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

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