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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"

22113 results found.

  1. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  2. GRB 250818A: AstroSat CZTI detection
  3. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  4. GRB 250818B: Swift/UVOT Detection
  5. GRB 250818B: SAO RAS optical observations
  6. Swift GRB 250818A: Global MASTER-Net observations report
  7. GRB 250818B: KAIT optical observations
  8. GRB 250818A: Swift/UVOT Upper Limits
  9. GRB 250818A: Enhanced Swift-XRT position
  10. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  11. GRB 250814A: Further GRAWITA TNG NIR observations
  12. GRB 250818B: Swift-XRT afterglow detection
  13. GRB 250818B: GOTO optical counterpart candidate
  14. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  15. GRB 250818A: Swift detection of a burst
  16. sb25081602: Swift-XRT observations
  17. GRB 250816A: SVOM/GRM observation of a short burst
  18. SVOM/sb25081602: detection of a likely X-ray transient
  19. GRB 250813B: Liverpool Telescope optical upper limits
  20. GRB 250814A: Further COLIBRÍ optical upper limit
  21. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  22. GRB 250814A: GRAWITA TNG NIR observations
  23. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  24. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  25. GRB250814A: TRT optical upper limits
  26. GRB 250814B: SVOM/GRM observation
  27. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  28. GRB 250814A: P200/WIRC observations of the afterglow candidate
  29. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  30. GRB 250814A: KAIT optical upper limit
  31. GRB 250814A: Swift-XRT refined Analysis
  32. GRB 250814A: Possible afterglow candidate from P200/WIRC
  33. GRB 250813B: Fermi GBM Observation
  34. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  35. GRB 250814A: J-band upper limit from WINTER
  36. GRB 250813B: NOT observations of the optical afterglow
  37. GRB 250814A: COLIBRÍ optical upper limit
  38. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  39. GRB 250814A: DDOTI Optical Upper Limit
  40. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  41. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  42. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  43. GRB 250813B: SVOM detection of a bright long burst
  44. EP250812a: Nickel optical upper limit
  45. EP250812a: NOT, NTT, and GS observations
  46. GRB 250812A: Swift/UVOT Detection
  47. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  48. EP250812a: Liverpool Telescope upper limits
  49. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  50. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  51. EP 250812a: GOTO optical upper limit
  52. GRB 250812A: Kilonova-Catcher optical afterglow detection
  53. EP250812a: Swift-XRT counterpart detection
  54. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  55. EP250812a: Einstein Probe detection of an X-ray transient
  56. GRB 250812A: Swift-XRT afterglow detection
  57. GRB 250812A: TRT likely optical counterpart detection
  58. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  59. GRB 250809A: Swift/UVOT Detection
  60. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  61. GRB 250809A: Swift-XRT refined Analysis
  62. GRB 250809A: LCOGT Optical Upper Limits
  63. GRB 250808A: VLT X-shooter candidate counterpart
  64. GRB 250809A: Swift detection of a gamma ray burst
  65. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  66. GRB 250808A: Swift-XRT candidate counterpart detection
  67. GRB 250807B: Swift/UVOT Detection
  68. GRB 250807B: Kilonova-Catcher optical afterglow detection
  69. GRB 250807A: Swift/UVOT Detection
  70. EP250807a: NTT z-band optical upper limit
  71. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  72. GRB 250807A: SVOM/GRM observation
  73. GRB 250807A: AstroSat CZTI detection of bright long burst
  74. GRB 250807B: Swift-XRT refined Analysis
  75. EP250807a: EP-WXT detection of a fast X-ray transient
  76. EP 250807.979: GOTO optical upper limit
  77. EP250807a: COLIBRÍ optical upper limit
  78. GRB 250807A: SVOM/VT optical observation
  79. GRB 250807B: Enhanced Swift-XRT position
  80. GRB 250807A: Enhanced Swift-XRT position
  81. GRB 250807B: Swift detection of a burst with an optical counterpart.
  82. GRB 250805A: Kilonova-Catcher optical upper limits
  83. EP250806a:SVOM/VT refined analysis
  84. GRB 250805A: Swift/UVOT Upper Limits
  85. GRB 250806A: Swift/UVOT U-band detection
  86. EP250806a: Liverpool telescope optical upper limit
  87. GRB 250807A: Swift detection of a burst with an optical counterpart
  88. EP250802a: EP-FXT follow-up observation
  89. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  90. EP250806a: SVOM /VT optical candidate
  91. GRB 250806A: J-band upper limit from WINTER
  92. GRB 250806A: KAIT optical upper limit
  93. GRB 250806A: SVOM/VT refined analysis
  94. EP250806a: COLIBRÍ optical upper limit
  95. GRB 250806A: Kilonova-Catcher optical upper limits
  96. EP250806a: Einstein Probe detection of an X-ray transient
  97. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  98. GRB 250806A: SVOM/VT optical upper limit
  99. GRB 250806A: SVOM detection of a soft burst
  100. GRB 250805A: SVOM/VT optical counterpart

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