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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. GRB250322A: STEP/T80S optical limits
  2. GRB 250322A: Gemini-South optical observations
  3. GRB 250322A: VLT optical observations
  4. GRB 250322A: VLT near-infrared observations
  5. FRB 250316A: DDOTI Continued Optical Observations
  6. GRB 250322A: NOT optical upper limits
  7. GRB 250322A: Enhanced Swift-XRT position
  8. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  9. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  10. GRB 250322A: MASTER optical observation
  11. EP250321a: Liverpool Telescope optical follow-up
  12. EP250321a: Mondy AZT-33IK Optical Observations
  13. GRB 250322A: Swift detection of a short burst
  14. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  15. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  16. EP250321a: KAIT optical observations
  17. EP250321A: COLIBRÍ Continuing Optical Observations
  18. GRB 250225B: GECAM-A detection
  19. GRB 250312A: GECAM-A detection
  20. GRB 250321B: Swift ToO observations
  21. EP250321a: WFST optical observations
  22. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  23. GRB 250321C: Fermi GBM Final Real-time Localization
  24. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  25. GRB 250320B: Fermi GBM Observation
  26. EP250321a: Xinglong 216 decaying optical observations
  27. GRB 250321A: Swift-BAT refined analysis
  28. GRB 250321A: Swift-XRT refined Analysis
  29. GRB 250320B: Fermi-LAT detection
  30. GRB 250321B: SVOM detection of a sub-threshold transient event
  31. EP250321a: SVOM/VT optical observation
  32. EP 250321A: Optical counterpart detection by LCO.
  33. EP250321a: Kinder optical follow-up observations
  34. GRB 250321A: Swift/UVOT Upper Limits
  35. GRB 250320B: SVOM/GRM observation of a long burst
  36. EP250321a: LCO optical counterpart detection
  37. EP250321a: Swift-XRT detection of an X-ray source
  38. EP250321A: COLIBRÍ Optical Observations
  39. EP250321a: VLT/X-shooter redshift z = 4.368
  40. GRB 250320B: AstroSat CZTI detection
  41. EP250321a: REM optical/NIR afterglow detection
  42. Fermi GRB 250320B: Global MASTER-Net observations report
  43. EP250321a: BOOTES-5/JGT optical afterglow detection
  44. EP250321a: TRT optical counterpart detection
  45. EP250321a: Global MASTER-Net observations report
  46. Swift GRB 250321A: Global MASTER-Net observations report
  47. Fermi GRB 250321A: Global MASTER-Net observations report
  48. EP250321a: Einstein Probe detection of an X-ray transient
  49. GRB 250321A: GOTO optical upper limits
  50. GRB 250321A: Swift-XRT localisation
  51. GRB 250314A: Keck/NIRC2 J-band upper limit
  52. EP250226a/GRB 250226A: KAIT optical observations
  53. GRB 250321A: Fermi GBM Observation
  54. GRB 250321A: Swift detection of a burst
  55. GRB 250321A: Fermi GBM Final Real-time Localization
  56. GRB 250320B: Fermi GBM Final Real-time Localization
  57. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  58. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  59. GRB 250320A: Fermi GBM Final Real-time Localization
  60. Fermi GRB 250319B: Global MASTER-Net observations report
  61. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  62. GRB 250313A: GRBAlpha detection
  63. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  64. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  65. GRB 250319B: Fermi GBM Final Localization
  66. GRB 250319A: Fermi GBM Final Localization
  67. GRB 250317D: EIRSAT-1 GMOD Detection
  68. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  69. GRB 250314A: ATCA radio upper limits
  70. EP250302a: VLA observations
  71. GRB 250317B: OHP/T193 continued follow-up
  72. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  73. GRB 250317C: SVOM/GRM observation of a long burst
  74. GRB 250317B: Leavitt Observatory optical upper limit
  75. GRB 250309B/AT2025dws: further ATCA observations
  76. GRB 250317B: Mondy AZT-33IK Optical Observations
  77. GRB 250317C: AstroSat CZTI detection
  78. GRB 250317B: NOT optical observations suggest an optical plateau phase
  79. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  80. GRB 250317C: GECAM-B detection
  81. GRB 250317B: OHP/T193 optical observations
  82. Fermi trigger No 763933627: Global MASTER-Net observations report
  83. GRB250312A: Swift/UVOT Upper Limits
  84. GRB 250317B: REM optical/NIR observations
  85. GRB 250317B: Swift-XRT observations
  86. GRB 250316A: Swift/UVOT Upper Limits
  87. GRB 250314A: REM optical/NIR upper limits
  88. GRB 250316A: AbAO AS-32 Optical Upper Limit
  89. EP 250317B: Fading optical counterpart detection by LCO
  90. GRB 250316A: Swift-XRT afterglow detection
  91. GRB 250317B: LCO detection of the fading optical afterglow
  92. GRB 250317B: refined SVOM/MXT analysis
  93. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  94. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  95. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  96. GRB 250317B: SVOM detection of a burst
  97. GRB 250316A: Fermi GBM Observation
  98. GRB 250316A: Swift-XRT observations
  99. Fermi trigger No 763862734: Global MASTER-Net observations report
  100. GRB 250317A: Fermi GBM Final Real-time Localization

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