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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"

27549 results found.

  1. GRB 250823A: Swift-XRT refined Analysis
  2. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  3. GRB 250824B: Fermi GBM Final Real-time Localization
  4. GRB 250823A: SVOM/VT optical observation
  5. GRB 250824A: Fermi GBM Final Real-time Localization
  6. GRB 250823A: Swift/UVOT Detection
  7. GRB 250818B: MeerKAT Detection
  8. GRB 250823A: Enhanced Swift-XRT position
  9. GRB 250823A: LCOGT Optical Detection
  10. GRB 250823A: BOOTES6/DPRT early optical detection
  11. GRB 250823A: Liverpool Telescope optical detection
  12. GRB 250823A: Swift detection of a burst
  13. GRB 250823A: Fermi GBM Final Real-time Localization
  14. Konus-Wind detection of GRB 250821B
  15. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  16. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  17. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  19. IPN triangulation of GRB 250821B (long/bright)
  20. GRB 250821A: Kilonova-Catcher optical upper limits
  21. EP250821a: Swift/XRT counterpart fading
  22. EP250821a: Swift/UVOT further observations.
  23. GRB 250821A: VLT/FORS2 Optical Observation
  24. GRB 250821A: GECAM-B detection
  25. EP250821a: SVOM/VT optical observation
  26. GRB 250821A: NOT z-band upper limit
  27. GRB 250821C: Fermi GBM Final Real-time Localization
  28. GRB 250821A: KAIT optical upper limit
  29. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  30. GRB 250821A: Swift-XRT refined Analysis
  31. GRB 250821B: Fermi GBM Detection
  32. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  33. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  34. GRB 250821A: Enhanced Swift-XRT position
  35. GRB 250821A: Swift/UVOT Upper Limits
  36. EP250821a: Swift XRT and UVOT counterpart detection
  37. GRB 250821A: LCOGT Optical Upper Limits
  38. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  39. GRB 250821A: Prompt enhanced Swift-XRT position
  40. GRB 250821A: Swift detection of a burst
  41. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  42. EP250821a: Einstein Probe detection of an X-ray transient
  43. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  44. GRB 250819A: Insight-HXMT detection
  45. GRB 250818B: 10 GHz VLA detection
  46. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  47. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  48. GRB 250814A: Swift/UVOT Upper Limits
  49. GRB 250813B: Swift/UVOT Upper Limit
  50. IPN triangulation of GRB 250816A (short)
  51. IPN triangulation of GRB 250814C (short)
  52. IPN triangulation of GRB 250804B (short)
  53. GRB 250818B: Kilonova-Catcher optical afterglow detection
  54. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  55. GRB 250818B: Liverpool Telescope optical detections
  56. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  57. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  58. GRB 250818A: AstroSat CZTI detection
  59. GRB 250818B: Swift/UVOT Detection
  60. GRB 250820A: Fermi GBM Final Real-time Localization
  61. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  62. GRB 250818B: TRT Optical Observation
  63. GRB 250818B: SAO RAS optical observations
  64. GRB 250818B: NOT optical observations
  65. GRB 250818A: Swift-XRT refined Analysis
  66. GRB 250818B: EP-FXT counterpart detection
  67. GRB 250818C: Fermi GBM Final Real-time Localization
  68. GRB 250818B: Keck redshift of the optical afterglow
  69. GRB 250818B: KAIT optical observations
  70. GRB 250818A: Swift/UVOT Upper Limits
  71. GRB 250818A: Enhanced Swift-XRT position
  72. GRB 250818B: SVOM/VT optical observation
  73. GRB 250814A: Further GRAWITA TNG NIR observations
  74. GRB 250818B: Swift-XRT afterglow detection
  75. GRB 250818B: SVOM detection of a short burst
  76. GRB 250818A: Swift detection of a burst
  77. GRB 250818A: Fermi GBM Final Real-time Localization
  78. sb25081602: Swift-XRT observations
  79. SVOM/sb25081602: detection of a likely X-ray transient
  80. GRB 250816A: Fermi GBM Final Real-time Localization
  81. GRB 250815A: Fermi GBM Final Localization
  82. GRB 250813B: Liverpool Telescope optical upper limits
  83. GRB 250814A: Further COLIBRÍ optical upper limit
  84. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  85. GRB 250814A: GRAWITA TNG NIR observations
  86. GRB 250812A: SVOM/VT optical continued observation
  87. GRB250814A: TRT optical upper limits
  88. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  89. GRB 250813B: SVOM/GRM observation
  90. GRB 250814A: P200/WIRC observations of the afterglow candidate
  91. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  92. GRB 250814A: KAIT optical upper limit
  93. GRB 250814A: Swift-XRT refined Analysis
  94. GRB 250814A: Possible afterglow candidate from P200/WIRC
  95. GRB 250813B: Fermi GBM Observation
  96. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  97. GRB 250814A: J-band upper limit from WINTER
  98. GRB 250813B: NOT observations of the optical afterglow
  99. GRB 250813B: SVOM/VT optical observations
  100. Subject GRB 250813B: SVOM/MXT refined analysis

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