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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"

18477 results found.

  1. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  2. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  3. GRB 250808B: SVOM detection of a burst through offline search
  4. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  5. EP250828a: Optical counterpart detection with Kinder observations
  6. EP250828a: Liverpool Telescope upper limits
  7. EP-WXT trigger 01709200800 : KAIT optical observations
  8. EP250828a: KAIT optical upper limit
  9. EP250827a: Swift/UVOT Detection
  10. EP250828a: NOT optical counterpart confirmation
  11. EP250828a: SVOM/VT optical candidate
  12. EP250828a: Seimei/TriCCS optical counterpart detection
  13. GRB 250828B: Swift detection of a burst
  14. EP250828a: Optical upper limit with Kinder observations
  15. EP250828a: Einstein Probe detection of an X-ray transient
  16. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  17. EP250827a: confirmation of optical rebrightening with LCO
  18. GRB 250826A: SVOM/GRM observation
  19. EP250827A: An optical rebrightening was detected by LCO.
  20. EP250827a: TRT optical observations
  21. EP250827a: Einstein Probe detection of an X-ray transient
  22. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  23. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  24. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  25. Fermi GRB 250824B: Global MASTER-Net observations report
  26. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  27. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  28. EP250821a: MeerKAT radio counterpart
  29. GRB 250823A: COLIBRÍ optical observations
  30. GRB 250823A: SVOM/VT optical observation
  31. GRB 250823A: Swift/UVOT Detection
  32. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  33. GRB 250823A: Enhanced Swift-XRT position
  34. GRB 250823A: LCOGT Optical Detection
  35. GRB 250823A: Swift detection of a burst
  36. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  37. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  38. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  39. GRB 250821A: Kilonova-Catcher optical upper limits
  40. GRB 250821A: VLT/FORS2 Optical Observation
  41. GRB 250821B: SVOM/GRM observation
  42. EP250821a: SVOM/VT optical observation
  43. GRB 250821A: NOT z-band upper limit
  44. GRB 250821A: KAIT optical upper limit
  45. GRB 250821A: Enhanced Swift-XRT position
  46. GRB 250821A: Swift/UVOT Upper Limits
  47. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  48. GRB 250821A: LCOGT Optical Upper Limits
  49. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  50. GRB 250821A: Swift detection of a burst
  51. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  52. EP250821a: Einstein Probe detection of an X-ray transient
  53. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  54. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  55. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  56. GRB 250814A: Swift/UVOT Upper Limits
  57. GRB 250813B: Swift/UVOT Upper Limit
  58. IPN triangulation of GRB 250816A (short)
  59. IPN triangulation of GRB 250814C (short)
  60. IPN triangulation of GRB 250804B (short)
  61. GRB 250818B: Kilonova-Catcher optical afterglow detection
  62. GRB 250818B: Swift/UVOT Detection
  63. GRB 250818B: SAO RAS optical observations
  64. GRB 250818B: KAIT optical observations
  65. GRB 250818A: Swift/UVOT Upper Limits
  66. GRB 250818A: Enhanced Swift-XRT position
  67. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  68. GRB 250814A: Further GRAWITA TNG NIR observations
  69. GRB 250818B: SVOM detection of a short burst
  70. GRB 250818A: Swift detection of a burst
  71. GRB 250816A: SVOM/GRM observation of a short burst
  72. GRB 250813B: Liverpool Telescope optical upper limits
  73. GRB 250814A: Further COLIBRÍ optical upper limit
  74. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  75. GRB 250814A: GRAWITA TNG NIR observations
  76. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  77. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  78. GRB250814A: TRT optical upper limits
  79. GRB 250814B: SVOM/GRM observation
  80. GRB 250814A: P200/WIRC observations of the afterglow candidate
  81. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  82. GRB 250814A: KAIT optical upper limit
  83. GRB 250814A: Swift-XRT refined Analysis
  84. GRB 250814A: Possible afterglow candidate from P200/WIRC
  85. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  86. GRB 250814A: J-band upper limit from WINTER
  87. GRB 250813B: NOT observations of the optical afterglow
  88. GRB 250814A: COLIBRÍ optical upper limit
  89. GRB 250813A: AstroSat CZTI detection
  90. GRB 250814A: DDOTI Optical Upper Limit
  91. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  92. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  93. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  94. GRB 250813B: SVOM detection of a bright long burst
  95. EP250812a: Nickel optical upper limit
  96. EP250812a: NOT, NTT, and GS observations
  97. GRB 250812A: Swift/UVOT Detection
  98. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  99. EP250812a: Liverpool Telescope upper limits
  100. EP250812a: refined analysis of the EP-WXT and EP-FXT observations

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