observations
  60. GRB 260411B: Ondrejov D50 optical afterglow detection
  61. GRB260411B: 3.6m DOT optical observation
  62. GRB 260411A: SVOM/GRM observation
  63. GRB 260411B: SVOM/GRM observation of a long burst
  64. GRB 260411B: Fermi GBM Detection
  65. GRB 260411B: GOTO optical counterpart candidate
  66. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  67. GRB 260410A: COLIBRÍ optical upper limit
  68. EP-WXT01709259790: Optical Upper limits with kinder observations
  69. EP-WXT01709259790: Xinglong optical upper limit
  70. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  71. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  72. EP260409a: SVOM/VT optical upper limits
  73. EP260409a: COLIBRÍ optical upper limits
  74. GRB 260310A / AT2026fgk: X-ray rebrightening
  75. EP260402a / GRB 260402A: Mephisto optical upper limits
  76. EP-WXT01709259586: Xinglong optical upper limit
  77. EP260403a: Mephisto optical upper limits
  78. EP260402a/GRB 260402A: Xinglong optical upper limit
  79. EP260321a: Upper limits from VLA radio observations
  80. EP260321a: uGMRT observations
  81. EP260405a: GMOS-N optical upper limits
  82. EP260405a: SVOM/VT optical upper limits
  83. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  84. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  85. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  86. GRB 260330B: SVOM/VT further optical observation
  87. EP260403a: LCO optical observations of the counterpart
  88. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  89. EP260403a: LCO optical counterpart detection
  90. EP260403a: COLIBRÍ optical counterpart candidate
  91. GRB 260330B: SVOM/VT optical candidate
  92. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  93. EP260324A / AT 2026hir: COLIBRÍ optical observations
  94. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  95. GRB 260402A: WINTER J-band upper limit
  96. GRB260402A: GROWTH-India Telescope optical upper limit
  97. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  98. GRB 260401A: SVOM/GRM observation
  99. GRB 260402A: Kilonova-Catcher optical upper limit
  100. GRB 260402A: MASTER optical observations

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