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

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