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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 260418A: Insight-HXMT/HE detection
  2. EP260416a: 1.3m DFOT optical observation
  3. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  4. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  5. Fermi GRB 260421C: Global MASTER-Net observations report
  6. GRB 260421C: Fermi GBM Final Real-time Localization
  7. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  8. Fermi GRB 260421B: Global MASTER-Net observations report
  9. GRB 260421B: BOOTES-7 early optical afterglow detection
  10. GRB 260421B: LCO optical afterglow confirmation
  11. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  12. GRB 260421B: TRT optical counterpart detection
  13. GRB 260421B: SVOM detection of a long burst
  14. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  15. GRB 260421B: Fermi GBM Final Real-time Localization
  16. Fermi GRB 260421A: Global MASTER-Net observations report
  17. GRB 260421A: Fermi GBM Final Real-time Localization
  18. EP260321a: VLA radio follow-up
  19. GRB 260412A: LCOGT Optical Upper Limits
  20. The EP-WXT trigger 01709260314 is likely a flaring star
  21. EP260416a: Optical follow-up observations with Kinder
  22. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  23. EP-WXT trigger 01709260303: KAIT optical observations
  24. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  25. The EP-WXT trigger 01709260303 is likely a flaring star
  26. GRB 260417A: SVOM/GRM observation
  27. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  28. GRB 260419B: Fermi GBM Final Real-time Localization
  29. GRB 260419A: Fermi GBM Final Real-time Localization
  30. Fermi trigger No 798275385: Global MASTER-Net observations report
  31. EP260417a: GROWTH-India Telescope optical upper limit
  32. Fermi GRB 260417B: Global MASTER-Net observations report
  33. EP260417b: GROWTH-India Telescope optical upper limit
  34. EP260416a: Ondrejov D50 optical detection
  35. GRB 260418B: Fermi GBM Final Real-time Localization
  36. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  37. EP260417a: Global MASTER-Net observations report
  38. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  39. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  40. GRB 260418A: Fermi GBM Final Real-time Localization
  41. EP260416a: GMG Optical Observation
  42. Fermi GRB 260417A: Global MASTER-Net observations report
  43. Konus-Wind detection of GRB 260411B
  44. GRB 260417B: Fermi GBM Final Real-time Localization
  45. GRB 260417A: AstroSat CZTI detection
  46. IPN triangulation of GRB 260411B
  47. EP260416a: LCO observations confirm end of flaring phase
  48. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  49. EP260417a: TRT optical counterpart detection
  50. EP260417a: Einstein Probe detection of an X-ray transient
  51. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  52. EP260417b: Einstein Probe detection of a fast X-ray transient
  53. EP-WXT trigger 01709259586: KAIT optical observations
  54. EP260416a: KAIT optical upper limit
  55. GRB 260414A: Insight-HXMT/HE detection
  56. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  57. EP260416a: WFST optical observations and rebrightening
  58. GRB 260417A: Fermi GBM Final Real-time Localization
  59. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  60. EP260416a: SVOM/VT optical observation
  61. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  62. GRB 260415B: Glowbug gamma-ray detection
  63. GRB 260411B: Glowbug gamma-ray detection
  64. GRB 260415A: Insight-HXMT/HE detection
  65. EP260416a: COLIBRÍ optical counterpart candidate
  66. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  67. EP260416a: Global MASTER-Net observations report
  68. EP260416a: Einstein Probe detection of an X-ray transient
  69. GOTO26djh/AT2026jpw : MASTER OT observation
  70. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  71. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  72. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  73. GRB 260415B: NuSTAR detection of long prompt emission
  74. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  75. GRB 260415B: Fermi GBM Final Localization
  76. GRB 260415A: Fermi GBM Final Real-time Localization
  77. Fermi trigger No 797912738: Global MASTER-Net observations report
  78. GRB 260414A: Glowbug gamma-ray detection
  79. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  80. EP260321a: CMO SAI J,K observations
  81. GRB 260412A: Insight-HXMT/HE detection
  82. GRB 260414A: Fermi GBM Final Real-time Localization
  83. The EP-WXT trigger 01709260122 is likely a flaring star
  84. Fermi GRB 260413A: Global MASTER-Net observations report
  85. GRB 260410A: Glowbug gamma-ray detection of a short burst
  86. GRB 260413A: Fermi GBM Final Real-time Localization
  87. GRB 260410B: Insight-HXMT/HE detection
  88. GRB 260410A: Insight-HXMT/HE detection
  89. Konus-Wind detection of GRB 260410A (short/hard)
  90. GRB 260411B: GECAM-B observation of a long burst
  91. EP260321a: SVOM/VT optical observations and color changes around peak
  92. GRB 260410A: CALET Gamma-Ray Burst Monitor detection
  93. The EP-WXT trigger 01709260010 is likely a flaring star
  94. GRB 260412A: GECAM-B observation of a long burst
  95. Fermi GRB 260412A: Global MASTER-Net observations report
  96. GRB 260412A: Fermi GBM Observation
  97. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  98. GRB 260411B: Fermi-LAT detection
  99. GRB 260412A: SVOM detection of a long burst
  100. GRB 260412A: Fermi GBM Final Real-time Localization

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