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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/ECLAIRs refined analysis
  2. GRB 260421B: 3.6m DOT optical observation
  3. EP260416a: ZTSh R band observations
  4. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  5. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  6. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  7. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  8. GRB 260419A: AstroSat CZTI detection
  9. GRB 260421B: SVOM/GRM observation
  10. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  11. GRB 260421B: EP-FXT follow-up observation
  12. The EP-WXT trigger 01709260362 is likely a flaring star
  13. GOTO26djh/AT2026jpw: ATCA radio detection
  14. GRB 260421B: J-band upper limit with WINTER
  15. GRB 260421B: LCO optical counterpart detection
  16. GRB 260421B: Fermi GBM Observation
  17. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  18. GRB 260421A: AstroSat CZTI detection
  19. GOTO26djh/AT2026jpw: radio detection at 15GHz
  20. GRB 260412A: SVOM/ECLAIRs refined analysis
  21. GRB 260421B: SVOM/VT optical observations
  22. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  23. GRB 260310A: Late-time Chandra X-ray Detection
  24. GRB 260418A: Insight-HXMT/HE detection
  25. EP260416a: 1.3m DFOT optical observation
  26. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  27. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  28. Fermi GRB 260421C: Global MASTER-Net observations report
  29. GRB 260421C: Fermi GBM Final Real-time Localization
  30. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  31. Fermi GRB 260421B: Global MASTER-Net observations report
  32. GRB 260421B: BOOTES-7 early optical afterglow detection
  33. GRB 260421B: LCO optical afterglow confirmation
  34. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  35. GRB 260421B: TRT optical counterpart detection
  36. GRB 260421B: SVOM detection of a long burst
  37. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  38. GRB 260421B: Fermi GBM Final Real-time Localization
  39. Fermi GRB 260421A: Global MASTER-Net observations report
  40. GRB 260421A: Fermi GBM Final Real-time Localization
  41. EP260321a: VLA radio follow-up
  42. GRB 260412A: LCOGT Optical Upper Limits
  43. The EP-WXT trigger 01709260314 is likely a flaring star
  44. EP260416a: Optical follow-up observations with Kinder
  45. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  46. EP-WXT trigger 01709260303: KAIT optical observations
  47. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  48. The EP-WXT trigger 01709260303 is likely a flaring star
  49. GRB 260417A: SVOM/GRM observation
  50. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  51. GRB 260419B: Fermi GBM Final Real-time Localization
  52. GRB 260419A: Fermi GBM Final Real-time Localization
  53. Fermi trigger No 798275385: Global MASTER-Net observations report
  54. EP260417a: GROWTH-India Telescope optical upper limit
  55. Fermi GRB 260417B: Global MASTER-Net observations report
  56. EP260417b: GROWTH-India Telescope optical upper limit
  57. EP260416a: Ondrejov D50 optical detection
  58. GRB 260418B: Fermi GBM Final Real-time Localization
  59. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  60. EP260417a: Global MASTER-Net observations report
  61. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  62. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  63. GRB 260418A: Fermi GBM Final Real-time Localization
  64. EP260416a: GMG Optical Observation
  65. Fermi GRB 260417A: Global MASTER-Net observations report
  66. Konus-Wind detection of GRB 260411B
  67. GRB 260417B: Fermi GBM Final Real-time Localization
  68. GRB 260417A: AstroSat CZTI detection
  69. IPN triangulation of GRB 260411B
  70. EP260416a: LCO observations confirm end of flaring phase
  71. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  72. EP260417a: TRT optical counterpart detection
  73. EP260417a: Einstein Probe detection of an X-ray transient
  74. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  75. EP260417b: Einstein Probe detection of a fast X-ray transient
  76. EP-WXT trigger 01709259586: KAIT optical observations
  77. EP260416a: KAIT optical upper limit
  78. GRB 260414A: Insight-HXMT/HE detection
  79. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  80. EP260416a: WFST optical observations and rebrightening
  81. GRB 260417A: Fermi GBM Final Real-time Localization
  82. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  83. EP260416a: SVOM/VT optical observation
  84. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  85. GRB 260415B: Glowbug gamma-ray detection
  86. GRB 260411B: Glowbug gamma-ray detection
  87. GRB 260415A: Insight-HXMT/HE detection
  88. EP260416a: COLIBRÍ optical counterpart candidate
  89. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  90. EP260416a: Global MASTER-Net observations report
  91. EP260416a: Einstein Probe detection of an X-ray transient
  92. GOTO26djh/AT2026jpw : MASTER OT observation
  93. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  94. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  95. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  96. GRB 260415B: NuSTAR detection of long prompt emission
  97. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  98. GRB 260415B: Fermi GBM Final Localization
  99. GRB 260415A: Fermi GBM Final Real-time Localization
  100. Fermi trigger No 797912738: Global MASTER-Net observations report

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