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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"

22917 results found.

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

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