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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. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  2. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  3. EP250821a: Einstein Probe detection of an X-ray transient
  4. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  5. GRB 250819A: Insight-HXMT detection
  6. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  7. GRB 250818B: 10 GHz VLA detection
  8. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  9. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  10. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  11. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  12. GRB 250814A: Swift/UVOT Upper Limits
  13. GRB 250813B: Swift/UVOT Upper Limit
  14. IPN triangulation of GRB 250816A (short)
  15. IPN triangulation of GRB 250814C (short)
  16. IPN triangulation of GRB 250804B (short)
  17. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  18. GRB 250818B: Kilonova-Catcher optical afterglow detection
  19. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  20. GRB 250818B: Liverpool Telescope optical detections
  21. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  22. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  23. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  24. GRB 250818A: AstroSat CZTI detection
  25. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  26. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  27. GRB 250818B: Swift/UVOT Detection
  28. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  29. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  30. GRB 250820A: Fermi GBM Final Real-time Localization
  31. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  32. GRB 250818B: TRT Optical Observation
  33. Fermi GRB 250816A: Global MASTER-Net observations report
  34. GRB 250818B: SAO RAS optical observations
  35. Swift GRB 250818A: Global MASTER-Net observations report
  36. GRB 250818B: NOT optical observations
  37. GRB 250818A: Swift-XRT refined Analysis
  38. GRB 250818B: EP-FXT counterpart detection
  39. GRB 250818A: Swift-BAT refined analysis
  40. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  41. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  42. GRB 250818C: Fermi GBM Final Real-time Localization
  43. GRB 250818B: Keck redshift of the optical afterglow
  44. Fermi trigger No 776849714: Global MASTER-Net observations report
  45. GRB 250818B: KAIT optical observations
  46. GRB 250818A: Swift/UVOT Upper Limits
  47. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  48. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  49. GRB 250818A: Enhanced Swift-XRT position
  50. GRB 250813B: SVOM/ECLAIRs refined analysis
  51. GRB 250818A: Fermi GBM Observation
  52. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  53. GRB 250818B: SVOM/VT optical observation
  54. GRB 250814A: Further GRAWITA TNG NIR observations
  55. GRB 250818B: Swift-XRT afterglow detection
  56. GRB 250818B: GOTO optical counterpart candidate
  57. GRB 250818B: SVOM detection of a short burst
  58. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  59. GRB 250818A: Swift detection of a burst
  60. GRB 250818A: Fermi GBM Final Real-time Localization
  61. sb25081602: Swift-XRT observations
  62. GRB 250816A: SVOM/GRM observation of a short burst
  63. SVOM/sb25081602: detection of a likely X-ray transient
  64. Fermi GRB 250814B: Global MASTER-Net observations report
  65. GRB 250816A: Fermi GBM Final Real-time Localization
  66. GRB 250814A: Swift-BAT refined analysis
  67. GRB 250815A: Fermi GBM Final Localization
  68. GRB 250813B: Liverpool Telescope optical upper limits
  69. GRB 250814A: Further COLIBRÍ optical upper limit
  70. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  71. GRB 250814A: GRAWITA TNG NIR observations
  72. GRB 250812A: SVOM/VT optical continued observation
  73. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  74. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  75. GRB250814A: TRT optical upper limits
  76. GRB 250814B: SVOM/GRM observation
  77. GRB 250814C: SVOM/GRM observation of a short burst
  78. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  79. GRB 250813B: SVOM/GRM observation
  80. GRB 250814A: P200/WIRC observations of the afterglow candidate
  81. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  82. GRB 250814A: KAIT optical upper limit
  83. GRB 250814A: Swift-XRT refined Analysis
  84. GRB 240814A: Fermi GBM Observation
  85. GRB 250814A: Possible afterglow candidate from P200/WIRC
  86. GRB 250813B: Fermi GBM Observation
  87. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  88. Fermi trigger No 776818276: Global MASTER-Net observations report
  89. Swift GRB250814.32: Global MASTER-Net observations report
  90. GRB 250814A: J-band upper limit from WINTER
  91. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  92. GRB 250813B: NOT observations of the optical afterglow
  93. GRB 250813B: SVOM/VT optical observations
  94. Subject GRB 250813B: SVOM/MXT refined analysis
  95. GRB 250814A: COLIBRÍ optical upper limit
  96. GRB 250814B: Fermi GBM Final Real-time Localization
  97. GRB 250813A: AstroSat CZTI detection
  98. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  99. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  100. GRB 250814A: DDOTI Optical Upper Limit

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