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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"
  1. GRB 260421B: SVOM/GRM observation
  2. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  3. GRB 260421B: EP-FXT follow-up observation
  4. The EP-WXT trigger 01709260362 is likely a flaring star
  5. GOTO26djh/AT2026jpw: ATCA radio detection
  6. GRB 260421B: J-band upper limit with WINTER
  7. GRB 260421B: LCO optical counterpart detection
  8. GRB 260421B: Fermi GBM Observation
  9. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  10. GRB 260421A: AstroSat CZTI detection
  11. GOTO26djh/AT2026jpw: radio detection at 15GHz
  12. GRB 260412A: SVOM/ECLAIRs refined analysis
  13. GRB 260421B: SVOM/VT optical observations
  14. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  15. GRB 260310A: Late-time Chandra X-ray Detection
  16. GRB 260418A: Insight-HXMT/HE detection
  17. EP260416a: 1.3m DFOT optical observation
  18. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  19. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  20. Fermi GRB 260421C: Global MASTER-Net observations report
  21. GRB 260421C: Fermi GBM Final Real-time Localization
  22. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  23. Fermi GRB 260421B: Global MASTER-Net observations report
  24. GRB 260421B: BOOTES-7 early optical afterglow detection
  25. GRB 260421B: LCO optical afterglow confirmation
  26. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  27. GRB 260421B: TRT optical counterpart detection
  28. GRB 260421B: SVOM detection of a long burst
  29. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  30. GRB 260421B: Fermi GBM Final Real-time Localization
  31. Fermi GRB 260421A: Global MASTER-Net observations report
  32. GRB 260421A: Fermi GBM Final Real-time Localization
  33. EP260321a: VLA radio follow-up
  34. GRB 260412A: LCOGT Optical Upper Limits
  35. The EP-WXT trigger 01709260314 is likely a flaring star
  36. EP260416a: Optical follow-up observations with Kinder
  37. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  38. EP-WXT trigger 01709260303: KAIT optical observations
  39. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  40. The EP-WXT trigger 01709260303 is likely a flaring star
  41. GRB 260417A: SVOM/GRM observation
  42. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  43. GRB 260419B: Fermi GBM Final Real-time Localization
  44. GRB 260419A: Fermi GBM Final Real-time Localization
  45. Fermi trigger No 798275385: Global MASTER-Net observations report
  46. EP260417a: GROWTH-India Telescope optical upper limit
  47. Fermi GRB 260417B: Global MASTER-Net observations report
  48. EP260417b: GROWTH-India Telescope optical upper limit
  49. EP260416a: Ondrejov D50 optical detection
  50. GRB 260418B: Fermi GBM Final Real-time Localization
  51. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  52. EP260417a: Global MASTER-Net observations report
  53. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  54. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  55. GRB 260418A: Fermi GBM Final Real-time Localization
  56. EP260416a: GMG Optical Observation
  57. Fermi GRB 260417A: Global MASTER-Net observations report
  58. Konus-Wind detection of GRB 260411B
  59. GRB 260417B: Fermi GBM Final Real-time Localization
  60. GRB 260417A: AstroSat CZTI detection
  61. IPN triangulation of GRB 260411B
  62. EP260416a: LCO observations confirm end of flaring phase
  63. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  64. EP260417a: TRT optical counterpart detection
  65. EP260417a: Einstein Probe detection of an X-ray transient
  66. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  67. EP260417b: Einstein Probe detection of a fast X-ray transient
  68. EP-WXT trigger 01709259586: KAIT optical observations
  69. EP260416a: KAIT optical upper limit
  70. GRB 260414A: Insight-HXMT/HE detection
  71. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  72. EP260416a: WFST optical observations and rebrightening
  73. GRB 260417A: Fermi GBM Final Real-time Localization
  74. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  75. EP260416a: SVOM/VT optical observation
  76. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  77. GRB 260415B: Glowbug gamma-ray detection
  78. GRB 260411B: Glowbug gamma-ray detection
  79. GRB 260415A: Insight-HXMT/HE detection
  80. EP260416a: COLIBRÍ optical counterpart candidate
  81. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  82. EP260416a: Global MASTER-Net observations report
  83. EP260416a: Einstein Probe detection of an X-ray transient
  84. GOTO26djh/AT2026jpw : MASTER OT observation
  85. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  86. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  87. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  88. GRB 260415B: NuSTAR detection of long prompt emission
  89. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  90. GRB 260415B: Fermi GBM Final Localization
  91. GRB 260415A: Fermi GBM Final Real-time Localization
  92. Fermi trigger No 797912738: Global MASTER-Net observations report
  93. GRB 260414A: Glowbug gamma-ray detection
  94. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  95. EP260321a: CMO SAI J,K observations
  96. GRB 260412A: Insight-HXMT/HE detection
  97. GRB 260414A: Fermi GBM Final Real-time Localization
  98. The EP-WXT trigger 01709260122 is likely a flaring star
  99. Fermi GRB 260413A: Global MASTER-Net observations report
  100. GRB 260410A: Glowbug gamma-ray detection of a short burst

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