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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. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  2. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  3. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  4. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  5. GRB 260419A: AstroSat CZTI detection
  6. GRB 260421B: SVOM/GRM observation
  7. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  8. GRB 260421B: EP-FXT follow-up observation
  9. The EP-WXT trigger 01709260362 is likely a flaring star
  10. GOTO26djh/AT2026jpw: ATCA radio detection
  11. GRB 260421B: J-band upper limit with WINTER
  12. GRB 260421B: LCO optical counterpart detection
  13. GRB 260421B: Fermi GBM Observation
  14. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  15. GRB 260421A: AstroSat CZTI detection
  16. GOTO26djh/AT2026jpw: radio detection at 15GHz
  17. GRB 260412A: SVOM/ECLAIRs refined analysis
  18. GRB 260421B: SVOM/VT optical observations
  19. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  20. GRB 260310A: Late-time Chandra X-ray Detection
  21. GRB 260418A: Insight-HXMT/HE detection
  22. EP260416a: 1.3m DFOT optical observation
  23. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  24. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  25. Fermi GRB 260421C: Global MASTER-Net observations report
  26. GRB 260421C: Fermi GBM Final Real-time Localization
  27. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  28. Fermi GRB 260421B: Global MASTER-Net observations report
  29. GRB 260421B: BOOTES-7 early optical afterglow detection
  30. GRB 260421B: LCO optical afterglow confirmation
  31. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  32. GRB 260421B: TRT optical counterpart detection
  33. GRB 260421B: SVOM detection of a long burst
  34. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  35. GRB 260421B: Fermi GBM Final Real-time Localization
  36. Fermi GRB 260421A: Global MASTER-Net observations report
  37. GRB 260421A: Fermi GBM Final Real-time Localization
  38. EP260321a: VLA radio follow-up
  39. GRB 260412A: LCOGT Optical Upper Limits
  40. The EP-WXT trigger 01709260314 is likely a flaring star
  41. EP260416a: Optical follow-up observations with Kinder
  42. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  43. EP-WXT trigger 01709260303: KAIT optical observations
  44. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  45. The EP-WXT trigger 01709260303 is likely a flaring star
  46. GRB 260417A: SVOM/GRM observation
  47. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  48. GRB 260419B: Fermi GBM Final Real-time Localization
  49. GRB 260419A: Fermi GBM Final Real-time Localization
  50. Fermi trigger No 798275385: Global MASTER-Net observations report
  51. EP260417a: GROWTH-India Telescope optical upper limit
  52. Fermi GRB 260417B: Global MASTER-Net observations report
  53. EP260417b: GROWTH-India Telescope optical upper limit
  54. EP260416a: Ondrejov D50 optical detection
  55. GRB 260418B: Fermi GBM Final Real-time Localization
  56. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  57. EP260417a: Global MASTER-Net observations report
  58. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  59. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  60. GRB 260418A: Fermi GBM Final Real-time Localization
  61. EP260416a: GMG Optical Observation
  62. Fermi GRB 260417A: Global MASTER-Net observations report
  63. Konus-Wind detection of GRB 260411B
  64. GRB 260417B: Fermi GBM Final Real-time Localization
  65. GRB 260417A: AstroSat CZTI detection
  66. IPN triangulation of GRB 260411B
  67. EP260416a: LCO observations confirm end of flaring phase
  68. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  69. EP260417a: TRT optical counterpart detection
  70. EP260417a: Einstein Probe detection of an X-ray transient
  71. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  72. EP260417b: Einstein Probe detection of a fast X-ray transient
  73. EP-WXT trigger 01709259586: KAIT optical observations
  74. EP260416a: KAIT optical upper limit
  75. GRB 260414A: Insight-HXMT/HE detection
  76. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  77. EP260416a: WFST optical observations and rebrightening
  78. GRB 260417A: Fermi GBM Final Real-time Localization
  79. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  80. EP260416a: SVOM/VT optical observation
  81. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  82. GRB 260415B: Glowbug gamma-ray detection
  83. GRB 260411B: Glowbug gamma-ray detection
  84. GRB 260415A: Insight-HXMT/HE detection
  85. EP260416a: COLIBRÍ optical counterpart candidate
  86. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  87. EP260416a: Global MASTER-Net observations report
  88. EP260416a: Einstein Probe detection of an X-ray transient
  89. GOTO26djh/AT2026jpw : MASTER OT observation
  90. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  91. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  92. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  93. GRB 260415B: NuSTAR detection of long prompt emission
  94. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  95. GRB 260415B: Fermi GBM Final Localization
  96. GRB 260415A: Fermi GBM Final Real-time Localization
  97. Fermi trigger No 797912738: Global MASTER-Net observations report
  98. GRB 260414A: Glowbug gamma-ray detection
  99. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  100. EP260321a: CMO SAI J,K observations

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