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

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