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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 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  2. GRB 260419A: AstroSat CZTI detection
  3. GRB 260421B: SVOM/GRM observation
  4. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  5. GRB 260421B: EP-FXT follow-up observation
  6. The EP-WXT trigger 01709260362 is likely a flaring star
  7. GOTO26djh/AT2026jpw: ATCA radio detection
  8. GRB 260421B: J-band upper limit with WINTER
  9. GRB 260421B: LCO optical counterpart detection
  10. GRB 260421B: Fermi GBM Observation
  11. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  12. GRB 260421A: AstroSat CZTI detection
  13. GOTO26djh/AT2026jpw: radio detection at 15GHz
  14. GRB 260412A: SVOM/ECLAIRs refined analysis
  15. GRB 260421B: SVOM/VT optical observations
  16. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  17. GRB 260310A: Late-time Chandra X-ray Detection
  18. GRB 260418A: Insight-HXMT/HE detection
  19. EP260416a: 1.3m DFOT optical observation
  20. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  21. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  22. Fermi GRB 260421C: Global MASTER-Net observations report
  23. GRB 260421C: Fermi GBM Final Real-time Localization
  24. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  25. Fermi GRB 260421B: Global MASTER-Net observations report
  26. GRB 260421B: BOOTES-7 early optical afterglow detection
  27. GRB 260421B: LCO optical afterglow confirmation
  28. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  29. GRB 260421B: TRT optical counterpart detection
  30. GRB 260421B: SVOM detection of a long burst
  31. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  32. GRB 260421B: Fermi GBM Final Real-time Localization
  33. Fermi GRB 260421A: Global MASTER-Net observations report
  34. GRB 260421A: Fermi GBM Final Real-time Localization
  35. EP260321a: VLA radio follow-up
  36. GRB 260412A: LCOGT Optical Upper Limits
  37. The EP-WXT trigger 01709260314 is likely a flaring star
  38. EP260416a: Optical follow-up observations with Kinder
  39. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  40. EP-WXT trigger 01709260303: KAIT optical observations
  41. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  42. The EP-WXT trigger 01709260303 is likely a flaring star
  43. GRB 260417A: SVOM/GRM observation
  44. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  45. GRB 260419B: Fermi GBM Final Real-time Localization
  46. GRB 260419A: Fermi GBM Final Real-time Localization
  47. Fermi trigger No 798275385: Global MASTER-Net observations report
  48. EP260417a: GROWTH-India Telescope optical upper limit
  49. Fermi GRB 260417B: Global MASTER-Net observations report
  50. EP260417b: GROWTH-India Telescope optical upper limit
  51. EP260416a: Ondrejov D50 optical detection
  52. GRB 260418B: Fermi GBM Final Real-time Localization
  53. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  54. EP260417a: Global MASTER-Net observations report
  55. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  56. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  57. GRB 260418A: Fermi GBM Final Real-time Localization
  58. EP260416a: GMG Optical Observation
  59. Fermi GRB 260417A: Global MASTER-Net observations report
  60. Konus-Wind detection of GRB 260411B
  61. GRB 260417B: Fermi GBM Final Real-time Localization
  62. GRB 260417A: AstroSat CZTI detection
  63. IPN triangulation of GRB 260411B
  64. EP260416a: LCO observations confirm end of flaring phase
  65. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  66. EP260417a: TRT optical counterpart detection
  67. EP260417a: Einstein Probe detection of an X-ray transient
  68. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  69. EP260417b: Einstein Probe detection of a fast X-ray transient
  70. EP-WXT trigger 01709259586: KAIT optical observations
  71. EP260416a: KAIT optical upper limit
  72. GRB 260414A: Insight-HXMT/HE detection
  73. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  74. EP260416a: WFST optical observations and rebrightening
  75. GRB 260417A: Fermi GBM Final Real-time Localization
  76. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  77. EP260416a: SVOM/VT optical observation
  78. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  79. GRB 260415B: Glowbug gamma-ray detection
  80. GRB 260411B: Glowbug gamma-ray detection
  81. GRB 260415A: Insight-HXMT/HE detection
  82. EP260416a: COLIBRÍ optical counterpart candidate
  83. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  84. EP260416a: Global MASTER-Net observations report
  85. EP260416a: Einstein Probe detection of an X-ray transient
  86. GOTO26djh/AT2026jpw : MASTER OT observation
  87. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  88. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  89. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  90. GRB 260415B: NuSTAR detection of long prompt emission
  91. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  92. GRB 260415B: Fermi GBM Final Localization
  93. GRB 260415A: Fermi GBM Final Real-time Localization
  94. Fermi trigger No 797912738: Global MASTER-Net observations report
  95. GRB 260414A: Glowbug gamma-ray detection
  96. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  97. EP260321a: CMO SAI J,K observations
  98. GRB 260412A: Insight-HXMT/HE detection
  99. GRB 260414A: Fermi GBM Final Real-time Localization
  100. The EP-WXT trigger 01709260122 is likely a flaring star

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