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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"

18936 results found.

  1. GRB 251126A: 1.3m DFOT optical afterglow detection
  2. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  3. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  4. GRB 251126A: Enhanced Swift-XRT position
  5. GRB 251126A: Kilonova-Catcher optical afterglow detection
  6. GRB 251126A: Nanshan/HMT optical afterglow detection
  7. GRB 251126A: GIT discovery of the likely optical afterglow
  8. GRB 251126A: Swift detection of a burst
  9. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  10. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  11. EP251124b: NOT r- and z-band optical upper limits
  12. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  13. EP251124b: EP-WXT detection of a fast X-ray transient
  14. EP251124a: Xinglong GWAC-F60A optical observation
  15. EP251124a: NOT r- and z-band optical upper limits
  16. EP251124a: Swift-XRT observations
  17. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  18. EP251124a: Optical upper limit with Kinder observations
  19. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  20. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  21. EP251124a: GROWTH-India Telescope optical upper limits
  22. EP251124a: Einstein Probe detection of an X-ray transient
  23. GRB 251116C: Swift-XRT confirmation of fading
  24. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  25. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  26. EP251118A: 3.6m DOT optical afterglow detection
  27. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  28. GRB 251122A / EP251122a: WFST optical observations
  29. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  30. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  31. GRB 251122A / EP251122a: LCO optical upper limits
  32. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  33. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  34. GRB 251122A / EP251122a: SVOM detection of a long burst
  35. EP251122a: Einstein Probe detection of an X-ray transient
  36. EP251118a: Continued Optical Detection with Kinder observations
  37. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  38. GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
  39. EP251118a: Xinglong-2.16m optical observation
  40. EP251118A: 1.3m DFOT optical afterglow detection
  41. GRB 251118A: Swift/UVOT Detection
  42. EP251118a / GRB 251118C: SAO RAS optical observations
  43. GRB 251118A: Swift-XRT afterglow detection
  44. GRB 251103A: SVOM/ECLAIRs and SVOM/GRM joint refined analysis
  45. EP251118a: Optical detection with Kinder observations
  46. LIGO/Virgo/KAGRA S251112cm: SVOM/VT optical observations and preliminary results
  47. EP251118a / GRB 251118C: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at CTIO
  48. GRB 251118C: Swift/BAT rates detection of a burst with a possible association with EP 251118A
  49. EP251118A / GRB 251118C : MASTER optical counterpart observations
  50. GRB 251118C: SVOM/GRM observation of a possible gamma-ray counterpart of EP251118a
  51. GRB 251119A: SVOM trigger sb25111901 is not a GRB
  52. EP251118a: VLT near-infrared observation
  53. GRB 251116D: SVOM/GRM observation of a long GRB
  54. GRB 251119A: SVOM detection of a possible burst
  55. EP251118a: NOT spectroscopic redshift of z = 1.216
  56. EP251118a: NOT candidate optical counterpart
  57. EP251118a: Einstein Probe detected of a fast X-ray transient
  58. LIGO/Virgo/KAGRA S251112cm: Upper limits from Glowbug gamma-ray observations
  59. GRB 251116C: SVOM/ECLAIRs refined analysis
  60. GRB 251116B: SVOM/ECLAIRs refined analysis
  61. GRB 251115A: Swift-XRT observations
  62. GRB 251117A: Swift/BAT-GUANO localization skymap of a short burst
  63. GRB 251117A: SVOM/GRM observation of a short burst
  64. GRB 251117A: Fermi-LAT detection
  65. LIGO/Virgo/KAGRA S251117dq: Identification of a GW compact binary merger candidate
  66. LIGO/Virgo/KAGRA S251112cm: J-GEM follow-up observations
  67. LIGO/Virgo/KAGRA S251112cm: WFST follow-up observations and preliminary results
  68. EP251023a: Assy AZT-20 optical observations
  69. EP251023a: UAFO and AbAO optical observations
  70. The EP-WXT trigger 01709247588: more evidence of flaring star from Mondy optical observations
  71. GRB 251025B: further Mondy optical observations
  72. GRB 251111A: Mondy optical upper limit
  73. LIGO/Virgo/KAGRA S251116en: Identification of a GW compact binary merger candidate
  74. LIGO/Virgo/KAGRA S251112cm: Observations with the NSF-DOE Vera C. Rubin Observatory
  75. GRB 251116B: LCO optical upper limits
  76. GRB 251116C: LCO optical upper limits
  77. IceCube-Cascade 251112A: Upper limits from a search for additional neutrino events in IceCube
  78. LIGO/Virgo/KAGRA S251112cm: GRANDMA observations of the skymap
  79. GRB 251013C: joint SVOM/ECLAIRs-GRM refined analysis
  80. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 4-Update Localization Volume
  81. LIGO/Virgo/KAGRA S251112cm: DECam GW-MMADS candidates
  82. LIGO/Virgo/KAGRA S251112cm: Updated Sky localization and false alarm rate estimate
  83. GRB 251113A: AstroSat CZTI detection
  84. LIGO/Virgo/KAGRA S251112cm: ATLAS targeted observations of the skymap
  85. LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources
  86. The EP-WXT trigger 01709248221 is likely a flaring star
  87. LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region
  88. GRB 251111A: SVOM/ECLAIRs refined analysis
  89. GRB 251025B: SVOM/ECLAIRs refined analysis
  90. GRB 251112A: Swift/UVOT Upper Limits
  91. GRB 251108C: AstroSat CZTI detection
  92. LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations
  93. Swift Trigger 1413695: a possible GRB 251112A
  94. GRB251111A: 1.3m DFOT optical upper limit
  95. GRB 251111A: Swift-XRT afterglow detection
  96. GRB 251111A: SVOM/VT optical observations with X-band data
  97. GRB 251111A: SVOM/VT optical observations with VHF data
  98. GRB 251111A: LCO optical observation
  99. GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection
  100. GRB 251106A: Swift/UVOT Upper Limits

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