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

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