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

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