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

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