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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 260419A: AstroSat CZTI detection
  2. GRB 260421B: SVOM/GRM observation
  3. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  4. GRB 260421B: EP-FXT follow-up observation
  5. The EP-WXT trigger 01709260362 is likely a flaring star
  6. GOTO26djh/AT2026jpw: ATCA radio detection
  7. GRB 260421B: J-band upper limit with WINTER
  8. GRB 260421B: LCO optical counterpart detection
  9. GRB 260421B: Fermi GBM Observation
  10. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  11. GRB 260421A: AstroSat CZTI detection
  12. GOTO26djh/AT2026jpw: radio detection at 15GHz
  13. GRB 260412A: SVOM/ECLAIRs refined analysis
  14. GRB 260421B: SVOM/VT optical observations
  15. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  16. GRB 260310A: Late-time Chandra X-ray Detection
  17. GRB 260418A: Insight-HXMT/HE detection
  18. EP260416a: 1.3m DFOT optical observation
  19. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  20. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  21. Fermi GRB 260421C: Global MASTER-Net observations report
  22. GRB 260421C: Fermi GBM Final Real-time Localization
  23. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  24. Fermi GRB 260421B: Global MASTER-Net observations report
  25. GRB 260421B: BOOTES-7 early optical afterglow detection
  26. GRB 260421B: LCO optical afterglow confirmation
  27. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  28. GRB 260421B: TRT optical counterpart detection
  29. GRB 260421B: SVOM detection of a long burst
  30. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  31. GRB 260421B: Fermi GBM Final Real-time Localization
  32. Fermi GRB 260421A: Global MASTER-Net observations report
  33. GRB 260421A: Fermi GBM Final Real-time Localization
  34. EP260321a: VLA radio follow-up
  35. GRB 260412A: LCOGT Optical Upper Limits
  36. The EP-WXT trigger 01709260314 is likely a flaring star
  37. EP260416a: Optical follow-up observations with Kinder
  38. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  39. EP-WXT trigger 01709260303: KAIT optical observations
  40. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  41. The EP-WXT trigger 01709260303 is likely a flaring star
  42. GRB 260417A: SVOM/GRM observation
  43. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  44. GRB 260419B: Fermi GBM Final Real-time Localization
  45. GRB 260419A: Fermi GBM Final Real-time Localization
  46. Fermi trigger No 798275385: Global MASTER-Net observations report
  47. EP260417a: GROWTH-India Telescope optical upper limit
  48. Fermi GRB 260417B: Global MASTER-Net observations report
  49. EP260417b: GROWTH-India Telescope optical upper limit
  50. EP260416a: Ondrejov D50 optical detection
  51. GRB 260418B: Fermi GBM Final Real-time Localization
  52. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  53. EP260417a: Global MASTER-Net observations report
  54. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  55. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  56. GRB 260418A: Fermi GBM Final Real-time Localization
  57. EP260416a: GMG Optical Observation
  58. Fermi GRB 260417A: Global MASTER-Net observations report
  59. Konus-Wind detection of GRB 260411B
  60. GRB 260417B: Fermi GBM Final Real-time Localization
  61. GRB 260417A: AstroSat CZTI detection
  62. IPN triangulation of GRB 260411B
  63. EP260416a: LCO observations confirm end of flaring phase
  64. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  65. EP260417a: TRT optical counterpart detection
  66. EP260417a: Einstein Probe detection of an X-ray transient
  67. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  68. EP260417b: Einstein Probe detection of a fast X-ray transient
  69. EP-WXT trigger 01709259586: KAIT optical observations
  70. EP260416a: KAIT optical upper limit
  71. GRB 260414A: Insight-HXMT/HE detection
  72. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  73. EP260416a: WFST optical observations and rebrightening
  74. GRB 260417A: Fermi GBM Final Real-time Localization
  75. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  76. EP260416a: SVOM/VT optical observation
  77. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  78. GRB 260415B: Glowbug gamma-ray detection
  79. GRB 260411B: Glowbug gamma-ray detection
  80. GRB 260415A: Insight-HXMT/HE detection
  81. EP260416a: COLIBRÍ optical counterpart candidate
  82. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  83. EP260416a: Global MASTER-Net observations report
  84. EP260416a: Einstein Probe detection of an X-ray transient
  85. GOTO26djh/AT2026jpw : MASTER OT observation
  86. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  87. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  88. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  89. GRB 260415B: NuSTAR detection of long prompt emission
  90. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  91. GRB 260415B: Fermi GBM Final Localization
  92. GRB 260415A: Fermi GBM Final Real-time Localization
  93. Fermi trigger No 797912738: Global MASTER-Net observations report
  94. GRB 260414A: Glowbug gamma-ray detection
  95. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  96. EP260321a: CMO SAI J,K observations
  97. GRB 260412A: Insight-HXMT/HE detection
  98. GRB 260414A: Fermi GBM Final Real-time Localization
  99. The EP-WXT trigger 01709260122 is likely a flaring star
  100. Fermi GRB 260413A: Global MASTER-Net observations report

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