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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"

27392 results found.

  1. GRB 250823A: Swift-XRT refined Analysis
  2. EP250821a: MeerKAT radio counterpart
  3. GRB 250823A: COLIBRÍ optical observations
  4. GRB 250823A: SVOM/VT optical observation
  5. GRB 250823A: Swift/UVOT Detection
  6. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  7. GRB 250823A: Fermi GBM Observation
  8. GRB 250823A: Enhanced Swift-XRT position
  9. GRB 250823A: LCOGT Optical Detection
  10. GRB 250823A: Swift detection of a burst
  11. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  12. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  13. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  14. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  15. GRB 250806A: Gemini observations of host galaxy candidate
  16. GRB 250821A: Kilonova-Catcher optical upper limits
  17. EP250821a: Swift/XRT counterpart fading
  18. GRB 250821A: Swift-BAT refined analysis
  19. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  20. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  21. GRB 250821A: VLT/FORS2 Optical Observation
  22. GRB 250821B: SVOM/GRM observation
  23. EP250821a: SVOM/VT optical observation
  24. GRB 250821A: NOT z-band upper limit
  25. GRB 250821A: KAIT optical upper limit
  26. GRB 250821A: Swift-XRT refined Analysis
  27. GRB 250821B: Fermi GBM Detection
  28. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  29. GRB 250821A: Enhanced Swift-XRT position
  30. GRB 250821A: Swift/UVOT Upper Limits
  31. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  32. EP250821a: Swift XRT and UVOT counterpart detection
  33. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  34. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  35. GRB 250821A: LCOGT Optical Upper Limits
  36. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  37. GRB 250821A: Swift detection of a burst
  38. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  39. EP250821a: Einstein Probe detection of an X-ray transient
  40. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  41. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  42. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  43. GRB 250814A: Swift/UVOT Upper Limits
  44. GRB 250813B: Swift/UVOT Upper Limit
  45. IPN triangulation of GRB 250816A (short)
  46. IPN triangulation of GRB 250814C (short)
  47. IPN triangulation of GRB 250804B (short)
  48. GRB 250818B: Kilonova-Catcher optical afterglow detection
  49. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  50. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  51. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  52. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  53. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  54. GRB 250818B: Swift/UVOT Detection
  55. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  56. GRB 250818B: SAO RAS optical observations
  57. GRB 250818A: Swift-XRT refined Analysis
  58. GRB 250818B: EP-FXT counterpart detection
  59. GRB 250818A: Swift-BAT refined analysis
  60. GRB 250818B: KAIT optical observations
  61. GRB 250818A: Swift/UVOT Upper Limits
  62. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  63. GRB 250818A: Enhanced Swift-XRT position
  64. GRB 250813B: SVOM/ECLAIRs refined analysis
  65. GRB 250818A: Fermi GBM Observation
  66. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  67. GRB 250814A: Further GRAWITA TNG NIR observations
  68. GRB 250818B: Swift-XRT afterglow detection
  69. GRB 250818B: SVOM detection of a short burst
  70. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  71. GRB 250818A: Swift detection of a burst
  72. sb25081602: Swift-XRT observations
  73. GRB 250816A: SVOM/GRM observation of a short burst
  74. GRB 250814A: Swift-BAT refined analysis
  75. GRB 250813B: Liverpool Telescope optical upper limits
  76. GRB 250814A: Further COLIBRÍ optical upper limit
  77. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  78. GRB 250814A: GRAWITA TNG NIR observations
  79. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  80. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  81. GRB250814A: TRT optical upper limits
  82. GRB 250814B: SVOM/GRM observation
  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. GRB 250814A: J-band upper limit from WINTER
  94. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  95. GRB 250813B: NOT observations of the optical afterglow
  96. GRB 250814A: COLIBRÍ optical upper limit
  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 250814A: DDOTI Optical Upper Limit
  100. GRB 250813B: EP-FXT counterpart detection

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