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

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