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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. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  2. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  3. EP250321a: KAIT optical observations
  4. EP250321A: COLIBRÍ Continuing Optical Observations
  5. GRB 250225B: GECAM-A detection
  6. GRB 250312A: GECAM-A detection
  7. GRB 250321B: Swift ToO observations
  8. EP250321a: WFST optical observations
  9. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  10. GRB 250321C: Fermi GBM Final Real-time Localization
  11. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  12. GRB 250320B: Fermi GBM Observation
  13. EP250321a: Xinglong 216 decaying optical observations
  14. GRB 250321A: Swift-BAT refined analysis
  15. GRB 250321A: Swift-XRT refined Analysis
  16. GRB 250320B: Fermi-LAT detection
  17. GRB 250321B: SVOM detection of a sub-threshold transient event
  18. EP250321a: SVOM/VT optical observation
  19. EP 250321A: Optical counterpart detection by LCO.
  20. EP250321a: Kinder optical follow-up observations
  21. GRB 250321A: Swift/UVOT Upper Limits
  22. GRB 250320B: SVOM/GRM observation of a long burst
  23. EP250321a: LCO optical counterpart detection
  24. EP250321a: Swift-XRT detection of an X-ray source
  25. EP250321A: COLIBRÍ Optical Observations
  26. EP250321a: VLT/X-shooter redshift z = 4.368
  27. GRB 250320B: AstroSat CZTI detection
  28. EP250321a: REM optical/NIR afterglow detection
  29. Fermi GRB 250320B: Global MASTER-Net observations report
  30. EP250321a: BOOTES-5/JGT optical afterglow detection
  31. EP250321a: TRT optical counterpart detection
  32. EP250321a: Global MASTER-Net observations report
  33. Swift GRB 250321A: Global MASTER-Net observations report
  34. Fermi GRB 250321A: Global MASTER-Net observations report
  35. EP250321a: Einstein Probe detection of an X-ray transient
  36. GRB 250321A: GOTO optical upper limits
  37. GRB 250321A: Swift-XRT localisation
  38. GRB 250314A: Keck/NIRC2 J-band upper limit
  39. EP250226a/GRB 250226A: KAIT optical observations
  40. GRB 250321A: Fermi GBM Observation
  41. GRB 250321A: Swift detection of a burst
  42. GRB 250321A: Fermi GBM Final Real-time Localization
  43. GRB 250320B: Fermi GBM Final Real-time Localization
  44. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  45. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  46. GRB 250320A: Fermi GBM Final Real-time Localization
  47. Fermi GRB 250319B: Global MASTER-Net observations report
  48. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  49. GRB 250313A: GRBAlpha detection
  50. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  51. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  52. GRB 250319B: Fermi GBM Final Localization
  53. GRB 250319A: Fermi GBM Final Localization
  54. GRB 250317D: EIRSAT-1 GMOD Detection
  55. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  56. GRB 250314A: ATCA radio upper limits
  57. EP250302a: VLA observations
  58. GRB 250317B: OHP/T193 continued follow-up
  59. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  60. GRB 250317C: SVOM/GRM observation of a long burst
  61. GRB 250317B: Leavitt Observatory optical upper limit
  62. GRB 250309B/AT2025dws: further ATCA observations
  63. GRB 250317B: Mondy AZT-33IK Optical Observations
  64. GRB 250317C: AstroSat CZTI detection
  65. GRB 250317B: NOT optical observations suggest an optical plateau phase
  66. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  67. GRB 250317C: GECAM-B detection
  68. GRB 250317B: OHP/T193 optical observations
  69. Fermi trigger No 763933627: Global MASTER-Net observations report
  70. GRB250312A: Swift/UVOT Upper Limits
  71. GRB 250317B: REM optical/NIR observations
  72. GRB 250317B: Swift-XRT observations
  73. GRB 250316A: Swift/UVOT Upper Limits
  74. GRB 250314A: REM optical/NIR upper limits
  75. GRB 250316A: AbAO AS-32 Optical Upper Limit
  76. EP 250317B: Fading optical counterpart detection by LCO
  77. GRB 250316A: Swift-XRT afterglow detection
  78. GRB 250317B: LCO detection of the fading optical afterglow
  79. GRB 250317B: refined SVOM/MXT analysis
  80. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  81. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  82. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  83. GRB 250317B: SVOM detection of a burst
  84. GRB 250316A: Fermi GBM Observation
  85. GRB 250316A: Swift-XRT observations
  86. Fermi trigger No 763862734: Global MASTER-Net observations report
  87. GRB 250317A: Fermi GBM Final Real-time Localization
  88. Fermi GRB 250316A: Global MASTER-Net observations report
  89. GRB 250314A: SVOM/GRM analysis
  90. GRB 250316A: Swift ToO observations
  91. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  92. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  93. The EP-WXT trigger 01709132801 is likely a flaring star
  94. GRB 250316A: Fermi GBM Final Real-time Localization
  95. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  96. GRB 250314A: EP-FXT afterglow detection
  97. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  98. GRB 250314A: Swift/UVOT Upper Limits
  99. GRB 250312B: GRBAlpha detection
  100. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection

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