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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 250814A: CMO SAI and SAO RAS izJ observations.
  2. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  3. GRB 250821A: Prompt enhanced Swift-XRT position
  4. GRB 250821A: Swift detection of a burst
  5. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  6. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  7. EP250821a: Einstein Probe detection of an X-ray transient
  8. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  9. GRB 250819A: Insight-HXMT detection
  10. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  11. GRB 250818B: 10 GHz VLA detection
  12. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  13. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  14. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  15. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  16. GRB 250814A: Swift/UVOT Upper Limits
  17. GRB 250813B: Swift/UVOT Upper Limit
  18. IPN triangulation of GRB 250816A (short)
  19. IPN triangulation of GRB 250814C (short)
  20. IPN triangulation of GRB 250804B (short)
  21. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  22. GRB 250818B: Kilonova-Catcher optical afterglow detection
  23. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  24. GRB 250818B: Liverpool Telescope optical detections
  25. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  26. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  27. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  28. GRB 250818A: AstroSat CZTI detection
  29. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  30. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  31. GRB 250818B: Swift/UVOT Detection
  32. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  33. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  34. GRB 250820A: Fermi GBM Final Real-time Localization
  35. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  36. GRB 250818B: TRT Optical Observation
  37. Fermi GRB 250816A: Global MASTER-Net observations report
  38. GRB 250818B: SAO RAS optical observations
  39. Swift GRB 250818A: Global MASTER-Net observations report
  40. GRB 250818B: NOT optical observations
  41. GRB 250818A: Swift-XRT refined Analysis
  42. GRB 250818B: EP-FXT counterpart detection
  43. GRB 250818A: Swift-BAT refined analysis
  44. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  45. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  46. GRB 250818C: Fermi GBM Final Real-time Localization
  47. GRB 250818B: Keck redshift of the optical afterglow
  48. Fermi trigger No 776849714: Global MASTER-Net observations report
  49. GRB 250818B: KAIT optical observations
  50. GRB 250818A: Swift/UVOT Upper Limits
  51. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  52. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  53. GRB 250818A: Enhanced Swift-XRT position
  54. GRB 250813B: SVOM/ECLAIRs refined analysis
  55. GRB 250818A: Fermi GBM Observation
  56. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  57. GRB 250818B: SVOM/VT optical observation
  58. GRB 250814A: Further GRAWITA TNG NIR observations
  59. GRB 250818B: Swift-XRT afterglow detection
  60. GRB 250818B: GOTO optical counterpart candidate
  61. GRB 250818B: SVOM detection of a short burst
  62. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  63. GRB 250818A: Swift detection of a burst
  64. GRB 250818A: Fermi GBM Final Real-time Localization
  65. sb25081602: Swift-XRT observations
  66. GRB 250816A: SVOM/GRM observation of a short burst
  67. SVOM/sb25081602: detection of a likely X-ray transient
  68. Fermi GRB 250814B: Global MASTER-Net observations report
  69. GRB 250816A: Fermi GBM Final Real-time Localization
  70. GRB 250814A: Swift-BAT refined analysis
  71. GRB 250815A: Fermi GBM Final Localization
  72. GRB 250813B: Liverpool Telescope optical upper limits
  73. GRB 250814A: Further COLIBRÍ optical upper limit
  74. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  75. GRB 250814A: GRAWITA TNG NIR observations
  76. GRB 250812A: SVOM/VT optical continued observation
  77. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  78. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  79. GRB250814A: TRT optical upper limits
  80. GRB 250814B: SVOM/GRM observation
  81. GRB 250814C: SVOM/GRM observation of a short burst
  82. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  83. GRB 250813B: SVOM/GRM observation
  84. GRB 250814A: P200/WIRC observations of the afterglow candidate
  85. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  86. GRB 250814A: KAIT optical upper limit
  87. GRB 250814A: Swift-XRT refined Analysis
  88. GRB 240814A: Fermi GBM Observation
  89. GRB 250814A: Possible afterglow candidate from P200/WIRC
  90. GRB 250813B: Fermi GBM Observation
  91. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  92. Fermi trigger No 776818276: Global MASTER-Net observations report
  93. Swift GRB250814.32: Global MASTER-Net observations report
  94. GRB 250814A: J-band upper limit from WINTER
  95. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  96. GRB 250813B: NOT observations of the optical afterglow
  97. GRB 250813B: SVOM/VT optical observations
  98. Subject GRB 250813B: SVOM/MXT refined analysis
  99. GRB 250814A: COLIBRÍ optical upper limit
  100. GRB 250814B: Fermi GBM Final Real-time Localization

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