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

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