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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"

16811 results found.

  1. EP-WXT trigger 01709200800 : KAIT optical observations
  2. EP250828a: KAIT optical upper limit
  3. EP250827a: Swift/UVOT Detection
  4. EP250828a: NOT optical counterpart confirmation
  5. EP250828a: SVOM/VT optical candidate
  6. EP250828a: Seimei/TriCCS optical counterpart detection
  7. EP250828a: Optical upper limit with Kinder observations
  8. EP250828a: Einstein Probe detection of an X-ray transient
  9. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  10. EP250827a: confirmation of optical rebrightening with LCO
  11. GRB 250826A: SVOM/GRM observation
  12. EP250827A: An optical rebrightening was detected by LCO.
  13. The EP-WXT trigger 01709200800 is likely a flaring star
  14. EP250827a: TRT optical observations
  15. EP250827a: Einstein Probe detection of an X-ray transient
  16. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  17. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  18. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  19. GRB 250821B: AstroSat CZTI detection
  20. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  21. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  22. EP250821a: MeerKAT radio counterpart
  23. The EP-WXT trigger 01709200707 is likely a flaring star
  24. GRB 250823A: COLIBRÍ optical observations
  25. The EP-WXT trigger 01709200706 is likely a flaring star
  26. GRB 250823A: SVOM/VT optical observation
  27. GRB 250823A: Swift/UVOT Detection
  28. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  29. GRB 250823A: Enhanced Swift-XRT position
  30. GRB 250823A: LCOGT Optical Detection
  31. GRB 250823A: Swift detection of a burst
  32. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  33. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  34. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  35. GRB 250821A: Kilonova-Catcher optical upper limits
  36. GRB 250821A: VLT/FORS2 Optical Observation
  37. GRB 250821B: SVOM/GRM observation
  38. EP250821a: SVOM/VT optical observation
  39. GRB 250821A: NOT z-band upper limit
  40. GRB 250821A: KAIT optical upper limit
  41. GRB 250821A: Enhanced Swift-XRT position
  42. GRB 250821A: Swift/UVOT Upper Limits
  43. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  44. GRB 250821A: LCOGT Optical Upper Limits
  45. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  46. GRB 250821A: Swift detection of a burst
  47. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  48. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  49. EP250821a: Einstein Probe detection of an X-ray transient
  50. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  51. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  52. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  53. GRB 250814A: Swift/UVOT Upper Limits
  54. GRB 250813B: Swift/UVOT Upper Limit
  55. IPN triangulation of GRB 250816A (short)
  56. IPN triangulation of GRB 250814C (short)
  57. IPN triangulation of GRB 250804B (short)
  58. GRB 250818B: Kilonova-Catcher optical afterglow detection
  59. GRB 250818B: Swift/UVOT Detection
  60. GRB 250818B: SAO RAS optical observations
  61. GRB 250818B: EP-FXT counterpart detection
  62. GRB 250818B: KAIT optical observations
  63. GRB 250818A: Swift/UVOT Upper Limits
  64. GRB 250818A: Enhanced Swift-XRT position
  65. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  66. GRB 250814A: Further GRAWITA TNG NIR observations
  67. GRB 250818A: Swift detection of a burst
  68. GRB 250816A: SVOM/GRM observation of a short burst
  69. GRB 250813B: Liverpool Telescope optical upper limits
  70. GRB 250814A: Further COLIBRÍ optical upper limit
  71. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  72. GRB 250814A: GRAWITA TNG NIR observations
  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. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  78. GRB 250814A: P200/WIRC observations of the afterglow candidate
  79. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  80. GRB 250814A: KAIT optical upper limit
  81. GRB 250814A: Swift-XRT refined Analysis
  82. GRB 250814A: Possible afterglow candidate from P200/WIRC
  83. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  84. GRB 250814A: J-band upper limit from WINTER
  85. GRB 250813B: NOT observations of the optical afterglow
  86. GRB 250814A: COLIBRÍ optical upper limit
  87. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  88. GRB 250814A: DDOTI Optical Upper Limit
  89. GRB 250813B: EP-FXT counterpart detection
  90. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  91. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  92. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  93. GRB 250813B: SVOM detection of a bright long burst
  94. EP250812a: Nickel optical upper limit
  95. EP250812a: NOT, NTT, and GS observations
  96. GRB 250812A: Swift/UVOT Detection
  97. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  98. EP250812a: Liverpool Telescope upper limits
  99. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  100. GRB 250812A: EP-FXT counterpart detection

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