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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.

Advanced Search Examples (click to copy):

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

36144 results found.

  1. GRB 260421B: EP-FXT follow-up observation
  2. GRB 260421B: J-band upper limit with WINTER
  3. GRB 260421B: LCO optical counterpart detection
  4. GRB 260421B: Fermi GBM Observation
  5. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  6. GRB 260421A: AstroSat CZTI detection
  7. GRB 260412A: SVOM/ECLAIRs refined analysis
  8. GRB 260421B: SVOM/VT optical observations
  9. GRB 260310A: Late-time Chandra X-ray Detection
  10. GRB 260418A: Insight-HXMT/HE detection
  11. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  12. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  13. Fermi GRB 260421C: Global MASTER-Net observations report
  14. GRB 260421C: Fermi GBM Final Real-time Localization
  15. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  16. Fermi GRB 260421B: Global MASTER-Net observations report
  17. GRB 260421B: BOOTES-7 early optical afterglow detection
  18. GRB 260421B: LCO optical afterglow confirmation
  19. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  20. GRB 260421B: TRT optical counterpart detection
  21. GRB 260421B: SVOM detection of a long burst
  22. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  23. GRB 260421B: Fermi GBM Final Real-time Localization
  24. Fermi GRB 260421A: Global MASTER-Net observations report
  25. GRB 260421A: Fermi GBM Final Real-time Localization
  26. GRB 260412A: LCOGT Optical Upper Limits
  27. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  28. EP-WXT trigger 01709260303: KAIT optical observations
  29. GRB 260417A: SVOM/GRM observation
  30. GRB 260419B: Fermi GBM Final Real-time Localization
  31. GRB 260419A: Fermi GBM Final Real-time Localization
  32. Fermi GRB 260417B: Global MASTER-Net observations report
  33. GRB 260418B: Fermi GBM Final Real-time Localization
  34. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  35. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  36. GRB 260418A: Fermi GBM Final Real-time Localization
  37. Fermi GRB 260417A: Global MASTER-Net observations report
  38. Konus-Wind detection of GRB 260411B
  39. GRB 260417B: Fermi GBM Final Real-time Localization
  40. GRB 260417A: AstroSat CZTI detection
  41. IPN triangulation of GRB 260411B
  42. EP-WXT trigger 01709259586: KAIT optical observations
  43. EP260416a: KAIT optical upper limit
  44. GRB 260414A: Insight-HXMT/HE detection
  45. GRB 260417A: Fermi GBM Final Real-time Localization
  46. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  47. GRB 260415B: Glowbug gamma-ray detection
  48. GRB 260411B: Glowbug gamma-ray detection
  49. GRB 260415A: Insight-HXMT/HE detection
  50. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  51. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  52. GRB 260415B: NuSTAR detection of long prompt emission
  53. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  54. GRB 260415B: Fermi GBM Final Localization
  55. GRB 260415A: Fermi GBM Final Real-time Localization
  56. GRB 260414A: Glowbug gamma-ray detection
  57. EP260321a: CMO SAI J,K observations
  58. GRB 260412A: Insight-HXMT/HE detection
  59. GRB 260414A: Fermi GBM Final Real-time Localization
  60. Fermi GRB 260413A: Global MASTER-Net observations report
  61. GRB 260410A: Glowbug gamma-ray detection of a short burst
  62. GRB 260413A: Fermi GBM Final Real-time Localization
  63. GRB 260410B: Insight-HXMT/HE detection
  64. GRB 260410A: Insight-HXMT/HE detection
  65. Konus-Wind detection of GRB 260410A (short/hard)
  66. GRB 260411B: GECAM-B observation of a long burst
  67. GRB 260410A: CALET Gamma-Ray Burst Monitor detection
  68. GRB 260412A: GECAM-B observation of a long burst
  69. Fermi GRB 260412A: Global MASTER-Net observations report
  70. GRB 260412A: Fermi GBM Observation
  71. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  72. GRB 260411B: Fermi-LAT detection
  73. GRB 260412A: SVOM detection of a long burst
  74. GRB 260412A: Fermi GBM Final Real-time Localization
  75. GRB 260411B: COLIBRÍ optical observations
  76. GRB 260410B: Fermi GBM Observation
  77. GRB 260411B: Ondrejov D50 optical afterglow detection
  78. GRB 260411A: SVOM/GRM observation
  79. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  80. GRB 260411B: SVOM/GRM observation of a long burst
  81. GRB 260409A: Insight-HXMT/HE detection
  82. GRB 260411B: Fermi GBM Detection
  83. GRB 260411B: GOTO optical counterpart candidate
  84. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  85. GRB 260411B: Fermi GBM Final Real-time Localization
  86. GRB 260411A: Fermi GBM Final Real-time Localization
  87. GRB 260410A: COLIBRÍ optical upper limit
  88. GRB 260410A: Fermi GBM Observation
  89. GRB 260410B: SVOM/GRM detection of a short faint burst
  90. GRB 260410B: Fermi GBM Final Real-time Localization
  91. GRB 260410A: Fermi-LAT detection
  92. GRB 260410A: Fermi GBM Final Real-time Localization
  93. EP260321a: Chandra X-ray Non-detection
  94. GRB 260409A: Fermi GBM Final Real-time Localization
  95. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  96. GRB 260407A: GECAM-A detection
  97. GRB 260407A: Insight-HXMT/HE detection
  98. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  99. GRB 260404A: Fermi GBM Final Localization
  100. GRB 260407A: Glowbug gamma-ray detection

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