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

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