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

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